OXIDATION BEHAVIORS OF Ni-Cr-BASED SUPERALLOY AT HIGH TEMPERATURES

Nickel-based superalloys,with different contents of graphite were oxidized in air at 800 ℃,900 ℃ and 950 ℃.Their oxidation behaviors were investigated by means of mass gain of oxidized,X-ray diffraction and scanning electron microscopy.The kinetic curve of the alloys oxidized at 800 ℃ and 900 ℃ with lower graphite contents obeyed the parabolic rate law and no oxide peeled off.When the temperature was raised to 950 ℃,the kineties followed beeline law and oxide peeled off.The oxide scales consisted of Cr2O3 and NiCr2O4 when alloys with 0% and 3% graphite were oxidized at 900 ℃.The oxidation mechanism of the alloys was suggested based on the phase composition analyses of the oxide layers.