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Nano- and micro-scale free volume in ultrafine grained Cu–1wt.%Pb alloy deformed by equal channel angular pressing

“…The theoretical background of GB diffusion in a hierarchical microstructure has previously been developed for the case of self-diffusion [33] and solute diffusion [34] in sintered nanocrystalline powders. Using this approach, the effective diffusivities corresponding to the "fast" and "ultra-fast" paths were determined in pure Cu and Cu-rich alloys using 63 Ni as tracer (cf.…”

Grain Boundary Diffusion in Metals: Recent Developments

“…37) Recently, a new, more transparent classification was introduced which explicitely reflects the existence of two types of short-circuit diffusion paths in the material. [38][39][40] This classification refers to the microstructure which is presented in Fig. 13(a) and is sketched in Fig.…”

“…To describe the term c 3 ðy; tÞ the Fisher model 34) was reformulated for inter-agglomerate boundary diffusion from a constant source. 40) The tracer concentrations c v ðx; y; tÞ in the bulk, c gb ðx; y; tÞ in nanocrystalline grain boundaries, and c a ðx; y; tÞ in inter-agglomerate boundaries are to be considered. The analytic solution was derived under following approximations (see Fig.…”

“…(15)- (37), Ni and Fe diffusion in the two-scale nanocrystalline -Fe-Ni alloy was measured with the radiotracers 63 Ni and 59 Fe and subsequently analyzed. 39,40) In the case described, Ni diffusion along nanocrystalline GBs was measured in the C, B, and AB conditions, with the GB diffusivity D gb measured directly in the C and AB regimes and the product P ¼ Á D gb determined in the B regime. Summarizing all results derived in different regimes of GB diffusion and assuming ' 0:5 nm, the temperature dependence of the GB-diffusion coefficient D gb in the nanocrystals is plotted in Fig.…”

“…The difference between D gb and D a was explained by the relaxed state of the nanocrystalline GBs and a non-equilibrium character of the inter-agglomerate boundaries 39,40) resulting from the specific preparation method of the nanocrystalline -Fe-Ni alloy which allowed growth of the nano-grains from about 20 to about 100 nm of the grain diameter during the heat treatment of the powder sintered.…”