Study On Heat Treatment Process Of The Ni-based Single Crystal Superalloys With Carbon Containing

Nickel-based single crystal superalloys as a kind of metal materials have the higher creep resistance,corrosion resistance,oxidation resistance and other capabilities during the high temperature.Thus,it is widely used in hot parts for the aero engine and ground gas turbines.In recent years,it was found that the microstructure of nickel-based single crystal superalloy has an important effect on its mechanical properties.And carbon addition and heat treatment have a great influence on the microstructure of superalloys.In this paper,the third-generation nickel-based single crystal superalloy DD90 with C-containing was used as the object of study.By adjusting the content of carbon in the alloy and changing the heat treatment process,study on the effects of carbon level on the solidification path,solidification characteristic temperature,eutectic and carbide phases.The effects of different heat treatment processes on the microstructure,eutectic structure and ?' phase of the alloy were studied by different heat treatment processes.And the carbide morphology is also compared between before heat treatment and after heat treatment.The main conclusion are as follows:1.The addition of carbon in the alloy causes the liquidus temperature,solidus temperature,carbide precipitation temperature and ?' phase precipitation temperature to decrease slightly.In addition,the solidification temperature range of the alloy is less sensitive to C level,with the increase of C level,the change range is not large.2.The addition of different carbon level does not have much effect on the dendrite spacing of the superalloy.With the increasing of carbon level,the volume fraction of eutectic in the alloy decreases,the volume fraction of the carbide phase increases and its size becomes larger.At the same time,the addition of carbon has no significant effect on the distribution,size and morphology of the ?' phase.With low carbon level of the alloy,the morphology of carbide is granular or massive:when the carbon level is high,the carbides were in Chinese characters.3.Due to the addition of carbon,the alloy solidification characteristics of the temperature decreased.After the same heat treatment with different carbon level,the higher carbon level of the alloy,the higher the degree of disappearance of the dendrites.With the increasing of carbon level,the size of ?' phase after heat treated increases,and the number of ?' phase decreases gradually.4.After different heat treatment processes,the alloy composition has reached the purpose of homogenization,and the segregation degree is significantly reduced.In addition,as the heat treatment temperature increases,the profile of the dendritic structure becomes blurred gradually.When setting the solution temperature at 1305? and above,the dendritic profile of the alloy almost completely disappeared.After the multi-step heat treatment process with the highest temperature of 1305?,the eutectic microstructure in the alloy is the lowest,and the ?'phase of the alloy has better cubic and high volume fraction.5.The heat treated carbide and the as-cast carbide composition is basically consistent,indicating that during the heat treatment processes,the carbides only decomposed,which makes the carbide size smaller and tends to disperse the distribution.The heat treatment of the multi-step solution treatment provides sufficient time for the decomposition of the carbides,which reduces the size of the heat treated carbides compared to the cast carbides.When the heat treatment temperature is increased,the carbide decomposition degree is improved.And the carbide morphologies in the alloy are simpler and the size is significantly reduced,and the carbides are mainly distributed in fine particles.