Title: Mechanisms of near-surface structural evolution in nanocrystalline materials during sliding contact,
Abstract: The wear-driven structural evolution of nanocrystalline Cu was simulated with
molecular dynamics under constant normal loads, followed by a quantitative
analysis. While the microstructure far away from the sliding contact remains
unchanged, grain growth accompanied by partial dislocations and twin formation
was observed near the contact surface, with more rapid coarsening promoted by
higher applied normal loads. The structural evolution continues with increasing
number of sliding cycles and eventually saturates to a stable distinct layer of
coarsened grains, separated from the finer matrix by a steep gradient in grain
size. The coarsening process is balanced by the rate of material removal when
the normal load is high enough. The observed structural evolution leads to an
increase in hardness and decrease in friction coefficient, which also saturate
after a number of sliding cycles. This work provides important mechanistic
understanding of nanocrystalline wear, while also introducing a methodology for
atomistic simulations of cyclic wear damage under constant applied normal
loads.