Phase transformations of the L12-Ti3Al phase in γ-TiAl alloy

Publication date: 5 May 2017
Source:Materials & Design, Volume 121
Author(s): Shouzhen Cao, Shulong Xiao, Yuyong Chen, Lijuan Xu, Xiaopeng Wang, Jianchao Han, Yi Jia
A new phase L12-Ti3Al was found in the Ti-46Al-6Nb alloy after rapid-cooling and then annealing at 850°C for 5h. The transformation kinetics involving the L12 phase were observed by transmission electron microscopy (TEM): The plate-like L12 phase precipitates in the massive γ (γm) phase and then partially transforms into α2 or B2 phase; the transformations of bulk α2 (αb)→L12/L12→γ were also observed to form a fine lamellar structure with an average interlamellar spacing <20nm. The orientation relationships between γ, α2 and L12 phases were confirmed by TEM observation and crystallographic calculation, which are (001)γ//(001)L12, [010]γ//[010]L12, [100]γ//[100]L12 and (0001)α2//{111}L12, 〈112¯0〉α2//〈11¯0〉L12. The L12 phase was also observed in Ti-the 47Al alloy after the quenching-annealing process. Thermodynamic analysis of the transformations indicates that the γ→L12 transformation is extremely susceptible to temperature changes while transformations between the α2 and L12 phases are not.

Graphical abstract

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