Preparation and oxidation of a gradient NiCoCrAlYSiB coating deposited by a combined system of arc ion plating and magnetron sputtering

A gradient NiCoCrAlYSiB coating was prepared by a combined system of arc ion plating and magnetron sputtering. After annealing, the elements of the gradient coating are chemically graded distributed with Al enrich in the outer layer and Cr enrich in the intermediate layer. In terms of the surface energy, the phase transformation from the transient alumina to stable α-alumina was discussed. After 300 h oxidation, both the NiCoCrAlYSiB coating and the gradient coating can improve the oxidation resistance of DSM 11 substrates greatly due to the formation of thin and dense alumina scales. The oxidation rate of the gradient coating was reduced further comparing with that of the NiCoCrAlYSiB coating. This was attributed to the formation of TiO2, Y2O3 and aluminum yttrium oxides in the alumina scale formed on the surface of gradient.