Co-deformation and dynamic annealing effects on the texture development during alpha–beta processing of a model Zr-Nb alloy

Abstract

The in-service properties and performance of dual-phase Zr and Ti alloys depend on their crystallographic texture, which develops during hot-working and is affected by interactions between the α and β phases during deformation, annealing and phase transformation. Recent work on hot-rolled Zr-2.5Nb has shown that the texture of the two phases are related, with coupled strengthening of the α near {112¯0}〈101¯0〉, which produces strong 0002 pole intensities along the transverse direction, and β with {001}〈110〉 rotated cube, particularly when the relative volume fraction is around 50:50. To investigate the origin of this texture coupling, we studied a hot-rolled model Zr alloy with 7 wt.% Nb, in which the as-deformed α + β microstructure is preserved on cooling. The alloy was hot-rolled to different reductions at 725∘C, which corresponds to a relative α:β volume fraction of 30:70, where the characteristic textures are known to develop quickly at first and then weaken with further reduction. The rolled material was characterised using both 2D and 3D electron backscatter diffraction (EBSD). This analysis uncovered evidence that both recrystallization and phase transformation cause the disappearance of specific α variants during rolling, favouring the formation of “soft” primary α grains flattened in 〈112¯0〉 and elongated along 〈101¯0〉 during rolling, which in turn has an effect on surrounding β orientations, promoting the stronger rotated cube component. At higher reductions, these elongated α-grains start to break up, as does the β surrounding it, forming bands of characteristic coupled textures. These observations imply that non-plasticity effects should be included in models of texture evolution during processing of α + β Zr and Ti alloys.