Effect Of Mo、Y₂O₃ And Pre-oxidation Treatment On The High Temperature Oxidation Resistance Of Ni Based Alloy

Ni based superalloy is the most widely used alloy material in superalloys.With the development of aerospace and other fields,higher standards have been put forward for the parameters of the engine thrust and the inlet temperature of the turbine,so that the superalloy should have better comprehensive properties,Therefore,it is necessary to study the superalloy more deeply,optimize the composition of the alloy,improve the production process and improve the high temperature performance of the alloy.In this paper,the effect of alloy composition and preoxidation temperature on the high temperature oxidation resistance of Ni-8A1 series alloys was systematically studied,which provides a theoretical basis for the practical application of nickel base superalloy.In this paper,Ni-8Al-xMo(x=0,5%,10%and 15%)alloys with different Mo content and Ni-8Al-xMo-yY2O3 alloys with different Mo and Y2O3 content(x=5%,10%and 15%,y=0.2%,0.5%and 0.8%)are prepared by powder metallurgy.The high temperature oxidation resistance of 100h with different compositions at 1000 ℃ was studied.Ni-8Al-5Mo-(0.5,0.8)Y2O3 and Ni-8Al-10Mo-(0.5,0.8)Y2O3 alloys were preoxidized at 450℃,650℃,850℃and 1000℃,respectively,and then oxidized to 10h at 1000℃,and the oxidation resistance of the alloys was compared with those of the untreated alloys.The results showed:1.The oxidation law of alloy is linear at the initial stage;When the oxidation is further oxidized,the law of oxidation of the alloy is in a transition section;As the oxidation proceeds,the oxide film begins to become thicker,and the oxidation rate of the alloy decreases gradually.The oxidation law presents a parabola trend.2.The best oxidation resistance of Ni-8Al-xMo(x=0,5%,10%and 15%)alloy is Ni-8Al-5Mo alloy,its oxidation weight gain is about 0.65(mg/cm),and the oxide film is the most smooth and the most closely combined with the matrix;the worst oxidation resistance of the alloy at high temperature is Ni-8A1 alloy,and its oxidation weight gain is about 1.84(mg/cm);4 kinds of alloy matrix of different Mo content is mainly composed of Ni3Al phase,and the oxide film is mainly composed of Al2O3 and part of NiO phase.When the content of Mo in the alloy reaches more than 10%,the TCP phase is easily precipitated.The formation of a large number of TCP phases has adverse effects on the high temperature properties of the superalloy.However,the addition of Mo improves the oxidation resistance of Ni-8A1 alloy at high temperature.3.After oxidation of 100h at Ni-8Al-xMo-yY2O3(x=5%,10%and 15%,y=0.2%,0.5%and 0.8%),the oxidation weight gain of Ni-8Al-10Mo-0.2Y2O3 alloy is the lowest,about 2.38(mg/cm2);and Ni-8Al-15Mo-0.8Y2O3 alloy oxidation weight gain is most obvious,about 38.59(mg/cm).And the matrix in the alloy is mainly Ni3Al phase and partial Ni phase.The oxide is mainly composed of NiO and Al2O3;and the surface of Ni-8A1-10Mo-0.2Y2O3 produces a relatively smooth,continuous and compact Al2O3 film,which has the best oxidation resistance at high temperature.4.The high temperature oxidation resistance of Ni-8Al-xMo-yY2O3(x=5%,10%and 15%,y=0.2%,0.5%and 0.8%)deteriorated with the increase of Y2O3 addition,which is mainly due to the unevenly dispersion distribution of Y2O3 in the alloy,the phase segregation of Y,and even the formation of low melting point eutectic with nickel,so that the alloy is brittle and the properties are brittle.At the same time,the oxidation products of Mo have high volatility.When they are oxidized at high temperature at 1000℃,the oxide basically volatilization,which will cause the powder of the surface material of the alloy,which greatly weaken the effect of Y2O3 on the oxide film.5.The effect of preoxidation at 1000 ℃ on Ni-8A1-10Mo-0.5 Y2O3 alloy is the most obvious.The weight increase of 1h after oxidation treatment at 1000℃and then recycled at 1000 ℃ for 10h is about 1.33(mg/cm2)as 1/9 of unpreoxidized treatment weight 11.97(mg/cm).6.The oxides formed on the surface of Ni-8Al-5Mo-(0.5,0.8)Y2O3 and Ni-8Al-10MM-(0.5,0.8)Y2O3 alloy are mainly composed of A1203,NiO phase and a small amount of MoO2 and NiAl2O4 phase.The oxide film on the surface of the alloy has a double layer structure,that is,the inner oxide is mainly Al2O3,and the outer layer is loose.The large granular nickel oxide or nickel aluminum oxide adheres to the inner oxide.