Creep in particle strengthened metals

Summary

The idea that the dislocations moving in a dispersion strengthened matrix meet the back stress which effectively reduces the applied stress was accepted. Assuming that the back stress does not depend on applied stress a new interpretation of the published creep data for aluminum strengthened by various volume fractions of alumina particles [4] is presented. From this assumption it follows that the back stress can be interpreted as the threshold stress; at the applied stresses lower than the threshold stress the creep controlled by the lattice dislocations overcoming dispersed particles does not take place. The threshold stress has been estimated for the temperature interval 473 to 773 K using eq. (13) and assuming the validity of the additivity rule expressed by eq. (11). In this temperature interval the creep is controlled by the diffusion in the matrix. The threshold stress increases with the volume fraction of Al₂O₃ particles. An estimate of the Orowan stress has shown that independently of the volume fraction of Al₂O₃ it is approximately twice as high as the threshold stress.

Generally, the concept of the back stress solves the known difficulties of interpretation of the steady state creep data for dispersion strengthened metallic materials at least if the assumption of the back stress independency on applied stress is acceptable.