Stain-Hardening Behavior of a Ductile Beta Ti-alloy with Transformation Induced Plasticity and Twinning Induced Plasticity

We investigated the strain hardening behavior of the metastable beta Ti-12Mo-5Zr (wt%) alloy combined with TWIP/TRIP effects (TRIP for Transformation Induced Plasticity and TWIP for Twinning Induced Plasticity). The evolution of the strain hardening exponent was analyzed by classical Hollomon theory. The three stages of strain-hardening behavior were divided, labeled as Stage I, Stage II and Stage III. Stage I corresponds to the transition from the elastic to plastic regimes (epsilon approximate to 0 similar to 0.02). Stage II relates to a continuous increase of the strain-hardening rate and the hardening exponent (epsilon approximate to 0.02 similar to 0.15). Then, the strain-hardening rate decreases and the hardening exponent reaches a stable value 0.34 in Stage III (epsilon approximate to 4.15 similar to 0.34). The evolution of microstructure within three stages was observed by employing techniques of optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Based on the experimental results, the governing mechanisms for deformation at different stages and strain-hardening behavior of Ti-12Mo-5Zr alloy were discussed.