The Nature of the β→α″ Transformation in Ti-Nb Alloys

Abstract

The martensitic transformation in Ti-Nb alloys can result in superelastic and shape memory behaviour but significant discrepancies exist between the transformation conditions reported for a given composition. To elucidate the reasons for these variations, in situ synchrotron diffraction experiments have been performed on Ti-24Nb (at.%) in two different microstructural conditions. Markedly different transformation behaviour was observed between these two conditions, including fully reversible superelastic behaviour below the apparent martensitic start temperature. These results could not be rationalised using thermally based transformation descriptions. As such, a new approach is introduced based upon the total stress level in a material.