Diffusion of chromium in nickel-base Ni-Cr-Fe alloys

Volume and grain boundary diffusion of chromium in Ni-16 mass% Cr-7 mass% Fe alloys (Inconel 600 M) containing 0.004 and 0.015 mass% C has been studied by a sperial radio-frequency sputter-microsectioning method with the radioactive tracer 51Cr in the temperature range between 858 and 1346 K. For the alloy containing 0.004 mass% C, temperature dependence of the volume diffusion coefficient, Dv, and that of the product of the segregation factor, s, the grain boundary width, δ, and the grain boundary diffusion coefficient, Dgb, can be expressed by Dv=4.0x10-4 exp(-283 kJ mol-1/RT) m2 s-1 and sδDgb=4.2x10-12 exp(-201 kJ mol-1/RT) m3 s-1, respectively. For the alloy containing 0.015 mass% C, their temperature dependence can be expressed by Dv=6.5x10-4 exp(-296 kJ mol-1/RT) m2 s-1 and sδDgb=1.3x10-9 exp(-274 kJ mol-1/RT) m3 s-1, respectively. It has been found that the variation of carbon content from 0.04 to 0.015 mass% gives only a little influence as the retardant to the volume diffusion of chromium, on the other hand, the small increase of carbon reduces sδDgb of chromium by about two orders of magnitude at 900 K. (orig./MM)