In-situ investigation of phase transformations in Ti-Nb-Zr alloys by simultaneous synchrotron diffraction and dilatometry

Ti-Nb-Zr alloys are promising materials for structural applications in the biomedical sector. Unfortunately, detailed understanding of the solid-state transformations occurring in these alloys is lacking, in particular concerning the diffusionless processes linked to the formation of ω phase. In this work we applied simultaneous in-situ synchrotron diffraction and dilatometry to study phase transformations in three Ti-Nb-Zr alloys containing 20, 27 and 35 wt% Nb, respectively, and fixed 13 wt% Zr. The applied thermal cycle consisted in heating to 850 °C followed by cooling to room temperature, applying a high heating and cooling rate of 30 °C/s to suppress diffusional phenomena. The investigation showed no transformation in the alloy richer in Nb, which is classified as β alloy, and the occurrence of three phenomena in the other two alloys: i) the reversion of α'' martensite to β phase on heating, followed by the β→α'' martensitic transformation on cooling; ii) the ω to β transformation on heating, followed by ω formation on cooling; iii) an anomalous expansion of the β lattice on heating, followed by an anomalous contraction on cooling that is also interpreted in terms of ω↔β transformation. Finally, it is shown that all these transformations can be followed by dilatometry, paving the way to systematic investigation of transformations in similar alloys in the future.