Martensitic {332}〈113〉 twin in β type Ti-Mo alloy

The formation mechanism of {332}〈113〉 twin, one of the deformation modes in metastable β type titanium alloys, was examined by high resolution transmission electron microscopy (HR-TEM) and simulation. The interface structure of twin resembled to α″ martensite. Peculiar movement of atoms to form {332}〈113〉 twin was explained by the β→α″ process followed by the α″→β twin inverse transformation process. The former process brought about convenient conditions to form {332}〈113〉 twin; the atom displacement direction was parallel to 〈113〉, habit plane agreed with {332}, shear strain was 0.2907 and volume change was 0.4% expansion. The parameters of α″ obtained by calculation were a=0.3050 nm, b=0.4913 nm and c=0.4596 nm. Subsequently α″→β twin inverse transformation generated by a shear strain of 0.0628 results in {332}〈113〉 twin having a shear strain of 0.3535. It was suggested that atom displacement and compressive stress field with the martensitic transformation would yield a single ω variant or many defects in the twin band.