Evidence of α → ω phase transition in titanium after high pressure torsion

Abstract

Evidence of a ? x phase transition in titanium after high pressure torsion It is well known that a high pressure x-phase is formed in Ti at high pressures in the range between 2 and 8 GPa. This martensitic-type transformation demonstrates very large hysteresis, and hence the x-phase can be retained in the material after release of pressure. Additionally, applied shear stresses are known to facilitate the a ? x transformation. This paper describes an investigation on the x-phase formation after high pressure torsion under a wide range of pressures and shear strains by means of X-ray diffraction and transmission electron microscopy. We show that the x-phase forms in Ti upon high pressure torsion deformation after 300 s under a pressure of 3 GPa. This suggests that the transformation kinetics are notably increased as compared with the kinetics of pressure-induced transformation.

Plastic Deformation of BaTiO3Ceramics by High-pressure Torsion and Changes in Phase Transformations, Optical and Dielectric Properties

“…[21][22][23][24] These results clearly show that, although substantial pressure is required to trigger the cubic-phase formation, the phase transition is facilitated with straining. This finding is consistent with earlier reports concerning the effect of strain on phase transitions in Ti, [38][39][40] Zr, [41] ZrO 2 [30] and some other metallic alloys. [42][43][44] The cubic phase present after HPT processing remains partially stable even after pressure release because of the formation of nanograins.…”

The α → ω Transformation in Titanium-Cobalt Alloys under High-Pressure Torsion

“…In contrast to [49], where the samples before HPT contained only α-phase, the starting state after annealing in β-area and quenching contains the mixture of α-and β-phases. A number of diffraction peaks typical for the (α + β) Ti-alloy can be seen in the XRD patterns in Figure 2a (lower curve).…”

“…Yu. Ivanisenko et al studied the HPT of pure titanium in non-constrained conditions (flat anvils) and observed the onset of α → ω transformation at 3 GPa [49]. The amount of ω-phase increased from 0% at 2 GPa to about 70% at 6 GPa (Figure 4) [49].…”

“…A number of SPD techniques include the application of high pressure, especially the high pressure torsion (HPT) one. It is known that the combination of shear strain with high pressure (i.e., in case of HPT) decreases the onset of the α → ω transition in comparison with quasi-hydrostatic conditions [2,[49][50][51]. The goal of this work is to study how the Co addition to Ti influences formation of the ω-phase under HPT.…”

Deformation-induced ambient temperature α-to-β phase transition and nanocrystallization in (α + β) titanium alloy

“…3,6 The high-pressure b phase has not been observed in pure titanium in most of the experiments, 4 except as claimed by Ahuja et al 7 for the observation of the o-to-b transition in the range 40-80 GPa. In addition to high pressure studies, shock 8,9 and severe plastic deformation 10 experiments performed at ambient temperature only show the a-to-o phase transformation in Ti and Ti-6Al-4V alloy. Also, complete transformation and significant refinement from the coarse-grained a-Zr to o-phase occurs during high-pressure torsion, and the nanocrystalline o-Zr phase is stable at room temperature and pressure.…”