Effect Of Rare Earth Elements On The Oxidation Behavior Of Co-Re-Cr Based Superalloys

Rare earth elements have excellent performance in superalloys,and adding trace amounts of rare earth elements to superalloys can reduce the oxidation rate of the alloy,strengthen the anti-spalling ability of the oxide film,and improve the high-temperature oxidation resistance of the alloy.In this paper,on the basis of Co-20Re-25-20Re-25 Cr-2Si alloy,the high temperature oxidation behavior of Co-20Re-25Cr-2Si-x Y/Dy（x=0.1,0.3,0.5,0.7,1.0）alloys were studied at 1000-1200℃ under high and low oxygen pressure.The effects of rare earth elements Y and Dy on the formation of protective Cr₂O₃ oxide film of Co-20Re-25Cr-2Si alloys were mainly studied to obtain the optimal addition value for the positive effect.The research results are helpful to further clarify and develop the high-temperature oxidation theory of multi-component two phase alloys,which has important guiding significance for the design of high-performance Co-Re-Cr based alloys at high temperatures.（1）The oxidation behavior of Co-20Re-25Cr-2Si-x Y（x=0.1,0.3,0.5,0.7,1.0 at.%）has been studied at 1000-1200℃,0.1 MPa pure O₂ and 3.0×10^-5 Pa O₂.The oxidation kinetic curve of the alloy as a whole was not completely regular under 0.1 MPa pure O₂,but compared with Co-20Re-25Cr-2Si,the oxidative weight loss behavior of Y-doped alloy was significantly improved.Rare earth Y showed the positive effect of active elements,and the high temperature oxidation resistance of Co-20Re-25Cr-2Si-x Y alloy was significantly improved.The oxidation kinetic curve of the alloy conforms to the parabolic law completely under 3.0×10^-5 Pa O₂.Under the joint action of adding rare earth Y and low oxygen pressure environment,the high temperature oxidation resistance of Co-20Re-25Cr-2Si alloy was not further improved,and even changed the semi-continuous structure of the Si internal oxidation zone,which intensified the internal oxidation of the alloy.However,this negative behavior is not absolute,and the0.5/0.7Y alloy at 1100℃ exhibits good resistance to high temperature oxidation..（2）The oxidation behavior of Co-20Re-25Cr-2Si-x Dy（x=0.1,0.3,0.5,0.7,1.0at.%）has been studied at 1000-1200℃,0.1 MPa pure O₂ and 3.0×10^-5 Pa O₂.Under the high oxygen pressure atmosphere,the amount of rare earth Dy required for the alloy to produce the positive active element effect is lower than that of the Y-doped alloy,and when the Dy content is 0.1%,the alloy translates into weight gain.However,this positive effect does not occur in all Dy-doped alloys,with the gradual increase of Dy content,the addition of Dy has a negative impact on improving the high temperature oxidation resistance of Co-20Re-25Cr-2Si alloy,and the weight gain of the alloy also increases significantly.Under the low oxygen pressure atmosphere,all alloys conform to the parabolic law and are oxidative weight gain.Dy-doped alloys are similar to Y-doped alloys and exhibit more severe oxidation behavior.Among them,trace and excessive addition will cause the alloy to form a thicker Cr₂O₃ oxide film.However,the effect of low oxygen pressure atmosphere on high temperature oxidation of alloy is the same as Y,not all show negative effects,at 1100℃,all Dy-doped alloys show better high temperature oxidation resistance than Co-20Re-25Cr-2Si alloy.