Grease lubricated fretting of silver coated copper electrical contacts

Fretting of silver coated electrical contacts has been studied in a crossed cylinder contact model setup at varying displacement amplitude. The contacts have been tested dry (unlubricated) and lubricated with lithium complex (LiX) and polypropylene (PP) thickened greases. The same polyalphaolefin (PAO) base oil blend was used, hence the thickener is the only difference between the greases. At low displacement amplitude no large difference between dry and lubricated conditions was found. Contact welding occurs for all contacts, also the lubricated. The grease is ejected from the contact area after only a few fretting cycles and the contact welds. A positive effect of grease lubrication on friction and wear is primarily seen at high vibration amplitude, where gross slip is the prevailing fretting regime. For the LiX grease lubricated contacts, fretting at intermediate displacement amplitudes show to be the most critical and the wear marks show much surface damage. Here, the PP grease showed better lubricating effect than the LiX grease.