Diffusion assisted dislocation climb in intermetallic gamma TiAl

Titanium aluminides based on the intermetallic gamma (TiAl) phase are being considered as light weight materials for high temperature applications in aeroengines or advanced energy conversion systems. However, for such applications the material suffers from insufficient creep resistance at the intended service temperature of 700 degreesC. The paper reports an experimental study of diffusion controlled deformation mechanisms in two-phase titanium aluminides which apparently cause the degradation of the strength properties at elevated temperatures. Electron microscope in situ heating studies were performed in order to characterize diffusion controlled dislocation climb. Climb velocities were analyzed in terms of diffusion coefficients and the critical vacancy supersaturation necessary for the operation of diffusion assisted dislocation sources. The experimental results will be discussed with regard to the structural stability of two-phase titanium alumindes and potential factors for improving their high temperature strength. (C) 2001 Elsevier Science B.V. All rights reserved.