Microstructure And Properties Of The Al₂O₃-Cu/(W,Cr) Electrical Contact Materials

Copper matrix composites are widely used in vacuum switch,resistance welding electrode and other fields due to their high conductivity and good thermal stability.Moreover,nano-Al₂O₃ oxide-dispersion-strengthened copper not only has high strength and conductivity,but also has high recrystallization temperature and good thermal stability.Tungsten has a high melting point,high density,high hardness,high strength,and a low thermal expansion coefficient.Chromium has high melting point and strength,small intercepting value,and great affinity to oxygen ensuring a good inhalation capacity of the contacts.These characteristics determine the application of copper-tungsten and copper-chromium alloys in the field of electrical contact materials.In addition,graphene and its derivatives have attracted more attention as the perfect reinforcement in metal matrix composites.The Al₂O₃-Cu/15W5Cr,Al₂O₃-Cu/25W5Cr and Al₂O₃-Cu/35W5Cr composites were fabricated by vacuum hot-pressing sintering and internal oxidation as well as0.3GO/Al₂O₃-Cu/35W5Cr and 0.5GO/Al₂O₃-Cu/35W5Cr composites.The JF04C electrical contact testing apparatus were used to investigate the mass transfer and electrical contact performance of the composites.The deformed microstructure and the effects of tungsten on the thermal deformation were characterized and analyzed through the isothermal compression tests.Constitutive equation was established and the hot processing maps were obtained.Furthermore,the 0.3GO/Al₂O₃-Cu/35W5Cr and 0.5GO/Al₂O₃-Cu/35W5Cr composites were fabricated using wet grinding and vacuum freeze-drying process.Consequently,the mechanical property,strengthening mechanism and electrical contact behavior were investigated.The results show that the nano-Al₂O₃ particles are evenly dispersed in the matrix,causing dislocation tangles.After electrical contact test at 30 V DC,10 A-30 A test conditions,the anodes of the Al₂O₃-Cu/25W5Cr and Al₂O₃-Cu/35W5Cr electrical contact materials achieve an increase in mass,while the mass of the cathodes decrease.The Al₂O₃-Cu/35W5Cr composite has better welding resistance.During arc erosion,tungsten undergoes re-sintering and appears needle-like structures.Besides,Cr particles are extruded into strips and W particles undergo a slight deformation during the hot compression.Further analysis demonstrated that a large amount of dislocations were stimulated in the W particle.The Al₂O₃-Cu/35W5Cr composite is still in the stage of dynamic recovery at 850°C,0.01 s^-1.In addition,with the increase of the W content,the flow stress and the activation energy of hot deformation of the composite increases correspondingly under the same deformation conditionThe relative density of the 0.3GO/Al₂O₃-Cu/35W5Cr and 0.5GO/Al₂O₃-Cu/35W5Cr contact materials is above 98%.W and Cr particles are distributed on the dispersed copper matrix uniformly without obvious agglomeration.Most of GO are reduced into RGO during the vacuum hot-pressing sintering process.Especially,in situ formed nano-Cr₃C₂ enhances the interface bonding by obtaining a anchoring effect as well as causing working hardening.Some hills and craters are formed on the anode and cathode surfaces,respectively.The W particles undergo the process of re-sintering at high temperature to form needle-like structures.For the two composites doped with GO,the material transfer direction is from the cathode to the anode.The tensile strength of the composites doped with GO increase by 45%and 34%,respectively.The0.5GO/Al₂O₃-Cu/35W5Cr composites have the best welding resistance.