Cover Story
- 2026
- 2025
- 2024
- 2023
Research on the Microstructure and Pore Characteristics of Fused Filament-Fabricated Porous Tungsten
2026, 55(11):2794-2801.
DOI: 10.12442/j.issn.1002-185X.20250453
Abstract:
Porous tungsten structures were prepared by fused filament fabrication (FFF). The microstructural evolution at each stage of the FFF process and the final pore characteristics of the sintered tungsten were investigated systematically. The results show that porous tungsten components with tightly bonded layers and no defects are successfully prepared by FFF. The maximum loading of commercial tungsten powder with a particle size of 3 μm reaches 56%, and the compounded feedstock exhibits excellent rheological properties. Furthermore, the influence of printing parameters on the green density was investigated, identifying the optimal combination: the nozzle diameter of 0.6 mm, a layer thickness of 0.1 mm, and the printing speed of 30 mm/s. The porous tungsten prepared by FFF shows a uniform pore distribution. As the sintering temperature increases, the average pore size decreases, the complexity of the pores increases, and the hardness and compressive strength increase.
Porous tungsten structures were prepared by fused filament fabrication (FFF). The microstructural evolution at each stage of the FFF process and the final pore characteristics of the sintered tungsten were investigated systematically. The results show that porous tungsten components with tightly bonded layers and no defects are successfully prepared by FFF. The maximum loading of commercial tungsten powder with a particle size of 3 μm reaches 56%, and the compounded feedstock exhibits excellent rheological properties. Furthermore, the influence of printing parameters on the green density was investigated, identifying the optimal combination: the nozzle diameter of 0.6 mm, a layer thickness of 0.1 mm, and the printing speed of 30 mm/s. The porous tungsten prepared by FFF shows a uniform pore distribution. As the sintering temperature increases, the average pore size decreases, the complexity of the pores increases, and the hardness and compressive strength increase.
Preparation and Water Cooling Verification of Pin-Fin Diamond/Copper Plates for Electronic Packaging
2026, 55(10):2501-2510.
DOI: 10.12442/j.issn.1002-185X.20250285
Abstract:
Thermal management in electronic packaging is one of the important technical bottlenecks hindering the development of integrated circuits. Diamond/copper composites have excellent performance in the field of thermal management, but the difficulty in their complex structure formation leads to applications restricted in the field of water cooling in electronic packaging. In this research, the sintering performance between the green body and the composite plate was enhanced by employing a silver doping strategy, thereby addressing the thermal management challenges in electronic packaging. Composite base plates and pin-fin type composite base plates were prepared, and their application benefits were evaluated in both indirect and direct water cooling scenarios. Results demonstrate that the silver-doped copper billet achieves good sintering performance when combined with tungsten-coated diamond/copper composite plates. The composite base plate and the pin-fin type composite base plate effectively reduce the temperature of the heating sheet by 5–6 °C and 4–5 °C during water-cooling tests respectively. The numerical simulation results are in good agreement with the experimental data, confirming the excellent thermal uniformity of the composite structures. This research successfully overcomes the limitations associated with the low thermal conductivity of traditional packaging components and the challenges in fabricating complex structures using diamond/copper composite materials.
Thermal management in electronic packaging is one of the important technical bottlenecks hindering the development of integrated circuits. Diamond/copper composites have excellent performance in the field of thermal management, but the difficulty in their complex structure formation leads to applications restricted in the field of water cooling in electronic packaging. In this research, the sintering performance between the green body and the composite plate was enhanced by employing a silver doping strategy, thereby addressing the thermal management challenges in electronic packaging. Composite base plates and pin-fin type composite base plates were prepared, and their application benefits were evaluated in both indirect and direct water cooling scenarios. Results demonstrate that the silver-doped copper billet achieves good sintering performance when combined with tungsten-coated diamond/copper composite plates. The composite base plate and the pin-fin type composite base plate effectively reduce the temperature of the heating sheet by 5–6 °C and 4–5 °C during water-cooling tests respectively. The numerical simulation results are in good agreement with the experimental data, confirming the excellent thermal uniformity of the composite structures. This research successfully overcomes the limitations associated with the low thermal conductivity of traditional packaging components and the challenges in fabricating complex structures using diamond/copper composite materials.
2026, 55(9):2117-2132.
DOI: 10.12442/j.issn.1002-185X.20250510
Abstract:
Lightweight high-entropy alloys (LWHEAs) represent a promising class of materials for advanced structural applications. However, achieving precise control over their phase formation and mechanical properties remains a significant challenge. Although the conventional empirical parameters (mixing enthalpy ΔHmix, valence electron concentration, atomic size mismatch δ, and electronegativity difference Φ) provide general guidance for phase stability in Ti-Al-based LWHEAs, their predictive accuracy is restricted. The Al/Ti atomic ratio (γ, namely Al/Ti ratio) is a more decisive and precise criterion for microstructure control. Guided by this parameter, a series of Ti(50–x)Al(6.5+x)V11.5Nb14.5Zr17.5 alloys were designed and synthesized. Results reveal that γ critically governs the precipitation, extent of short-range ordering, and grain refinement of B2 phase. Additionally, a moderate γ value of approximately 2.0 (Ti46Al10.5 alloy) yields an optimal synergy of high yield strength (>1 GPa) and considerable tensile ductility (>20%), whereas excessively high γ leads to embrittlement. This work considers γ as a key compositional parameter and provides a practical framework for designing high-performance LWHEAs through integrated parametric and element-ratio control.
Lightweight high-entropy alloys (LWHEAs) represent a promising class of materials for advanced structural applications. However, achieving precise control over their phase formation and mechanical properties remains a significant challenge. Although the conventional empirical parameters (mixing enthalpy ΔHmix, valence electron concentration, atomic size mismatch δ, and electronegativity difference Φ) provide general guidance for phase stability in Ti-Al-based LWHEAs, their predictive accuracy is restricted. The Al/Ti atomic ratio (γ, namely Al/Ti ratio) is a more decisive and precise criterion for microstructure control. Guided by this parameter, a series of Ti(50–x)Al(6.5+x)V11.5Nb14.5Zr17.5 alloys were designed and synthesized. Results reveal that γ critically governs the precipitation, extent of short-range ordering, and grain refinement of B2 phase. Additionally, a moderate γ value of approximately 2.0 (Ti46Al10.5 alloy) yields an optimal synergy of high yield strength (>1 GPa) and considerable tensile ductility (>20%), whereas excessively high γ leads to embrittlement. This work considers γ as a key compositional parameter and provides a practical framework for designing high-performance LWHEAs through integrated parametric and element-ratio control.
2026, 55(8):1849-1857.
DOI: 10.12442/j.issn.1002-185X.20250473
Abstract:
In response to the need for in-situ repair of deep cracks in a naval ship, a 4 mm-deep 30° U-shaped groove was prepared on 921A steel. Groove filling experiments were conducted using local dry underwater oscillating laser wire feed welding under the conditions of air and shallow water. The microstructure and properties of the welds were analyzed. The results indicate that sound welds without significant defects are obtained in both air and shallow water. Owing to the effective shielding gas protection within the local dry cavity and the rapid cooling effect underwater, the shallow water weld exhibits a bright white surface with densely distributed fish-scale patterns. The air weld includes a higher fraction of acicular ferrite, whereas the rapid cooling in water promotes the formation of lath martensite. The main alloying elements under both environments exhibit a smooth transition near the fusion lines with good metallurgical bonding. However, due to the higher cooling rate in the shallow water compared with that in air, there is a greater fluctuation in elemental distribution, along with higher contents of Si, Mn, and Mo and a slightly lower Cr content in the shallow water weld. The shallow water weld shows higher overall hardness than the air weld, though the hardness distribution trends across different zones are similar in both cases. Tensile tests reveal that fracture occurs in the base metal under both environments, with the tensile strength and yield strength ranking as follows: shallow water weld>air weld>base metal. However, electrochemical corrosion tests indicate that the shallow water weld has inferior corrosion resistance compared to the air weld.
In response to the need for in-situ repair of deep cracks in a naval ship, a 4 mm-deep 30° U-shaped groove was prepared on 921A steel. Groove filling experiments were conducted using local dry underwater oscillating laser wire feed welding under the conditions of air and shallow water. The microstructure and properties of the welds were analyzed. The results indicate that sound welds without significant defects are obtained in both air and shallow water. Owing to the effective shielding gas protection within the local dry cavity and the rapid cooling effect underwater, the shallow water weld exhibits a bright white surface with densely distributed fish-scale patterns. The air weld includes a higher fraction of acicular ferrite, whereas the rapid cooling in water promotes the formation of lath martensite. The main alloying elements under both environments exhibit a smooth transition near the fusion lines with good metallurgical bonding. However, due to the higher cooling rate in the shallow water compared with that in air, there is a greater fluctuation in elemental distribution, along with higher contents of Si, Mn, and Mo and a slightly lower Cr content in the shallow water weld. The shallow water weld shows higher overall hardness than the air weld, though the hardness distribution trends across different zones are similar in both cases. Tensile tests reveal that fracture occurs in the base metal under both environments, with the tensile strength and yield strength ranking as follows: shallow water weld>air weld>base metal. However, electrochemical corrosion tests indicate that the shallow water weld has inferior corrosion resistance compared to the air weld.
2026, 55(7):1701-1708.
DOI: 10.12442/j.issn.1002-185X.20250073
Abstract:
Large-scale and complex thick-walled titanium alloy casings produced by investment casting are key components in heavy-duty gas turbine. Characterized by their large contour size, substantial wall thicknesses, and complex shapes, these castings often face challenges such as difficult monolithic molding, numerous shrinkage pore and shrinkage cavity defects, and low dimensional accuracy, limiting the assembly and use of high-power gas turbines. The solidification temperature field and flow field during centrifugal investment casting process were investigated using the ProCAST software. Results show that the potential isolated liquid phase regions are identified. According to the characteristics of centrifugal casting, the mathematical models for designing spiral runner and inclined riser are derived. Based on this, an integrated gating system is developed, which combines exhaust gas and slag collection, flow regulation, and temperature field optimization, thereby significantly reducing solidification defects in castings. Furthermore, a wax mold splicing scheme is designed, and a wax mold tree for the gating system is constructed, featuring a straight runner, cross runner, and inner runner with cross-sectional area ratios of 1:2.5:6. Additionally, through the integration of dimensional calibration and shell reinforcement tooling, high-quality castings with complete filling, good metallurgical quality, and precise dimensional accuracy are achieved. This work provides effective technical guidance for the manufacturing of titanium alloy casings in heavy-duty gas turbines, and the gating system configuration offers reference value for other large-scale and complex thick-walled titanium alloy castings.
Large-scale and complex thick-walled titanium alloy casings produced by investment casting are key components in heavy-duty gas turbine. Characterized by their large contour size, substantial wall thicknesses, and complex shapes, these castings often face challenges such as difficult monolithic molding, numerous shrinkage pore and shrinkage cavity defects, and low dimensional accuracy, limiting the assembly and use of high-power gas turbines. The solidification temperature field and flow field during centrifugal investment casting process were investigated using the ProCAST software. Results show that the potential isolated liquid phase regions are identified. According to the characteristics of centrifugal casting, the mathematical models for designing spiral runner and inclined riser are derived. Based on this, an integrated gating system is developed, which combines exhaust gas and slag collection, flow regulation, and temperature field optimization, thereby significantly reducing solidification defects in castings. Furthermore, a wax mold splicing scheme is designed, and a wax mold tree for the gating system is constructed, featuring a straight runner, cross runner, and inner runner with cross-sectional area ratios of 1:2.5:6. Additionally, through the integration of dimensional calibration and shell reinforcement tooling, high-quality castings with complete filling, good metallurgical quality, and precise dimensional accuracy are achieved. This work provides effective technical guidance for the manufacturing of titanium alloy casings in heavy-duty gas turbines, and the gating system configuration offers reference value for other large-scale and complex thick-walled titanium alloy castings.
