Formation of a novel α ₂  + β ₀ modulated microstructure in a Mo‐modified γ‐TiAl alloy

Abstract The α 2 decomposition in γ‐TiAl‐based alloys during long‐term service at elevated temperatures affects the mechanical properties and reliability of components. However, the formation mechanism of the precipitates, β 0 phase in Mo‐modified γ‐TiAl alloys in particular, has not been clarified. In the present work, the formation of a novel α 2 + β 0 modulated microstructure in Ti–43.5Al–4Nb–1Mo–0.5B (at%) alloy at 700 °C has been investigated by using scanning and transmission electron microscopy. Six equivalent β 0 phase variants nucleate at the α 2 /γ lamellar interfaces and grow into a plate shape within α 2 lamellae. The β 0 phase mainly exists as clusters of three or multiple plates. This distinctive growth pattern exhibits notable differences from conventional phase transformation modes, offering a fresh perspective for comprehending phase transformation behaviors. The formation of the β 0 phase in α 2 lamellae is controlled by the diffusion of Nb/Mo atoms (mainly Mo). The lattice distortion between the β 0 and α 2 phases promotes the nucleation of new β 0 plates, revealing the significant impact of interphase interactions on the microstructural evolution. The lattice of the central α 2 phase enclosed by β 0 variants is rotated around the [0001] α2 axis of the α 2 matrix by 10.53° to minimize the elastic strain energy. The results offer insights into the mechanism of α 2 decomposition as a function of alloy composition, providing a basis for controlling the microstructure and improving the mechanical properties of β‐stabilized γ‐TiAl alloys, and thus opening new window of opportunity in the design and development of high‐temperature structural materials.