Persistent slip bands in cyclically deformed nickel polycrystals

Abstract

The influence of the plastic strain amplitude ( ϵ pa) and the crystallographic grain orientation on the occurrence of the ladder-like dislocation substructure characteristic of persistent slip bands (PSBs) was studied by scanning electron microscopy (SEM) on individual grains of cycled nickel polycrystals. The ladder substructures were found to occur in the range of plastic strain amplitudes of 1×10 −4≤ ϵ pa≤1×10 −3 on grains having considerable different axial orientations. Studies of the slip activity show that all ladder dislocation patterns are correlated with the well-known PSBs. Apart from projection effects, the ladder-like dislocation configuration of PSBs remains unchanged for all grain orientations. The effect of crystallographic orientation concerns only the matrix surrounding the PSBs which is determined by the axial grain orientation. An increase of ϵ pa results in a reduction of the mean PSB wall spacing and in higher effective PSB volume fractions. The mean shear plastic strain amplitude of primary PSBs in polycrystals is estimated to be about 2×10 −3.