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Deformation and Diffusion Modes in Nanocrystalline Materials

“…In recent years, it has definitely been recognised that triple junctions of GBs have structure and properties different from those of the GBs that they adjoin. [34][35][36][37]83,84 In particular, as it has been shown in experiments, 83,84 the triple junction diffusion coefficient D tj highly (by three or more orders) exceeds the GB diffusion coefficient D gb in polycrystalline materials. Also, following experimental data, 83 creep associated with enhanced diffusion along triple junctions contributes to plastic flow of coarse-grained polycrystalline aluminium.…”

“…Following Rabukhin, 83 the triple junction diffusional creep is characterised by rather unusual dependence of plastic strain rate on grain size d. More precisely, the grain size exponent is 24 in this case, 83…”

Triple junction diffusion and plastic flow in fine-grained materials

“…Here _ e e c is the plastic strain rate associated with grain boundary diffusional creep (Coble creep) and _ e e tj is the plastic strain rate associated with triple junction diffusional creep considered in detail by Rabukhin [35]. The Coble creep strain rate is given as follows (e.g.…”

“…The creep associated with enhanced triple junction diffusion is characterized by the plastic strain rate [35] _ e e tj ¼ 20…”

“…(Grain boundary dislocations commonly are stopped by triple junctions in plastically deformed poly-and nanocrystalline solids, in which case the length l characterizes the grain boundary regions with stopped boundary dislocations in vicinity of triple junctions. Following [35], these dislocationrich regions of grain boundaries affect the triple junction diffusional creep, in which case the length scale l appears in (4) for the corresponding strain rate.) With (3) and (4) substituted into (2), we have the following formula for the yield stress that characterizes the diffusional deformation mechanisms in materials with a small grain size:…”