Strain effects on the wear rate of severely deformed copper

TL;DR

This study investigates how severe plastic deformation via high pressure torsion affects copper's wear rate, revealing that wear resistance improves up to a certain strain level and then saturates, with microstructural changes playing a key role.

Contribution

It provides the first detailed characterization of wear behavior across inhomogeneous strains in HPT-processed copper, highlighting saturation effects beyond specific strain levels.

Findings

Wear rate decreases to 25% of original after ~15 strain

Microhardness and microstructure saturate at high strains

Wear resistance shows directional dependence with shear direction

Abstract

A variety of severe plastic deformation (SPD) techniques have been developed to process materials to high strains and impart microstructural refinement. High pressure torsion (HPT) is one technique that imparts inhomogeneous strain to process discs with low strain in the center and high strain at the outer edge. In the literature, this inhomogeneity is typically ignored when characterizing wear properties after HPT. In this work, the wear rate of pure copper discs processed by HPT was characterized by conducting dry sliding reciprocating wear tests at a few judicious locations on the discs. From only two discs, the wear resistance across many ranges of strains was captured. These measurements agreed with the literature for other SPD processes at varying strains. Wear rates dropped and plateaued at about 25% that of the unprocessed state when processing past equivalent strains of around 15, after which microstructural and microhardness saturation has also been observed. Some indication of a relationship between the direction of the imposed SPD shearing and the sliding wear direction was also observed. The incremental microstructure, microhardness, and wear resistance evolution past equivalent strains of ~15 indicate that for high purity copper these properties receive no clear benefit from higher SPD strains.