Effect Of The Initial Microstructure Of GH4169 Superalloy On Microstructure And Properties Of Welded Joint

As a precipitation strengthened high temperature nickel-based alloy,GH4169 superalloy has been widely used in aerospace and energy industries due to its excellent high temperature properties.The matrix phase and the main strengthening phase of this alloy is ? phase and metastable ?? phase,respectively.The metastable ?? phase will transform into the more stable orthorhombic ? phaseduring the high temperature service.However,a large content of needle-like ? phase in the matrix will deteriorate the properties of the material.After long-term service at elevated temperature,the defects of GH4169 superalloy components are usually repaired by low heat input techniques.In this paper,heat treatment at high temperature was used to obtain different content of ? phase in as-received GH4169 superalloy,and then the varestraint test and TIG welding were carried out for the base metal with different content of ? phase.The microstructure of HAZ and the mechanical properties of the welded joint were studied by optical microscope,scanning electron microscope,energy dispersive spectrometry,Vickers hardness tester and tensile tester.The results show that the ? phase tended to precipitate firstly at grain boundaries and twin boundaries during heat treatment at 925?.The intergranular ? phase appears needle-like or chainlike shape,while the intragranular ? phase appears parallel needle-like shape and the ? phasesin different orientations often distribute in 120°.In varestraint test,when the strain is 0.5% and 1.0%,the increase of the ? phase in the base metal has little effect on the maximum crack length and total crack length,but when the strain reaches 2.0%,the existence of the ? phase will obviously increase the maximum crack length and total crack length.The increase of the ? phase in the base metal will obviously increase the crack sensitivity of GH4169 superalloy.The ? phase can promote the formation of ?/Laves eutectic constituent in Region 1 of HAZ,but it can inhibit the grain coarsening in Region 2 of HAZ.The ? phase and Laves phase can lead to the depletion of Nb elements in the ? matrix and deteriorate the properties of this material.The hardness distribution curves of HAZ in as-welded state exhibit a "V" shape,while after aging treatment the hardness curves exhibit a "?" shape.In as-welded state,the main factor that affectes the hardness of HAZ is grain size.After aging treatment,the content of ?? phase plays the key role on hardness of HAZ.