Microstructural and hardness evolutions of a cold-rolled cobalt

Abstract

Abstract The microstructural and hardness evolutions of cold-rolled cobalt (Co) were investigated by electron backscatter diffraction, electron channeling contrast imaging, transmission electron microscope and Vickers hardness tests. The original Co has a dual phase structure with a mixture of hexagonal closed-packed and face-centered cubic structures. More than half fraction of the boundaries in the original Co present a particular orientation of ~ 71 ° / 11 2 ‾ 0 > . During cold rolling, different deformation mechanisms including dislocation slip, twinning, martensite phase transformation and stacking faults were activated, and their mutual interactions eventually refined the grains to nano scale. Multiple twinning systems including { 10 1 ‾ 2 } , { 11 2 ‾ 2 } and { 10 1 ‾ 1 } were activated, which play a dominant role at the early deformation stage, while these twins were eventually refined through dislocation – twin interactions. Basal a, pyramidal c+a and partial dislocations were all triggered to accommodate the local strain. Partial dislocation gliding is responsible for the reversible martensite phase transformation. The Vickers hardness results indicate a stable strain hardening process during the whole cold rolling process.