On the mechanism of superelasticity in Gum metal

Abstract The deformation mechanisms of the β -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 ″ ) phase transformation. Oxygen increases the resistance to shear by increasing C ′ and limits the extent of α ″ growth. Prior deformation aids α ″ formation of by providing nuclei, such as { 1 1 2} 1 1 1 > twins and stress-induced ω plates. The formation of twins and ω plates, both observed in TEM, are believed to be a result of a low G 1 1 1 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.