NONLINEAR DEFORMATION MECHANISMS DURING NANOINDENTATION

Experiments involving the indentation of single crystals of both tungs ten and an iron alloy show that the observed yield phenomena can be pr edicted using a superdislocation model driven by the change in shear s tress between the elastically and fully plastic loading conditions. A low density of dislocation multiplication sites is required to support elastic loading which approaches applied shear stresses on the order of the theoretical shear strength of the material. Oxide Nm thickness and crystal orientation are examined as parameters in controlling the yield phenomena. A model based on activation of dislocation multiplica tion sources is suggested to explain the initiation of the yield point during indentation and the overall load-depth relationship during ind entation. (C) 1998 Acta Metallurgica Inc.