Effect Of Al Content On Microstructure And Properties Of A Cast Ni-Based Superalloy

K4002 alloy is a kind of cast nickel-base superalloy reinforced with ?' phase.The highest temperature used can reach 1050?.It is the best alloy in polycrystal nickel-base superalloy with mechanical properties at middle temperature and high temperature,which has tissue stability,oxidation resistance and hot corrosion resistance.It is mainly used in high-pressure turbine blades of aeroengines,the key components for casting whole turbine and scramjet engine.Al is the important element of forming ?' phase and has an important influence on the microstructure and high temperature properties of superalloys.Therefore,proper adjustment of the Al content in the alloy has an important influence on the microstructure and properties of alloys.In this paper,K4002 alloy as the base alloy,thermodynamic simulation of Al element,combined with the actual alloys of different Al contents to study the different Al content of cast superalloy.The microstructure and precipitations of alloys with different Al content under both as-cast and heat treatment conditions were investigated by OM,SEM,DSC,EDS and EPMA.Meanwhile tensile properties of alloys of different Al element at room temperature and high temperature were studied.Thermodynamic equilibrium calculation results by JMatPro shows that the equilibrium precipitated phases of K4002 alloy at 900? have y' and MC,M6C and M23C6 and a small amount of MB2.The ?' phase mainly has Al,and also has a part of the Ti.MC carbide is rich in Hf and Ta,M6C is enriched in W and Cr,M23C6 is enriched in Cr,and a small amount of MB2 borides are mainly enriched in B and Ti.With the increase of Al content,the liquidus line of three alloys decreased continuously.In Alloy II,it is found that the M6C phase isn't precipitated and a large amount of ?(NiAl)phase precipitated in Alloy ?.The content of ?' phase in Alloy ?was the highest.When JMatPro was used to simulate,the Al element increased from 5.5%to 8.5%,and the ?' phase precipitation temperature first increased and then decreased.With the increase of Al content,the precipitation temperature of MC carbide in the alloy continuously increases.It was found that the harmful phase of NiAl phase began to precipitate when the content of Al more than 7.6%,and precipitation amount of NiAl phase increased with the increase of Al content.The precipitate temperature and the mount precipitation of TCP phase(? phase,? phase)increase with the increase of Al content.The lattice mismatch degree of alloys increases negatively with the increase of Al content increased.With the increase of Al content,the room temperature strength of Alloy ? was the highest in four kinds of alloys.The microstructure of as-cast K4002 alloy shows typical dendritic morphology.The area of dendrite distributes blocky or striped MC carbides and sunflower or sunflower-like ?/?' eutectic.With the content of Al increasing,and the content of NiAl phase in Alloy ? and Alloy ? increased gradually.A small amount of ?-W precipitated in Alloy ?.With the increase of Al content,the segregation degree of Al,Ti,Co and W tended to decrease,and the negative segregation elements of Cr and Ta become positive segregation elements.Through aging heat treatment,the amount of eutectic and NiAl phase in Alloy ?to Alloy ? gradually decreases,and the NiAl phase in alloy ? basically disappears.The tensile strength of K4002 alloy is the highest at room temperature in four kinds of alloys.The tensile strength of the alloy I was the highest at 1200?.At 1200?,the source of K4002 alloy and Alloy ? cracks mainly generated at the interface between the eutectic and carbide,the source of the Alloy ? and Alloy ? cracks mainly in the interface of the eutectic and NiAl phase.