Tailoring the Microstructure of a β-Solidifying TiAl Alloy by Controlled Post-solidification Isothermal Holding and Cooling

In this study, the microstructure of a beta-solidifying TiAl alloy was modified by means of temperature-controlled cooling. The microstructural evolution of the Ti-44.5Al-4Nb-2Cr-0.1B alloy in different cooling processes was investigated. The results showed firstly that both the solidification-segregation (S-segregation) and beta-segregation were reduced considerably by raising the temperature or extending the time in the single beta-phase region. Then samples were cooled through the beta + alpha phase region at the cooling rates of 2, 50, and 650 K/min. The B2-phase and some large gamma-phases exist in lamellar microstructure, which might be more evident at a higher cooling rate. Further, the Burgers relationships of {0001} (alpha 2)//{110} (beta(B2)) and {110} (alpha 2)//{111} (beta(B2)) were identified in the fast cooling microstructure, and the non-Burgers equiaxed alpha-grains grew easily at a slow cooling rate.