A dilatometer and in situ synchrotron X-ray diffraction study: α-quenching and reheating of a Nb-rich titanium aluminide alloy

Abstract Intermetallic γ-TiAl-based alloys are currently used as structural materials for turbine blades in aero engines. Additive manufacturing is increasingly considered as an additional manufacturing route for components consisting of γ titanium aluminides; however, the high heating and cooling rates result in chemical and thermodynamical disequilibrated microstructures. In our study, in situ synchrotron X-ray diffraction was applied to follow the formation of the disequilibrium microstructure during quenching and to study its re-equilibration during a subsequent annealing treatment in a Nb-rich γ-TiAl-based alloy. The quenched sample showed an incomplete massive transformation, with large remaining α 2 grains. During reheating, the analysis of the collected data showed that equilibration of the quenched microstructure takes place in several reordering and transformation steps, e.g., orthorhombic distortion of the hexagonal α 2 phase (around 550 °C), almost complete transformation of the supersaturated quenched α 2 to γ (around 850 °C), and retransformation of γ to new α 2 (around 1050 °C). Graphical abstract