Ideal orientations and persistence characteristics of hexagonal close packed crystals in simple shear

The ideal positions and fibres of hexagonal close packed (hcp) crystals subjected to simple shear are explored in orientation space for the first time using the viscoplastic full constraints crystal plasticity approach with the help of an orientation persistence factor developed earlier for face-centred cubic crystals. Five ideal fibres are identified; these are named B, P, Y and C(1)-C(2), and correspond to a high activity of < a > type slip (B, P and Y) as well as pyramidal < c+a > (C(1)-C(2)). Although the numerical examples are given for the case of magnesium, the main features are the same for other hcp crystals. The characteristics of the three-dimensional lattice rotation fields are also investigated in Euler space. It has been found that the rotation field is asymmetric around the ideal fibres: convergent on one side and divergent on the other. The main drift of orientations is in the direction of the material spin. Some simulation results obtained with the Taylor viscoplastic polycrystal code for simple shear of magnesium are interpreted with the help of the persistence characteristics of the rotation field. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.