Temperature-Dependent Friction and Wear Behavior of PTFE and MoS2

An investigation of the temperature-dependent friction behavior of PTFE, MoS2, and PTFE-on-MoS2 is presented. Friction behavior was measured while continuously varying contact temperature in the range -150 to 175 degrees C while sliding in dry nitrogen, as well as for self-mated PTFE immersed in liquid nitrogen. These results contrast with previous reports of high-friction transitions and plateaus for pure and composite MoS2 at temperatures below about -20 degrees C; instead, we have found persistently weak thermal behavior between 0 and -196 degrees C, providing new insight about the molecular mechanisms of macroscale friction. The temperature-dependent friction behavior characteristic of self-mated PTFE was found also for PTFE-on-MoS2 sliding contacts, suggesting that PTFE friction was defined by subsurface deformation mechanisms and internal friction even when sliding against a lamellar lubricant with extremely low friction coefficient (mu similar to 0.02). The various relaxation temperatures of PTFE were found in the temperature-dependent friction behavior, showing excellent agreement with reported values acquired using rheological techniques measuring energy dissipation through internal friction. Additionally, hysteresis in friction behavior suggests an increase in near-surface crystallinity upon exceeding the high-temperature relaxation, T-alpha similar to 116 degrees C.