Effect of creep strain on microstructural stability and creep resistance of a TiAi/Ti3ai lamellar alloy |
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| Authors: | J A Wert M F Bartholomeusz |
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| Affiliation: | (1) Department of Materials Science and Engineering, University of Virginia, 22903 Charlottesville, VA;(2) Corporate Research and Development Laboratory, Reynolds Metals Co., 23219 Richmond, VA |
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| 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 (εmin) 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 (εmin) associated with DIS is thus attributed primarily to a change of creep mechanism resulting from microstructural refinement. |
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