In situ synchrotron X-ray diffraction study of stress-induced martensitic transformation in a metastable β-type Ti-33Nb-4Sn alloy

In this study, the stress-induced martensitic (SIM) transformation of a recently developed metastable β-type Ti-33Nb-4Sn alloy consisting of a mixture of β and α″ phases are investigated by in situ synchrotron X-ray diffraction (SXRD). It is shown that though the SIM transformation covers a wide strain range, some remaining β phase is still observed after loading, indicating that the SIM transformation is incomplete. During SIM, the parameter of bα″ increases with macroscopic strain within the strain range of 1.5-4.7%, while the parameters of aα″ ([100]α″) and cα″ ([002]α″) remain constant or decrease with increasing strain, respectively. This provides a plausible explanation for why the (020)α″ peak intensifies, but the (002)α″ peak decreases and even eliminates in the loading direction during loading. Additionally, the activation sequence of different deformation mechanisms is clarified unambiguously.