Carbon permeability of nickel and Ni-Cu alloys

Abstract

A Ni-20Cr alloy and variants containing 5, 10 and 20Cu (all in wt.%) were carburised in H2-5% CH4 at 1,000 °C. All alloys formed internal carburisation zones containing Cr3C2 and Cr 7C3. The Ni-20Cr alloy also developed a surface deposit of graphite, but the copper-bearing alloys did not. Measured parabolic rate constants for intragranular carburisation were used to calculate carbon permeabilities from Wagner`s diffusion analysis. The value obtained for Ni-20Cr was in good agreement with the product of independently measured carbon solubility and diffusion coefficient values for nickel. Permeabilities found for copper-bearing alloys were similar, showing that the presence of copper had little effect on carbon diffusion in nickel. This finding is used in analysing the mechanism by which nickel undergoes metal dusting.