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

TL;DR

This study investigates how wear rate and surface microstructure evolve in nanocrystalline Ni-W during cyclic wear, revealing a new gradient microstructure and the significance of deformation mechanisms in microstructure stability.

Contribution

It uncovers the formation of a gradient nanograined microstructure during wear and highlights the role of deformation mechanisms in microstructure evolution in nanocrystalline Ni-W.

Findings

Discovery of a gradient nanograined microstructure after wear

Connection between wear rate and subsurface microstructure

Microstructure similarity in differently prepared samples

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.