Electrical contact materials are generally Ag-or Cu-based composites and play a critical role in ensuring the reliability and efficiency of electrical equipments and electronic instruments.The MAX(M is an early transi...Electrical contact materials are generally Ag-or Cu-based composites and play a critical role in ensuring the reliability and efficiency of electrical equipments and electronic instruments.The MAX(M is an early transition metal,A is an element from III or IV main groups,and X is carbon or/and nitrogen)phase ceramics display a unique combination of properties and may serve as an ideal reinforcement phase for electrical contact materials.The biological materials evolved in nature generally exhibit three-dimensional(3D)interpenetrating-phase architectures,which may offer useful inspiration for the architectural design of electrical contact materials.Here,a series of bi-continuous Ag-Ti_(3)SiC_(2) MAX phase composites with high ceramic contents exceeding 50 vol.%and having micron-and ultrafine-scaled 3D interpenetrating-phase architectures,wherein both constituents were continuous and mutually interspersed,were exploited by pressureless infiltration of Ag melt into partially sintered Ti_(3)SiC_(2) scaffolds.The mechanical and electrical properties as well as the friction and wear performance of the composites were investigated and revealed to be closely dependent on the ceramic contents and characteristic structural dimensions.The composites exhibited a good combination of properties with high hardness over 2.3 GPa,high flexural strength exceeding 530 MPa,decent fracture toughness over 10 MPa·m^(1/2),and good wear resistance with low wear rate at an order of 10^(-5)mm^(3)/(N·m),which were much superior compared to the counterparts made by powder metallurgy methods.In particular,the hardness,electrical conductivity,strength,and fracture toughness of the composites demonstrated a simultaneous improvement as the structure was refined from micron-to ultrafine-scales at equivalent ceramic contents.The good combination of properties along with the facile processing route makes the Ag-Ti_(3)SiC_(2)3D interpenetrating-phase composites appealing for electrical contact applications.展开更多
Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the...Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.展开更多
基金supports from the National Key R&D Program of China(No.2020YFA0710404)the National Natural Science Foundation of China(No.52173269),the KC Wong Education Foundation(No.GJTD-2020-09)the Liaoning Revitalization Talents Program,and the Youth Innovation Promotion Association CAS(No.2019191).
文摘Electrical contact materials are generally Ag-or Cu-based composites and play a critical role in ensuring the reliability and efficiency of electrical equipments and electronic instruments.The MAX(M is an early transition metal,A is an element from III or IV main groups,and X is carbon or/and nitrogen)phase ceramics display a unique combination of properties and may serve as an ideal reinforcement phase for electrical contact materials.The biological materials evolved in nature generally exhibit three-dimensional(3D)interpenetrating-phase architectures,which may offer useful inspiration for the architectural design of electrical contact materials.Here,a series of bi-continuous Ag-Ti_(3)SiC_(2) MAX phase composites with high ceramic contents exceeding 50 vol.%and having micron-and ultrafine-scaled 3D interpenetrating-phase architectures,wherein both constituents were continuous and mutually interspersed,were exploited by pressureless infiltration of Ag melt into partially sintered Ti_(3)SiC_(2) scaffolds.The mechanical and electrical properties as well as the friction and wear performance of the composites were investigated and revealed to be closely dependent on the ceramic contents and characteristic structural dimensions.The composites exhibited a good combination of properties with high hardness over 2.3 GPa,high flexural strength exceeding 530 MPa,decent fracture toughness over 10 MPa·m^(1/2),and good wear resistance with low wear rate at an order of 10^(-5)mm^(3)/(N·m),which were much superior compared to the counterparts made by powder metallurgy methods.In particular,the hardness,electrical conductivity,strength,and fracture toughness of the composites demonstrated a simultaneous improvement as the structure was refined from micron-to ultrafine-scales at equivalent ceramic contents.The good combination of properties along with the facile processing route makes the Ag-Ti_(3)SiC_(2)3D interpenetrating-phase composites appealing for electrical contact applications.
基金the National Natural Science Foundation of China(Nos.52001310 and 52130002)the National Science and Technology Major Project(No.J2019-VI-0019-0134)+1 种基金KC Wong Education Foundation(No.GJTD-2020-09)Institute of Metal Res earch Innovation Fund(No.2023-ZD01)。
文摘Compared with the conventional Charpy impact test method,the oscillographic impact test can help in the behavioral analysis of materials during the fracture process.In this study,the trade-off relationship between the strength and toughness of a DZ2 axle steel at various tempering temperatures and the cause of the improvement in impact toughness was evaluated.The tempering process dramatically influenced carbide precipitation behavior,which resulted in different aspect ratios of carbides.Impact toughness improved along with the rise in tempering temperature mainly due to the increase in energy required in impact crack propagation.The characteristics of the impact crack propagation process were studied through a comprehensive analysis of stress distribution,oscilloscopic impact statistics,fracture morphology,and carbide morphology.The poor impact toughness of low-tempering-temperature specimens was attributed to the increased number of stress concentration points caused by carbide morphology in the small plastic zone during the propagation process,which resulted in a mixed distribution of brittle and ductile fractures on the fracture surface.