A Comparison of Ag/W,Ag/WC, and Ag/Mo Electrical Contacts

Three Ag/R (where R = W, WC, or Mo) powder metal electrical contacts of 50/50 (volume percent) composition were prepared by an identical press-sinter-infiltrate process to have comparable microstructures. Their thermophysical, mechanical, and electrical performance properties were compared. Hardness, electrical conductivity, and thermal expansion are proportional to the refractory properties. Contact millivolt drop is highest in Ag/W followed by Ag/Mo and Ag/WC. Contact erosion at 30 A switch test is highest in Ag/W followed by Ag/WC and Ag/Mo. Arc affected zone microstructure explained the difference in millivolt drop properties. High current tests at 1600 A showed a different crack formation pattern and erosion mode among the three materials. The differences are explained in terms of particle-particle bond strength, silver wetting characteristic, and thermal shock resistance properties.