Influence of Chromium Carbides on the High Temperature Oxidation Behavior and on Chromium Diffusion in Nickel-Base Alloys
Résumé
Two simple cast nickel alloys Ni-30Cr-0.2C and Ni-30Cr-0.8C were oxidized at 1000, 1100 and 1200°C. Their behaviors were characterized using thermogravimetry techniques and their parabolic and chromia volatilization constants were determined by analysing the m x (dm/dt) versus -m curves. The obtained constants were generally in good agreement with experimental mass gain kinetics and chromium balance sheets. A higher carbon content i.e. a higher carbides density leads to higher values of the transient linear oxidation constant Kl , of the parabolic constant Kp , and obviously also of the volatilization constant Kv. Chromium diffusion coefficients through the zone affected by oxidation were calculated from oxidation kinetics and chromium gradients. They increase when carbide density increases.
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