EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Severe plastic deformation (SPD) leads not only to strong grain refinement and material strengthening but also can drive phase transformations. The fundamentals of the α→ω and β→ω phase transformations in Ti-Co, Ti-Nb and Ti-Ni based alloys induced by high pressure torsion (HPT) at the same conditions depending on the amount of the β-alloying elements were studied. Scanning electron microscopy, transmission electron microscopy and sinchrotrom X-ray diffraction (XRD) techniques techniques were used for characterization of microstructure evolution and phase transformations. It was found, that β-phase completely and more easily transformed into the ω-phase during HPT, while the α-phase partialy transformed into the ω-phase and its transformation depends on the content of alloying element in the initial α-phase. The less the amount of the alloying element in the α-phase, the more the amount of the α-phase is transformed into the ω-phase. The effect of the adding alloying component on the ω-phase thermal stability was also studied by means of the differential scanning calorimetry technique and in situ high-temperature XRD measurements. It was found, that in the systems with negative mixing enthalpy (Ti-Co, Ti-Ni) the ω-phase decomposed into the α- and intermetallic phases at higher temperature than in the system with positive mixing enthalpy (Ti-Nb), where only the reverse ω to α-phase transformation was observed.