Vickers microhardness and microstructure relationship of Ti-6Al-4V alloy under cyclic forward-reverse torsion and monotonic torsion loading

The effect of strain reversal on the hardening and grain refinement of Ti-6Al-4V alloy due to cyclic forward-reverse torsion (CFRT) has been investigated in this study by twisting the bars with different strain reversal amplitude. The results showed that microhardness and its distribution were very sensitive to CFRT and increased distinctly after pre-CFRT pure shear deformation. It was observed that the ultimate microhardness and homogeneity were superior for CFRT as compared to monotonic torsion (MT), while the hardenability exponent of MT is higher than CFRT. Besides microhardness in the center layer and surface layer of a bar exhibited different evolutionary process with the increasing amplitude of strain reversal. Grain refinement induced by latticed dislocation tangle and work hardening enhanced by strain gradient were also discussed to reveal the evolution of microstructure and microhardness.