Isothermal Oxidation Behavior of a Cast Ni3Al-Base Superalloy MX 246A

The oxidation behavior of a cast Ni3 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/m2·h under the condition of 1100°C./100h, while the undoped alloy MX246 is 0.2683 g/m2·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 NiAl2O4 and NiCr2O4. as well as a considerable quantity of α-Al2O3. 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 HfO2 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.