| FGH4096 powder superalloy is a key material for high-performance aero-engine hightemperature parts developed in my country in the 1980 s.Because of its low crack growth rate,good comprehensive mechanical properties and good fatigue resistance,long life and corrosion resistance at 700°C,it has been used in the manufacture of advanced aero-engine turbine disks at home and abroad.There is still a big gap between my country’s FGH4096 alloy and similar foreign powder high-temperature alloys(René88DT).The specific manifestations are low temperature bearing capacity,short service life,and poor service stability.This is related to the O,N impurities in the alloy and its formation.The inclusions are closely related.Therefore,how to control the O and N content in the alloy and the size of the inclusions formed to further improve the purity of the alloy is very important.At present,the FGH4096 master alloy in my country is mostly prepared by vacuum induction melting.With the advancement of alloy preparation technology,the control requirements and indicators for the content of O and N in superalloys are becoming more and more stringent.For example,the Aviation Materials Institute clearly requires that the O content in FGH4096 alloy is not more than 50 ppmw,and the N content is not more than 30 ppmw.In spite of this,the smelting control technology of impurities and inclusions in powdered superalloys in my country has not yet completely broken through,which restricts the further improvement of aero-engine performance.In recent years,melt superheat treatment has gradually become an important means to improve the purity of alloys and improve the solidification structure.By keeping the alloy melt at a certain temperature higher than its melting point for a certain period of time and then rapidly cooling it,the structure that is beneficial to the performance of the alloy obtained when the superheating temperature is high can be well retained.Based on this idea,if the FGH4096 alloy can be melt-overheated,the refining reaction can take place at a higher temperature,so that the impurities and inclusions in it can be effectively removed,and the good structure of the FGH4096 alloy can be retained to room temperature through rapid cooling.,You can get FGH4096 alloy ingot with excellent metallurgical quality.Therefore,this study took FGH4096 alloy as the research object,and carried out melt overheating experiments under different overheating temperatures(93℃,133℃,193℃)and overheating time(10mni,20 min,30min)on the alloy,and revealed the effect of overheating parameters.The influence law and mechanism of alloy composition,element evaporation rate,purification behavior and organization.Studies have shown that with the increase of the overheating temperature,the mass loss rate of the ingot after smelting gradually increases.Melt overheat treatment can change the microstructure of the melt,which affects the segregation behavior,precipitation phase and MC carbide of the alloy.In addition,the melt overheat treatment has a certain effect on the purity of the alloy.When the superheating temperature of the alloy increases,the loss rate of the alloy composition gradually increases,which is mainly caused by the evaporation loss of the Cr element.When the degree of superheat is 85℃ and 133℃,the content of O and N impurity elements in the alloy is relatively low.With the increase of superheat,the content of O and N impurity elements rebounds.The thermodynamic mechanism affecting the content of O and N is analyzed..In addition,the overheating of the melt will reduce the segregation of alloy components and refine the dendrites.This is related to the dissolution of atomic groups under higher superheat and the reduction of nucleation nuclei resulting in uniform nucleation under larger undercooling. |
