Review - Phase Transitions in Ti Alloys Driven by the High Pressure Torsion
Boris B. Straumal, А. С. Горнакова, Gregory Davdian, Andrey Mazilkin, Ł. Gondek, M. Szczerba, Anna Korneva
Abstract
The high pressure torsion (HPT) of various binary Ti alloys with β-stabilizers (Fe, Co, Ni, Mo, Nb) was studied. Before HPT, the samples were annealed and contained (i) pure β-phase, (ii) α+β mixture with different portion of phases, (iii) α′ or α′′ martensites, (iv) the mixture of α-Ti and respective intermetallic phase. The microstructure of Ti alloys before and after HPT was studied by scanning and transmission electron microscopy (also high resolution one), X-rays diffraction (including the high-temperature in situ one), differential scanning calorimetry, atomic probe tomography, synchrotron irradiation. During HPT the (usual) strong grain refinement took place. Also, it was observed that HPT can lead to various phase transitions in the Ti alloys. In particular, the metastable high-pressure ω-phase and α′ martensite can form. The composition of phases (similar to their grain size) reached the steady-state value after about 1.5 plunger revolutions. In some cases, the equifinality of the HPT-driven phase transitions was observed. Equifinality means that the composition and portion of phases after HPT do not depend on the composition and portion of phases before HPT.