Mechanisms underlying TRIP effect on ductility enhancement in titanium alloys

The transformation-induced plasticity (TRIP) effect has been widely introduced into advanced metal structural materials to assist dislocation slip in carrying plastic deformation. In this work, the deformation responses of stress-induced α′′-martensite (SIM) under different yield strengths and early plastic behaviors were investigated for TRIP titanium alloys. Accordingly, the comprehensive theoretical calculations focusing on phase stability and modulus mismatch were employed for screening TRIP-dominated target composition. The designed Ti-0.56Al-8.04Mo-2.18Cr (wt.%) alloy achieved a synergistic enhancement of yield strength-ductility after simple thermomechanical processing. Our results clarified the conventional understanding for deformation behaviors of SIM at the early plastic stage. Concurrently, the mechanism underlying the retention of > 0.52 ductility at approaching 700 MPa yield strength for TRIP-dominated titanium alloys has been systematically elucidated. Moreover, three SIM-SIM interaction modes, that is, shear displacement, SIM splitting, and SIM blocking, and detwinning phenomena in α′′-martensite during unloading were also captured.