Creep behavior of Ti-Al binary alloys containing 27.5mol.%Al (initial grain size d0= 75 μm) and 34.0mol.%Al (d0= 60 μm) has been investigated at 1050-1250 K under 70-500 MPa. The effect of d0in the range 30-170 μm has also been studied. In Ti-34Al sigmoidal-type primary stage is observed at 1200 and 1250 K under a limited range of stress. Characteristics of the minimum creep rate can be classified into three regions. The stress exponent and the activation energy, and also the grain-size exponent, have a set of unique values in each region. In a lower stress region, a dislocation recovery process seems to be the rate-controlling process, independent of the composition. In a higher stress region, structure becomes unstable during creep and the materials become weak. The restoration and/or stress relief process in this region depends on the composition: dynamic recrystallization in Ti-27Al and deformation twinning in Ti-34Al.
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