Microstructural stability and creep properties of middle Nb γ-TiAl alloy with a modulated microstructure

In this work, a modulated structure composed of nano-scale Ti₂AlNb (O phase) and α₂ phase was obtained in middle Nb γ-TiAl alloy. The O phase nucleates at the α₂/γ interface and is orthogonal to the α₂/γ interface. The creep testing results show that the modulated structure exhibited the better creep performance compared with the fully lamellar microstructure, manifesting in a smaller minimum creep rate and creep strain after creep for 200 h. The O phase in α₂ lamellae suppressed the α₂ →γ phase transformation and constructed the coherent interface with adjacent γ lamellae, which replaced part of the semi coherent α₂/γ interface, to reduce the generation of interfacial dislocation loops, thereby improving the creep resistance. Besides, discontinuous precipitations (DPs) caused by (α₂/γ) → β₀(ω₀) + γ phase transformation were observed in the crept samples, contributing to the microstructure degradation. The present work shows significant engineering significance and scientific value for improving the creep performance and microstructure stability for middle Nb–TiAl alloys.