Incipient plasticity in single crystals was investigated by nano-indentation with a spherical indenter. For very low loads, the surface deformation could be limited to a single slip line, making modelling of the deformation easier. A recently developed nano-etching technique was used to investigate the corresponding dislocation structure. Single pile-ups of a few dislocation half-loops were observed and fully characterized. A simple elastic model, based upon calculation of the Peach Koehler force induced by the pile-ups and the spherical indenter stress field, was used to determine the equilibrium positions of

dislocations in these pile-ups. A comparison between the experimental and calculated structures has led to the determination of the lattice friction stress for edge and screw dislocations in MgO single crystals. This stress was found to be 65MPa for edge dislocations and 86MPa for screw dislocations.

Quantitative Analysis of Dislocation Pile-Ups Nucleated During Nanoindentation in MgO. Y.Gaillard, C.Tromas, J.Woirgard: Acta Materialia, 2006, 54[5], 1409-17