Grain boundary self-diffusion in high-purity Fe-50 and 60 mass % Cr alloys

Grain boundary diffusivity of 51 Cr and 59 Fe in high purity Fe-50 mass% Cr and Fe-60 mass% Cr alloys have been measured in the temperature range from 473 to 1273 K by use of a serial lathe sectioning technique. Below 653 K, the grain boundary diffusivity has been determined from the type C kinetics, whereas above 923 K it has been obtained from the type B kinetics. Linear Arrhenius lines have been observed for both types of B and C kinetics. Putting the grain boundary width δ at 5.10–10 m for the type B kinetics, the Arrhenius lines for the grain boundary self-diffusion coefficients Dgb in Fe-50 mass% Cr alloy obtained from both types kinetics are smoothly expressed as a single line. They can be expressed as :[math] for chromium and[math] for iron.The grain boundary diffusivities of 51 Cr and 59 Fe in Fe-60 mass% Cr alloy measured above 973 K are only slightly larger than those in Fe-50 mass% Cr alloy. The ratio of the activation energy for grain boundary diffusion to that for volume diffusion in the Fe-50 mass% Cr alloy is 0.35 which is much smaller than 0.6-0.7 observed in many metals and alloys.