Influence of mode of plastic straining on the microstructure of Ni and Ti deformed through rolling and torsion

The influence of the mode of deformation (rolling and torsion) on the microstructures in Ni and Ti was studied. The microstructure of samples deformed to the same von Mises equivalent strains were characterized by electron backscatter diffraction (EBSD) and X-ray line profile analysis (XLPA). The maximum equivalent strains for Ni and Ti were 2.65 and 0.5, respectively. It was found that despite the same equivalent strains, significant differences were found in the microstructures deformed by rolling or torsion. For instance, the Ni sample rolled to the equivalent strain of 2.65 has larger grain size with less distorted grain interiors than in the specimen torsion tested to the same strain. This difference resulted in a lower stored energy in the rolled sample. The difference in stored energy and lattice strain between rolled and torsion deformed samples is attributed to differences in slip activity in each mode of deformation. In the case of Ti, the initial texture resulted in different contributions of < c >/< c + a > dislocation slip and twinning to plastic deformation during rolling and torsion. Due to the higher twinning activity in the Ti specimen rolled to the strain of 0.5, the fraction of < c >/< c + a > dislocations is smaller than in the torsion tested sample. Despite the different microstructures, the stored energies in the two Ti materials do not differ significantly, as the lower fraction of < c >/< c + a > dislocations in the rolled sample is compensated by their less clustered arrangement.