Microstructure And Mechanical Properties Of Electron Beam Welding Joint Of Anisotropic GH4169 Superalloy Fabricated By Laser Solid Forming

The laser three-dimensional forming technology can realize the manufacturing of metal components by the way of synchronous powder feeding laser cladding.The technology can be used for the mold free,flexible,full dense near net forming of complex structural parts,and also for the rapid manufacturing of metal parts under high temperature and heavy academic load.It is a typical microstructure feature of laser solid forming GH4169 alloy to grow coarse columnar crystal with anisotropic epitaxial growth.In view of the anisotropic characteristics of GH4169 alloy produced by laser stereo forming technology and the limitations of the current laser stereo forming technology which is difficult to produce large-scale complex structural parts,this paper proposes to use vacuum electron beam welding technology to realize the connection of laser stereo forming metal components,so as to solve the problem of large-scale complex metal parts manufactured by laser stereo forming technology,and studies The effect of crystal orientation difference of base metal on the microstructure and mechanical properties of GH4169 electron beam weld.This project can provide a theoretical basis for the fabrication of large-scale complex metal structures by vacuum electron beam welding.The specific research work and main conclusions are as follows:The microstructure of the vacuum electron beam welded joint of GH4169 alloy sample formed by laser stereo forming was studied.The results show that the change of the orientation difference(0°、45° and 90°)of the base metal crystal on both sides of the vacuum electron beam weld can affect the preferred orientation of the weld structure and the content of the large angle grain boundary.The change of the orientation of the base metal crystal on one side of the weld can change the dendrite growth direction of the weld structure Then,the preferred orientation of the weld structure changes,resulting in different texture of the weld structure,and the content of large angle grain boundary will also be affected by the texture.The content of large angle grain boundary of the(0°、45° and 90°)base metal crystal orientation difference weld increases first and then decreases,and the plastic deformation ability of the weld increases first and then decreases.However,the preferential orientation of the original structure can be changed or even eliminated by pre weld heat treatment and post weld heat treatment(solution and aging),and the coarse columnar crystal can be transformed into equiaxed crystal with smaller size.The mechanical properties of EBW with different base metal crystal orientation difference(0°、45° and 90°)were analyzed.The results showed that the hardness values of EBW with different orientation difference(0°、45° and 90°)were similar,and all of them floated up and down at 265 hv,and the floating range was not more than25 hv.However,the hardness values in the middle region of each weld were about 15 hv higher than that in the upper region.The hardness values of the weld structure of the pre weld heat-treated joint and the post weld heat-treated joint are similar,both of them float up and down at 480 hv,and the floating range is not more than 20 hv.The tensile strength of welded joint decreased from 0°、45° and 90° orientation difference,which were 721 MPa,720.7MPa and 702 MPa respectively.The tensile strength of base metal was the best,which was 732.7MPa.The tensile strength of the pre weld heat treatment sample and the post weld heat treatment sample are 751 MPa and 748 MPa respectively,which are higher than that of the deposited sample,The results show that the content of Schmitt factor in the weld center area is higher than that in the weld fusion line area.Under the external load,the structure of the weld center area changes first,and the structure of the weld fusion line area changes later.For the whole welded joint,the distribution of Schmitt factor is different in different regions of weld structure with different base metal crystal orientation difference.The higher the content of Schmitt factor,the greater the deformation degree of the structure,which determines the fracture position of the welded joint.The fracture positions of the welded joint with 0°、45° and 90° orientation difference are respectively the weld area,the base metal area,the weld area,and the content characteristics of Schmitt factor The deformation coordination ability,deformation uniformity and plastic deformation ability of(0 °、 45 ° and 90 °)orientation difference weld all increased first and then decreased,and 90° orientation difference weld showed the worst performance in all performance indexes.After the tensile strength test,the fracture location of the welded joint after the pre weld heat treatment and post weld heat treatment is in the weld area.The deformation of the tensile specimen after heat treatment before fracture is about 50% of that of the deposited specimen.