Abstract
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.
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