Abstract
Creep of a TiAl/Ti3Al alloy with a lamellar microstructure causes progressive spheroidization of the lamellar microstructure. Microstructural observations reveal that deformation-induced spheroidization (DIS) occurs by deformation and fragmentation of lamellae in localized shear zones at interpacket boundaries and within lamellar packets. Deformation-induced spheroidization substantially increases the interphase interfacial area per unit volume, demonstrating that DIS is not a coarsening process driven by reduction of interfacial energy per unit volume. Creep experiments reveal that DIS increases the minimum creep rate (emin) during creep at constant stress and temperature; the activation energy (Q c ) and stress exponent (n) for creep are both reduced as a result of DIS. Values ofn andQ c for the lamellar microstructure are typical of a dislocation creep mechanism, while estimated values ofn andQ c for the completely spheroidized microstructure are characteristic of a diffusional creep mechanism. The increase in (emin) associated with DIS is thus attributed primarily to a change of creep mechanism resulting from microstructural refinement.
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