2026, 55(6):1465-1472.
DOI: 10.12442/j.issn.1002-185X.20250042
Abstract:
In the process of preparing and processing aluminum alloy rings, micro residual stress is generated, while macro residual stress is also generated. The release and redistribution of macro residual stress cause the deformation of the workpiece during processing and service, which will affect its dimensional accuracy. The superposition of macro residual stress and external force reduces the strength and fatigue limit of the workpiece. Under the combined action of micro-residual stress and external force, it is easy to cause stress concentration in the micro-area, so that the workpiece produces micro-cracks under far less than the yield stress, and ultimately fractures. The most important process affecting the residual stress in aluminum alloy forgings is the quenching process after solution treatment. In this paper, the macro residual stress of 7050 aluminum alloy ring during solution-cold bulging process was detected by blind hole method, and the macro finite element simulation of 7050 aluminum alloy ring during solution-cold bulging process was carried out by ABAQUS software. The macro residual stress evolution law of 7050 aluminum alloy ring during solution-cold bulging process was analyzed. It is concluded that the introduction of appropriate cold bulging process after solution quenching can greatly reduce the macro residual stress of 7050 aluminum alloy. The cross-scale analysis of residual stress is realized by the combined application of multi-scale simulation methods: Based on the crystal plastic finite element simulation method, the micro-area of interest is determined according to the macro-finite element simulation results, and the strain history of the micro-area is extracted. The strain history is applied to the micro-polycrystal model at the corresponding position by ABAQUS software to study the distribution law of micro-residual stress and its relationship with the microstructure.
In the process of preparing and processing aluminum alloy rings, micro residual stress is generated, while macro residual stress is also generated. The release and redistribution of macro residual stress cause the deformation of the workpiece during processing and service, which will affect its dimensional accuracy. The superposition of macro residual stress and external force reduces the strength and fatigue limit of the workpiece. Under the combined action of micro-residual stress and external force, it is easy to cause stress concentration in the micro-area, so that the workpiece produces micro-cracks under far less than the yield stress, and ultimately fractures. The most important process affecting the residual stress in aluminum alloy forgings is the quenching process after solution treatment. In this paper, the macro residual stress of 7050 aluminum alloy ring during solution-cold bulging process was detected by blind hole method, and the macro finite element simulation of 7050 aluminum alloy ring during solution-cold bulging process was carried out by ABAQUS software. The macro residual stress evolution law of 7050 aluminum alloy ring during solution-cold bulging process was analyzed. It is concluded that the introduction of appropriate cold bulging process after solution quenching can greatly reduce the macro residual stress of 7050 aluminum alloy. The cross-scale analysis of residual stress is realized by the combined application of multi-scale simulation methods: Based on the crystal plastic finite element simulation method, the micro-area of interest is determined according to the macro-finite element simulation results, and the strain history of the micro-area is extracted. The strain history is applied to the micro-polycrystal model at the corresponding position by ABAQUS software to study the distribution law of micro-residual stress and its relationship with the microstructure.
2026, 55(5):1209-1215.
DOI: 10.12442/j.issn.1002-185X.20250197
Abstract:
Pu-Ga alloys are vital nuclear materials. However, the nucleation and growth of helium bubbles significantly affect their microstructural evolution and mechanical properties. In this work, a phase-field model was developed to simulate the formation and evolution of helium bubbles in Pu-Ga alloys during room-temperature aging. The model analyzed the morphological evolution of helium bubbles under different aging time and temperatures. According to phase-field simulation results, the variation curves of average diameter and number density of bubbles were obtained. The results show that at room temperature, bubble size and spatial distribution remain nearly unchanged, while the number density increases linearly. These simulation results align well with published experimental data. Further analysis indicates that aging temperature primarily affects growth kinetics of bubbles by influencing point defect mobility rate. In contrast, the exceptionally low diffusion coefficient at room temperature is the key factor leading to the unique evolution trends observed in bubble size and number density. This study provides a mesoscale theoretical model for accurately predicting the growth behavior of helium bubble in Pu-Ga alloys.
Pu-Ga alloys are vital nuclear materials. However, the nucleation and growth of helium bubbles significantly affect their microstructural evolution and mechanical properties. In this work, a phase-field model was developed to simulate the formation and evolution of helium bubbles in Pu-Ga alloys during room-temperature aging. The model analyzed the morphological evolution of helium bubbles under different aging time and temperatures. According to phase-field simulation results, the variation curves of average diameter and number density of bubbles were obtained. The results show that at room temperature, bubble size and spatial distribution remain nearly unchanged, while the number density increases linearly. These simulation results align well with published experimental data. Further analysis indicates that aging temperature primarily affects growth kinetics of bubbles by influencing point defect mobility rate. In contrast, the exceptionally low diffusion coefficient at room temperature is the key factor leading to the unique evolution trends observed in bubble size and number density. This study provides a mesoscale theoretical model for accurately predicting the growth behavior of helium bubble in Pu-Ga alloys.
2026, 55(4):1078-1089.
DOI: 10.12442/j.issn.1002-185X.20250305
Abstract:
Discontinuously reinforced titanium matrix composites (DRTMCs) exhibit advantages such as light weight, high strength, and heat resistance, demonstrating broad application prospects in aerospace, consumer electronics, and other fields. Inspired by the multi-scale architectures of natural materials, the design of DRTMCs has evolved from uniformly distributed single reinforcements to architecture reinforcement configurations, and further to the coordinated design and regulation of multi-scale reinforcement architectures coupled with hierarchical titanium matrix. This progression has enriched their microstructure, leading to the formation of multi-scale heterogeneous structures. Such structures fully leverage synergistic strengthening mechanisms to enhance strengthening efficiency. Moreover, these composites effectively avoid strain localization to ensure favorable plasticity while maintaining excellent damage resistance. This review summarizes typical configuration design strategies and their evolutionary pathways in DRTMCs, elucidates the underlying strengthening-toughening mechanisms, and proposes future research directions based on current advancements to advance the application of high-performance titanium matrix composites in critical fields.
Discontinuously reinforced titanium matrix composites (DRTMCs) exhibit advantages such as light weight, high strength, and heat resistance, demonstrating broad application prospects in aerospace, consumer electronics, and other fields. Inspired by the multi-scale architectures of natural materials, the design of DRTMCs has evolved from uniformly distributed single reinforcements to architecture reinforcement configurations, and further to the coordinated design and regulation of multi-scale reinforcement architectures coupled with hierarchical titanium matrix. This progression has enriched their microstructure, leading to the formation of multi-scale heterogeneous structures. Such structures fully leverage synergistic strengthening mechanisms to enhance strengthening efficiency. Moreover, these composites effectively avoid strain localization to ensure favorable plasticity while maintaining excellent damage resistance. This review summarizes typical configuration design strategies and their evolutionary pathways in DRTMCs, elucidates the underlying strengthening-toughening mechanisms, and proposes future research directions based on current advancements to advance the application of high-performance titanium matrix composites in critical fields.
2026, 55(3):665-673.
DOI: 10.12442/j.issn.1002-185X.20250081
Abstract:
To address the issues of rapid cooling rate during the solidification in underwater welding and the deterioration of the microstructure and properties, this work conducted local dry underwater welding experiments on 2205 duplex stainless steel using adjustable ring-mode laser. Meanwhile, compared with in-air welds, the effects of the power ratio between center and ring lasers on weld formation, microstructure and mechanical properties were investigated. The results show that the center laser mainly affects the penetration depth. With the increase in proportion of central power, the oxidation degree and surface roughness of the weld become more severe. In terms of microstructure, the underwater weld exhibits an increase in Widmanst?tten austenite content, but a decrease in or even disappearance of intragranular austenite, compared to welds produced with the same parameters in air. With the increase in proportion of ring laser, the austenite content in the weld shows no significant change, the grain size and aspect ratio of the weld decrease, the directionality of columnar crystal growth on both sides of the weld weakens, and the number of low-angle grain boundary increases. In terms of performance, the underwater joints exhibit slightly higher tensile strength but lower elongation than those welds in air. As the proportion of ring laser power increases from 1/3 to 2/3, the elongation of underwater joints increases by about 50%.
To address the issues of rapid cooling rate during the solidification in underwater welding and the deterioration of the microstructure and properties, this work conducted local dry underwater welding experiments on 2205 duplex stainless steel using adjustable ring-mode laser. Meanwhile, compared with in-air welds, the effects of the power ratio between center and ring lasers on weld formation, microstructure and mechanical properties were investigated. The results show that the center laser mainly affects the penetration depth. With the increase in proportion of central power, the oxidation degree and surface roughness of the weld become more severe. In terms of microstructure, the underwater weld exhibits an increase in Widmanst?tten austenite content, but a decrease in or even disappearance of intragranular austenite, compared to welds produced with the same parameters in air. With the increase in proportion of ring laser, the austenite content in the weld shows no significant change, the grain size and aspect ratio of the weld decrease, the directionality of columnar crystal growth on both sides of the weld weakens, and the number of low-angle grain boundary increases. In terms of performance, the underwater joints exhibit slightly higher tensile strength but lower elongation than those welds in air. As the proportion of ring laser power increases from 1/3 to 2/3, the elongation of underwater joints increases by about 50%.
2026, 55(2):345-364.
DOI: 10.12442/j.issn.1002-185X.20250370
Abstract:
Refractory metals, including tungsten (W), tantalum (Ta), molybdenum (Mo), and niobium (Nb), play a vital role in industries, such as nuclear energy and aerospace, owing to their exceptional melting temperatures, thermal durability, and corrosion resistance. These metals have body-centered cubic crystal structure, characterized by limited slip systems and impeded dislocation motion, resulting in significant low-temperature brittleness, which poses challenges for the conventional processing. Additive manufacturing technique provides an innovative approach, enabling the production of intricate parts without molds, which significantly improves the efficiency of material usage. This review provides a comprehensive overview of the advancements in additive manufacturing techniques for the production of refractory metals, such as W, Ta, Mo, and Nb, particularly the laser powder bed fusion. In this review, the influence mechanisms of key process parameters (laser power, scan strategy, and powder characteristics) on the evolution of material microstructure, the formation of metallurgical defects, and mechanical properties were discussed. Generally, optimizing powder characteristics, such as sphericity, implementing substrate preheating, and formulating alloying strategies can significantly improve the densification and crack resistance of manufactured parts. Meanwhile, strictly controlling the oxygen impurity content and optimizing the energy density input are also the key factors to achieve the simultaneous improvement in strength and ductility of refractory metals. Although additive manufacturing technique provides an innovative solution for processing refractory metals, critical issues, such as residual stress control, microstructure and performance anisotropy, and process stability, still need to be addressed. This review not only provides a theoretical basis for the additive manufacturing of high-performance refractory metals, but also proposes forward-looking directions for their industrial application.
Refractory metals, including tungsten (W), tantalum (Ta), molybdenum (Mo), and niobium (Nb), play a vital role in industries, such as nuclear energy and aerospace, owing to their exceptional melting temperatures, thermal durability, and corrosion resistance. These metals have body-centered cubic crystal structure, characterized by limited slip systems and impeded dislocation motion, resulting in significant low-temperature brittleness, which poses challenges for the conventional processing. Additive manufacturing technique provides an innovative approach, enabling the production of intricate parts without molds, which significantly improves the efficiency of material usage. This review provides a comprehensive overview of the advancements in additive manufacturing techniques for the production of refractory metals, such as W, Ta, Mo, and Nb, particularly the laser powder bed fusion. In this review, the influence mechanisms of key process parameters (laser power, scan strategy, and powder characteristics) on the evolution of material microstructure, the formation of metallurgical defects, and mechanical properties were discussed. Generally, optimizing powder characteristics, such as sphericity, implementing substrate preheating, and formulating alloying strategies can significantly improve the densification and crack resistance of manufactured parts. Meanwhile, strictly controlling the oxygen impurity content and optimizing the energy density input are also the key factors to achieve the simultaneous improvement in strength and ductility of refractory metals. Although additive manufacturing technique provides an innovative solution for processing refractory metals, critical issues, such as residual stress control, microstructure and performance anisotropy, and process stability, still need to be addressed. This review not only provides a theoretical basis for the additive manufacturing of high-performance refractory metals, but also proposes forward-looking directions for their industrial application.
