Creep Threshold Stresses in TiN-Dispersion Strengthened Stainless Steels

Threshold stresses for creep were determined by cumulative stress-decrement tests. The results show the threshold stress to be independent of specimen strain and applied stress but to increase with volume fraction of TiN dispersoid. It is concluded that the threshold stress is derived solely from the presence of the dispersion. This variation of threshold stress has been used to check the predictions of recent models of the threshold condition based on the climb bypass of particles. Extensive measurements of the particle dispersion were used in the comparison. Those models based on general dislocation climb around the particles produce a gross underestimate, by two orders of magnitude of the predicted value of threshold stress. Closest numerical agreement with measurements was obtained by the models which incorporated some degree of localized dislocation climb.