Deformation induced martensite and superelasticity in a β-metastable titanium alloy

This work investigates the formation of deformation induced martensite and shape-memory effects of water quenched β-rich microstructures of a β metastable titanium alloy denominated β-Cez (developed by the Cezus company). In highly β metastable microstructures — solution treatments for 1 h at 920 (β domain) or 860°C (α+β domain) — the β phase transforms to a martensite that is stress-assisted in nature. Solution treatment at a slightly lower temperature (850°C) increases the stability of the β phase and the martensite thus becomes a strain-induced type. Decreasing the solution treatment temperature further (800°C) leads to a sufficiently stable β phase so that no martensite is formed under tensile deformation and only slip is activated. These different ways of accommodating deformation result in various mechanical responses. In particular, the stress-assisted martensite in this alloy is partly reversible under unloading, which produces significant superelasticity.