The grain-boundary diffusivities of 59Fe and 57Co in a binary Fe-50at%Co alloy were determined at 883 to 1123K by serial sputter-microsectioning of specimens which had been unidirectionally solidified at rates of 12000, 60 or 32mm/h. Above the order–disorder transformation temperature (1003K), the Arrhenius plots of grain-boundary diffusivities in alloy solidified at the 3 rates were straight lines. The diffusivities in the 32mm/h specimen were higher than those in the 60 and 12000mm/h specimens. Below 1003K, all of the Arrhenius plots of the diffusivities exhibited a marked downward curvature due to atomic ordering. Analysis of the depth profiles showed that atomic ordering had a large effect upon diffusion along sub-grain boundaries rather than diffusion along random grain boundaries.

Grain Boundary Self-Diffusion in Directionally Solidified Equi-Atomic Fe–Co Alloy. H.Nitta, Y.Iijima, K.Tanaka, Y.Yamazaki, C.G.Lee, T.Matsuzaki, T.Watanabe: Materials Science and Engineering A, 2004, 382[1-2], 250-6