2026, 55(1):105-115.
DOI: 10.12442/j.issn.1002-185X.20250150
Abstract:
Wire arc additive manufacturing (WAAM) holds significant application value in the aerospace field, but the instability of heat input leads to prominent issues such as poor geometric conformity and numerous internal defects in aluminum alloy thin-walled components. To address the restrictions of traditional methods in multi-physics coupling optimization, this study proposed a data-driven solution by constructing a dataset of process parameters (current, scanning speed and wire feed rate) and forming quality (path/interlayer wall thickness consistency and porosity). A back propagation (BP) neural network model was established and optimized using the genetic algorithm (GA), combined with the non-dominated sorting genetic algorithm II (NSGA-II) for multi-objective optimization. The results show that the optimized GA-BP model significantly improves the prediction accuracy of path wall thickness consistency and porosity, but its optimization effect on interlayer wall thickness consistency prediction is restricted. Four types of optimization strategies are proposed based on the 50 Pareto solution sets obtained through NSGA-II, and validation tests indicate the model prediction error of 8.89%, accurately achieving the collaborative optimization of forming quality indicators.
Wire arc additive manufacturing (WAAM) holds significant application value in the aerospace field, but the instability of heat input leads to prominent issues such as poor geometric conformity and numerous internal defects in aluminum alloy thin-walled components. To address the restrictions of traditional methods in multi-physics coupling optimization, this study proposed a data-driven solution by constructing a dataset of process parameters (current, scanning speed and wire feed rate) and forming quality (path/interlayer wall thickness consistency and porosity). A back propagation (BP) neural network model was established and optimized using the genetic algorithm (GA), combined with the non-dominated sorting genetic algorithm II (NSGA-II) for multi-objective optimization. The results show that the optimized GA-BP model significantly improves the prediction accuracy of path wall thickness consistency and porosity, but its optimization effect on interlayer wall thickness consistency prediction is restricted. Four types of optimization strategies are proposed based on the 50 Pareto solution sets obtained through NSGA-II, and validation tests indicate the model prediction error of 8.89%, accurately achieving the collaborative optimization of forming quality indicators.
2025, 54(12):2985-2992.
DOI: 10.12442/j.issn.1002-185X.20250168
Abstract:
The high-temperature mechanical properties of Ta-8W-2Hf alloy doped with Re (1wt%) and C (0.01wt%) were investigated at room temperature, 1300 °C, and 1500 °C. Results show that fine and dispersed precipitates Ta2C are detected in crystallized TaWHfReC alloy, which significantly enhance mechanical properties of the alloy. The strength of TaWHfReC alloy is much higher than that of TaWHf alloy, especially at 1300 and 1500 °C. At 1300 °C, the ultimate tensile strength of the TaWHf alloy is 322 MPa, while that of the TaWHfReC alloy reaches 392 MPa. When the temperature rises to 1500 °C, precipitated-phase strengthening remains effective in the TaWHfReC alloy, achieving an ultimate tensile strength of 268 MPa. Additionally, at 1300 °C, the elongation of the TaWHfReC alloy reaches 23.5%, which is nearly twice of that of the TaWHf alloy. The significant improvement in the mechanical properties of the TaWHfReC alloy at elevated temperatures is primarily attributed to the interaction between dislocations and the fine Ta2C precipitated phase. The fine and uniformly distributed particles effectively inhibit dislocation motion and exhibit a pronounced strengthening effect at high temperatures.
The high-temperature mechanical properties of Ta-8W-2Hf alloy doped with Re (1wt%) and C (0.01wt%) were investigated at room temperature, 1300 °C, and 1500 °C. Results show that fine and dispersed precipitates Ta2C are detected in crystallized TaWHfReC alloy, which significantly enhance mechanical properties of the alloy. The strength of TaWHfReC alloy is much higher than that of TaWHf alloy, especially at 1300 and 1500 °C. At 1300 °C, the ultimate tensile strength of the TaWHf alloy is 322 MPa, while that of the TaWHfReC alloy reaches 392 MPa. When the temperature rises to 1500 °C, precipitated-phase strengthening remains effective in the TaWHfReC alloy, achieving an ultimate tensile strength of 268 MPa. Additionally, at 1300 °C, the elongation of the TaWHfReC alloy reaches 23.5%, which is nearly twice of that of the TaWHf alloy. The significant improvement in the mechanical properties of the TaWHfReC alloy at elevated temperatures is primarily attributed to the interaction between dislocations and the fine Ta2C precipitated phase. The fine and uniformly distributed particles effectively inhibit dislocation motion and exhibit a pronounced strengthening effect at high temperatures.
2025, 54(11):2717-2728.
DOI: 10.12442/j.issn.1002-185X.20240618
Abstract:
Four types of Mg-5Zn porous scaffolds with different pore geometries, including body-centered cubic (bcc), the rhombic dodecahedron (RD), gyroid (G), and primitive (P) types, were designed and fabricated using selective laser melting. Their forming quality, compression mechanical properties, and degradation behavior were investigated. Results indicate that the fabricated scaffolds exhibit good dimensional accuracy, and the surface chemical polishing treatment significantly improves the forming quality and reduces porosity error in porous scaffolds. Compared to the ones with rod structures (bcc, RD), the scaffolds with surface structures (G, P) have less powder particle adhesion. The G porous scaffold exhibits the best forming quality for the same design porosity. The predominant failure mode of scaffolds during compression is a 45° shear fracture. At a porosity of 75%, the compression property of all scaffolds meets the compressive property requirements of cancellous bone, while bcc and G structures show relatively better compression property. After immersion in Hank's solution for 168 h, the B-2-75% pore structure scaffold exhibits severe localized corrosion, with fractures in partial pillar connections. In contrast, the G-3-75% pore structure scaffold mainly undergoes uniform corrosion, maintaining structural integrity, and its corrosion rate and loss of compressive properties are less than those of the B-2-75% structure. After comparison, the G-pore structure scaffold is preferred.
Four types of Mg-5Zn porous scaffolds with different pore geometries, including body-centered cubic (bcc), the rhombic dodecahedron (RD), gyroid (G), and primitive (P) types, were designed and fabricated using selective laser melting. Their forming quality, compression mechanical properties, and degradation behavior were investigated. Results indicate that the fabricated scaffolds exhibit good dimensional accuracy, and the surface chemical polishing treatment significantly improves the forming quality and reduces porosity error in porous scaffolds. Compared to the ones with rod structures (bcc, RD), the scaffolds with surface structures (G, P) have less powder particle adhesion. The G porous scaffold exhibits the best forming quality for the same design porosity. The predominant failure mode of scaffolds during compression is a 45° shear fracture. At a porosity of 75%, the compression property of all scaffolds meets the compressive property requirements of cancellous bone, while bcc and G structures show relatively better compression property. After immersion in Hank's solution for 168 h, the B-2-75% pore structure scaffold exhibits severe localized corrosion, with fractures in partial pillar connections. In contrast, the G-3-75% pore structure scaffold mainly undergoes uniform corrosion, maintaining structural integrity, and its corrosion rate and loss of compressive properties are less than those of the B-2-75% structure. After comparison, the G-pore structure scaffold is preferred.
2025, 54(10):2525-2532.
DOI: 10.12442/j.issn.1002-185X.20240282
Abstract:
Flow behavior and grain structure evolution were studied for 2196 aluminum-lithium alloy during hot compression deformation. Based on extrusion simulation and profile trial production, grain structure control of typical I-shaped thin-walled profiles was achieved. The results show that the alloy exhibits excellent hot deformability in a relatively wide parameter range. The dominate mechanism of microstructure evolution is dynamic recovery, although some localized dynamic recrystallization is also observed. At lower temperatures (350, 400 ℃) and higher strain rates (10 s-1), strain concentration leads to a small amount of local dynamic recrystallization. Compared to experimental compression deformation, the larger strain of extrusion process promotes the formation of dynamic recrystallization. The differences of deformation conditions on profile section lead to non-homogeneous grain structure. Based on the equipment capability, relatively uniform microstructure be obtained under deformation conditions of 430 ℃ and strain rate of 0.005–0.95 s-1 on profile section, while maintaining lower fraction of recrystallization and abundant sub-grain structure, which is benefit for the strength and toughness matching.
Flow behavior and grain structure evolution were studied for 2196 aluminum-lithium alloy during hot compression deformation. Based on extrusion simulation and profile trial production, grain structure control of typical I-shaped thin-walled profiles was achieved. The results show that the alloy exhibits excellent hot deformability in a relatively wide parameter range. The dominate mechanism of microstructure evolution is dynamic recovery, although some localized dynamic recrystallization is also observed. At lower temperatures (350, 400 ℃) and higher strain rates (10 s-1), strain concentration leads to a small amount of local dynamic recrystallization. Compared to experimental compression deformation, the larger strain of extrusion process promotes the formation of dynamic recrystallization. The differences of deformation conditions on profile section lead to non-homogeneous grain structure. Based on the equipment capability, relatively uniform microstructure be obtained under deformation conditions of 430 ℃ and strain rate of 0.005–0.95 s-1 on profile section, while maintaining lower fraction of recrystallization and abundant sub-grain structure, which is benefit for the strength and toughness matching.
2025, 54(9):2177-2188.
DOI: 10.12442/j.issn.1002-185X.20240452
Abstract:
The transient liquid-phase (TLP) diffusion bonding of GH5188 with a BNi-5 interlayer was focused on. Parameters were chosen and optimized for GH5188 alloy according to the TLP joining mechanism. The microstructure evolution and mechanical properties of the joints were studied. Results show that the relatively complete isothermal solidification zone (ISZ) ensures a reliable connection of the base metal (BM). Within the temperature range of 1110–1190 °C, higher bonding temperatures can widen ISZ and promote joint composition homogenization, thus improving mechanical properties. However, the increase in precipitated phase has an adverse effect on the mechanical properties of the joint. The maximum shear strength, reaching 482 MPa, is achieved at 1130 °C, representing 84.6% of BM strength. Within the pressure range of 5–15 MPa, both precipitated phases in adiabatic solidification zone (ASZ) and voids generated by partial melting increase. On the contrary, their sizes decrease significantly under higher bonding pressure, resulting in an upward trend in alloy mechanical properties. The maximum shear strength of 490 MPa is attained at a bonding pressure of 15 MPa. The joint exhibits a typical mixed fracture pattern, with the small brittle M23C6 phase and voids significantly impacting mechanical properties. Nano-indentation tests indicate that ASZ is a potential source of cracks.
The transient liquid-phase (TLP) diffusion bonding of GH5188 with a BNi-5 interlayer was focused on. Parameters were chosen and optimized for GH5188 alloy according to the TLP joining mechanism. The microstructure evolution and mechanical properties of the joints were studied. Results show that the relatively complete isothermal solidification zone (ISZ) ensures a reliable connection of the base metal (BM). Within the temperature range of 1110–1190 °C, higher bonding temperatures can widen ISZ and promote joint composition homogenization, thus improving mechanical properties. However, the increase in precipitated phase has an adverse effect on the mechanical properties of the joint. The maximum shear strength, reaching 482 MPa, is achieved at 1130 °C, representing 84.6% of BM strength. Within the pressure range of 5–15 MPa, both precipitated phases in adiabatic solidification zone (ASZ) and voids generated by partial melting increase. On the contrary, their sizes decrease significantly under higher bonding pressure, resulting in an upward trend in alloy mechanical properties. The maximum shear strength of 490 MPa is attained at a bonding pressure of 15 MPa. The joint exhibits a typical mixed fracture pattern, with the small brittle M23C6 phase and voids significantly impacting mechanical properties. Nano-indentation tests indicate that ASZ is a potential source of cracks.
