Phase stability and microstructural evolution of Ti2AlNb alloys-a review

Ti2AlNb alloys are potential next-generation aerospace materials due to their lightweight and high-temperature strength and oxidation resistance properties. Heat treatment of this alloy results in five major microstructures, including fully B2 and α2 + B2, lamellar, bimodal lamellar, equiaxed, and duplex O-phase microstructure. Recently, widmanstätten and plate-like O phase have also been reported. Modern manufacturing methods have made fabrication of high-temperature alloys easy and economical. However, they need post-heat treatments to improve the microstructure and mechanical properties. In this review article, a sequence of various developments in the study of features and thermo-mechanical control on the evolution of various microstructures of the Ti2AlNb intermetallic alloys will be presented. In addition, other aspects such as orientation relationships between different phases, factors affecting grain growth and, phase evolution mechanisms will be discussed. The effect of each heat treatment on every feature of the microstructure will be summarized in each section.