Influence of Chromium Carbides on the High Temperature Oxidation Behavior and on Chromium Diffusion in Nickel-Base Alloys

Abstract

Two simple cast nickel alloys Ni–30Cr–0.2C and Ni–30Cr–0.8C were oxidized at 1,000, 1,100 and 1,200°C. Their behaviors were characterized using thermogravimetry techniques and their parabolic and chromia volatilization constants were determined by analyzing the $\hbox{m} \cdot \frac{\hbox{dm}}{\hbox{dt}}$ versus −m curves. The constants obtained were generally in good agreement with experimental mass-gain kinetics and chromium-balance aspects. A higher carbon content i.e., a higher carbides density leads to higher values of the transient linear-oxidation constant K _l , of the parabolic constant K _p , and obviously also of the volatilization constant K _v . Chromium diffusion coefficients through the zone affected by oxidation were calculated from the oxidation kinetics and chromium gradients. They increase when the carbide density increases.