Effect of Graphite Addition on Oxidation Behavior of Ni-Cr-Based Superalloy at 900 °C

Nickel-based alloys with different contents of graphite were prepared by powder metallurgy method. High temperature oxidation resistance of these alloys was studied by high temperature test at 900 °C for 100 h in static air. Morphology of oxides was studied by SEM and their composition was analyzed by XRD. The result shows that the kinetic curves of oxidation for nickel-based alloys with lower content of graphite obey the parabolic law. The oxide films consist of Cr2O3 and NiCr2O4 when the alloy contains no graphite. The oxide film consists of Cr2O3when the alloy contains 3% graphite. If graphite content increases to 6%, the oxidative decomposition of graphite leads to severe initial oxidation, and mass gain takes place significantly; the cavity after decomposition of graphite accelerates the process of oxidation reaction. The oxidation mechanism of the alloy has also been suggested by the phase composition analyses of oxide film.