Microstructural Evolution and Strain-Hardening in TWIP Ti Alloys

Abstract

a b s t r a c tA multiscale dislocation-based model was built to describe, for the first time, the microstructural evolution and strain-hardening of {332} 113 TWIP (twinning-induced plasticity) Ti alloys. This model not only incorporates the reduced dislocation mean free path by emerging twin obstacles, but also quantifies the internal stress fields present at β-matrix/twin interfaces. The model was validated with the novel Ti-11Mo-5Sn-5Nb alloy (wt.%), as well as an extensive series of alloys undergoing {332} 113 twinning at various deformation conditions. The quantitative model revealed that solid solution hardening is the main contributor to the yield stress, where multicomponent alloys or alloys containing eutectoid β-stabilisers exhibited higher yield strength. The evolution of twinning volume fraction, intertwin spacing, dislocation density and flow stress were successfully described. Particular attention was devoted to investigate the effect of strain rate on the twinning kinetics and dislocation annihilation. The modelling results clarified the role of each strengthening mechanism and established the influence of phase stability on twinning enhanced strain-hardening. Strain-hardening stems from the formation of twin obstacles in early stages, whereas the internal stress fields provide a long-lasting strengthening effect throughout the plastic deformation. A tool for alloy design by controlling TWIP is presented.

Effect of Different Cold Rolling Reduction on the Microstructure and Mechanical Properties of Ti-3573 Titanium Alloy

“…The deformation patterns of strain-induced martensite and deformation twins can be determined by adding Ta, Mo and Nb element into the alloy. According to report, the β titanium alloy can activate {332}< 113 > deformation twins to enhanced TWIP effect through observation of Ti-xMo alloys [10]. The samples in this paper contain sufficient Mo element, which helps to improve the strengthening effect.…”

“…It is well known that a combination of mechanical twinning (TWIP effect) and SIM transformation (TRIP effect) can improve the strain hardening capability and subsequently the uniform elongation of titanium alloys. The TRIP/ TWIP deformation mode plays an important role in increasing the rate of strain hardening and enhancing the formability of the material except for dislocation slip, which is because stress-induced martensite and deformation twins can hinder dislocation motion during deformation [9,10]. The deformation patterns of strain-induced martensite and deformation twins can be determined by adding Ta, Mo and Nb element into the alloy.…”