Strain effects on the wear rate of severely deformed copper

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.