Interrelated Effects of Temperature and Environment on Wear and Tribochemistry of an Ultralow Wear PTFE Composite

A particular alumina-PTFE nanocomposite has distinguished itself with unusually large wear reductions at trace filler loadings. Recent studies have shown that the formation of carboxylic acid end groups in humid environments is a critical part of the wear reduction mechanism. This finding has significant implications for the utility of the material for space and high temperature applications. In this paper, wear rate, morphology, composition, and chemistry of the wear surfaces were characterized as a function of environmental composition and surface temperature to better understand the environmental limitations of this solid lubricating system and the associated wear resistance mechanisms. The following results were found: (1) ultralow wear rates were retained with increasing interface temperature up to 100 degrees C, (2) all samples ran in to low wear regardless of the environmental conditions (dry conditions caused an eventual transition to high wear), (3) carboxylates were detected after sliding in dry environments despite high wear rates, and (4) the amount of oxygen in the environment had no detectable effect on steady-state wear rates. Although high wear rates in dry environments were associated with reduced evidence of carboxylates, low wear rate interfaces at high temperatures produced even less evidence of carboxylates in the running films. Although the formation of carboxylic acid end groups almost certainly drives reduced wear rates by stabilizing the pin surface and anchoring transfer films, the results suggest that their presence or absence is not an independent predictor of wear performance.