2025, 54(8):1997-2007.
DOI: 10.12442/j.issn.1002-185X.20240238
Abstract:
The formation mechanism of freckle defects in large-sized UGTC47 directionally-solidified columnar crystal blades for heavy-duty gas turbines and their effect on the stress rupture property were investigated using optical microscope, scanning electron microscope, and endurance performance test. The results indicate that freckle defects form in both the middle and root regions of the blade tenon, whose formation mechanism is the density inversion caused by liquid phase segregation, resulting in fluid convection under the action of gravity, and leading to the fracture of dendrite arms and the formation of freckles. At 900 ℃/380 MPa, the proportion of freckle area has a significant impact on the endurance performance of the UGTC47 alloy. With the increase in freckle content, the stress rupture life of the alloy is decreased from 131.83 h without freckle defects to 33.66 h with freckle content of 62%.
The formation mechanism of freckle defects in large-sized UGTC47 directionally-solidified columnar crystal blades for heavy-duty gas turbines and their effect on the stress rupture property were investigated using optical microscope, scanning electron microscope, and endurance performance test. The results indicate that freckle defects form in both the middle and root regions of the blade tenon, whose formation mechanism is the density inversion caused by liquid phase segregation, resulting in fluid convection under the action of gravity, and leading to the fracture of dendrite arms and the formation of freckles. At 900 ℃/380 MPa, the proportion of freckle area has a significant impact on the endurance performance of the UGTC47 alloy. With the increase in freckle content, the stress rupture life of the alloy is decreased from 131.83 h without freckle defects to 33.66 h with freckle content of 62%.
2025, 54(7):1847-1856.
DOI: 10.12442/j.issn.1002-185X.20240112
Abstract:
The I phase (Mg3Zn6Gd, icosahedral quasicrystal phase) is widely considered as the strengthening phase in Mg-Zn-Gd system alloys, providing more significant improvements in the mechanical properties compared to the W phase (Mg3Zn3Gd2, cubic phase). However, both the W phase and the I phase typically coexist in the as-cast Mg-Zn-Gd alloy, thereby weakening its mechanical properties. There has been limited systematic research dedicated to investigating the crystallization mechanism of these phases during solidification. In this study, the equilibrium solidification and Scheil solidification paths of Mg-xZn-2Gd (x=0–12, wt%) alloys were calculated by Thermo-Calc software. The effects of cooling rate and alloy composition on the fraction of the I phase were studied. The results show that the equilibrium solidification structure of the alloy with a Zn/Gd atomic ratio of 6.0 only contains the I phase. In contrast, limited solute diffusion in the solid phase hampers the transformation of the W phase into the I phase during non-equilibrium solidification, forming a mixed structure composed of both the W phase and the I phase. The variation of cooling rate and alloy composition affects the solute enrichment rate in the Liquid during the solidification process of the primary α-Mg phase and alters the solute content and temperature of the residual Liquid when the secondary phase begins to crystallize, and influences the type and fraction of the secondary phase as determined by the solidification driving force. The increased solidification cooling rates and Zn/Gd atomic ratio inhibit the W phase and promote the formation of the I phase during Mg-Zn-Gd alloy preparation, resulting a higher proportion of the I phase in the alloy.
The I phase (Mg3Zn6Gd, icosahedral quasicrystal phase) is widely considered as the strengthening phase in Mg-Zn-Gd system alloys, providing more significant improvements in the mechanical properties compared to the W phase (Mg3Zn3Gd2, cubic phase). However, both the W phase and the I phase typically coexist in the as-cast Mg-Zn-Gd alloy, thereby weakening its mechanical properties. There has been limited systematic research dedicated to investigating the crystallization mechanism of these phases during solidification. In this study, the equilibrium solidification and Scheil solidification paths of Mg-xZn-2Gd (x=0–12, wt%) alloys were calculated by Thermo-Calc software. The effects of cooling rate and alloy composition on the fraction of the I phase were studied. The results show that the equilibrium solidification structure of the alloy with a Zn/Gd atomic ratio of 6.0 only contains the I phase. In contrast, limited solute diffusion in the solid phase hampers the transformation of the W phase into the I phase during non-equilibrium solidification, forming a mixed structure composed of both the W phase and the I phase. The variation of cooling rate and alloy composition affects the solute enrichment rate in the Liquid during the solidification process of the primary α-Mg phase and alters the solute content and temperature of the residual Liquid when the secondary phase begins to crystallize, and influences the type and fraction of the secondary phase as determined by the solidification driving force. The increased solidification cooling rates and Zn/Gd atomic ratio inhibit the W phase and promote the formation of the I phase during Mg-Zn-Gd alloy preparation, resulting a higher proportion of the I phase in the alloy.
2025, 54(6):1630-1640.
DOI: 10.12442/j.issn.1002-185X.20250028
Abstract:
Laser beam welding (LBW) has emerged as one of the most promising connection techniques for lightweight equipment fabricated by magnesium alloys due to the less deformation, narrow heat-affected zone, and excellent welding efficiency. However, a variety of porosity defects are commonly found in the laser welded joints. The causes of laser-welded pores are complicated. The number, size and distribution characteristics of porosity affect the mechanical properties of magnesium alloy joints, and thus seriously affecting the reliable applications of magnesium alloy lightweight equipment. This study reviewed the mechanism of pores formation in the microstructure of laser welding joints of magnesium alloys, and discussed the influence of porosity on mechanical properties. The pore manipulation was proposed. The key basic research and applications of LBW of magnesium alloys were pointed out. This review may provide valuable insights for the development of joining and manufacturing technology of magnesium alloy lightweight parts in automotive and aerospace fields.
Laser beam welding (LBW) has emerged as one of the most promising connection techniques for lightweight equipment fabricated by magnesium alloys due to the less deformation, narrow heat-affected zone, and excellent welding efficiency. However, a variety of porosity defects are commonly found in the laser welded joints. The causes of laser-welded pores are complicated. The number, size and distribution characteristics of porosity affect the mechanical properties of magnesium alloy joints, and thus seriously affecting the reliable applications of magnesium alloy lightweight equipment. This study reviewed the mechanism of pores formation in the microstructure of laser welding joints of magnesium alloys, and discussed the influence of porosity on mechanical properties. The pore manipulation was proposed. The key basic research and applications of LBW of magnesium alloys were pointed out. This review may provide valuable insights for the development of joining and manufacturing technology of magnesium alloy lightweight parts in automotive and aerospace fields.
2025, 54(5):1217-1228.
DOI: 10.12442/j.issn.1002-185X.20230827
Abstract:
The effects of V content (0.1wt%, 0.2wt%) on the carbide evolution and mechanical properties of ultra-clean 30Cr2Ni4MoV rotor steel under different heat-treatment states (as tempered and as step cooled) were investigated by SEM, EBSD, XRD, TEM, and APT. The results show that both tempered steels show lath martensite microstructure. The increase in V content has no obvious effect on the carbide type (M23C6, M2C and MC) and size, but promotes the precipitation of more and finer V-riched carbides MC, which refines the prior austenite grain size of the 0.2V steel. The refinement of grain size and precipitation of finer MC carbides increase the yield strength of the 0.2V steel by 147 MPa through grain refining strengthening and precipitation strengthening. After step cooling heat-treatment, the microstructures and the type of carbides in both steels remain stable and the size of carbide grows slightly. Meanwhile, the yield strength of them shows a slight decrease due to the carbide coarsening. As for 0.2V steel, the mobility of dislocations decreases due to precipitation of more MC carbides, which induces the decrease in critical stress σf of crack propagation and promotes the tendency of crack initiation and propagation. Therefore, compared with that of 0.1V steel, the fracture appearance transition temperature of 0.2V steel increases by 21 ℃.
The effects of V content (0.1wt%, 0.2wt%) on the carbide evolution and mechanical properties of ultra-clean 30Cr2Ni4MoV rotor steel under different heat-treatment states (as tempered and as step cooled) were investigated by SEM, EBSD, XRD, TEM, and APT. The results show that both tempered steels show lath martensite microstructure. The increase in V content has no obvious effect on the carbide type (M23C6, M2C and MC) and size, but promotes the precipitation of more and finer V-riched carbides MC, which refines the prior austenite grain size of the 0.2V steel. The refinement of grain size and precipitation of finer MC carbides increase the yield strength of the 0.2V steel by 147 MPa through grain refining strengthening and precipitation strengthening. After step cooling heat-treatment, the microstructures and the type of carbides in both steels remain stable and the size of carbide grows slightly. Meanwhile, the yield strength of them shows a slight decrease due to the carbide coarsening. As for 0.2V steel, the mobility of dislocations decreases due to precipitation of more MC carbides, which induces the decrease in critical stress σf of crack propagation and promotes the tendency of crack initiation and propagation. Therefore, compared with that of 0.1V steel, the fracture appearance transition temperature of 0.2V steel increases by 21 ℃.
2025, 54(4):837-853.
DOI: 10.12442/j.issn.1002-185X.20250097
Abstract:
Brazing filler metals are widely applied, which serve as an industrial adhesive in the joining of dissimilar structures. With the continuous emergence of new structures and materials, the demand for novel brazing filler metals is ever-increasing. It is of great significance to investigate the optimized composition design methods and to establish systematic design guidelines for brazing filler metals. This study elucidated the fundamental rules for the composition design of brazing filler metals from a three-dimensional perspective encompassing the basic properties of applied brazing filler metals, formability and processability, and overall cost. The basic properties of brazing filler metals refer to their mechanical properties, physicochemical properties, electromagnetic properties, corrosion resistance, and the wettability and fluidity during brazing. The formability and processability of brazing filler metals include the processes of smelting and casting, extrusion, rolling, drawing and ring-making, as well as the processes of granulation, powder production, and the molding of amorphous and microcrystalline structures. The cost of brazing filler metals corresponds to the sum of materials value and manufacturing cost. Improving the comprehensive properties of brazing filler metals requires a comprehensive and systematic consideration of design indicators. Highlighting the unique characteristics of brazing filler metals should focus on relevant technical indicators. Binary or ternary eutectic structures can effectively enhance the flow spreading ability of brazing filler metals, and solid solution structures contribute to the formability. By employing the proposed design guidelines, typical Ag based, Cu based, Zn based brazing filler metals, and Sn based solders were designed and successfully applied in major scientific and engineering projects.
Brazing filler metals are widely applied, which serve as an industrial adhesive in the joining of dissimilar structures. With the continuous emergence of new structures and materials, the demand for novel brazing filler metals is ever-increasing. It is of great significance to investigate the optimized composition design methods and to establish systematic design guidelines for brazing filler metals. This study elucidated the fundamental rules for the composition design of brazing filler metals from a three-dimensional perspective encompassing the basic properties of applied brazing filler metals, formability and processability, and overall cost. The basic properties of brazing filler metals refer to their mechanical properties, physicochemical properties, electromagnetic properties, corrosion resistance, and the wettability and fluidity during brazing. The formability and processability of brazing filler metals include the processes of smelting and casting, extrusion, rolling, drawing and ring-making, as well as the processes of granulation, powder production, and the molding of amorphous and microcrystalline structures. The cost of brazing filler metals corresponds to the sum of materials value and manufacturing cost. Improving the comprehensive properties of brazing filler metals requires a comprehensive and systematic consideration of design indicators. Highlighting the unique characteristics of brazing filler metals should focus on relevant technical indicators. Binary or ternary eutectic structures can effectively enhance the flow spreading ability of brazing filler metals, and solid solution structures contribute to the formability. By employing the proposed design guidelines, typical Ag based, Cu based, Zn based brazing filler metals, and Sn based solders were designed and successfully applied in major scientific and engineering projects.
2025, 54(3):545-553.
