Microstructure evolution and mechanical properties of a Ti-45Al-8.5Nb-(W, B, Y) alloy obtained by controlled cooling from a single β region

An accurate temperature-controlled approach was developed to investigate the microstructure evolution of a high-Nb-containing TiAl alloy. The Ti-45Al-8.5Nb-(W, B, Y) alloy was subjected to controlled heating and cooling from the single β phase region (1500 °C) under various processing parameters. Three typical microstructures involving full lamellar (FL), near lamellar (NL) and quenched martensite plates exist in the cooled microstructures. The initial microstructural homogeneity obtained by isothermal holding within the β phase region can effectively reduce the microsegregation in the subsequent cooling process. The fraction of α₂ phase and the lamellar spacing significantly decrease with an increased cooling rate. Furthermore, the crystalline orientations between coarsened block γ retained β/B2 and α₂ martensite were identified, and the phase transition mechanism was analysed. Lastly, the microhardness of these treated samples was tested, and the microstructure-dependent mechanical properties were evaluated and discussed.