니켈기 초합금의 고온부식 저항성에 미치는 합금원소의 영향

Abstract

Ni-based superalloys are widely used in gas turbines blades and air craft engine blades because of its excellent mechanical property, oxidation resistance and hot corrosion resistance. The operating environments of superalloys include S, V, and corrosive impurities from fossil fuel involving deposition of molten salt layer on the metal. The effect of alloying elements on the hot corrosion behavior still need to be investigated particularly for the interactions between them, considering the complicated composition of superalloys. In this study, the effects of alloying elements on the hot corrosion resistance are examined by using statistical methods. Ni-(0∼15)Co-(8∼15)Cr-(0∼5)Mo-(0∼10)W-(3∼8)Al(0∼5)Ti-(0∼10)Ta-0.01C-0.01B were designed by Response Surface Method. The mass gain after cyclic hot corrosion at 700 ℃ or 900 ℃ was analyzed statistically to evaluate the effects of alloying elements on the hot corrosion rate. The phase, composition and structure of the oxide scales were examined by X-ray diffractometry and electron probe microanalysis. hot corrosion resistance at 700 ‘C was improved by increasing Whereas W and Mo degrade the hot corrosion resistance. Ti and Ta slightly increase hot corrosion resistance. Co-Cr, Co-Al, Cr-W, W-Al and Al-Ta couples appeared to have interactions in a way to reduce the effect of each other element.. The oxide scales were composed of Cr2O3 and (Ni,Co)O. It was shown that hot corrosion resistance at 900 ‘C was improved by increasing concentration of Ti, Co or Cr. The degrading effects of W and Mo on the hot corrosion resistance of superalloys were more significant at 900 ‘C than at 700 ’C. Al did not show a consistent effect on the hot corrosion behavior. Ta slightly increased hot corrosion resistance. Interaction effects were found for Co-Cr, Cr-W and Mo-Ti. The corrosion scales were mainly composed of TiO2, Al2O3 and TiTaO4.