DOI: 10.12442/j.issn.1002-185X.20240361
Abstract:
CuS-C50, the cathode materials for magnesium ion batteries, was synthesized by adding the surfactant cetyltrimethyl ammonium bromide (CTAB) and adjusting the percentage of ethylene glycol to 50vol% in hydrothermal synthesis process. Results show that CuS-C50 has the complete nanoflower structure. In aluminum chloride-pentamethylcydopentodiene/tetrahydrofuran (APC/THF) electrolyte, the CuS-C50 exhibits a high specific capacity of 331.19 mAh/g when the current density is 50 mA/g and still keeps a specific capacity of 136.92 mAh/g over 50 cycles when the current density is 200 mA/g. Results of morphology characterizations indicate that the complete nanoflower structure can provide more active sites and reduce the barriers for Mg2+ movement, eventually improving the charge and discharge performance of the CuS cathode materials for magnesium ion batteries.
CuS-C50, the cathode materials for magnesium ion batteries, was synthesized by adding the surfactant cetyltrimethyl ammonium bromide (CTAB) and adjusting the percentage of ethylene glycol to 50vol% in hydrothermal synthesis process. Results show that CuS-C50 has the complete nanoflower structure. In aluminum chloride-pentamethylcydopentodiene/tetrahydrofuran (APC/THF) electrolyte, the CuS-C50 exhibits a high specific capacity of 331.19 mAh/g when the current density is 50 mA/g and still keeps a specific capacity of 136.92 mAh/g over 50 cycles when the current density is 200 mA/g. Results of morphology characterizations indicate that the complete nanoflower structure can provide more active sites and reduce the barriers for Mg2+ movement, eventually improving the charge and discharge performance of the CuS cathode materials for magnesium ion batteries.
2025, 54(2):385-393.
DOI: 10.12442/j.issn.1002-185X.20240591
Abstract:
AgCu filler was used to braze Zr and CoCrFeMnNi high-entropy alloy (HEA). The effects of brazing temperature and holding time on the microstructure and mechanical properties of the joints were analyzed. The results show that the typical microstructure of the joints brazed at 850 ℃ for 10 min is HEA/Crss/Zr(Cr,Mn)2/Zr2(Co,Cu,Ni,Fe)+Zr2(Ag,Cu)+Zr(Cr,Mn)2/Zr. The joints have the maximum shear strength of 103.1 MPa. As the brazing temperature or holding time rises, the thickness of Cr-rich solid solution and Zr(Cr,Mn)2 layer are increased, the content of Zr2(Co,Cu,Ni,Fe) and Zr(Cr,Mn)2 phase is increased whereas the content of Zr2(Ag,Cu) phase is decreased. Finally, the failure mechanism of the joint was analyzed. Under the action of shear force, as the brazing temperature or holding time rises, the fracture position of the joint shifts from the Zr(Cr, Mn)2 layer to the Zr2(Co, Cu, Ni, Fe) phase fracture in the center of the brazing seam.
AgCu filler was used to braze Zr and CoCrFeMnNi high-entropy alloy (HEA). The effects of brazing temperature and holding time on the microstructure and mechanical properties of the joints were analyzed. The results show that the typical microstructure of the joints brazed at 850 ℃ for 10 min is HEA/Crss/Zr(Cr,Mn)2/Zr2(Co,Cu,Ni,Fe)+Zr2(Ag,Cu)+Zr(Cr,Mn)2/Zr. The joints have the maximum shear strength of 103.1 MPa. As the brazing temperature or holding time rises, the thickness of Cr-rich solid solution and Zr(Cr,Mn)2 layer are increased, the content of Zr2(Co,Cu,Ni,Fe) and Zr(Cr,Mn)2 phase is increased whereas the content of Zr2(Ag,Cu) phase is decreased. Finally, the failure mechanism of the joint was analyzed. Under the action of shear force, as the brazing temperature or holding time rises, the fracture position of the joint shifts from the Zr(Cr, Mn)2 layer to the Zr2(Co, Cu, Ni, Fe) phase fracture in the center of the brazing seam.
2025, 54(1):1-9.
DOI: 10.12442/j.issn.1002-185X.20240473
Abstract:
The pressure-actuated metal seal with soft metal coating has been widely used in complex working conditions such as high temperature, low temperature and high pressure. The investigation of the characteristics and binding strength of the transition layer between the soft metal coating and the superalloy substrate is important to improve the sealing performance and to model and simplify the working through-process of metal sealing. The distribution characteristics of elements at soft metal-substrate interface and the binding strength between coating and substrate under different thicknesses and material combinations of coating layer were studied by experimental methods. The results indicate that the thickness of soft metal coating has little influence on the interface morphology of GH4169-Cu, GH4169-Ag and Cu-Ag, but has an influence on the thickness of transition layer between different metals, while this influence is weakened with increasing the coating thickness, and the thickness of transition layer is about 2 μm when the coating thickness is more than 30 μm. The cross-cut test shows that the Cu, Ag and Cu-Ag coatings are all well combined with nickel-based superalloy GH4169 substrate. The materials of soft metal, i.e. the coating materials, have significant influence on the characteristic of transition layer and the surface characteristics of coating after cross-cut test.
The pressure-actuated metal seal with soft metal coating has been widely used in complex working conditions such as high temperature, low temperature and high pressure. The investigation of the characteristics and binding strength of the transition layer between the soft metal coating and the superalloy substrate is important to improve the sealing performance and to model and simplify the working through-process of metal sealing. The distribution characteristics of elements at soft metal-substrate interface and the binding strength between coating and substrate under different thicknesses and material combinations of coating layer were studied by experimental methods. The results indicate that the thickness of soft metal coating has little influence on the interface morphology of GH4169-Cu, GH4169-Ag and Cu-Ag, but has an influence on the thickness of transition layer between different metals, while this influence is weakened with increasing the coating thickness, and the thickness of transition layer is about 2 μm when the coating thickness is more than 30 μm. The cross-cut test shows that the Cu, Ag and Cu-Ag coatings are all well combined with nickel-based superalloy GH4169 substrate. The materials of soft metal, i.e. the coating materials, have significant influence on the characteristic of transition layer and the surface characteristics of coating after cross-cut test.
2024, 53(12):3281-3290.
DOI: 10.12442/j.issn.1002-185X.20240097
Abstract:
Near-α titanium alloy and Ti2AlNb alloy powders premixed with different proportions were prepared on the near-α titanium alloy substrate by laser deposition technique, and the microstructure characteristics were analyzed and discussed. Results show that numerous river-like sub-grain structures are formed inside the equiaxed B2 grains of the laser-deposited premixed titanium alloy powders with the proportion of Ti2AlNb above 40wt%, whereas the needle-like structure within coarse columnar β grains exist with the proportion of Ti2AlNb below 40wt%. It is noteworthy that the decrease in laser power and scanning speed can accelerate the formation of sub-grain structures. Based on the analysis of experimental results, it can be inferred that the formation of sub-grain structure not only is related to the precipitation of O phase due to composition micro-segregation at sub-grain boundaries, but also is inseparable from the stacking faults caused by the internal stress during the laser deposition.
Near-α titanium alloy and Ti2AlNb alloy powders premixed with different proportions were prepared on the near-α titanium alloy substrate by laser deposition technique, and the microstructure characteristics were analyzed and discussed. Results show that numerous river-like sub-grain structures are formed inside the equiaxed B2 grains of the laser-deposited premixed titanium alloy powders with the proportion of Ti2AlNb above 40wt%, whereas the needle-like structure within coarse columnar β grains exist with the proportion of Ti2AlNb below 40wt%. It is noteworthy that the decrease in laser power and scanning speed can accelerate the formation of sub-grain structures. Based on the analysis of experimental results, it can be inferred that the formation of sub-grain structure not only is related to the precipitation of O phase due to composition micro-segregation at sub-grain boundaries, but also is inseparable from the stacking faults caused by the internal stress during the laser deposition.
2024, 53(11):3101-3110.
DOI: 10.12442/j.issn.1002-185X.20240027
Abstract:
The sub-stable β-type TB18 titanium alloy exhibits a significant strengthening effect through solutionizing-ageing and possesses excellent potential for achieving a balanced combination of strength and toughness. As a result, it has emerged as a favoured material for manufacturing high-end aviation components. This work aimed to investigate the impact of solid solution treatment on the microstructure and mechanical properties of TB18 titanium alloy. Specifically, the effects of different solution temperatures, solution times, and slow cooling rates after solutionizing on the alloy"s microstructure and mechanical properties were illustrated. The goal is to understand the mechanism behind the interaction between solution treatment and the microstructure-mechanical properties of TB18 titanium alloy. The results indicated that following the solutionizing and aging treatment within the β single-phase region, lamellar and needle-like αs phases precipitated within the β matrix. The presence of lamellar αs phases contributed to the improvement of the toughness of the TB18 titanium alloy. Furthermore, it was observed that the fracture toughness of the TB18 titanium alloy improved with an increase in the thickness of the lamellar αsphases. Elevated solutionizing temperature or prolonged solid solution holding time can result in the coarsening of β grains in TB18 titanium alloy, leading to a decrease in material strength and plasticity. When increasing the cooling rate from 0.25 ℃/min to 1 ℃/min after solutionizing, the fine αs phases uniformly distributed within the TB18 titanium alloy after aging treatment, and the tensile strength increased to 1343 MPa while the elongation was 5 %. By subjecting the TB18 titanium alloy to a solutionizing regime at a temperature of 870 ℃ for 2 hours, followed by air cooling, it achieved a favorable combination of strength and toughness. Further aging at 530 ℃ for 4 hours, again with air cooling, results in a tensile strength of 1315 MPa, yield strength of 1225 MPa, elongation of 8.5%, impact toughness of 29.2 J/cm2, and fracture toughness value of 88.4 MPa . m1/2.
The sub-stable β-type TB18 titanium alloy exhibits a significant strengthening effect through solutionizing-ageing and possesses excellent potential for achieving a balanced combination of strength and toughness. As a result, it has emerged as a favoured material for manufacturing high-end aviation components. This work aimed to investigate the impact of solid solution treatment on the microstructure and mechanical properties of TB18 titanium alloy. Specifically, the effects of different solution temperatures, solution times, and slow cooling rates after solutionizing on the alloy"s microstructure and mechanical properties were illustrated. The goal is to understand the mechanism behind the interaction between solution treatment and the microstructure-mechanical properties of TB18 titanium alloy. The results indicated that following the solutionizing and aging treatment within the β single-phase region, lamellar and needle-like αs phases precipitated within the β matrix. The presence of lamellar αs phases contributed to the improvement of the toughness of the TB18 titanium alloy. Furthermore, it was observed that the fracture toughness of the TB18 titanium alloy improved with an increase in the thickness of the lamellar αsphases. Elevated solutionizing temperature or prolonged solid solution holding time can result in the coarsening of β grains in TB18 titanium alloy, leading to a decrease in material strength and plasticity. When increasing the cooling rate from 0.25 ℃/min to 1 ℃/min after solutionizing, the fine αs phases uniformly distributed within the TB18 titanium alloy after aging treatment, and the tensile strength increased to 1343 MPa while the elongation was 5 %. By subjecting the TB18 titanium alloy to a solutionizing regime at a temperature of 870 ℃ for 2 hours, followed by air cooling, it achieved a favorable combination of strength and toughness. Further aging at 530 ℃ for 4 hours, again with air cooling, results in a tensile strength of 1315 MPa, yield strength of 1225 MPa, elongation of 8.5%, impact toughness of 29.2 J/cm2, and fracture toughness value of 88.4 MPa . m1/2.
Study of high-temperature oxidation behavior of electrodeposited Ni/Cr coatings on Zr alloy surfaces
2024, 53(10):2805-2800.
