Influence of a prior pressurization treatment on creep behaviour of an ultrafine-grained Zr-2.5%Nb alloy

Abstract

The effect of an application of an external high hydrostatic pressure on creep behaviour, the microstructure, and nanoscale porosity in an ultrafine-grained cladding Zr-2.5 wt%Nb alloy processed by equal channel angular pressing (ECAP) was investigated by comparative creep testing. The results show that, under identical creep loading conditions, ECAP processed specimens subjected to subsequent high hydrostatic pressurization treatment prior to creep exposure exhibited no substantial differences in creep behaviour compared to specimens processed by ECAP only. The selected level of high hydrostatic pressurization treatment used in this study is not indicative of an effective removal of nanoscale porosity resulting from ECAP processing. By comparison to the as-received state, an increasing number of ECAP passes leads to a significant weakening of creep resistence of the alloy. It is suggested that the reasons for the occurrence of creep weakening after ECAP processing are an accumulation of high-angle grain boundaries, multiplication of dislocations, coarsening and/or dissolution of the Nd-rich second phase precipitates, and dislocation/particle interactions.