Progress in deformation mechanisms and emerging functionalities of metastable β titanium alloys: Insights from advanced characterizations

Metastable β titanium alloys, characterized by diverse microstructural evolution due to a high content of β stabilizers, offer great potential for achieving high multifunctionality, such as excellent strength and ductility combination, biocompatibility, superelasticity, shape memory, and machinability. Advanced characterization plays a critical role in establishing structure–property relationships at the nano- and micro-scales in real time. This review explores the classification, phase, and deformation mechanism at room, elevated, and cryogenic temperatures, multifunctionality such as strength-ductility, biocompatibility, and shape memory, alongside future development directions. Notably, the reasons and roles of kinking and hetero-deformation in plasticity and strengthening are novelly analyzed. Furthermore, it also first evaluates and summarizes the relationship among deformation mechanisms, microstructural evolution, and mechanical properties in a wide temperature range. In metastable β titanium alloys, a metastable engineering strategy is employed to systematically activate various mechanisms, which operate synergistically to achieve excellent multifunctionality. Finally, the research gaps and prospects are highlighted, including quantification and interaction of deformation mechanisms, interatomic potential and stacking fault energy, and the pursuit of advanced multifunctionality.