Sensitivity of alpha-Zy4 high-temperature deformation textures to the beta-quenched precipitate structure and to recrystallization: Application to hot extrusion

Hot extrusion of Zircaloy-4 tubes usually starts from beta-quenched microst ructures and induces strong textures. Individual crystallographic orientati ons were investigated by transmission electron microscopy using the electro n backscatter pattern (EBSP) technique as well as Kikuchi patterns. Basal p oles were found close to the tangential direction of the tubes in regions e xhibiting fine and homogeneously distributed precipitates (FHDPs). In contr ast, regions with large and isolated precipitates (LIPs) had more variable orientations. Laboratory plane strain compression tests were performed and the induced textures were compared with numerical simulations using a polyc rystalline viscoplastic self-consistent model. The beta-quenched material w as modeled as a mixture of LIP and FHDP regions, each having a different se t of slip system hardnesses. with a volume fraction depending on the previo us thermal history. The model was subsequently applied to predict the textu re evolution during extrusion with metadynamic recrystallization taking pla ce thereafter. The calculation suggests that recrystallization modifies the orientation of those grains where [c + a] crystallographic slip has been s ignificantly activated during deformation. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. AII rights reserved.