Evolution of grain and subgrain structure during cold rolling of commercial-purity titanium

The evolution of microstructure in commercial-purity titanium during cold rolling to a thickness strain of 2.6 was quantified using electron backscatter diffraction. The measurements were analyzed in terms of the mean grain size and the density of boundaries (the ratio of total boundary length to the scanned area). The density of high-angle boundaries as a function of thickness strain had three distinct stages, each of which was associated with a different mechanism of microstructure formation, i.e., (i) twinning, (ii) an increase in dislocation density and the formation of substructure, and (iii) the formation of deformation-induced high-angle boundaries. The influence of twinning on the kinetics of microstructure evolution was also interpreted.