Embrittlement of metastable β-Ti alloy induced by isothermal ω precipitates

In this work, a ductile-to-brittle transition was observed when Ti-16Nb-16Zr-6Sn (in wt. %) alloy, by aging at 300 °C, reversed from α′′-Ti alloy into metastable β-Ti alloy with isothermal ω nano-precipitates. In particular, the fracture surface was mixed with intergranular cleavages and shallow dimples. It was found that this brittle fracture was initiated by intragranular cracking without formation of obvious slip bands. This is attributed to the dispersion of isothermal ω nano-precipitates. Although stress-assisted α′′ martensite was then triggered by stress concentration of initial cracks, only shallow dimples developed on fracture surface, providing very limited toughening effect. Conceptually, Yoffee diagram integrated with principle of stress-assisted martensite is used to understand this new pathway of embrittlement induced by isothermal ω nano-precipitates in metastable β-Ti alloy. [Display omitted]