Micro-mechanical aspects of texture evolution in nickel and nickel–cobalt alloys: role of stacking fault energy

Abstract

The micro-mechanisms associated with the evolution of deformation texture in nickel and nickel–cobalt alloys, with stacking fault energy (SFE) ranging from high to low, has been investigated. Pure nickel and nickel-20 wt.% cobalt alloy, which are high SFE materials, develop a characteristic copper-type texture, which is attributed to dislocation slip. In the medium SFE nickel-40 wt.% cobalt alloy, the texture is copper-type up to 95% reduction; however, subsequent reduction to 98% causes the texture to shift towards brass-type. Microstructural examination suggests that the occurrence of Cu-type shear bands (SBs) preferentially in the Cu {1 1 2}-oriented grains has led to this texture transition. In nickel-60 wt.% cobalt alloy, which is a low SFE material, texture is brass-type from the early stages of rolling. Deformation mechanisms show a gradual transition from deformation twinning to Bs-type SBs, as a function of strain. The strength of the final texture is a synergistic effect of twinning and shear banding. The absence of Cu component during the process of brass-type texture evolution goes against Wassermann’s prediction of texture transition. A modified theory for the formation of brass-type texture is proposed.