Deformation twinning activity and twin structure development of pure titanium at cryogenic temperature

We compared deformation twinning activity and twin structure development of pure Ti at cryogenic temperature and room temperature by conducting unidirectional rolling at 77 K and 293 K. Twinning activity was significantly higher in rolling at 77 K than in rolling at 293 K. This was because lowering the deformation temperature increased the necessity for twinning operation to compensate for reduced accommodation of strain along the c-axis of the crystal structure, caused by inhibition of slips. Twin structure was also entirely different between the two rolling temperatures. Compared to the case of rolling at 293 K, rolling at 77 K generated thin and numerous individual twins in the twinned grains, thereby giving rise to the development of a totally different twin structure. The differences in twin structure were caused by the combined effect of significant local stress concentration at grain boundaries and a reduction in stacking fault energy by rolling at 77 K. The twin structure strongly contributed to severe twinning-induced grain refinement that occurs at cryogenic temperature.