Effect of Pre-oxidation Treatment on High Temperature Oxidation Behavior of Co-20Cr-xSi-2Al Alloy

The selective oxidation behavior of Co-20 Cr-x Si-2 Al-0.6Y（x=0-3） alloy under three oxygen partial pressures of 10^-17, 10^-25and 0.2 atm（1 atm=101325 Pa） at 900 ℃ was studied. A cyclic oxidation experiment of the alloy at 1000 ℃ was performed. The results show that the surface oxide of the alloy without adding Si is Cr₂O₃. With the increase of Si content, the surface oxide of the alloy becomes Cr₂ O₃ and Al₂O₃, mainly Cr₂O₃, and the internal oxide is Al₂O₃. When the Si content is up to3 wt%, a nearly continuous band-shaped Al₂ O₃ oxide film is formed inside. Under 10^-17atm oxygen partial pressure, the outer oxide film of the Co-20 Cr-2 Al-2 Si-0.6Y alloy after pre-oxidation is Cr₂O₃, and the inner oxide is Al₂O₃. Under 10^-25atm oxygen partial pressure, the surface of the alloy is Al₂O₃, Cr₂ O₃ film and distributed granular α-Co phase. In the cyclic oxidation experiment, the spinel outer oxide film and Al₂ O₃ inner oxide are formed on the surface under air atmosphere. The oxidation film on the Co-20 Cr-2 Al-0.6Y alloy formed in pre-oxidizing at 900 ℃ under 10^-17atm oxygen partial pressure has the best resistance to high temperature oxidation.