Gradient Composition Design Of The Nickel-based Superalloys For The Integral Turbine Blade-Disc Of Aero-Engine Based On Thermodynamic Calculations

With the increasing performance requirements of areo-engine in industry,the integration of aero-engine turbine disk and blade manufacturing has become a hot topic of research,and additive manufacturing technology provides the possibility for the manufacturing of the integral turbine blade-disc with complex shape.However,turbine discs and blades are made of different nickel-based superalloys,and their connection has become a key problem in integrated manufacturing.Based on thermodynamic calculation,gradient composition design of the alloys at the junction of turbine disk and blade has been carried out in this study to provide theoretical basis for additive manufacturing of integral blade-disc.Based on CALPHAD approach and Nickel-based superalloy thermodynamic database,this study aims at the possible brittle phases formed in nickel-based superalloys fabricated by additive manufacturing technology.The research is mainly focused on the forming condition of the Laves phase in GH4169 alloy and the temperature range of μ phase in K417G alloy.The composition optimization of GH4169 and K417G alloy has been performed.Finally,five transition gradient components from GH4169 alloy to K417G alloy were designed.The main research results are as follows:(1)For the Laves phase in GH4169 alloy used for aero-engine turbine disc,the Ni-Fe-Nb ternary system was selected,and the composition range of the Laves phase was analyzed by thermodynamic calculation.Based on this,the formation condition of the Laves phase in Ni-Fe-Nb-xCr,Ni-Fe-Nb-yTi,Ni-Fe-Nb-zMo and Ni-Fe-Nb-xCr-yTi-zMo systems was further discussed.The results showed that Fe,Cr and Nb were the main components to form Laves phase,and the segregation of Ti and Nb promoted the formation of the Laves phase.Finally,by adjusting the contents of Fe,Cr and Ti,the mole percent of the Laves phase was decreased from the original 0.5%to 0.33%.(2)The effect of major component contents on equilibrium precipitation phases in K417G alloy used for aero-engine turbine blade was studied.The quantitative relationship between mole percent of equilibrium percipication phases and temperature was established.The harmful μ phase can not precipitate above 790℃ by decreasing the contents of Cr and Mo in K417G alloy.(3)A linear gradient component trasition was designed between the optimized compositions of GH4169 alloy and K417G alloy,in which 5 equally spaced transition components were selected.Their equilibrium precipitation phases in the range of 600℃-1400℃ were studied,and the contents of Mo and Co were optimized to reduce or eliminate the harmful phases of μ and α(Cr).The quantitative relationship between mole percent of precipitation phases and temperature was established.The above research results are expected to provide a basis for the design of the gradient transition layer of the integral turbine blade-disc fabricated by additive manufacturing technology.