Study of Carbide Transformations during High-Temperature Oxidation of Nickel-Base Superalloys

Microstructure phenomena resulting from high-temperature oxidation of three nickel-base superalloys were studied by microstructure examinations. Disappearance, nature modification, volume fraction evolution or precipitation of carbides were observed in the alloys near the external surface, depending on the temperature and the chemical composition of the alloys. Thermodynamic calculations allowed to better know what happened to carbon and to quantify its new distribution. The alloys studied lost a more or less great part of their sub-surface carbon content at 1200°C while carbon seemingly diffused deeper in the alloy at 1100°C and 1000°C. The latter part of carbon promoted the coarsening of the pre-existing carbides, some modifications of their natures or the precipitation of new carbides in the matrix, then the occurrence of a new-carbides zone.