Gaseous contaminants modify the friction and wear response of precious metal electrical contact alloys

An in situ electrical contact resistance and friction coefficient measuring device has been installed in a scanning Auger microprobe. A pin-on-plate experimental configuration is used. This tribology system has been used to characterize the friction, wear, and electrical contact resistance of a Pd-alloy pin (ASTM B540) sliding on an Au-alloy plate (ASTM B541). Studies, with and without H₂S in the atmosphere, of wear in 1.6×10^-6-Torr O₂, 700-Torr 5% O ₂ in N₂, and 700-Torr He are reported. The presence of H₂S reduces the friction coefficient and decreases the wear track width on the Au alloy. The lower friction is associated with absorption and reaction of the H₂S with the Au-alloy plate. In the ambients containing H₂S, large accumulations of S in wear tracks are observed; however, no increase in the electrical contact resistance occurs. In the 700-Torr ambients containing H₂S, Cu segregates to the wear track surfaces to the exclusion of other metallic elements and forms Cu₂S layers. A concomitant shift occurs in the S and Cu Auger peak positions when the Cu₂S film thickens