Micro-mechanisms of deformation texture evolution in nanocrystalline nickel-cobalt alloys

Abstract

Deformation mechanisms in nanocrystalline Ni-x wt% Co alloys (x = 0, 20, 40, 60), having stacking fault energy values from high to low, have been investigated with regard to the evolution of microstructure and texture during room temperature rolling. In all the materials, no new texture peak appears until 20% thickness reduction and the texture is similar to initial fiber texture, which indicates that grain boundary-mediated deformation mechanisms are more active. The development of characteristic copper-type and brass-type rolling textures is visible beyond 40% reduction. High SFE materials, namely pure Ni and Ni-20Co alloy, develop a copper-type texture at large reduction, whereas in low SFE Ni-40Co and Ni-60Co alloys, the texture is close to brass-type. The evolution of copper-type texture is attributed to the activity of ½{111}<110> type dislocations and cross slip in nanocrystalline grains, which is aided by deformation-driven grain growth. Crystal plasticity simulations suggest that the evolution of brass-type texture evolution in low SFE nanocrystalline alloys is due to 1/6{111}<112> type partial dislocation slip. The activity of partial slip is promoted by the suppression of grain growth and cross slip in high cobalt containing alloys. The evolution of deformation texture and microstructures in nanocrystalline nickel-cobalt alloys is governed by the combined effects of grain size and SFE.