Revealing cellular reaction mechanisms and high-temperature structure stability in β-stabilized TiAl alloy

This study reveals that the cellular reaction (CR) is dominated by grain boundary (GB) migration mechanism controlled by element diffusion, during which the α2 → γ + βo phase transformation occurs. CR transforms supersaturated α2/γ lamellar system from metastable to equilibrium state via microstructure coarsening. Moreover, elements enrichment of Ti and Nb, Mo Ti, Nb and Mo occurs during CR, triggering the α2 → γ + βo phase transformation. Increasing the aging temperature accelerates the CR rate and extending the soaking time transforms more volume of α₂/γ lamellae into pearlitic-like microstructure (PM). The PM exhibits almost negligible coarsening with the increase in aging temperature and extension of soaking time in the temperature between 950 and 1100 °C, indicating excellent thermal stability far beyond the service temperatures of TiAl intermetallics. Therefore, PM is a worthy pursuit in microstructural design for high-temperature application of TiAl alloy.