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

In this study, the microstructure of a β-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 β-segregation were reduced considerably by raising the temperature or extending the time in the single β-phase region. Then samples were cooled through the β + α phase region at the cooling rates of 2, 50, and 650 K/min. The B2-phase and some large γ-phases exist in lamellar microstructure, which might be more evident at a higher cooling rate. Further, the Burgers relationships of {0001} _α2//{110} _β(B2) and {11\( \bar{2} \)0} _α2//{111} _β(B2) were identified in the fast cooling microstructure, and the non-Burgers equiaxed α-grains grew easily at a slow cooling rate.