DOI: 10.12442/j.issn.1002-185X.20240037
Abstract:
After the Fukushima nuclear accident in Japan, accident tolerant fuel (ATF) cladding technology has attracted widespread attention in the industry. The cladding of Cr coatings on zirconium (Zr) alloys for nuclear fuel cladding in nuclear reactor cores is considered to be the most likely technology to be commercially available in the near future. At present, most of the preparation methods for Cr coatings have the disadvantages of expensive equipment, low deposition rate and weak shape adaptability. And the molten salt electrodeposition technology has the advantages of high cathodic current efficiency, fast electrodeposition speed, and strong adaptability of substrate shape, which is expected to solve the problem of efficient and low-cost preparation of high-quality Cr coatings on the surface of cladding Zr alloys. In order to realize the preparation of Cr coating on the surface of Zr alloy by molten salt electrodeposition, this paper adopted aqueous solution electrodeposition and molten salt electrodeposition methods to prepare Ni transition layer and Cr coating on the surface of Zr alloy substrate sequentially, and carried out the characterization of the organization structure, the bonding force and nano-hardness test as well as the study of the high-temperature oxidation behavior of the Zr/Ni/Cr specimens obtained from the preparation. The results showed that the Ni/Cr coating on the surface of Zr alloy was uniform and dense, and the bonding force between the coating and the substrate was about 151N. The hardness and modulus of elasticity of Zr/Ni/Cr increased gradually from inner to outer layers with a quasi-gradient transition. The surface roughness of the Cr coating was about 2 μm, and the hardness and modulus of elasticity were 2.86 GPa and 172.86 GPa, respectively. The Zr/Ni/Cr specimens showed nearly parabolic and nearly linear patterns during steam oxidation at high temperatures of 1000°C and 1200°C, respectively, indicating that the Ni/Cr coatings were able to provide good protection to the Zr alloy matrix at 1000℃. The high-temperature oxidation failure mechanism of Ni/Cr coatings on Zr alloy surfaces was closely related to the rapid diffusion of the Ni transition layer, the oxidation and diffusion depletion of the Cr layer, and the weakening of the Cr layer due to the rapid diffusion of Zr along the Cr grain boundaries.
After the Fukushima nuclear accident in Japan, accident tolerant fuel (ATF) cladding technology has attracted widespread attention in the industry. The cladding of Cr coatings on zirconium (Zr) alloys for nuclear fuel cladding in nuclear reactor cores is considered to be the most likely technology to be commercially available in the near future. At present, most of the preparation methods for Cr coatings have the disadvantages of expensive equipment, low deposition rate and weak shape adaptability. And the molten salt electrodeposition technology has the advantages of high cathodic current efficiency, fast electrodeposition speed, and strong adaptability of substrate shape, which is expected to solve the problem of efficient and low-cost preparation of high-quality Cr coatings on the surface of cladding Zr alloys. In order to realize the preparation of Cr coating on the surface of Zr alloy by molten salt electrodeposition, this paper adopted aqueous solution electrodeposition and molten salt electrodeposition methods to prepare Ni transition layer and Cr coating on the surface of Zr alloy substrate sequentially, and carried out the characterization of the organization structure, the bonding force and nano-hardness test as well as the study of the high-temperature oxidation behavior of the Zr/Ni/Cr specimens obtained from the preparation. The results showed that the Ni/Cr coating on the surface of Zr alloy was uniform and dense, and the bonding force between the coating and the substrate was about 151N. The hardness and modulus of elasticity of Zr/Ni/Cr increased gradually from inner to outer layers with a quasi-gradient transition. The surface roughness of the Cr coating was about 2 μm, and the hardness and modulus of elasticity were 2.86 GPa and 172.86 GPa, respectively. The Zr/Ni/Cr specimens showed nearly parabolic and nearly linear patterns during steam oxidation at high temperatures of 1000°C and 1200°C, respectively, indicating that the Ni/Cr coatings were able to provide good protection to the Zr alloy matrix at 1000℃. The high-temperature oxidation failure mechanism of Ni/Cr coatings on Zr alloy surfaces was closely related to the rapid diffusion of the Ni transition layer, the oxidation and diffusion depletion of the Cr layer, and the weakening of the Cr layer due to the rapid diffusion of Zr along the Cr grain boundaries.
2024, 53(9):2405-2412.
DOI: 10.12442/j.issn.1002-185X.20230822
Abstract:
The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aero-engine, and the laser ignition method can accurately reflect the fire retardancy of titanium alloy under local heating. Due to the limitations of laser ignition experiments on the microscopic boundary and the transient propagation mechanism of the temperature field, molecular dynamics (MD) simulations and JMatPro calculation were applied to study the temperature field of Ti-6Al and Ti-48Al alloys. The results show that a molten pool is formed on the surface of Ti-Al alloys under continuous laser irradiation, and the temperature field of the molten pool is normally distributed from the center to the edge. When the center temperature reaches the critical point of ignition, the extended combustion occurs, and the extended combustion path advances along the direction of the air flow. Compared with Ti-6Al alloy, Ti-48Al alloy has higher fire retardancy under laser ablation. This is due to the better heat transfer performance of Ti-48Al, which leads to the weakening of the heat concentration effect near the boundary of the spot temperature field. So it is necessary to increase the partial pressure of oxygen, and thus to reduce the ignition point of the alloy in order to achieve the ignition boundary condition of Ti-48Al alloy under the same laser heat source. In the aspect of extended combustion path, the boundary heat collection effect of specimens shown by MD models reveals another mechanism affecting combustion expansion path besides the direction of air flow. That is, the heat generated by the laser spot is interrupted when it is transmitted to the boundary of the specimen along the short side direction, resulting in a concentration of heat near the boundary. So the combustion path also tends to expand along this direction.
The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aero-engine, and the laser ignition method can accurately reflect the fire retardancy of titanium alloy under local heating. Due to the limitations of laser ignition experiments on the microscopic boundary and the transient propagation mechanism of the temperature field, molecular dynamics (MD) simulations and JMatPro calculation were applied to study the temperature field of Ti-6Al and Ti-48Al alloys. The results show that a molten pool is formed on the surface of Ti-Al alloys under continuous laser irradiation, and the temperature field of the molten pool is normally distributed from the center to the edge. When the center temperature reaches the critical point of ignition, the extended combustion occurs, and the extended combustion path advances along the direction of the air flow. Compared with Ti-6Al alloy, Ti-48Al alloy has higher fire retardancy under laser ablation. This is due to the better heat transfer performance of Ti-48Al, which leads to the weakening of the heat concentration effect near the boundary of the spot temperature field. So it is necessary to increase the partial pressure of oxygen, and thus to reduce the ignition point of the alloy in order to achieve the ignition boundary condition of Ti-48Al alloy under the same laser heat source. In the aspect of extended combustion path, the boundary heat collection effect of specimens shown by MD models reveals another mechanism affecting combustion expansion path besides the direction of air flow. That is, the heat generated by the laser spot is interrupted when it is transmitted to the boundary of the specimen along the short side direction, resulting in a concentration of heat near the boundary. So the combustion path also tends to expand along this direction.
2024, 53(8):2109-2122.
DOI: 10.12442/j.issn.1002-185X.20230663
Abstract:
The corrosion properties of pure zirconium (Zr) with different grain sizes in acid, alkali, and salt environments were studied. The microstructures of pure Zr were observed by optical microscope, X-ray diffractometer, and electron backscattered diffraction probe. The corrosion resistance of pure Zr was analyzed by electrochemical corrosion test and immersion test. Results show that pure Zr with grain size of 4–32 μm can be obtained after annealing at 800 °C for different durations, and the relationship between grain size and annealing duration is D3-D03=3.35t. The electrochemical corrosion and immersion corrosion test results show that the pure Zr with grain size of about 24 μm (annealing at 800 °C for 20 h) possesses the optimal corrosion resistance.
The corrosion properties of pure zirconium (Zr) with different grain sizes in acid, alkali, and salt environments were studied. The microstructures of pure Zr were observed by optical microscope, X-ray diffractometer, and electron backscattered diffraction probe. The corrosion resistance of pure Zr was analyzed by electrochemical corrosion test and immersion test. Results show that pure Zr with grain size of 4–32 μm can be obtained after annealing at 800 °C for different durations, and the relationship between grain size and annealing duration is D3-D03=3.35t. The electrochemical corrosion and immersion corrosion test results show that the pure Zr with grain size of about 24 μm (annealing at 800 °C for 20 h) possesses the optimal corrosion resistance.
2024, 53(7):1817-1825.
DOI: 10.12442/j.issn.1002-185X.20230636
Abstract:
(Fe63.3Mn14Si9.1Cr9.8C3.8)99.5?xCuxAg0.5 (x=1, 2, 3, 4, 5, at%) alloys were prepared by water-cooled copper crucible magnetic levitation vacuum melting furnace. The effects of Cu contents on microstructure, corrosion resistance, and antibacterial performance of the alloys were investigated. The results show that the medium entropy alloys possess fcc phase after solid solution and aging treatment. With the increase in Cu content, the Cu-enriched and Ag-enriched fcc2 phase is precipitated on the fcc1 Fe-rich matrix. The corrosion resistance of the alloys in 3.5wt% NaCl solution is superior to that of AISI304. The corrosion current density first decreases and then increases, and the impedance arc radius first increases and then decreases, indicating an initial enhancement and subsequent weakening of the corrosion resistance as the Cu content increases. Moreover, the corrosion rate of the alloys in Escherichia coli suspension shows a trend of increasing first and then decreasing. When x=2 the alloy exhibits the best corrosion resistance, and there is a trade-off effect between the corrosion resistance and antibacterial performance. The fcc2 phase effectively enhances the antibacterial performance of the alloy, and the alloy of x=5 shows the optimal antibacterial rate of 99.94%.
(Fe63.3Mn14Si9.1Cr9.8C3.8)99.5?xCuxAg0.5 (x=1, 2, 3, 4, 5, at%) alloys were prepared by water-cooled copper crucible magnetic levitation vacuum melting furnace. The effects of Cu contents on microstructure, corrosion resistance, and antibacterial performance of the alloys were investigated. The results show that the medium entropy alloys possess fcc phase after solid solution and aging treatment. With the increase in Cu content, the Cu-enriched and Ag-enriched fcc2 phase is precipitated on the fcc1 Fe-rich matrix. The corrosion resistance of the alloys in 3.5wt% NaCl solution is superior to that of AISI304. The corrosion current density first decreases and then increases, and the impedance arc radius first increases and then decreases, indicating an initial enhancement and subsequent weakening of the corrosion resistance as the Cu content increases. Moreover, the corrosion rate of the alloys in Escherichia coli suspension shows a trend of increasing first and then decreasing. When x=2 the alloy exhibits the best corrosion resistance, and there is a trade-off effect between the corrosion resistance and antibacterial performance. The fcc2 phase effectively enhances the antibacterial performance of the alloy, and the alloy of x=5 shows the optimal antibacterial rate of 99.94%.
2024, 53(6):1608-1615.
DOI: 10.12442/j.issn.1002-185X.20230207
Abstract:
The harsh environment with strong acid, high oxidability and irradiation raises urgent demand for advanced structural materials used for reprocessing dissolver of spent nuclear fuels. In this paper, hot compression behavior of a Zr-1.0Ti-0.35Nb alloy was investigated at the strain rates of 0.01, 0.1, 1 s-1 and in the temperature range of 670 ~750 °C. Microstructural evolution during the hot compression was analyzed. The results reveal that the strain rate and deformation temperature both significantly affect the hot deformation behaviour of Zr-1.0Ti-0.35Nb alloy. Flow stress increases with accelerated strain rate, and decreases with elevated temperature. Beyond peak stress, the flow curve exhibits apparent characteristic of dynamic recrystallization characteristics. Elevated deformation temperature favors dynamic recrystallization and grain growth. An Arrhenius-type constitutive model was established based on the obtained peak stress values, in which the activation energy is calculated as 225.8 kJ/mol suggesting a Ti-induced elevation of activation energy and the hardening index is 5.62. A correlation coefficient of 0.97427 and average relative error of 6.15% are obtained between the experimental and predicted values, demonstrating sound applicability of the constitutive model that is expected to guide processing optimization for the new Zr-1.0Ti-0.35Nb alloy.
