Effects of rare-earth elements on the isothermal oxidation of the alumina scale forming NbSiTiAlHf alloys fabricated by spark plasma sintering

The multicomponent alloys prepared by traditional arc melting usually present microstructural and compositional inhomogeneity, which makes it difficult to distinguish and isolate the factors that affect their properties. To study the effects of the rare-earth elements on the oxidation behavior of NbSiTiAlHf alloys, the Y, Dy, and La doped alloys with controlled microstructures and compositions were prepared by a combined process of arc melting, breaking, ball milling and spark plasma sintering. The investigated alloys have a nominal composition of Nb-13.5Si-23Ti-37Al-5Hf-0.5X (at%), where X = Y, Dy and La, respectively. The results showed that the scales formed on all alloys were identified to be primarily consisted of Al 2 O 3 , with minor amounts of TiO 2 presented on the surface or in the upper layer of the scales. The scale growth rate has the lowest value (1.48 ×10 −11 cm 2 /s) for the 0.5 at% Dy-doped alloy. The benefits of Y were less effective with a growth rate of 1.71 × 10 −11 cm 2 /s for the 0.5 at% Y-doped alloy. Conversely, the 0.5 at% La-doped alloy showed the maximum scale growth rate of 3.21 × 10 −11 cm 2 /s. The discussion subsequently focuses on the influences of doping Y, Dy and La on the oxidation behavior of NbSiTiAlHf alloys. It is proposed that Dy could be more effective than Y to improve the oxidation resistance of the NbSiTiAlHf alloys, while La could present the opposite effect.