FRETTING CORROSION IN ELECTRIC CONTACTS

Fretting corrosion is a form of accelerated atmospheric oxidation which occurs at the interface of contacting materials undergoing slight, cyclic relative motion. In electric contacts involving non-noble metals, fretting action can cause rapid increases in contact resistance, proceeding to virtual open circuits in a matter of minutes in the worst cases. Experimental results of resistance increase due to fretting action are given for 36 different contact plating combinations, including hard and soft materials and noble as well as non-noble metals. Effects of contact load, both mechanical and electrical, were studied. The results show that all nonnoble metals are susceptible to some degree to fretting corrosion and will suffer contact resistance increases. The beneficial effects of boundary lubricants are demonstrated. Fretting corrosion phenomena were studied on a laboratory test rig designed to produce a particularly damaging fretting motion. Actual and simulated connector configurations were also tested and found to exhibit similar trends in resistance increase, but at a slower rate. Differential thermal expansion is identified as one source of fretting motion in connectors.