The harsh environment with strong acid, high oxidability and irradiation raises urgent demand for advanced structural materials used for reprocessing dissolver of spent nuclear fuels. In this paper, hot compression behavior of a Zr-1.0Ti-0.35Nb alloy was investigated at the strain rates of 0.01, 0.1, 1 s-1 and in the temperature range of 670 ~750 °C. Microstructural evolution during the hot compression was analyzed. The results reveal that the strain rate and deformation temperature both significantly affect the hot deformation behaviour of Zr-1.0Ti-0.35Nb alloy. Flow stress increases with accelerated strain rate, and decreases with elevated temperature. Beyond peak stress, the flow curve exhibits apparent characteristic of dynamic recrystallization characteristics. Elevated deformation temperature favors dynamic recrystallization and grain growth. An Arrhenius-type constitutive model was established based on the obtained peak stress values, in which the activation energy is calculated as 225.8 kJ/mol suggesting a Ti-induced elevation of activation energy and the hardening index is 5.62. A correlation coefficient of 0.97427 and average relative error of 6.15% are obtained between the experimental and predicted values, demonstrating sound applicability of the constitutive model that is expected to guide processing optimization for the new Zr-1.0Ti-0.35Nb alloy.
2024, 53(5):1252-1261.
DOI: 10.12442/j.issn.1002-185X.E20230036
Abstract:
Four-layer aluminum brazing sheets (4343/3003/6111/3003) with honeycomb sandwich structure are used as candidates for floor of high-speed train and ship deck, which are often exposed to corrosive environments. Microstructure and surface conditions of optimized 6111 aluminum alloy, which serves as the main support layer of this four-layer brazing sheet, have a great effect on the corrosion properties, which were investigated by a set of 6111 aluminum alloy ground with sandpaper of different grits. The results show that the AlFeSi(Mn, Cu) phase acts as cathode, due to its higher potential than that of the matrix, and forms a multi-stage system with adjacent matrix, which aggravates the surface corrosion. A smoother surface exhibits better corrosion resistance. Specifically, when lowering surface roughness from 18.03 μm to 0.92 μm, the surface volume decreases from 0.629 mm3 to 0.029 mm3, and the average number of intermetallic particles AlFeSi (Mn, Cu) is reduced from 1631 mm-2 to 917 mm-2, with area fraction decreasing from 3.93% to 0.92%. As a consequence, the average corrosion depth decreases from 237 μm to 95 μm.
Four-layer aluminum brazing sheets (4343/3003/6111/3003) with honeycomb sandwich structure are used as candidates for floor of high-speed train and ship deck, which are often exposed to corrosive environments. Microstructure and surface conditions of optimized 6111 aluminum alloy, which serves as the main support layer of this four-layer brazing sheet, have a great effect on the corrosion properties, which were investigated by a set of 6111 aluminum alloy ground with sandpaper of different grits. The results show that the AlFeSi(Mn, Cu) phase acts as cathode, due to its higher potential than that of the matrix, and forms a multi-stage system with adjacent matrix, which aggravates the surface corrosion. A smoother surface exhibits better corrosion resistance. Specifically, when lowering surface roughness from 18.03 μm to 0.92 μm, the surface volume decreases from 0.629 mm3 to 0.029 mm3, and the average number of intermetallic particles AlFeSi (Mn, Cu) is reduced from 1631 mm-2 to 917 mm-2, with area fraction decreasing from 3.93% to 0.92%. As a consequence, the average corrosion depth decreases from 237 μm to 95 μm.
2024, 53(4):933-946.
DOI: 10.12442/j.issn.1002-185X.20230402
Abstract:
The adsorption and dissociation of CO and CO2 molecules on UO2 (111) slab were investigated by the first-principles calculations based on density functional theory with the addition of Hubbard term for calculation correction. Different static and dynamic adsorption mechanisms under different configurations were analyzed, and the adsorption sites included top, hollow, and bridge sites. In the static calculations, the variation of adsorption parameters, such as adsorption configuration, adsorption energy, and charge transfer, during adsorption process was investigated. ab-initio molecular dynamics (AIMD) was employed to study the dissociation process of CO2 molecules and the changes in charge density difference. Results show that the adsorption of CO molecules can be categorized into two types: (1) stable adsorption, including chemical and physical adsorptions; (2) unstable adsorption. The adsorption types of CO2 on UO2 (111) slab only include the chemical adsorption of stable adsorption and unstable adsorption. No physical adsorption exists. The optimal configuration for the adsorption of both CO and CO2 molecules is short-bridge vertical (B-short-Ver) adsorption. Additionally, at 0 K, the CO2 molecules at the configurations related to B-short-Ver adsorption and long-bridge vertical adsorption on UO2 (111) slab spontaneously dissociate after adsorption. AIMD simulation results show that both configurations dissociate at 300 K.
The adsorption and dissociation of CO and CO2 molecules on UO2 (111) slab were investigated by the first-principles calculations based on density functional theory with the addition of Hubbard term for calculation correction. Different static and dynamic adsorption mechanisms under different configurations were analyzed, and the adsorption sites included top, hollow, and bridge sites. In the static calculations, the variation of adsorption parameters, such as adsorption configuration, adsorption energy, and charge transfer, during adsorption process was investigated. ab-initio molecular dynamics (AIMD) was employed to study the dissociation process of CO2 molecules and the changes in charge density difference. Results show that the adsorption of CO molecules can be categorized into two types: (1) stable adsorption, including chemical and physical adsorptions; (2) unstable adsorption. The adsorption types of CO2 on UO2 (111) slab only include the chemical adsorption of stable adsorption and unstable adsorption. No physical adsorption exists. The optimal configuration for the adsorption of both CO and CO2 molecules is short-bridge vertical (B-short-Ver) adsorption. Additionally, at 0 K, the CO2 molecules at the configurations related to B-short-Ver adsorption and long-bridge vertical adsorption on UO2 (111) slab spontaneously dissociate after adsorption. AIMD simulation results show that both configurations dissociate at 300 K.
2024, 53(3):617-624.
DOI: 10.12442/j.issn.1002-185X.20230268
Abstract:
We proposed an efficient method to fabricate superhydrophobic, wear and corrosion resistant groove-textured surfaces based on TB6 (Ti-10V-2Fe-3Al) titanium alloy substrates. The smooth surface of the titanium alloy was ablated using a nanosecond laser to create a surface with a parallel groove pattern. In order to further improve the surface hydrophobicity, the laser treated surface was irradiated by an ultraviolet lamp for 1 h and subsequently immersed in a 3wt% octadecyltrichlorosilane solution for 2 h for chemical modification. The wettability of the groove-textured surfaces with varying groove spacing was investigated by analyzing surface morphology and chemical composition. Results show that the average coefficient of friction (COF) of the superhydrophobic surface is reduced by 34%, 56%, and 59% compared with that of the original hydrophilic surface under dry, water, and oil lubrication conditions, respectively. The mechanism variation of the CoF was also discussed. Potentiokinetic polarization testing demonstrates that the prepared superhydrophobic surface provides corrosion protection for the titanium alloy substrate.
We proposed an efficient method to fabricate superhydrophobic, wear and corrosion resistant groove-textured surfaces based on TB6 (Ti-10V-2Fe-3Al) titanium alloy substrates. The smooth surface of the titanium alloy was ablated using a nanosecond laser to create a surface with a parallel groove pattern. In order to further improve the surface hydrophobicity, the laser treated surface was irradiated by an ultraviolet lamp for 1 h and subsequently immersed in a 3wt% octadecyltrichlorosilane solution for 2 h for chemical modification. The wettability of the groove-textured surfaces with varying groove spacing was investigated by analyzing surface morphology and chemical composition. Results show that the average coefficient of friction (COF) of the superhydrophobic surface is reduced by 34%, 56%, and 59% compared with that of the original hydrophilic surface under dry, water, and oil lubrication conditions, respectively. The mechanism variation of the CoF was also discussed. Potentiokinetic polarization testing demonstrates that the prepared superhydrophobic surface provides corrosion protection for the titanium alloy substrate.
2024, 53(2):465-473.
DOI: 10.12442/j.issn.1002-185X.20230032
Abstract:
Molybdenum has high melting point, low thermal expansion coefficient and excellent stability. It has broad application prospects in plasma propulsion and electric vacuum devices so that its secondary electron emission characteristics have gradually attracted the attention of researchers. Firstly, the secondary electron yield (SEY) and secondary electron spectrum (SES) of molybdenum were studied experimentally. Then the test data were analyzed by the relevant model. Finally, the SEY model of molybdenum is established by Monte Carlo method to analyze the influence of work function on SEY. The results show that the maximum value of SEY is 1.77, which is significantly lower than that of silver-plated aluminum alloy. When the incident electron energy changes, the most probable energy of the true secondary electron peak of the SES is basically unchanged, while the position and intensity of the elastic backscattered electron peak change accordingly. Among all kinds of secondary electrons, true secondary electrons are most affected by the work function.
Molybdenum has high melting point, low thermal expansion coefficient and excellent stability. It has broad application prospects in plasma propulsion and electric vacuum devices so that its secondary electron emission characteristics have gradually attracted the attention of researchers. Firstly, the secondary electron yield (SEY) and secondary electron spectrum (SES) of molybdenum were studied experimentally. Then the test data were analyzed by the relevant model. Finally, the SEY model of molybdenum is established by Monte Carlo method to analyze the influence of work function on SEY. The results show that the maximum value of SEY is 1.77, which is significantly lower than that of silver-plated aluminum alloy. When the incident electron energy changes, the most probable energy of the true secondary electron peak of the SES is basically unchanged, while the position and intensity of the elastic backscattered electron peak change accordingly. Among all kinds of secondary electrons, true secondary electrons are most affected by the work function.
2024, 53(1):1-7.
DOI: 10.12442/j.issn.1002-185X.20230842
Abstract:
Thermal stability and thermo-mechanical properties of Pd20Pt20Cu20Ni20P20 high entropy metallic glass (HEMG) were investigated by differential scanning calorimetry, X-ray diffraction, and thermomechanical analysis. Results show that compared with other classical precious metal-based metallic glasses, Pd20Pt20Cu20Ni20P20 HEMG presents comparable performance with distinct characteristics.
Thermal stability and thermo-mechanical properties of Pd20Pt20Cu20Ni20P20 high entropy metallic glass (HEMG) were investigated by differential scanning calorimetry, X-ray diffraction, and thermomechanical analysis. Results show that compared with other classical precious metal-based metallic glasses, Pd20Pt20Cu20Ni20P20 HEMG presents comparable performance with distinct characteristics.
2023, 52(12):4055-4064.
DOI: 10.12442/j.issn.1002-185X.20230281
Abstract:
A novel method of electromagnetic coupling treatment (EMCT) was proposed to control the residual stress of 2A02 aluminum alloy blade forging in compressor, aiming at solving the industrial problem of machining deformation of large-size thin-wall parts due to residual stress releasing. The effects of electric and magnetic field treatment on the residual stress and mechanical properties of forgings were studied. The microstructure was analyzed by quasi-in-situ EBSD. The results show that compared with a single physical field, the EMCT has the most significant relaxation effect on residual stress. When the magnetic field intensity is 1.5 T and the electric field intensity is 750 V/m, the maximum reduction of residual stress of blade forging is 53%. EMCT can improve the plasticity of aluminum alloy without damaging the strength. Under the above parameters, the elongation is increased by 14.3% and the resistance is decreased by 4.9%. EBSD quasi-in-situ analysis shows that after EMCT, the geometric dislocation density of forgings is reduced by 58.2%, the small-angle grain boundaries are reduced, the plug dislocations are dispersed and annihilated, the local strain is reduced, and the macroscopic stress is relaxed.
