The role of solute segregation in grain boundary diffusion

Abstract

In measurements of grain boundary transport it is the product of the grain boundary enrichment ratio and the grain boundary diffusivity that is usually obtained. This work presents the first study in which these two terms are separated and in which the role of the grain boundary composi­tion in grain boundary diffusion is analysed in detail. This leads to the general prediction that the grain boundary diffusion of solute and solvent will be reduced by strongly segregating solutes if they do not simultaneously enhance the bulk diffusivities. The converse occurs if the solute weakly segregates but strongly enhances the bulk diffusivities. The diffusion measurements are made in iron–tin alloys in the tempera­ture range 563–750 °C by using radiotracers, and the segregation measure­ments, similarly, by Auger electron spectroscopy. The measured bulk diffusivities are similar to those found previously. The grain boundary diffusivities, determined via Suzuoka’s (1964) analysis, for iron and tin in pure iron have pre-exponential coefficients of 225 x 10 -4 and 9.2 x 10 -4 m 2 s -1 and activation energies of 165770 and 166600 J mol -1 respectively. Contrary to the increase in the bulk diffusivity produced by the ‘fast’ diffuser, tin, both grain boundary diffusivities are sharply reduced as the tin content rises. These and earlier results are interpreted through the effect of tin segregation on the grain boundary energy described by the theory of Borisov et al . (1964).

Grain Boundary Diffusion in Ceramics

“…All these features tend to amplify the influence of impurities on boundary diffusion. In metals the tendency is for strongly segregating impurities to reduce grain boundary diffusivity probably by blocking the fast diffusivity sites [30]. In NiO, for example, the effect of Cr doping is similar, but is so strong that boundary diffusivity is almost entirely blocked despite the fact that Cr doping increases the concentration of lattice vacancies, and hence lattice diffusivity [31].…”

Diffusion in Nanocrystalline Metals and Alloys—A Status Report

“…The data of n-Fe refer to relaxed GBs. Literature data of Fe diffusion in the ferromagnetic phase of crystalline a-Fe (c-Fe), [45] in grain boundaries of Fe (g-Fe) [46] and in nanocrystalline c-Fe±Ni [10,24] …”

Thermal vacancy formation andD03ordering in nanocrystalline intermetallic(Fe3Pasquini1, Rempel2, Würschum3 et al. 2001Phys. Rev. B181110View full textAdd to dashboardCite

“…In both alloys a strong segregation of Zr or Nb at grain boundaries occurs, stabilizing the nanostructure. Since a strong segregation leads to a decrease of the grain-boundary diffusivity, 31 and diffusion is closely linked with thermal defect formation, Zr or Nb segregation may explain the absence of thermal defect formation in grain boundaries in these systems.…”