Influence of Plastic Anisotropy and Strain path on strain-induced Phase Transformation of Cobalt

The objective of this paper is to contribute to a better understanding of the deformation mechanisms of a rolled polycrystalline cobalt sheet. In order to achieve this goal, a particular attention is given to the strain-induced phase transformation and the forming parameters on which it may depend such as the plastic anisotropy or the loading path. In situ phase quantification by X-ray diffraction during tensile tests, on samples cut out from a cold rolled sheet material in three different directions (at 0°, 45° and 90° from the rolling direction), has enabled to study the influence of plastic anisotropy on the strain-induced phase transformation of metastable retained Face Centered Cubic phase to Hexagonal Close Packed phase. Results show that the martensitic phase transformation can be activated by basal slip in the first stage of plasticity but it also indicates that the latter is delayed when sample is strained in tension for an angle of 45° to the rolling direction. Post mortem analyses on a stamped sample by the Nakazima test have revealed that the phase transformation continues for higher strain levels. A particular interest is paid to the coupling between strain-hardening mechanisms and phase transformation and is discussed given the plastic anisotropy of cobalt aggregate. Graphical Abstract Evolution of Metastable Cobalt FCC Volume Proportion During Mechanical Loading