Statistics of oxidation resistance of Ni-(0-15)Co-(8-15)Cr-(0-5)Mo-(0-10)W-(3-8)Al-(0-5)Ti-(0-10)Ta-0.1C-0.01B superalloys at 1000 °C by compositional variations

The effects of alloying elements (Co, Cr, Mo, W, Al, Ti, and Ta) on the oxidation resistance of Ni-(0-15)Co-(8-15)Cr-(0-5)Mo-(0-10)W-(3-8)Al-(0-5)Ti-(0-10)Ta-0.1C-0.01B alloys were studied. The sample compositions were designed by the Box-Behnken method of design of experiments (DOE). The alloying elements show complicated effects on the mass gain due to oxidation, depending on the alloy composition. Al reduces the mass gain largely. The other elements except Al do not appear to exert a strong effect on the oxidation rate on average, but their influences are shown clearly in the alloys with a low Al content. Co, W, and Ta reduce the oxidation rate, while Cr, Mo, and Ti promote oxidation. Ta is the most effective element in reducing the oxidation rate of the alloy with a low Al concentration. It is confirmed that a continuous Al(2)O(3)layer is essentially required for high oxidation resistance. The oxide scale of easily oxidized alloys has various oxides such as NiCr2O4, NiAl2O4, NiO, Cr2O3, CrTaO4, and TiO2.