Synchrotron X-ray diffraction study of the phase transformations in titanium alloys

Abstract

High-resolution synchrotron X-ray diffraction was used to study the phase transformations in titanium alloys. Three titanium alloys were investigated: Ti -6Al -4V, Ti -6Al -2Sn -4Zr -2Mo -0.08Si and b21s. Both room and high temperature measurements were performed. The room temperature experiments were performed to study the structure of the alloys after different heat treatments, namely as received (AR), furnace cooling (FC), water quenching (WQ) and water quenching followed by ageing. The a, a 0 , a 00 and b phases were observed in different combinations depending on the heat treatment conditions and the alloy studied. A multicomponent hexagonal close packed (hcp) a phase, with different c and the same a lattice parameters, was detected in Ti -6Al -4Vafter FC. High temperature synchrotron X-ray diffraction was used for 'in situ' study of the transformations on the sample surface at elevated temperatures. The results were used to trace the kinetics of surface oxidation and the concurrent phase transformations taking place under different conditions. The influence of the temperature and oxygen content on the lattice parameters of the a phase was derived and new data obtained on the coefficients of thermal expansion in the different directions of the hcp a phase, for Ti -6Al -4V and Ti -6Al -2Sn -4Zr -2Mo -0.08Si. D

Lattice expansion of Ti–6Al–4V by nitrogen and oxygen absorption

“…The α and β values of the bulk alloy are always lower than those determined in the present experiments on powder. For comparison, the data of Malinov et al [8] are contrasted with the present results in Fig. 4 The differences displayed by Fig.…”

“…Results of analogous experiments performed on bulk Ti6Al-4V alloy are reported in the literature [8][9][10]. The expansion coefficients determined from tests in vacuum (pressure of 2.5 × 10 − 3 mbar) [8] were α = 1.043 × 10 − 5°C− 1 and β = 1.448 ×…”

“…The expansion coefficients determined from tests in vacuum (pressure of 2.5 × 10 − 3 mbar) [8] were α = 1.043 × 10 − 5°C− 1 and β = 1.448 ×…”

“…In spite of the widespread use of titanium and titanium alloys, in particular for high-temperature applications, only recently have results of investigations by high-temperature Xray diffraction (HT-XRD) been published [8][9][10]. In the present work HT-XRD has been employed to examine Ti-6Al-4V powder heated up to 600°C in argon of commercial purity.…”

On the effect of hydrogen on the elastic moduli and acoustic loss behaviour of Ti-6Al-4V

“…Using the diffusivity of hydrogen in β titanium, calculated from the equation given by Wasilewski and Kehl [42], and the lattice parameter for the β phase in Ti-6-4 reported by Malinov et al [44], the relaxation time at 298 K for octahedraloctahedral movement, τ oct , was calculated to be 1.1×10 −9 s and for tetrahedral-tetrahedral movement, τ tet , as 5.6×10 −10 s. The relaxation time determined from the experimental values aggregated in the present study, τ av , is 3.4×10 −9 s. This is on the order of τ oct Figure 6. (colour online) Behaviour of Q −1 with inverse temperature for the resonance with frequency 412 kHz at 298 K. Two fits for Snoek-like behaviour, with E act fixed at 23 kJ mol −1 are also shown.…”