Concurrent transitions in wear rate and surface microstructure in nanocrystalline Ni-W

Abstract

Nanocrystalline metals are promising materials for wear-resistant applications due to their superior strength and hardness, but prior work has shown that cyclic loading can lead to coarsening. In this study, scratch wear tests were carried out on nanocrystalline Ni-19 at.% W films with an as-deposited grain size of 3 nm, with systematic characterization performed after different wear cycles. A new gradient nanograined microstructure is observed and a direct connection between wear rate and subsurface microstructure is discovered. A second Ni-W specimen with the same composition and a 45 nm average grain size is produced by annealing the original specimen. Subsequent wear testing shows that an identical subsurface microstructure is produced in this sample, emphasizing the importance of the cross-over in deformation mechanisms for determining the steady-state grain size during wear.