Effect Of Al And Ti Contens On Microstructure In Inconel 718 Alloy

Inconel 718 is a widely used nickel-based superalloy in the world,which can be applied in the manufacture of gas turbines,aero engines,turbine disks,blades,bolts,guides,compressor discs and other components.However,the ?? phase will rapidly coarsen and transform to the ? phase,when the temperature exceeds 650 °C,which limits the application of the alloy in the higher temperature service components.Researchers attempt to further improve the service temperature and microstructure stability of Inconel 718 alloy by adjusting its composition,while retaining its forgeability,weldability and low cost.Therefore,studying the effect of alloying elements on microstructure have important guiding for composition optimization and performance improvement.Based on this,four kinds of samples were prepared by adjusting Al and Ti elements.The types and microstructure of precipitates in modified Inconel 718 alloys were studied,in order to provide guidance for regulating microstructures.Based on a large number of experiments and observations,the main conclusions are as follows:(1)Four different precipitate configurations were obtained by adjusting the mass ratio of Al/Ti.A separately precipitates ?' phase and ??? phase were obtained in an alloy of Al:Ti=1:3(wt.%);Al:Ti=1:1(wt.%)alloys obtained two types of composite structure,?"/??/?" and ?'/?";the single spherical ?? phase is obtained in the alloy of Al:Ti=2:1(wt.%);the ??/???/?? composite structure is obtained in the alloy of Al:Ti=3:1(wt.%).The mass ratio of Al/Ti has significant influence in structure of the precipitates.(2)As the mass ratio of Al/Ti increases,the amount of ??? phase precipitate decreases and the number of ?? phase precipitates increases.The precipitates at the grain boundary tends to change from needle-like to short-rod and then to granular.(3)Aging at 700 °C for 100 h,the composite structure and the single ?' phase showed good stability.Aging at 700 °C for 1000 h,the composite structures of ???/??/???and ??/??? precipitated in the alloy Al:Ti=1:1(wt.%)are decomposed and decomposed into isolated ??? phase and ?? phase.(4)After long-term aging at 800 °C,both single ?' phase and ?'/? "/?? composite structure can exist stably.However,the composite structure ?'/?" /?? in the alloy Al:Ti=3:1(wt.%)has higher strength and excellent high temperature stability.As the mass ratio of Al/Ti increases,the hardness value of the alloy increases.(5)The coarsening kinetics of ??? phase,??/??/?? phase and ?? phase are consist with LSW theoretical prediction.