Abstract:

There have been limited studies investigating the effects of greases in reducing surface degradation due to fretting in electrical contacts operating below 1 N of contact load. This paper investigates the influence of various grease chemistries when applied on hemisphere-on-flat gold-plated electrical contacts undergoing fretting with a contact load of 9.8 cN. Changes in both the electrical contact resistance (ECR) and coefficient of friction were used to assess the performance of the greases. Surface analysis was performed to understand the material transfer process between the contacts. It was observed that greases showed potential to mitigate fretting wear at low contact loads. Among the various grease chemistries tested, one polyalphaolefin-based grease maintained stable ECR below 100 mΩ for more than 10 million fretting cycles. Greases having polyalphaolefins (PAOs) as the base oil maintained boundary lubrication during the entirety of fretting. In contrast, a polybutene-based grease exhibited hydrodynamic lubrication leading to increasing contact separation and thus poor electrical performance. Interestingly, all the tested greases favored the transfer of the hard-gold plating on the hemispherical contact to the flat, which was coated with medium-hard gold. The kinematic viscosity and the applied thickness of grease on the contact influenced the fretting behavior. Greases with higher kinematic viscosities had more contact failures and lower median cycles-to-failure. For a PAO-based grease that did not fail while fretting with a thin layer, increasing the grease thickness by threefold reduced the cycles required for failure.