Superplastic behavior of Zn–22%Al containing nano-scale dispersion particles Original Research Article

A creep investigation was performed on Zn–22%Al in which dispersion particles were introduced by cryomilling. The results show that the particles have no significant effect on the sigmoidal relation between stress and strain rate previously reported for dispersion-free Zn–22%Al. An examination of the creep structure reveals two observations that are common to regions I (the low-stress region of the sigmoidal plot) and II (intermediate-stress region). First, after deformation, only some grains contain dislocations, many of which are attached to the particles. Second, most of the dislocations are parallel and tend to be curved. An analysis of the results indicates that regions II and I are controlled by the same deformation process, in which the sliding of groups of grains is accommodated by dislocation motion in the blocking grains. This deformation process incorporates a threshold stress whose origin is most likely related to the interaction between dislocations and dispersion particles.