Influence of cosegregation on grain boundary diffusion: Experimental study in ultra high purity FeNiSb solid solutions

Abstract

We have studied the influence of cosegregation on grain boundary (G.B.) diffusion in FeSb and FeSbNi high purity solid solutions with radioactive tracers and Auger electron spectroscopy. Using these two techniques to measure respectively the grain boundary diffusivity and the G.B. composition, we were able to monitor the variations of the G.B. diffusion coefficients as a function of the G.B. chemical composition. We observe that antimony segregation (in FeSb) and antimony and nickel cosegregation (in FeNiSb) lead to a large decrease of the G.B. diffusion of the three species. This behavior is explained assuming a modification of the G.B. structure induced by the strong iron-antimony or nickel-antimony interactions. Iron and antimony G.B. diffusion coefficients are identical in Fe(Sb) and Fe(NiSb) when the G.B. concentration of antimony is the same: the presence of nickel just increases the G.B. antimony content. In ternary alloys the segregation of nickel excludes the iron atoms from the G.B. core. Adding nickel in pure iron strongly affects the antimony G.B. heterodiffusion. This clearly indicates that the dispersion observed in G.B. heterodiffusion measurements can be explained by cosegregation effects due to highly active impurities.