Microstructure Evolution And Dynamic Deformation Behavior Of Laser Welded Joint Between Ni-Based Single Crystal And Polycrystalline

Laser welding technology has been widely used in the aerospace engine manufacturing and repair of blisk because of its significant advantages.As one of the important hot-end components of aero-engine and gas turbine,the welded components of blisk will unavoidably serve in the high-temperature,high-pressure and high-speed service environment.Especially,it will be subjected to the high-speed dynamic loadings when under the condition of high-speed operation.Therefore,the joint between Ni-based single crystal and polyscrystalline used for aero-engine blisks was fabricated using laser welding technique in this study and investigated the microstructure evolution,microhardness,alloying element distribution and the tensile deformation behavior under various strain rates to reveal the effects of strain rate on the tensile properties and deformation behavior of the welded joint.The research results show that the microstructures of DD407/GH4169 welded joints are divided into GH4169 base material(BM),GH4169 heataffected zone(HAZ),fusion zone(FZ),DD407 HAZ and DD407 BM.In this study,the heat treatment of direct double aging was identified as the standard heat treatment for the welded joint.There are a lot of ?' phase precipitated in the FZ of the welded joint after direct double aging and the number,shape and size of the ?' phase at the two sides of the fusion line are different.The ?'phase in the region between the fusion line center line and the fusion line of DD407 is cube shape;while the ?' phase and the second ?' phase in the region between the fusion line center line and the fusion line of GH4169 are formed as sphere or ellipsoid.The hardness in FZ of as-welded joint is lower than the corresponding BMs and not uniform,there is softening zone in the GH4169 HAZ.After the post-weld heat treatment,the hardness of the FZ is observed to obviously increase.And the joint hardness is more uniform than that before the postweld heat treatment.At the same time,the hardness of GH4169 BM is also improved,so the softening phenomenon of HAZ is relieved,and the hardness value of DD407 BM is not greatly affected.With the increase of aging time,the hardness values of various regions in the joints decreased differently.The hardness value of GH4169 BM decreased more obviously than that of FZ and DD407 BM.At the strain rate lower than 100s-1,the fracture elongation of the welded joint is 2.96%,which is up to 65%of that of the DD407 BM.With the increase of the strain rate,the decrease of plastic deformation ability of the welded joint is more significant than that of the corresponding BMs.The plastic deformation behavior of the welded joint is not completely controlled by the deformation behavior of the two kinds of BMs of GH4169 and DD407.The fracture elongations of the welded joint deformed at various strain rates are less than that of the two kinds of BMs,which is related with that the deformation compatibility of the various microstructures in the welded joint is weaker than that of the BMs during the plastic deformation process.