Orientation stability in equal channel angular extrusion. Part II: Hexagonal close-packed materials

The orientation stability in equal channel angular extrusion (ECAE) of hexagonal close-packed (hcp) crystals using a 90 degrees die is investigated based on the three-dimensional lattice rotation fields from rate-dependent crystal plasticity simulations. The results show that for the major slip and twinning modes considered, the relatively stable orientations in ECAE are distributed along the h1(0) to h6(0) fibers in the Euler space and feature characteristic alignments of the (a)- or (c)-axis with respect to the macroscopic deformation axes. The application of such simulations is demonstrated by comparing the predictions with experimental ECAE textures in high-purity titanium and other hcp polycrystalline materials, including commercial-purity zirconium, beryllium and magnesium alloys. The simulation results for ECAE are also applied to derive the relatively stable orientations in conventional simple shear deformation. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.