Volume and Grain-Boundary Self-Diffusion in a High-Purity Fe-50 mass% Cr Alloy

Abstract

Volume and grain-boundary self-diffusion coefficients of 51Cr and 59Fe in a high-purity Fe–49.7 mass% Cr alloy containing 13 mass ppm carbon and 6 mass ppm nitrogen have been determined in the temperature range between 923 and 1453 K by use of the sputter-microsectioning technique. Linear Arrhenius lines for volume self-diffusion coefficients of both tracers have been observed across the α–σ phase-transformation temperature 1103 K, which is consistent with the suppression of the formation of the σ-phase by purification. The Arrhenius equations can be expressed by DFe = 1.2 × 10—4 exp(—256 kJ mol—1/RT) m2 s—1 and DCr = 1.3 × 10—4 exp(—259 kJ mol—1/RT) m2 s—1. Downward curved Arrhenius lines for the grain boundary diffusivity aδDgb (s segregation factor, δ width of grain boundary, and Dgb grain boundary diffusion coefficient) of both tracers have been observed. This is attributed to the formation of very thin layer of the (Cr, Fe)23C6 phase at the grain boundary near the surface of the specimens.