Surface Segregation of Sulfur During Oscillatory Pin-on-Plate Wear Studies of Precious Metal Electrical Contact Alloys: I. Friction and Electrical Contact Resistance

摘要

An oscillatory pin-on-plate experimental configuration was used to investigate friction and electrical contact resistance phenomena of a gold base (ASTM B541) and a palladium base (ASTM B540) alloy couple. Effects which could be attributed to surface segregation were noted. Measurements were made in controlled environments of dry helium, dry carbon dioxide and dry air at atmospheric pressure. A load cell was used to measure the friction force continuously. No lubrication was employed. A U-shaped pin was used with electrical connections to measure electrical contact resistance for both forward and reverse direct currents. Friction coefficients were initially high but decreased to a steady value of approximately 0.2 as the number of oscillatory cycles increased for dry carbon dioxide and dry air. The friction results for dry helium were much more erratic. Friction coefficients are much less sensitive to the nature of the contact interface than is electrical contact resistance. The electrical contact resistance always had initial values of 1 to 10 milliohms, but it tended to increase by up to three orders of magnitude in a nonreproduceable manner for all three gases. Sharp fluctuations in electrical contact resistance were common. Electrical polarity was reversed, but due to the large variability in contact resistance no effect was identified. The results are interpreted in the following paper as arising from wear segregation of sulfur to the contact interface during the oscillatory cycles. (ERA citation 09:040552)