In situ X-ray diffraction study of athermal and isothermal omega-phase crystal lattice in Ti-Nb-based shape memory alloys

It is currently not still sufficiently clear whether “athermal” and “isothermal” ω-phases formed in Ti-based alloys are two different phases, or are indeed one phase, albeit with different formation mechanisms and kinetics. An X-ray diffraction study of a crystal structure of both athermal and isothermal ω-phases formed in a thermomechanically treated Ti–Nb–Zr alloy was conducted to clarify this situation. It was concluded that the ω-phase formed by two different kinetics: athermal, upon subzero cooling, and isothermal upon 300°C-ageing, possesses a unique crystal lattice structure with c/a=0.613±0.003, but differ in the intensity of the microstress relaxation phenomena accompanying their formation, which are more prominent in the latter than in the former. •Athermal and isothermal omega-phase formation in Ti-Nb-based SMA.•In situ X-ray diffraction study of omega-phase.•Comparison of athermal and isothermal omega-phases' crystal lattice structures.