Research On Laser Welding Of Superalloy Bolt Assemblies

GH4169 is precipitation-hardened Ni-based superalloy,as the preferred material of high pressure rotor bolt assembly.Laser welding is an indispensable and important link in the preparation process.However,the deterioration of properties and even failure during long-term service is owed to the transformation from ?" metastable phase to ? stable phase.In order to meet the requirements of high strength and large size of the bolt assembly for aero engines,the aviation field will adopt the super strength GH159 cobalt-based superalloy to replace GH4169 nickel-based superalloy as the bolt material for the research and development of the bolt assembly of larger size.In consideration of the cost,the leaf springs of the bolt assembly are still GH4169.Therefore,this paper takes GH4169 and GH159 as the research objects to deeply study the weld forming mechanism,microstructure evolution and its influence on the mechanical properties of bolt assembly during similar material laser welding of GH4169 and dissimilar material laser welding of GH159/GH4169 under different welding heat input.SYSWELD software was used to conduct numerical simulation of GH4169 laser welding,and the main conclusions are as follows:(1)In the laser welding of GH4169 with a thickness of 1.6mm,with the increase of welding heat input,the width and depth of weld seams also increase,and the weld geometry is stemless wine glass.Inevitably,porosity is observed at the bottom of all weld seams.From the fusion line to the center of fusion zone(FZ),the microstructure changes from dendritic to equiaxed,and the main precipitation phase is Laves phase.The dissolution of ?" and ?' in the heat affected zone(HAZ)on both sides of the FZ increases along the direction of the FZ.This results in a decrease in the hardness of the HAZ.(2)Co-based superalloys GH159 and Ni-based superalloys GH4169 have been joined by laser beam welding in this work.The results show that weld seams exhibit a nail shape and full penetration is attained at the heat input from 35.2J/mm to 44.8J/mm.Porosity is observed in all dissimilar joints inevitably.It is determined that the precipitated phase in the FZ is also Laves phase.From the fusion line to the center of FZ,the microstructure is also transformed from dendritic to equiaxed.Static recrystallization occurs in the HAZ on the GH159 side and the incremental grain size towards the FZ.The increasing dissolution of ?" and ?' towards the FZ is attained at in the HAZ on the GH4169 side.These are the reasons for the gradual decrease of the hardness of the HAZ along the weld direction.(3)The tensile strength of the welded joint decreases with the increase of heat input in either the similar material laser welding of GH4169 or the dissimilar material laser welding of GH159/GH4169,and the tensile failure occurs in the FZ with the lowest hardness value.The microstructure of FZ is quantitatively analyzed.The results show that increasing welding heat input results in a rise in the weld dendritic arm spacing and the volume fraction of Laves phase.The weld strength is mainly affected by the weld dendrite size(fine grain strengthening)and the volume fraction of Laves phase(solid solution strengthening).(4)The weld pool morphology,welding temperature field and residual stress field of GH4169 laser welding were numerically simulated by using SYSWEID software.The simulated pool morphology is in good agreement with that measured by experiment.The correctness of the established numerical simulation model is confirmed.Therefore,the model can not only meet the requirements of changing weld penetration depth of GH4169 laser welding,but also provide a reference for numerical simulation of GH159/GH4169 laser welding.