The volume and grain-boundary self-diffusion coefficients of 59Fe in a high-purity Fe-49.7wt%Cr alloy, containing 13ppm[wt]C and 6ppm[wt]N, were determined between 923 and 1453K by using sputter-microsectioning techniques. Linear Arrhenius plots for the volume self-diffusion coefficients of both tracers were obtained across the α-σ phase-transformation temperature (1103K). This was consistent with suppression of the formation of the σ-phase by purification. The bulk diffusion equation was:

D (m2/s) = 1.2 x 10-4exp[-256(kJ/mol)/RT]

Downward-curved Arrhenius plots were observed for the grain boundary diffusivity. This was attributed to the formation of a very thin layer of the (Cr,Fe)23C6 phase at the grain boundary near to the surface of the specimens.

Y.Yamazaki, M.Sugihara, S.Takaki, K.Abiko, Y.Iijima: Physica Status Solidi A, 2002, 189[1], 97-105