Effects of primary α grains on rolling reductions and deformation modes in Zr alloys: Experiments and modeling

Abstract

Microstructure and texture evolution of β-quenched Zr-xNb-0.4Mo (x = 0, 0.4, 0.6 and 1.0 wt %) alloys during the cold rolling process were systematically investigated. The Zr-xNb-0.4Mo alloys exhibit the area fractions of the martensitic structure are 33.2%, 69.4%, 100% and 100% with an increase in Nb content. Under the same rolling gap (1.2 mm), the rolling reductions are 24%, 28%, 29.7% and 30%, respectively. To understand the reason for the gradual increase of rolling reductions until approximately 30%, a visco-plastic self-consistent (VPSC) model was employed to predict the texture evolution and relative activity of different deformation modes. The variation of average Schmid factors (SFs) and the variation of the relative activity of different deformation modes before and after cold rolling were calculated and compared. With the increase of Nb content, a similar variation law between the variation of average SF and the variation of relative activity was found. The basal <a> slip in Zr-0.4Nb-0.4Mo alloy is difficult to activate due to the initial texture of Zr-0.4Nb-0.4Mo alloy. Pyramid <c+a> slip can accommodate the strain along the normal direction (ND), which is beneficial to the high plasticity of Zr alloys during cold rolling. By comparing the variation of average SF of pyramid <c+a> slip, it is found that the larger rolling reductions of Zr-0.6Nb-0.4Mo alloy and Zr-1.0Nb-0.4Mo alloys can be attributed to the activation of pyramid <c+a> slip. The existence of primary α grains can decrease the average SF and inhibit the activation of pyramid <c+a> slip. The cold rolling can make the martensite plates crushed and refined, but not to the primary α grains.