Statistical heterogeneity of plastic deformation: An investigation based on surface profilometry

The present paper investigates the intrinsic spatial heterogeneity of plastic deformation of crystalline materials by analysing surface profiles recorded by atomic force microscopy and scanning white light interferometry. Profiles were recorded before and after compressive deformation of three types of alkali halide single crystals: as-grown (AG) KCl and LiF and irradiated (IR) LiF. The profiles were characterized in terms of their height–height correlation function and scale-dependent roughness. We also investigated the statistics of surface step heights and found scale-free distributions over about three orders of magnitude in step (nm to μm) in the AG crystals. A different picture was observed in IR LiF at low plastic strains, where we could identify well-defined characteristic step heights. We discuss these findings in terms of slip avalanches caused by collective motion of dislocations.