Sensitivity of alpha-Zy4 high-temperature deformation textures to the beta-quenched precipitate structure and to recrystallization: Application to hot extrusion
Résumé
Hot extrusion of Zircaloy-4 tubes usually starts from beta-quenched microstructures and induces strong textures. Individual crystallographic orientations were investigated by transmission electron microscopy using the electron backscatter pattern (EBSP) technique as well as Kikuchi patterns. Basal poles were found close to the tangential direction of the tubes in regions exhibiting fine and homogeneously distributed precipitates (FHDPs). In contrast, 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 polycrystalline viscoplastic self-consistent model. The beta-quenched material was modeled as a mixture of LIP and FHDP regions, each having a different set of slip system hardnesses. with a volume fraction depending on the previous thermal history. The model was subsequently applied to predict the texture evolution during extrusion with metadynamic recrystallization taking place thereafter. The calculation suggests that recrystallization modifies the orientation of those grains where [c + a] crystallographic slip has been significantly activated during deformation.