| The development level of aero-engine determines the performance of aircraft,which has become one of the important indicators to measure a country’s scientific and technological level and comprehensive national power.As the core hot-end component of aero-engine,turbine disk has the worst working conditions and the most complex failure mode,which directly determines whether the aero-engine can serve safely.Therefore,the material of turbine disk should have as high fatigue,durability and creep resistance as possible in its service temperature range.The powder superalloy,represented by FGH4096 alloy,solves the problems of solidification segregation and deformation difficulty caused by high alloying of turbine disk,and significantly improves the mechanical properties and hot workability of turbine disk.Therefore,the powder superalloy has become the preferred material of advanced aero-engine turbine disk.However,the inclusion defects in powder superalloys have become the biggest challenge restricting its development.In order to improve its purity,a large number of studies have been carried out at home and abroad.At present,vacuum induction melting,electroslag remelting and vacuum consumable melting have become the main means of preparing high purity powder superalloy.However,due to the limitation of temperature,vacuum and reaction equilibrium,the removal of trace impurity elements and inclusions in P/M Superalloy by traditional smelting process has reached a limit.In order to solve the problem of impurity removal barriers in traditional smelting methods,this study innovatively proposed a new process for preparing FGH4096 master alloy by electron beam smelting,and studied the effects of smelting parameters such as vacuum degree,smelting power and smelting time on denitrification behavior.At the same time,the denitrification mechanism of FGH4096 master alloy prepared by electron beam smelting were analyzed by using the theories of metallurgical thermodynamics and kinetics.The results show that the nitrogen content in the FGH4096 master alloy can be reduced from 17 ppmw to less than 1 ppmw after electron beam smelting.Increasing the smelting power or prolonging the smelting time will promote the removal of nitrogen effectively.The solid solubility of nitrogen in the alloy decreases gradually as the vacuum increases,and increases gradually as the melt temperature increases,but a more significant effect is observed for the vacuum.The inclusions in the near-surface area of the melt can be removed by dissolution,and the inclusion particles floating above the melt level can be decomposed under the action of electron beam bombardment.The rate constant for the nitrogen removal process increases with the increase of melt temperature,but the promotion effect weakens after reaching a certain value.The removal of nitrogen tends to be controlled by the second-order reaction,the first-order reaction and the 1.5th-order reaction,respectively,when the smelting power varies from 9 k W to 15 k W.At 9 k W,the denitrification rate constant decreased with the time.However,at 12 k W and 15 k W,the denitrification rate constant gradually decreases at the early stage of smelting,but increases at the later stage,which should be related to the content of oxygen and sulfur.When the content of surface active elements increases,the denitrification rate accelerates. |
