Effect of fine precipitation of coherent disordered phase on creep strength of L12-ordered Co3Ti

Compressive creep tests were performed under constant stress over a range of temperatures from 923 to 1073 K on precipitation strengthened L12-ordered Co3Ti. The creep rates decrease appreciably by the fine precipitation of coherent disordered f.c.c. Co-rich phase when the applied stress is low. An analysis of the creep data is developed taking a threshold stress into account of the creep equations. The significance of the threshold stress is discussed based upon the transmission electron microscope observations of the interaction between dislocations and precipitates. The superdislocations produced during deformation tend to be strongly attracted and dissociate as they meet the coherent disordered precipitates because the anti-phase boundary energy in the disordered phase is zero. The extra stress necessary to pull the dislocation out of the precipitates may play an important role to establish the threshold stress which is expected to be beneficial to the improvement of the creep strength of L12-ordered intermetallics for high temperature structural applications.