In this study, the deformation behaviour of metastable β-type Ti-33Nb-4Sn alloys in different thermo-mechanical treatment states is investigated by tensile tests and in situ synchrotron X-ray diffraction (SXRD). In the case of solution-treated alloy, stress-induced martensitic (SIM) transformation takes place over a wide strain range of 0.5-14%. During this SIM transformation, the parameter of b α" ([020] α") increases with macroscopic strain within strain range of 1.5-4.7%, giving rise to that the α" variants, with b α"-axis ([020] α") parallel to tensile direction, are formed preferentially to accommodate the macroscopic strain during loading. Similar SIM transformation behaviour also occurs in cold-rolled alloy with the exception that the extent of SIM

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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.