Effect of molybdenum on isothermal oxidation behavior of 4th generation nickel-based single crystal superalloys

The isothermal oxidation behavior of fourth-generation nickel-based single crystal superalloys with 2-4 wt% Mo content were studied at 900 °C and 1100 °C.At 1100 °C, the oxide layer can be divided into three layers, the outermost layer is Ni–Co oxide, the intermediate layer is spinel and heavy metal element oxide, and the innermost layer is Al2O3 layer. With the increase of Mo content, the oxide layer accumulates more growth stress, resulting in more severe spallation. At 900 °C, the oxide layer can be divided into three layers, the outermost layer is Ni–Co oxide, the intermediate layer is Cr–Al oxide, and the innermost layer has obvious selective oxidation of Al element. The volatilization of oxide promotes the diffusion of O into the matrix, thus promoting the oxidation of heavy metal elements in the matrix. With the increase of Mo content, this phenomenon is more obvious. The results show that the increase of Mo content of alloy promotes the oxidation of Mo, W and Re elements, which let the volatilization of the oxide and the spalling of the oxide layer more severe, thus decreasing the oxidation resistance of the alloy.