The Influence Of Characteristics Due To High-content γ’ On Microstructures And Properties Of Difficult-to-Deform GH4151 Alloy And The Exploration Of Alloys With Higher Service Temperature

Nickel base superalloys have been widely used in the field of aerospace due to its excellent mechanical properties at elevated temperature.To further improve the service temperature of turbine disk,the wrought superalloys with higher content ofγ’ phase(≥ 50 wt.%)have been developed at home and abroad,and the service temperature could reach 800℃ or above.However,the characteristics of γ’ phase become more obvious,which contributes to the complex microstructure and difficulty in preparing the alloys.Besides,there exists a bottleneck in further increasing the service temperature of wrought superalloy by adding more γ’ phase.Therefore,this paper systematically studies the characteristics of high-content γ’phase,its influence on microstructures and properties,and provides controlling methods to optimize fabrication processes.Based on the characteristics,the paper also explores the wrought superalloy systems with higher service temperature.Experimental and theoretical basis for understanding γ’ phase and design alloys serving at elevated temperature are proposed.As-cast superalloy ingot with high-content γ’ phase is inclined to crack during solidification.The crack mechanism of the ingot is studied systematically.Massiveγ’ phase(～48.8 wt.%)and complex second phases are precipitated during solidification due to high alloying degree.Thermal stress is also obviously accumulated and promotes cracking at the interface between matrix and second phases.A criterion of cracking during solidification of GH4151 ingot and numerical analysis method for controlling the stress of ingot are proposed.The numerical method could predict cracking sensibility of ingot after solidification.Furthermore,the influences of high alloying and high-content γ’ phase on hot workability is analyzed systematically.A three-stage homogenization process is designed.Dendritic γ’ phase with micron size could precipitate during cooling when the cooling rate is lower than critical rate 15℃/min,which could increase the workability of ingot.A control model and numerical analysis for cogging are established,which could predict the deformation and cracking behavior.The effects of high-content γ’ phase on room temperature impact toughness and creep property at high temperature are revealed.It is suggested that the impact toughness at room temperature can be improved through larger secondary γ’ phase by increasing the aging temperature.The creep behavior and mechanism under different conditions are analyzed systematically.The coordinated deformation mechanism of intragranular sliding,grain boundary oxidation damage and matrix softening is revealed.It is pointed out that increasing service temperature could be obtained by increasing work of separating grain boundary and stability of matrix microstructure.The mechanism provides theory basis for designing alloys with higher service temperature.Furthermore,carbide dispersive precipitation strengthening alloy system is further explored.It is indicated that the alloy rich in C,Mo and W can precipitate dispersive nanometer M6C carbide after solidification,which could provide strengthening effect.The alloy rich in C,Ta/Hf could precipitate a large amount of MC carbide after solidification.The results show that structure of the carbide dispersive precipitation strengthening alloy system could be modified.The alloy also has the ability of carbide dispersion and the microstructure stability of high temperature aging.Therefore,the alloy system has the potential to improve the service temperature.Besides,SiC fiber reinforced superalloy matrix composites are also explored.Matrix element Ni,Co and Fe dominate the severe interfacial reaction.Thus,the interfacial reactions between existing superalloy and SiC fiber is hard to control effectively.In summary,the paper clarifies the characteristics of high-content γ’ phase and reveals the influence of high-content γ’ phase on microstructures and properties.In addition,control methods based on the characteristics are provided.The reliability of increasing service temperature by in-situ precipitating carbide and externally introducing SiC fiber is explored.The paper provides experimental and theoretical basis for increasing the service temperature of nickel-based wrought superalloy.