Mechanical properties and microstructural evolution of nanocrystalline titanium at elevated temperatures

An investigation was initiated to study the mechanical properties and microstructural evolution of nanocrystalline titanium in the temperature range of 473-923 K after processing by high-pressure torsion (HPT) under a pressure of 5.0 GPa for up to 10 turns. The results show there is a significant improvement in both the tensile strength and the ductility in nanocrystalline Ti by comparison with coarse-grained (CG) Ti at elevated temperatures. The strength of HPT-processed Ti drops to that of CG Ti at temperatures above 773 K because of grain growth. An investigation of the mechanical behavior at elevated temperatures reveals an increasing-decreasing-increasing trend in the elongations to failure with increasing temperature. An elongation of >130% was achieved both at 673 K and above 773 K for the HPT-processed samples and this was significantly larger than for the CG Ti. The highest measured elongation was ~200% for the HPT-processed sample tested at 923 K. A good combination of strength and elongation to failure was achieved in the temperature range of 573-773 K after HPT processing.