Effects of Hafnium and Yttirium on the Oxidation-Resistence of Ni3Al/CrMoB Alloy

The effects of Hf and Y on the oxidation resistance of Ni3Al-7.8Cr-4Mo-0.03B alloy were studied in the present paper. The isothermal oxidation kinetic curves of the alloy at 1000 and 1100 °C were investigated, and the structure of oxidized surface was analyzed by X-ray diffraction. The research on the microstructure and composition of the oxides was conducted by means of a scanning electron microscope with EDAX unit and X-ray energy spectrometer. The results show that the addition of hafnium and yttrium significantly improves the oxidation resistance of this alloy. The positive effects are due to the formation of more stable oxide HfO2, which increase the adhesion strength between substrate and oxide layer, and meanwhile restrain the segregation of sulfur on the interface of oxidation scale and substrate. Besides these, the addition of hafnium and yttrium also change the morphology and composition of the oxides scale, the degree of inner oxidation, and the diffusion layer as well.