Strain path effects on the microstructure evolution and mechanical properties of Zr702

Abstract

A commercial-purity Zr702 was grain-refined from 20 mu m to 0.2-0.5 p m by equal channel angular pressing. Grain refinement was most evident in the first pass but was insignificant during the subsequent passes. Two microstructural characteristics evolved: a lamellar structure and an equiaxed sub.-rain structure during the route A pressing and the route B-C pressing, respectively. Due to the rotation of specimen in between passes, two sets of geometrically necessary boundaries were formed during the route B-C pressing. The mechanism of grain refinement during the route A pressing was evolution of high-angle geometrically necessary boundaries from the low-angled ones, while that during the route B-C pressing was decomposition and rearrangement of pre-existing boundaries. The yield stress of severely deformed specimens increased with the reducing grain size according to a Hall-Petch relationship. (c) 2004 Elsevier B.V. All rights reserved.