Transient mechanisms in diffusional creep in a titanium aluminide

Abstract

Although the classic diffusional creep theories did not predict any transient creep, a significant transient creep stage has been observed in the diffusional creep regime at intermediate temperatures. To explain this discrepancy between the classic diffusional creep theories and experimental observations, several mechanisms have been proposed. These models were reviewed recently. The an elastic transient creep models are based on grain boundary sliding and lattice dislocation bowing and predict a magnitude of transient strain about 0.5 times of elastic strain. Raj has proposed a model based on diffusion. According to this model, the transient stage arises because of the stress redistribution in initial stages. The other models are based on dislocation annihilation. The dislocation annihilation models are successful in predicting the larger magnitudes of transient strain which are often observed. These models, however, do not predict any an elastic strain. In this paper, the authors report the results of a few an elastic experiments in the diffusional creep regime. These critical experiments help in addressing the following fundamental issues; (1) the proper method for defining the transient strain, and (2) the mechanism of transient creep in the diffusional creep regime.