Investigation of primary and secondary creep deformation mechanism of TiAl |
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Authors: | Soo W Nam H S Cho Sun-Keun Hwang Nack J Kim |
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Affiliation: | (1) Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92697-2575, USA; |
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Abstract: | Creep deformation behaviors in lamellar TiAl alloys have been investigated. As in the case with metals, the normal primary
creep stage was observed. As creep strain increased within the primary regime, dislocation density decreased, and creep activation
energy increased from 300 kJ/mol, the activation energy of the self-diffusion of Ti in TiAl, to about 380 kJ/mol, that of
steady state creep deformation. During primary creep deformation of lamellar TiAl, as the initial dislocation density decreased,
the α2 -phase was found to transform to a γ-phase, generating new dislocations which contributed to the creep deformation. In other
words, this phase transformation is the source of the dislocation generation for continuous creep deformation. Therefore,
we suggest that phase transformation is the rate controlling processes having an activation energy of about 400 kJ/mol, which
is higher than that of self-diffusion. A small amount of prestrain was found to be responsible for the reduction of initial
dislocation density. In addition, this prestrained specimen showed significantly reduced primary creep strain, and the creep
activation energy in the primary stage was measured to be about 380 kJ/mol. These results clearly confirm the suggested creep
deformation mechanism of lamellar TiAl alloys. |
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Keywords: | TiAl creep lamellar phase transformation |
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