Investigation On Preparation,Microstructure And Properties Of Ag-WC（TiB₂）-Gr Contact Materials

As the core component of a circuit breaker,the contact plays the roles of switch-on,switchoff and carrying current,and its performance directly affects the reliability,stability and service life of the integral electrical system.As circuit breakers become increasing miniaturization,high load and more intelligence,the strict performance requirements are put forward on contact materials,such as higher breaking capacity,longer life and lighter weight.Subsequence,it is of significance to develop higher performance,longer life and lighter weight silver-based contact material for circuit breakers.In this thesis,the Ag-WC-Gr contact materials with different particle sizes of WC and different graphene contents along with the Ag-WC-TiB₂-Gr contact materials with different WC/TiB₂ ratios were prepared by powder metallurgy,and the microstructure and properties of the contact materials were characterized and tested.The following conclusions can be drawn from above investigations.As the size of WC particle decreases,the relative density and electrical conductivity of Ag12wt.%WC-0.1wt.%Gr contact materials decrease and the hardness increase.The optimum combined performance of the contact material prepared with 2μm WC particle can be obtained,the relative density,electrical conductivity and hardness of 97.64%,82.22%IACS and 64.42 HV,respectively.The make-arc duration/energy of the contact materials increases,the break-are duration/energy of the contact materials decreases and then increases,the contact resistance decreases,the welding force and the net mass loss increase.With increase of the graphene content,the electrical conductivity decreases,the contact resistance decreases and then increases,the welding force increases and then decreases,the break-arc duration becomes longer,the break-arc energy increases and the net mass loss increases and then decreases.As the ratio of WC/TiB₂ decreases,the density and electrical conductivity of Ag12wt.%（WC-TiB₂）-0.1wt.%Gr contact materials decrease,and the Ag-9wt.%WC-3wt.%TiB₂0.1wt.%Gr contact material prepared with a WC/TiB₂ ratio of 3:1 has the optimum combined performance,and the density,conductivity and hardness are 10.08g/cm3,69.88%IACS and 74.60HV,respectively.For the Ag-12wt.%（WC-TiB₂）-0.1wt.%Gr contact materials,make-arc duration/energy and break-arc duration/energy together with welding force fluctuates and contact resistance and net mass loss increase.The crater formed on the anode of the contact material progressively changes into a loose porous structure,while the protrusion formed on the cathode gradually become flat surface.