Conventional NiCoCrAlYSiB coating and（NiCoCrAlYSiB＋AlSiY）gradient coating were prepared by using arc ion plating（AIP）on the Ni base single crystal superalloy substrate. Comparative studies of the morphology and microstructure together with high temperature oxidation behaviors at 1000,1100 and 1150℃for the two different coatings were investigated.The results show that after vacuum annealing,the conventional coating is mainly composed of generalγ′/γand a small quantity ofβ-NiAl dispersed inγ′/γwhile the outer layer of the gradient coating consists ofβ-NiAl and dispersedα-Cr and Cr_3Si inβ-NiAl and the inner layer consists of Cr-rich phases plus minorβ-NiAl.The conventional coating has excellent oxidation resistance only at 1000℃.while it degraded rapidly at 1100℃and 1150℃,on which surface spinel formation was observed;however, the gradient coating has more excellent oxidation resistance than the conventional one at all the three temperatures.After oxidation for 300 h at 1100℃,there still exists a great amount ofβ-NiAl,and even after oxidation for 300 h at 1150℃,Al content is higher than 8%（mass fraction）,in which a small amount ofβ-NiAl and supersaturatedγ′/γinsure the formation and self repair of alumina.
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