Abstract
Abstract The oxidation behavior of a cast Ni 3 Al-base superalloy MX246A in air over the temperature range of 1000°C to 1200°C for period up to 100h has been studied. The results indicate that the average oxidation rate of MX246A containing 0.5Hf and 0.01 Y additions is as low as 0.0639g/m 2 ·h under the condition of 1100°C./100h, while the undoped alloy MX246 is 0.2683 g/m 2 ·h. An analysis of structure of the surface oxidation scales through X-ray, and a research into the microstructure and composition of the oxide by means of a scanning electronic microscope with an EDAX unit. The results show that oxidation scale are composed of besides NiO NiAl 2 O 4 and NiCr 2 O 4 . as well as a considerable quantity of α-Al 2 O 3 . The results also show that the addition of Hf and Y into MX246A significantly improves the oxidation resistance property of the alloy. Hf is effective mainly in the formation of HfO 2 which is more stable in the strengthening of adhesion between the oxidation layer and the substrate, while Y restrains the segregation of Sulfur on the oxidation scale/substrate interface, as well as changing the morphology and composition of the oxidation scale, the degree of inner oxidation and the diffusion layer.
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