New insights into ω-embrittlement in high misfit metastable β-titanium alloys: Mechanically-driven ω-mediated amorphization

omega-embrittlement is ubiquitous in metastable beta-titanium (Ti) alloys, while the fundamental understanding on the damage-fracture mechanism hitherto remains elusive. In this study, we systematically investigate omega-embrittlement of high misfit Ti-10Cr (wt.%) alloys by coupling experiments and first-principles calculation. It is found that brittle cleavage-like fracture prevails in tensile samples, irrespective of the quenching or subsequent aging states. Microscopically, cracks nucleation and propagation proceed along slip bands, inside which omega-lattices are first disordered and then the localized (beta + omega)-amorphous-like structures are developed in the shape of white patches. The underlying mechanism of mechanically-driven localized amorphization is that due to the remarkable covalent character of atomic bonding of x-precipitates caused by composition partitioning of the Cr element, omega-precipitates impart extremely high energy barrier opposed to dislocation gliding and render dislocations pile-up ahead of omega-precipitates, thus leading to their lattice disordering. It is unveiled that the hydrostatic pressure, serving as the driving force for dislocations pile-up, plays a critical role in this unusual cleavage-like fracture of Ti-10Cr alloys caused by mechanically-driven omega-mediated localized amorphization. Accompanied by the transition from the co-operation of deformation twining and ordinary dislocation slip in the quenched Ti10Cr alloys to the exclusive ordinary dislocation slip in the long-time aged Ti-10Cr samples, it is unexpected that the resulting tensile fracture strength monotonically decreases to a stress level of similar to 100 MPa. These findings provide new insights into the damage and fracture behavior of high misfit beta-titanium alloys, such as Ti-Cr alloys. (C) 2021 The Authors. Published by Elsevier Ltd.

Automated summary

This study systematically investigates omega-embrittlement of high misfit Ti-10Cr alloys and reveals that the lattice disordering of omega precipitates plays a key role in crack propagation. Mechanically-driven localized amorphization significantly affects the cleavage-like fracture behavior of Ti-10Cr alloys. The hydrostatic pressure, serving as the driving force for dislocations pile-up, is critical in this unusual fracture mechanism.