Heterogeneous microstructure and texture evolution during fabrication of Zr-Sn-Nb zirconium alloy sheets

Abstract

Zirconium alloys are widely used as fuel cladding and structural materials for nuclear reactors due to the low neutron absorption cross-section, good corrosion resistance and acceptable mechanical properties. These properties are greatly dependent on microstructural and textural features, such as grain morphology, grain size, crystallographic texture and distribution of precipitates. It is necessary to understand microstructure and texture evolution during fabrication in order to optimize the manufacturing process and to improve the service performance. In this work, microstructure and texture evolution during fabrication of Zr-Sn-Nb new zirconium alloy sheets are investigated using XRD, SEM-ECC, TEM and EBSD. The results show that the random texture formed by β quenching transforms into tilt basal texture after hot rolling. The basal texture keeps stable during the following fabrication stages. The texture of the rolling sheets is mainly characterized as <101̄0> direction parallel to rolling direction (<101̄0>//RD), while the texture of the annealing sheets is <12̄10> direction parallel to rolling direction (<12̄10>//RD). The microstructure evolves from a weave Widmansätten structure of β quenching stage to heterogeneous deformation structures associated with hot and cold rolling and then to a fully recrystallized structure after final annealing. The cold rolling sheets present more heterogeneous structures in which the C axes of less deformed grains mostly concentrate in the normal direction. The larger grains in annealed structures mostly belong to the <12̄10>//RD basal texture while the smaller grains are in the <10̄10>//RD orientation. The reason for the heterogeneous deformation structures and texture evolution during annealing are discussed according to the deformation and recrystallization mechanisms.