Effect of Fretting on the Contact Resistance of Palladium Electroplate Having a Gold Flash, Cobalt-Gold Electroplate, and DG R156

Contact resistance stability is a function of the contact materials, design, and conditions of connector use. The purpose of the present work was to identify certain potentially unstable materials systems when fretting occurs at the contact interface. In previous studies of fretting, it was found that variable resistance can be caused by wearout of the finish to base substrate or underplate, or to the formation of frictional polymers when platinum group contact metals are used. An evaluation of the fretting of cobalt-gold electroplate, palladium electroplate having a pure gold flash, and DG R156 was made with these materials mated to themselves or to each other. A bench test apparatus was employed with wire contacts joined in crossed rod configuration. It was found that mated to themselves and for the conditions of this test, unlubricated cobalt-gold plate performed well, although DG R156 was nearly as good and gold flashed palladium was poor. Unlubricated cobalt-gold plate mated to DG R156 was good, followed by cobalt-gold plate joined to gold flashed palladium, which was marginal. Again, for the conditions of this test, gold flashed palladium versus DG R156 was poor. Lubrication with a thin film of a polyphenylether attenuated the contact resistance changes in all cases by lowering the rate of wear of the material or, with palladium-containing systems, by causing the frictional polymers that formed to be nonadherent. The tendency of a connector to degrade by fretting depends on its design. If material systems are to be conducted which perform poorly in the bench test, it is recommended that connector tests be conducted which tend to cause micromotion at the contact interface. Procedures involving shock, vibration, and cycling temperature may be employed for this purpose.