Unique discontinuous yielding mechanism of fine-grained metastable β-type Ti-Nb-Mo alloy

Abstract

The fundamental mechanisms of discontinuous yielding in a ternary Ti-Nb-Mo alloy with a fine-grained microstructure were investigated using the in-situ synchrotron radiation X-ray technique. The findings indicate that although the martensitic transformation initiated at the elastic deformation stage and progressed with the propagation of the Lüders-like deformation, the rapid large-scale dislocation multiplication within the β-matrix was the underlying cause of the discontinuous yielding phenomenon. Furthermore, the presence of high-density dislocations facilitated martensitic transformation within the Lüders band, which allowed the martensitic transformation to persist even after the front of the Lüders band passed, resulting in an unconventional propagation behavior of the Lüders band. This unique deformation mechanism enables the alloy to rapidly regenerate work hardening after the yield drop, leading to a markedly increase in uniform elongation of the present alloy. This study provides new information on the discontinuous yielding of the metastable Ti-based alloys.