Effects of Processing Methods on the Contact Performance Parameters for Silver-Tungsten Composite Materials

A comparative study of electrical, mechanical, and microstructural properties of silver-tungsten contact materials (49 and 64 volume percent Ag) prepared by two different processing methods, namely press-sinter (PS) and press-sinter-infiltrate (PSI), is reported. Even with the same elemental composition, tungsten particle size and distribution, the two different techniques of preparation have resulted in no difference in electrical contact resistance, minor differences in microhardness, transverse rupture strength and thermal expansion, and significant differences in contact life and arc erosion properties. Oxidation weight gains at 600°C and 700°C are similar but the oxide layer morphology is quite different at 700°C. The oxidation rate at 700°C is more than ten times of that at 600°C. Silver tungstate is found to be absent at 700°C. High contact resistance is due to the formation of porous tungsten oxides and a porous tungsten layer where silver is removed by the electric arc. The arc erosion is dependent on crack formation and propagation which are not fully understood.