Metal Transfer Characteristics in Arcing Pd-Ag 40 wt. Percent Versus Au Capped Pd-Ag 40 wt. Percent Metal Alloy Contacts

The surface elemental composition of metal alloy contacts used in relays can change after the contacts have undergone arcing. In this work, selective area Auger electron spectroscopy was Used to analyze the elemental composition of the surfaces of Pd-Ag 40 wt.% versus Au capped Pd-Ag 40 wt.% metal alloy contacts, after they were subjected to arcing. When a contact pair consisting of Pd-Ag 40 wt.% as the cathode and Au capped Pd-Ag 40 wt.% as the anode is subjected to arcing, the Au capped anode surface is rich in Ag within a range of 6 wt.% to 14.5 wt.%, under an area covered by an Auger electron beam of 150µm diameter. Since the measurements are an integrated value over the area covered by the Auger beam, the silver could be concentrated in smaller clumps thus posing a tarnish problem. Tests were carried out by other investigators in this laboratory to determine the effect of the Ag segregation phenomenon[I]. Arced contacts were exposed to a sulfur containing environmerit and subsequent contact resistance and noise measurements did not show any Significant deleterious effects concerning contact performance.