On the role of grain-boundary migration during the creep of zinc

Abstract

Constant engineering strain-rate tensile tests have been carried out in the temperature range 20 to 150°C on high purity Zn, Zn-0.14 at. % Cu (alloy C) and Zn-0.16 at. % Al (alloy A) alloys. Measurements of angular distribution of orientations of grain boundaries have been used to study grain-boundary migration during deformation. Significant cavitation, with increasing propensity at higher test temperatures, occurred in the two alloys but not in pure Zn. A striking feature of the observations in pure Zn and alloy C, as the test temperature was raised, was the formation and subsequent decay of a diamond pattern of uncavitated grain boundaries, a majority of which were preferentially aligned at ~45° to the stress axis. By comparison the changes in the angular distribution of grain boundaries was least marked in alloy A. Cavitation was observed in alloy C to maintain grain boundaries in the 45° orientation. At the test temperature of 150°C alloy C, which was prone to the formation of diamond grain-boundary configuration, developed much larger volume fraction of cavities than alloy A. These results are discussed in terms of the different distribution coefficients of Cu and Al in Zn, the different rates of grain-boundary migration in pure Zn and the two alloys and the differences in the substructural features (cells) formed during high-temperature deformation.