The effect of high hydrostatic pressure on creep behaviour of pure Al and a Cu–0.2 wt% Zr alloy processed by equal-channel angular pressing

Abstract

The effect of an application of high hydrostatic pressure on the microstructure, nanoscale porosity and creep behaviour of high purity aluminium and a Cu–0.2wt% Zr alloy processed by equal-channel angular pressing (ECAP) was examined with an emphasis on creep resistance and lifetime. It was found that, under the same loading conditions, specimens subjected to a subsequent high hydrostatic compression pressure prior to creep exposure exhibited longer times to creep fracture than those pressed by ECAP only. However, this impact continuously decreases with the increasing number of ECAP passes. A detailed quantitative microstructure study was conducted using TEM, SEM, electron backscatter diffraction (EBSD) and a small-angle X-ray scattering (SAXS) method and dilatometry. These analyses revealed that a general increase in the creep resistance of pressurized material may be explained by an increase in the density and the corresponding decrease in the nanoporosity of the material. Further, it was revealed that the fraction of high-angle grain boundaries increases with increasing number of ECAP passes. It is the accumulation of high-angle grain boundaries that accounts for the observed decrease in the pressurization-induced increment of creep life of the material with the increasing number of ECAP passes.