Dislocation generation and motion at the incipient stages of surface plasticity in barite

Force–penetration curves on nanoindented barite (001) surfaces have been recorded and microstructure imaged with atomic force microscopy (AFM). Pop-ins in the penetration curves have been correlated to the appearance of permanent concave traces in the surface and to the emission of specific dislocations, some of which can cross-slip resulting in terraces winding around the nanoindentation contact point. The dislocations identified in barite can be related to special deformation mechanisms previously reported in metals. The effective shear stress, which results in permanent traces associated with plasticity, as obtained from the AFM data, is compared with the theoretical values estimated for a perfect crystal.