The Effect of Environment and Materials Properties on the Friction and Wear Behavior of Precious Metal Electrical Contact Alloy Couples

The friction and wear behavior of the gold base (ASTM B541) and palladium base (ASTM B540) alloy couple has been investigated in three environments as a function of the metallurgical state of the alloys. One environment was laboratory air with 35-45 percent relative humidity (RH); careful controls were imposed to prevent spurious contamination by organic materials. A second environment was high purity air, contained in a glove box and controlled to less than 1 ppm hydrocarbon and 1 ppm water contamination. The third environment was ultra-high-purity helium, again controlled in a glove box to impurity levels of less than 1 ppm oxygen, water, and organic contaminants. The microstructures and hardnesses of the alloys were varied by age hardening heat treatments and/or cold rolling. Hardness for the gold base alloy varied from HK = 332 to HK = 354, with the hardnesses of the palladium base alloy varying from HK = 337 to HK = 353. Friction and wear measurements were made with a pin-on-disk configuration with the palladium alloy serving as the pin and the gold alloy acting as the plate. The poorest friction performance was found in the helium environment where both magnitudes and break-in characteristics varied extensively. The friction coefficient varied from 0.25 to 2.0; the variation for a specific Pin-plate combination masked pin-plate material differences, except for cold rolled plates which had the worst performance. The poor performance in helium is Compared with improved performance in the oxygen containing atmospheres where friction coefficients ranged from 0.1 to 0.25. In oxygen containing environments, the break-in was minimal and reproducible.