A novel method of electromagnetic coupling treatment (EMCT) was proposed to control the residual stress of 2A02 aluminum alloy blade forging in compressor, aiming at solving the industrial problem of machining deformation of large-size thin-wall parts due to residual stress releasing. The effects of electric and magnetic field treatment on the residual stress and mechanical properties of forgings were studied. The microstructure was analyzed by quasi-in-situ EBSD. The results show that compared with a single physical field, the EMCT has the most significant relaxation effect on residual stress. When the magnetic field intensity is 1.5 T and the electric field intensity is 750 V/m, the maximum reduction of residual stress of blade forging is 53%. EMCT can improve the plasticity of aluminum alloy without damaging the strength. Under the above parameters, the elongation is increased by 14.3% and the resistance is decreased by 4.9%. EBSD quasi-in-situ analysis shows that after EMCT, the geometric dislocation density of forgings is reduced by 58.2%, the small-angle grain boundaries are reduced, the plug dislocations are dispersed and annihilated, the local strain is reduced, and the macroscopic stress is relaxed.
2023, 52(11):3794-3800.
DOI: 10.12442/j.issn.1002-185X.20220806
Abstract:
Aimed at improving the performance and compactness of the heat pipe heat exchangers, different forms of double-pipe heat exchanger units with densely longitudinal fins are obtained by metal additive manufacturing method. The manufacturing deviation is summarized, which shows that the internal structure is complete. The optical measurement shows that the roughness distribution on both sides of the inclined fin is not uniform. The steady state experiments are implemented to investigate the heat transfer characteristics of four densely longitudinal fins enhanced compact double-pipe heat exchanger units. The configurations are classified into two categories of straight fin type (DPHE-1) and periodically arranged fin type (DPHE-2). Within the Re ranging from 2000 to 15000, the tested results show that, due to the increase of heat transfer area and the enhancement of flow mixing effect, the DPHE-2 gives 1.3~1.4 folds averaged Nusselt number and 12.6~28.6 averaged friction factor than the DPHE-1. Comparing their overall heat transfer performance, the long fin scheme in DPHE-1 type performs best.
Aimed at improving the performance and compactness of the heat pipe heat exchangers, different forms of double-pipe heat exchanger units with densely longitudinal fins are obtained by metal additive manufacturing method. The manufacturing deviation is summarized, which shows that the internal structure is complete. The optical measurement shows that the roughness distribution on both sides of the inclined fin is not uniform. The steady state experiments are implemented to investigate the heat transfer characteristics of four densely longitudinal fins enhanced compact double-pipe heat exchanger units. The configurations are classified into two categories of straight fin type (DPHE-1) and periodically arranged fin type (DPHE-2). Within the Re ranging from 2000 to 15000, the tested results show that, due to the increase of heat transfer area and the enhancement of flow mixing effect, the DPHE-2 gives 1.3~1.4 folds averaged Nusselt number and 12.6~28.6 averaged friction factor than the DPHE-1. Comparing their overall heat transfer performance, the long fin scheme in DPHE-1 type performs best.
2023, 52(10):3433-3441.
DOI: 10.12442/j.issn.1002-185X.20230296
Abstract:
Combined with digital image correlation (DIC) technique, in-situ fatigue tests with different stress ratios (R = 0.1 and R = -1) at room temperature were carried out to analyze the mesoscopic surface crack propagation mechanism of selected laser melted Ni-based superalloy (SLM-IN718) in the very high cycle fatigue regime. The results show that: firstly, the DIC analysis results indicated that a plastic strain zone, similar to a butterfly shape, appeared at the crack tip when SLM-IN718 was loaded, which is consistent with the adoption of the Von Mises yield criterion; Secondly, the strain field characteristics and displacement field characteristics in front of the crack tip were analyzed to determine the existence of crack closure effect in SLM-IN718. The crack closure effect was also evaluated, i.e., for SLM-IN718, crack opened when the load reached 53% and 29% of the maximum load under R = 0.1 and R = 0, respectively; In addition, a considered the crack closure effect model was developed to evaluate the size of the plastic zone in front of the crack tip. The calculated values were in good agreement with the measured values; Finally, the surface crack propagation mechanism of SLM-IN718 under low stress conditions was suggested based on DIC analysis results.
Combined with digital image correlation (DIC) technique, in-situ fatigue tests with different stress ratios (R = 0.1 and R = -1) at room temperature were carried out to analyze the mesoscopic surface crack propagation mechanism of selected laser melted Ni-based superalloy (SLM-IN718) in the very high cycle fatigue regime. The results show that: firstly, the DIC analysis results indicated that a plastic strain zone, similar to a butterfly shape, appeared at the crack tip when SLM-IN718 was loaded, which is consistent with the adoption of the Von Mises yield criterion; Secondly, the strain field characteristics and displacement field characteristics in front of the crack tip were analyzed to determine the existence of crack closure effect in SLM-IN718. The crack closure effect was also evaluated, i.e., for SLM-IN718, crack opened when the load reached 53% and 29% of the maximum load under R = 0.1 and R = 0, respectively; In addition, a considered the crack closure effect model was developed to evaluate the size of the plastic zone in front of the crack tip. The calculated values were in good agreement with the measured values; Finally, the surface crack propagation mechanism of SLM-IN718 under low stress conditions was suggested based on DIC analysis results.
2023, 52(9):3332-3337.
DOI: 10.12442/j.issn.1002-185X.20230035
Abstract:
To study the mechanism of structure damage and the law of performance weakening of TiAl alloy turbine under pressure, an experimental method is designed that compresses and then stretches the TiAl alloy turbine. The slips and microcracks on the surface and inside of the compressed turbine journal are analyzed by scanning electron microscope (SEM), and the tensile fracture morphology is observed. The experimental results show that the residual tensile strengths of the compressed TiAl turbines gradually decrease as the pressure on the turbine. When the pressure reaches 610 MPa, the residual tensile strength is only 86 MPa, and the strength loss rate is as high as 70%. During the compression process of TiAl alloy, the deformation damage characteristics, which are mainly inter-lamellar cracks and supplemented by trans- lamellar cracks, are formed. Lamellar cracks in the direction of maximum shear stress at 45 ° to the compression axis are the main form of compression damage found in the TiAl alloy. The tensile fracture of TiAl alloy turbine after compression damage occurred at the thin journal near the casting riser side of turbine. The microcracks in the lamellar structure after compression deformation continue to expand under the subsequent tensile stress until the ligament bridge is penetrated, and the small cracks merge into large cracks, resulting in a mixed fracture morphology along the layer and through the layer on the fracture surface.
To study the mechanism of structure damage and the law of performance weakening of TiAl alloy turbine under pressure, an experimental method is designed that compresses and then stretches the TiAl alloy turbine. The slips and microcracks on the surface and inside of the compressed turbine journal are analyzed by scanning electron microscope (SEM), and the tensile fracture morphology is observed. The experimental results show that the residual tensile strengths of the compressed TiAl turbines gradually decrease as the pressure on the turbine. When the pressure reaches 610 MPa, the residual tensile strength is only 86 MPa, and the strength loss rate is as high as 70%. During the compression process of TiAl alloy, the deformation damage characteristics, which are mainly inter-lamellar cracks and supplemented by trans- lamellar cracks, are formed. Lamellar cracks in the direction of maximum shear stress at 45 ° to the compression axis are the main form of compression damage found in the TiAl alloy. The tensile fracture of TiAl alloy turbine after compression damage occurred at the thin journal near the casting riser side of turbine. The microcracks in the lamellar structure after compression deformation continue to expand under the subsequent tensile stress until the ligament bridge is penetrated, and the small cracks merge into large cracks, resulting in a mixed fracture morphology along the layer and through the layer on the fracture surface.
2023, 52(8):2757-2764.
DOI: 10.12442/j.issn.1002-185X.20220619
Abstract:
In order to investigate the properties of rubidium tungsten bronze and cesium tungsten bronze nanopowders with different shapes and their film, rubidium and cesium tungsten bronze nanopowders were prepared by hydrothermal reaction and a subsequent heat-treatment. Tungsten bronze transparent insulation film was prepared by spin coating method on a piece of glass. The synthesized powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and the photothermal properties of the powders were studied. The near infrared shielding performance and heat insulation performance of tungsten bronze films were analyzed by UV-Vis NIR spectroscopy. The results show that the tungsten bronze nanopowders after heat treatment have excellent photothermal properties and have a promising application prospect in cancer photothermal therapy. Compared with the film made by rod-shaped powers, the film made by laminar rubidium and cesium-tungsten bronze powders have higher near-infrared shielding performance of 95% and 98.8%, respectively. Compared with blank glass, the indoor temperature using glass with laminar rubidium and cesium tungsten bronze films decreased by 9.4℃ and 8.5℃ respectively. In summary, sheet rubidium and cesium tungsten bronze have excellent near-infrared shielding performance, and have great application prospects in the fields of energy saving and photothermal therapy.
In order to investigate the properties of rubidium tungsten bronze and cesium tungsten bronze nanopowders with different shapes and their film, rubidium and cesium tungsten bronze nanopowders were prepared by hydrothermal reaction and a subsequent heat-treatment. Tungsten bronze transparent insulation film was prepared by spin coating method on a piece of glass. The synthesized powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and the photothermal properties of the powders were studied. The near infrared shielding performance and heat insulation performance of tungsten bronze films were analyzed by UV-Vis NIR spectroscopy. The results show that the tungsten bronze nanopowders after heat treatment have excellent photothermal properties and have a promising application prospect in cancer photothermal therapy. Compared with the film made by rod-shaped powers, the film made by laminar rubidium and cesium-tungsten bronze powders have higher near-infrared shielding performance of 95% and 98.8%, respectively. Compared with blank glass, the indoor temperature using glass with laminar rubidium and cesium tungsten bronze films decreased by 9.4℃ and 8.5℃ respectively. In summary, sheet rubidium and cesium tungsten bronze have excellent near-infrared shielding performance, and have great application prospects in the fields of energy saving and photothermal therapy.
2023, 52(7):2415-2423.
DOI: 10.12442/j.issn.1002-185X.20220555
Abstract:
Powder metallurgy Ni-based superalloy turbine discs serve at high temperatures and high stress levels for a long time, and the comprehensive mechanical properties of the superalloy have stringent requirements, while the surface morphology and microstructure have a significant impact on the performance of the superalloy, which generally requires surface shot peening treatment. Based on this, this work systematically investigates the surface/subsurface microstructure and deformation of the FGH4113A superalloy at different shot peening intensities and explores the quantitative relationship between them. The result indicates that the dislocation pile-up occurs in the subsurface and induces the formation of deformation twins. Meanwhile, the number of deformation twins rises with the increase in shot peening intensity. Furthermore, the dislocations triggered by shot peening induce a large number of low angular grain boundaries in the deformed layer, which results in grain refinement to reinforce the superalloy hardening effect. In addition, with the increase of shot peening intensity, the characteristics of superalloy surface roughness, surface residual compressive stress, hardened layer thickness, and surface microhardness display an increasing trend and exhibit a good linear or power exponential relationship. This finding can provide data to support the regulation of shot peening parameters in the actual production process.
Powder metallurgy Ni-based superalloy turbine discs serve at high temperatures and high stress levels for a long time, and the comprehensive mechanical properties of the superalloy have stringent requirements, while the surface morphology and microstructure have a significant impact on the performance of the superalloy, which generally requires surface shot peening treatment. Based on this, this work systematically investigates the surface/subsurface microstructure and deformation of the FGH4113A superalloy at different shot peening intensities and explores the quantitative relationship between them. The result indicates that the dislocation pile-up occurs in the subsurface and induces the formation of deformation twins. Meanwhile, the number of deformation twins rises with the increase in shot peening intensity. Furthermore, the dislocations triggered by shot peening induce a large number of low angular grain boundaries in the deformed layer, which results in grain refinement to reinforce the superalloy hardening effect. In addition, with the increase of shot peening intensity, the characteristics of superalloy surface roughness, surface residual compressive stress, hardened layer thickness, and surface microhardness display an increasing trend and exhibit a good linear or power exponential relationship. This finding can provide data to support the regulation of shot peening parameters in the actual production process.