The mechanism of enhancing room temperature ductility of TC4 alloys via high strain rate multidirectional forging processing

It is important to enhance the room temperature ductility of titanium alloy for its application in complex structural parts. In this study, high strain rate multi-direction forging (MDF) technique is used to refine the grain size of TC4 alloy, and both the evolution regularity and the formation mechanism of the microstructure are elucidated. Dynamic recrystallization (DRX) is enhanced by high strain rate deformation, and thus the fine uniform equiaxed α phase is obtained. After 2 passes of MDF at 880 °C with the strain rate of 13 s −1 , the mean grain size of α phase is refined to 3.2 μm, and the samples exhibit a high ductility of up to 25.9 % with the yield strength and the ultimate tensile strength of 944 MPa and 1060 MPa, respectively. The ductility enhancement mechanism is due to the refined equiaxial α phase, which increases the strain hardening rate of the alloy by the high density of geometrically necessary dislocation (GND) and the activated <c+a> slip system, and thus the crack initiation is inhibited. • The effect of MDF on the microstructure and mechanical properties of Ti-6Al-4V alloy was investigated. • TC4 alloy obtains a high proportion of fine equiaxial α-phases after MDF. • Work hardening is significantly enhanced by the presence of a high density of GNDs and the full activation of the <c+a>slip system in the alloy after 2-passes MDF at 880 °C.