Compression deformation behaviours of ultrafine and coarse grained commercially pure titanium

Abstract

Hot compression deformation behaviours of ultrafine grained (UFG) and coarse grained (CG) commercially pure (CP)-Ti were investigated and compared by isothermal simulation tests. Strains over 50% were achieved in these tests over a temperature range of 298–823 K and strain rate of 10−4–10−2 s−1. The results show that the peak stresses of UFG and CG CP-Ti fall with increasing deformation temperature and decreasing strain rate. Within the plastic deformation regime, the compressive stress–strain responses of UFG and CG CP-Ti exhibit quite different features, which strongly depend on the temperature and strain rate. The flow stress of CG CP-Ti monotonically increases with strain, while that of UFG CP-Ti increases first and then tends to be constant after a peak value below recrystallisation temperature. The stress–strain curves of UFG CP-Ti show similar characteristic with those of CG CP-Ti as the temperature is above recrystallisation temperature. Strain rate sensitivity values m of the UFG CP-Ti increase with the rise in temperature and are higher than those of CG CP-Ti. It can be concluded that deformation of UFG CP-Ti is controlled by grain boundary and dislocation activity.