The influence of sliding velocity and temperature on the ductile-to-brittle transition in asperity-level wear: A molecular dynamics study

During sliding contact, asperities may undergo either ductile smoothing or brittle fracture, producing debris. A critical junction scale, $d^{\ast }$, governed by material properties, dictates this transition. Previous studies using molecular dynamics (MD) simulations with tunable interatomic potentials revealed this scale under quasi-static conditions—fixed temperature and low sliding velocities. Here, we extend that work to investigate how temperature and sliding velocity influence the ductile-to-brittle transition at the asperity level. Material properties governed by short-range atomic interactions, such as stiffness and surface energy, remain relatively constant with temperature. In contrast, shear strength, influenced by longer-range interactions, decreases with rising temperature, promoting a brittle-to-ductile shift in asperity behavior. Incorporating temperature-dependent shear strength into the $d^{\ast }$ expression successfully predicts the lower bound of the transition. However, capturing the upper bound requires an additional term to account for ductile fracture energy. At higher sliding velocities, a new brittle failure mode emerges: Instead of a single crack forming at the asperity base, multiple dynamically propagating cracks develop, resulting in fragmented debris. Finally, long-time scale MD simulations of rough-on-rough contact under adiabatic conditions reveal how interface heating influences wear during extended sliding. Regardless of velocity, asperities initially fracture and generate debris that aggregates into a single rolling particle. This particle grows steadily until the surrounding material nears its liquefaction temperature, triggering collapse. These simulations reproduce known wear regimes: an early, high-wear running-in phase followed by a steady-state mild wear stage. Notably, tangential work, heat generation, and wear rate depend primarily on total sliding distance rather than velocity.