High Temperature Oxidation Behavior of NiCr-CrAl Coating

NiCr-CrAl coating and simple aluminide coating were prepared by pack cementation on the surface of nickel-based superalloy K438. Compared with the simple aluminide coating, the cyclic oxidation behavior of the NiCr-CrAl coating at 1 000 ℃ was studied by oxidation kinetics analysis, morphology observation and phase analysis. The results show that both the simple aluminide coating and the NiCr-CrAl coating were composed of β-NiAl phase. The oxidation mass gain of NiCr-CrAl coating was less than that of the simple aluminide coating after cyclic oxidation for 300 h. The oxidation products of the simple aluminide coating was composed of α-Al2O3, NiAl2O4 and TiO2, meanwhile, the degradation of transformation from NiAl to Ni3Al occured obviously during oxidation process, indicating the oxidation resistance reduction. The dense α-Al2O3 remained in the oxidation products on the surface of NiCr-CrAl coating and the coating had slight degradation after 300 h oxidation, showing good high temperature oxidation resistance.