The dynamic response of a metastable β Ti–Nb alloy to high strain rates at room and elevated temperatures

Abstract

A metastable β Ti–Nb alloy, Ti–25Nb–3Zr–3Mo–2Sn (wt.%), has been subjected to high strain rate deformations (1000 s−1) at the temperatures of 293 K, 573 K and 873 K by Split Hopkinson Pressure Bar compressive tests. The microstructural evolution and deformation mechanisms of the metastable Ti–Nb–Zr–Mo–Sn alloy have been investigated by X-ray diffraction, electron backscatter diffraction and transmission electron microscopy. Multiple deformation mechanisms including {332} <113> and {112} <111> mechanical twinning, stress-induced α” and ω phase transformations and dislocation slip were identified at 293 K. Among them, {332} <113 > twinning is the dominant deformation mechanism and induced pronounced strain hardening at 293 K. At 573 K, {332} <113> and {112} <111 > mechanical twinning occur in conjunction with dislocation slip. Though the direct contribution to strengthening by mechanical twinning is relatively small at 573 K, it enhances both the multiplication and annihilation of dislocations thereby impacting the strain hardening behaviour of the Ti–Nb–Zr–Mo–Sn alloy. With an increase in temperature to 873 K, the plastic strain is accommodated by dislocation slip only. The deformation mechanisms which are active during deformations at different temperatures also influence the development of texture in the Ti–Nb–Zr–Mo–Sn alloy.