It was recalled that the flow stress of polycrystals was controlled by processes which occurred in the grain interior, as well as in the grain boundary and its immediate vicinity. The early stages of the evolution, with strain, of dislocation sub-structures in these 2 regions in polycrystalline stainless steel were studied at 293, 673 and 1123K in order to represent low-temperature thermal, intermediate-temperature athermal and high-temperature thermal regimes, respectively. Specimens with grain sizes of 4 or 12 were used in order to determine the effect of the grain size. Transmission electron microscopic studies of deformed specimens revealed the differing roles which were played by the grain boundary and grain interior in various temperature regimes. In the low-temperature regime, the grain boundaries acted as obstacles to moving dislocations and a high density of dislocations was found in the vicinity of the grain boundary. In the intermediate temperature regime, the dislocations which spread easily into the grain interior rearranged themselves to form cell walls. In the high-temperature regime, the grain boundaries transformed to the equilibrium state and did not contain any grain boundary dislocations. The distribution of dislocations within the grains was homogeneous at all strains. Significantly higher values of the dislocation density in the vicinity, as well as in the grain interior, were found in material with a finer grain size at all strains.

M.Janecek, K.Tangri: Journal of Materials Science, 1995, 30[15], 3820-6