Solid-Solid Transitions in Titanium and Zirconium at High Pressures

Abstract

The body-centered cubic to hexagonal close-packed transformations in titanium and zirconium have been studied by means of differential thermal analysis at pressures in the range 0-65 kbar and at cooling and heating rates of 3-5°C/sec. The transitions occurred at different temperatures upon heating and upon cooling and these hysteresis intervals did not appear to vary much with increasing pressure and/or contamination. Alloying with the tantalum containers and consequent lowering of the transition temperatures was unavoidable in most of the experiments.The Ti transition decreases only slightly in temperature with increasing pressure; a zero pressure volume change of less than 0.3% is suggested. The Zr transition exhibits a slope of about -2.4°C/kbar until a new transition is encountered near 58 kbar; the transition from bodycentered cubic to the new Zr polymorph is without much hysteresis, and the phase boundary exhibits a slope of about 0.6°C/kbar. Discontinuities of about 17% in resistance at room temperature are detected near 51-59 kbar for Zr and 80-90 kbar for Ti, there being a decrease for Zr and an increase for the resistance of Ti.

New Mechanism for theαtoωMartensitic Transformation in Pure Titanium

“…The original α matrix is then oriented relative to the ω matrix such that (0001) α (0111) ω and [1120] α [0111] ω . These orientation relations are seen in some experiments, but not others [5,6,7].…”

“…The original α matrix is then oriented relative to the ω matrix such that (0001) α (0111) ω and [1120] α [0111] ω . These orientation relations are seen in some experiments, but not others [5,6,7].Our mechanism identification method matches possible supercells of α and ω to determine the lattice strain, and atom positions to determine the necessary internal relaxations; similar to [8]. While there are infinitely many possible supercells, we consider only 6 and 12 atom supercells with principal strains less than 1.333 and greater than 0.75 = 1.333 −1 .…”

“…The pressure driven α(hcp) → ω(hexagonal) transformation in pure titanium, discussed here and reviewed extensively by Sikka et al [3], has significant technological implications in the aerospace industry because the ω phase formation lowers toughness and ductility. This transformation was first observed by Jamieson [4], and has since been extensively studied using static high-pressure [5] and shockwave methods [6]. Because of experimental difficulties in directly observing martensitic transformation mechanisms, they are usually inferred from the orientation relationships between the initial and final phases.…”

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

“…Experimentally determined transition pressure for the α-ω phase transition in pure titanium lies at room temperature between 2 and 12 GPa, depending on the experimental conditions [38][39][40][41][42][43][44][45][46].…”

“…The α → ω allotropic transformation takes place at high pressures in titanium, zirconium and hafnium as well as in their alloys [3][4][5][6][7][8][9][10]. The transition pressure, the ability of high pressure ω-phase to retain after pressure release, and the pressure interval where α-and ω-phases coexist depend on the conditions of high-pressure treatment [2,[36][37][38][39][40][41][42][43][44][45][46][47][48]. A number of SPD techniques include the application of high pressure, especially the high pressure torsion (HPT) one.…”