The role of strain rate and texture in the deformation of commercially pure titanium at cryogenic temperature

Abstract

In this work, we explore the effect of strain rate and crystallographic texture on the hardening behaviour and ductility of grade 2 commercially pure titanium (CP–Ti) plate at both room (298 K) and cryogenic temperature (123 K). EBSD technique was used to characterise the microstructural features and analyse the deformation twins and active slip systems in α-Ti. Using the SEM fractography, the necking resistance was estimated by measuring the reduction of cross-sectional area. As the strain rate decreases, the elongation was improved with the enhancement of strain-hardening and necking resistance, whereas this behaviour was relatively strain rate insensitive at 298 K. Consequently, the total elongations were increased from 38% (298 K) to 65% (123 K), and from 28% (298 K) to 35% (123 K) in tension parallel and transverse to the rolling direction of the plate, respectively. The combined effect of strain rate and (cryogenic) temperature affected the transition of deformation mechanisms involved in the twinning and dislocation slip, thereby leading to the three or four multi-stage strain-hardening behaviour. The results reveal that in addition to the dislocation slip, the deformation twinning contributed to the strain-hardening, and improvement of total elongation of α-titanium at cryogenic temperature.