Indentation-induced deformation behaviour was characterized at the nano-scale, for bulk polycrystalline materials, in order to understand the strengthening factors of macroscopic properties; especially the grain-boundary effect. Compared with the deformation behaviour in the vicinity of a single grain boundary and the grain interior of an interstitial-free steel, plasticity initiation occurred at a lower applied stress when near to the grain boundary; meaning that 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. The strengthening factors of the matrix and the grain boundaries were evaluated separately for Fe–C tempered martensite. The contribution from grain boundaries depended upon the morphology of the precipitates on grain boundaries. Combining the dislocation pile-up model with the Hall–Petch relationship, the existence of a film-like carbide on the grain boundary markedly affected the locking parameter.

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