On the mechanism of superelasticity in Gum metal

The deformation mechanisms of the ββ-Ti alloy, Gum metal, were investigated with the aid of in situ synchrotron X-ray diffraction (SXRD) and transmission electron microscopy (TEM). SXRD showed that Gum metal undergoes a reversible stress-induced martensitic (α″α″) phase transformation. Oxygen increases the resistance to shear by increasing C′C′ and limits the extent of α″α″ growth. Prior deformation aids α″α″ formation of by providing nuclei, such as {{1 1 2}<<1 1 1>> twins and stress-induced ωω plates. The formation of twins and ωω plates, both observed in TEM, are believed to be a result of a low G111 in this alloy. Features similar to the “giant faults” seen previously were observed in TEM; their formation is believed to be a result of {{1 1 2}<<1 1 1>> shear.