Microstructure, Texture and Deformation Mechanism of Zr702 Processed by Equal Channel Angular Pressing (ECAP)

Abstract

The commercial purity zirconium (Zr702) has been deformed by Equal Channel Angular Press (ECAP) up to eight passes using route A and BC. The deformation microstructure and the bulk texture have been characterized by Electron Backscattered Diffraction (EBSD) in SEM and X-rays diffraction (XRD), respectively. The homogeneously lamellar deformation structure in route A and the equiaxed deformation structure with local heterogeneity in route BC have both been determined. In both cases the subgrain size flattened at about 0.33 ìm after 2 passes but average misorientation increased with increasing strain. After 8 passes high angle fraction is over 70% both in route A and route BC. The bimodal {0002} pole texture (high strain rolling texture) in route A and the strong unimodal {0002} pole texture with weak high strain rolling texture in route BC have been identified. The boundary texture has been analysed both in sample frame and crystallographic frame. It was found in sample frame that the boundary texture of high angle boundaries developed gradually in route A and more strongly than that in route BC, implying that the boundary characters evolved from the mixed characters (tilted and twist) to tilted boundary in route A. Based on the deformation structures and the bulk textures, the deformation mechanism of large local orientation rotation and the stability of the dislocation structures have been proposed to interpret the grain refinement and the texture development of Zr702 during ECAE processing.