Wear of alumina-PTFE against brass and aluminum: Role of interfacial films and tribochemistry

Abstract

PTFE matrix composites reinforced with α-Al2O3 fillers are considered a gold standard polymeric solid lubricant. α-Al2O3 PTFE exhibits ultra-low wear rates (k ∼10−8 mm3/Nm) when sliding against steel in the presence of water vapor. Mechanochemical interactions involving the breaking of PTFE chains, and subsequent oxidation in the presence of water vapor helps promote growth of interfacial films that are strongly bound to the sliding interface. In the absence of moisture, wear rates of α-Al2O3 PTFE can increase by as much as three orders of magnitude, underscoring its importance to ultra-low wear behavior. A similar increase in wear rates of α-Al2O3 PTFE in humid environments has recently been observed when sliding against brass counter surfaces, though reasons for this increase remain unclear. These findings suggest that mechanisms of ultra-low wear not only rely on ambient humidity but are also strongly dependent on the counter surface chemistry. In the present work, we test the hypothesis that counter surface chemistry drives alumina PTFE wear by systematically investigating the wear of an α-Al2O3 PTFE composite against brass and aluminum substrates within the context of the morphological and mechanochemical evolution of the sliding interface. Wear tests are conducted under reciprocating, dry sliding conditions. Results presented in this work offer insights on mechanochemical mechanisms that drive wear of α-Al2O3 PTFE against brass and aluminum, and provide a framework for developing strategies for controlling wear.