Evidence of dislocation dependent behaviour in superelastic Ti2448 (Ti-24Nb-4Zr-8Sn, wt%)

Within the literature significant variations in martensite start temperature (Ms) can be observed for samples of identical composition. However, the factors affecting Ms are not well understood, limiting industrial uptake. Recently, claims that the isothermal variant of the & omega; phase (& omega;iso) may be driving many changes in Ms have been called into question due to the absence of any compositionally distinct & omega;isofollowing thermal cycling. In the present study, in situ synchrotron X-ray diffraction has been employed to conclusively show that dramatic changes in Ms can be replicated without any formation of & omega;iso. Dislocations have been shown to be mobile at the temperatures reached and, as such, an alternative mechanism based on the total stress model has been proposed. This added understanding can rationalise many of the discrepancies observed in the literature, and ultimately improve industrial uptake of this class of material.

Automated summary

Significant variations in martensite start temperature (Ms) have been observed in the literature for samples of identical composition, but the factors affecting Ms remain unclear, limiting industrial applications. Claims that the isothermal variant of the ω phase (ωiso) may drive changes in Ms have been questioned due to the absence of distinct ωiso following thermal cycling. In this study, synchrotron X-ray diffraction confirmed that dramatic changes in Ms can occur without ωiso formation, suggesting an alternative mechanism based on the total stress model. This improved understanding can resolve discrepancies in the literature and enhance industrial uptake of these materials.