Relationships between the fretting wear behavior and the ball cratering resistance of solid lubricant coatings

Employing solid lubricant coatings to reduce friction is one of the most effective methods to mitigate fretting damage. However, facing numerous available coatings, users often feel confounded, and the selection of the optimum coating for a specific application is still a tough task. Some simple methods are expected to help the selection. Ball cratering as a promising technique is becoming popular in the developing process of new coatings to assess their abrasion resistance. The objective of this paper is to identify the relationships between the fretting behavior and the ball cratering resistance of coatings, and attempt to use ball cratering to pre-select coatings for fretting conditions in order to cut down the number of candidate coatings and shorten the fretting tests. In this study, several bonded solid lubricant coatings, principally based on PTFE or MoS2, were investigated by ball cratering and fretting tests. The results showed that the coatings in ball cratering presented similar tribological performance as in fretting tests in terms of endurance and wear resistance, i.e., the coatings with good ball cratering resistance also exhibited long lifetime in fretting tests, so ball cratering can be considered as a simple test to pre-select solid lubricant coatings for fretting applications.