Persistent Slip Bands

Abstract

Abstract The slip activity and shear strain of persistent slip bands (PSBs) in polycrystalline nickel were studied after half-cycle deformation on well-polished specimen surfaces at different stages of fatigue life using the combination of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Although the local shear strain of PSBs seems to be nearly independent of the stage of fatigue life, the half-cycle slip activity of PSBs significantly depends on it. In-situ deformation experiments in the scanning electron microscope (SEM) showed that during half-cycle loading the slip steps do not proportionally develop to the applied plastic strain and not the whole accumulated PSB volume is active. The reactivation of the cumulative PSB volume is different for individual PSBs and grains, and evolves more slowly than the reactivation of grains. PSBs in polycrystals are subjected to a development history — their activity changes both temporally as well as spatially. Possible reason for this behaviour could be hardening effects due to secondary slip within the PSBs. Detailed investigations of the dislocation structure developed at different stages of fatigue life using the electron channelling contrast (ECC) in the SEM give more information about it.