High-temperature compression induced α to γ phase transformation and related phase morphology transition in TiAl alloy

Titanium aluminide (TiAl) alloys are promising for aerospace and automotive applications due to their low density, high strength and excellent oxidation and creep resistance. Among them, the β-solidifying TNM (Ti-Al-Nb-Mo-B) alloys exhibit remarkable mechanical properties and thermal stability. Hot deformation is commonly used to shape these alloys, typically below the (α + β) phase region (below the γ-solvus temperature). In this study, hot compression was performed at 1280 °C (in the (α + β) phase region) with two thickness reductions at a strain rate of 10 ‐2 s -1 . Unexpectedly, the γ phase resurged abnormally from the α phase despite its thermodynamic instability at equilibrium. The formed γ phase follows the Blackburn orientation relationship (OR) and exhibits lamellar and nodular morphologies. Crystallographic analysis reveals that the activation of the basal slip in the α phase under the compression triggered this transformation. The early formed γ lamellae then evolved through fragmentation, spheroidization, coarsening and boundary sliding, leading to the morphology change from lamellae to nodules. These insights advance the understanding of TNM alloys for high-performance and high-temperature applications. • Abnormal α to γ transition by hot compression was evidence by in-situ HEXRD and EBSD. • Its morphology transition (lamellar to nodulous form) with deformation was revealed. • The formation of γ is induced by the basal slip of α. • Morphology transition is realized by fragmentation, spheroidization and GB sliding.