The Research Of Selective Laser Melting Forming GH4099 Artifact

GH4099 alloy is widely used in combustion chambers,stiffeners and other components of aeroengines due to its excellent comprehensive mechanical properties.In recent years,in order to meet the complex structural requirements of aerospace components,additive manufacturing of GH4099 alloy has attracted more and more attention.However,there is no additive manufacturing method for precise and complex components of GH4099 alloy.In this paper,the laser metal direct forming and selective laser melting forming process of GH4099alloy were studied,and the microstructure and mechanical properties of the alloy were analyzed.On this basis,the production of GH4099 alloy high-low temperature connectors was completed.The main research results of this paper are as follows:（1）The optimal process of laser metal direct forming GH4099 alloy is obtained:laser power is 800～1000 W,spot diameter is 2.8 mm,scanning rate is 6 mm/s,powder feeding rate is 16±0.5 g/min,overlap ratio between channels is 30%,that is,channel spacing is1.6～1.8 mm,layer thickness is 1.3 mm.The microstructure of GH4099 sample prepared by laser direct forming process is fish scale structure.The epitaxial growth of columnar dendrite is parallel to the deposition direction,and there is a clear boundary between layers.The channels in the same layer intersect,and the adjacent channels overlap with each other.There is a banded structure with white stripes,which corresponds to the bottom position of the laser molten pool in the forming process.When the laser power is small,the internal Vickers hardness of the formed sample is 290.0 HV_0.1,which is higher than that at the edge of 270HV_0.1.With the increase of laser power,the difference in Vickers hardness between the internal and the edge of the formed sample decreases,which is close to 300 HV_0.1.（2）The optimal process of selective laser melting forming GH4099 alloy was obtained:the thickness of powder coating was 40μm,the laser power was set to 285 W,the scanning rate was set to 960 mm/s,the scanning spacing was 110μm,the laser spot diameter was 80μm,and the deflection between each laser scanning path was set to 67°.The width of the micro-channel formed in the laser scanning path is similar to the diameter of the laser spot,and the micro-channels are overlapped and connected to each other to form a dense structure without obvious defects such as unmelting.In the direction of laser deposition,the micro-melting pool is stacked in fish-scale layers,and partial remelting occurs in the process of laser cyclic deposition.The dendrite orientation changes greatly in the process of through-layer growth,forming obvious lamellar structure.In the layer-by-layer deposition process of selective laser melting forming,there is no transfer of alloying elements in the deposition direction,and the distribution of alloying elements in the sample matrix is uniform.With the increase of deposition height,the microhardness gradually decreases,and tends to be stable at1.5 cm height.The hardness values on X-Y and X-Z surfaces are similar,both of which are about 330 HV_0.1.After solution treatment at 1110°C for 0.5 h,the band structure and intracrystalline dendrite sub-structure of the deposited GH4099 alloy disappeared.With the increase of solution time to 2 h,complete recrystallization occurred,the segregation at grain boundary was eliminated,and a large number of twin structures were formed in the grain.The tensile strength of the specimen bar in the horizontal direction is 1080.0 MPa,which is greater than 905.5 MPa in the deposition direction,but the yield strength in the deposition direction is756.4 MPa,higher than 654.3 MPa in the horizontal direction,and the ratio of yield strength to tensile strength is larger.Vertical and horizontal strength and toughness meet the traditional forging standards.（3）In order to meet the accuracy requirements of high-low temperature connector for aircraft,the workpiece is manufactured by selective laser melting.Firstly,the support structure is added at the main force position of the workpiece to reduce the deformation of the workpiece.The offset of 3 mm is added at the outer edge of the numerical model to assist machining to improve the dimensional accuracy of the workpiece.Then,the GH4099 alloy workpiece was fabricated by SLM technology,and the solution treatment was carried out at1160°C for 1 h.The tensile strength reached more than 1000 MPa,and the section shrinkage was higher than 30%.The strength of the alloy reached the design requirements.After subsequent heat treatment,the workpiece is separated from the substrate,which can significantly reduce the failure probability of the workpiece in the forming process.For the damaged area,surfacing repair can also be carried out after adding tooling,and the forming accuracy of the workpiece is not affected after high temperature calibration.Finally,the high-low temperature connectors meeting the accuracy requirements were obtained.