Phase-field study of the spinodal decomposition rate of β phase in oxygen-added Ti–Nb alloys

Abstract

In this study, the β-phase spinodal decomposition in oxygen-added Ti–Nb alloys is simulated at 700–1073 K using the phase-field method. The results show that the addition of low amounts of oxygen remarkably enhances the β-phase spinodal decomposition at high temperatures. The β phase in Ti-23Nb-XO (at.%) alloys (X = 2, 3, 4, and 5) separates into the β1 phase, i.e., (Ti)(O, Va)3, and the β2 phase, i.e., (Ti, Nb)(Va)3, at 1073 K. Moreover, nanoscale concentration modulation is introduced. In Ti-23Nb-1O (at.%) alloy, the β-phase spinodal decomposition occurs at a temperature below 1000 K. The volume fraction and composition of the β1 and β2 phases depend on the heat treatment condition and alloy composition, in particular, the oxygen content. The spinodal decomposition of Ti–Nb–O alloys take about 10−2–10−3 s at 1073 and 900 K, which is significantly faster than that in Ti-40Nb (at.%) alloy at 600–700 K. Hence, the spinodal decomposition in Ti–Nb–O alloys is presumed to progress even during water quenching. The results suggest that the control of the microstructure of Ti–Nb–O alloys requires careful control of both the alloy composition and heat treatment conditions, including the cooling rate.