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.

Keywords:

• Nickel–cobalt alloys
• deformation texture
• twinning
• shear banding

Acknowledgements

The authors acknowledge the use of microscopy facilities at the Advanced Facility for Microscopy and Microanalysis (AFMM), Indian Institute of Science. The authors are grateful to Drs. Carlos Tome’ and Ricardo Lebensohn for providing the VPSC 7b software for texture simulations.