Indentation-induced deformation behaviour was characterized in nano-scale for bulk polycrystalline materials to understand strengthening factors of macroscopic properties especially for the grain boundary effect. Compared with deformation behaviour in the vicinity of single grain boundary and grain interior of an interstitial free steel, plasticity initiation occurred at a lower applied stress near the grain boundary, which meant the grain boundary was an effective dislocation source. The subsequent deformation after plasticity initiation was affected by the grain boundary as a barrier to dislocation motion. Strengthening factors of matrix and grain boundaries were evaluated separately for the Fe–C tempered martensite. The contribution of grain boundaries depended upon the morphology of precipitates on grain boundaries. Combining the dislocation pile-up model and the Hall–Petch relation, the existence of the film-like carbide on the grain boundary remarkably affected the locking parameter k.

Analysis of Grain Boundary Effect of Bulk Polycrystalline Materials through Nanomechanical Characterization. T.Ohmura, K.Tsuzaki: Journal of Physics D, 2008, 41[7], 074015 (6pp)