Effect of Widmanstätten-Type α2-Ti3Al Plates on Creep in γ-TiAl Based Alloy

In this study the effect of Widmanstätten-type morphology α₂ plates on creep has been investigated by preparing nearly equiaxed γ (N_γ) and nearly equiaxed γ having Widmanstätten-type α₂ plates within grain (Wα₂). Creep tests were conducted at 1073 K under constant stresses, high stress and low stress, in air. At the high stress, Wα₂ shows creep rate smaller than N_γ in transient stage, both specimens show similar minimum creep rate and the creep strain at minimum creep rate is 3 % for Wα₂ and 10 % for N γ, since N γ shows prolonged primary region. In acceleration stage, both show similar behavior with rupture time of about 50 h and rupture elongation of 60 %. At the low stress, on the other hand, reverse behavior occurs, that is, W α₂ shows creep rate higher than Nγ in transient stage. The regions near grain boundaries progressively deformed for both specimens at high stress level, whereas deformed region is extended within grain interiors. From these results it is suggested that α₂ plate act as the obstacle for dislocation motion in the γ matrix at high stress and that interfacial dislocation promote the creep deformation at low stress.