Spinodal decomposition of the γ-phase upon quenching in the Ti–Al–Nb ternary alloy system

The γ-TiAl with L10 crystal structure shows extensive solubility for Nb at elevated temperatures. Recently (Rios et al., Acta materialia 2009; 57:6243), we have demonstrated that the high-Nb γ-TiAl phase becomes unstable upon rapid cooling into a nano-scale two-phase microstructure. In this paper, using detailed compositional and microstructural analyses, we have demonstrated that this phase goes through a spinodal decomposition that results in the compositionally distinct phases identified as a lower-Nb γ-phase and the h-phase, which is rich in Nb and forms by the ordering of this element in the γ-phase.