Scuffing mechanism of near-surface material during lubricated severe sliding contact

Scuffing, defined as a sudden catastrophic failure of lubricated sliding contact, is one of the least understood tribological failure processes, in spite of its great technological significance. It is usually accompanied by a large sudden rise in friction, contact temperature, and noise. Occurrence of scuffing results in loss of surface integrity and functionality of the tribological components. Although extensive phenomenological studies have been conducted on scuffing because of its implication regarding machine-element reliability, the basic mechanism of the failure process is still not well understood. Consequently, prediction and sometimes prevention of scuffing failure are difficult. Based on the recent observation of microstructural changes accompanying scuffing failure and various other phenomenological observations, a scuffing mechanism is proposed that involves adiabatic shear instability in the near-surface material at the sliding contact interface. Localized shear instability occurs when the rate of thermal softening due to the heat of plastic deformation exceeds the rate of work hardening—this is scuffing initiation. Propagation of scuffing to final catastrophic failure is determined by a balance between heat generation and heat dissipation. If the rate of heat generation by more plastic deformation exceeds the rate of heat dissipation, scuffing propagates; otherwise, the scuffing process is quenched. Once validated, this proposed mechanism will facilitate the prediction of scuffing based on material properties. It will also provide a mechanism-based strategy for scuffing failure prevention in tribological components.