Sliding wear of nanocrystalline Ni–W: Structural evolution and the apparent breakdown of Archard scaling

Sliding wear of nanocrystalline Ni–W alloys with grain sizes of 3–47 nm, a range which spans the transition in deformation mechanisms from intra- to inter-granular, has been studied through pin-on-disk wear testing. The extreme conditions produced during sliding wear are found to result in structural evolution and a deviation from Archard scaling for the finest grain sizes; in the finest nanocrystalline materials wear resistance is higher than would be expected based on hardness alone. The repetitive sliding load is found to lead to a modest amount of grain growth and grain boundary relaxation, which in turn leads to local hardening in the wear track. Analysis of the dynamic microstructure suggests that it is produced primarily as a result of local plasticity and is not principally due to frictional heating.