Effect of strain reversal on microstructure and mechanical properties of Ti-6Al-4V alloy under cyclic torsion deformation

Abstract

Abstract Generally, torsion deformation has been recognized as a method of severe plastic deformation (SPD) to obtain a higher shear strain. The effect of strain reversal on the microstructure and mechanical properties was investigated using commercially Ti-6Al-4V alloy by twisting the rods with different effective strain amplitude, such as 180#x00B0;, 270#x00B0;, 360#x00B0; and 450#x00B0; per half cycle. In this work, the microstructure evolution and fracture morphology were carried out by a scanning electron microscope (SEM) and transmission electron microscope (TEM). An Instron 3382 was used for determining ultimate compression strength (UCS). The results show that UCS is very sensitive to cyclic forward-reverse torsion (CFRT) processing and increase distinctly after pre-CFRT. And the value of UCS reaches maximum at 180#x00B0; per half cycle. Besides, monotonic torsion (MT) by twisting the rods in one direction until the fracture occurs was also compared with CFRT. It is found that the ability of work hardening and accumulation of plastic strain is higher for CFRT as compared to MT, which is due to the latticed dislocation in the interior of the grains under CFRT deformation. Grain refinement and fracture feature were discussed to reveal the deformation mechanism of CFRT and MT. The discussion of microstructure evolution and strengthening mechanisms will provide a view to extrapolation to larger strains, finer structures and larger stresses.