Study On The Manufacture Of Nickel-based Superalloy Gradient Materials By Laser Additive Manufacturing And Its Heat Treatment Process

Among the 100 major projects and projects to be implemented in the "Thirteenth FiveYear Plan",aero engines and gas turbines are listed as the first place,which shows that it plays an important role in the development of national strategic industries and national defense security construction.Low fuel consumption,low noise,and high thrust-to-weight ratio are important indicators for the performance of advanced aero engines in the future.For this reason,the development of high structural efficiency and light weight dual-alloy leaf disc structure is the main development trend at present.Laser additive manufacturing technology has a series of characteristics such as short processing cycle,high precision in forming dimensions,and environmental protection.In the experiment,a laser preset powder layer melting forming process(L-PLM)was used to prepare samples.The temperature field and thermal behavior of the molten pool during the laser forming process have important effects on the microstructure and comprehensive mechanical properties of the formed material.Therefore,the simulation of the temperature field and the microstructure and properties of the laser melt-formed nickelbased superalloys have great research significance and practical value for the subsequent heat treatment.In this paper,a combination of simulation and experiment is used to study the temperature field and related thermal behavior of the nickel-based superalloy during laser melting of the laser powder powder by using COMSOL Multiphysics 5.4 finite element software.OM,XRD,SEM,TEM,micro hardness test,universal material testing machine,etc.were used to characterize the structure,crystal structure,phase composition,hardness,and tensile properties of L-PLM formed gradient component samples.The hot-rolled GH4169 substrate and the ascast K417G substrate are used to simulate turbine disks and blades.The feasibility of forming the overall blade disk structure on the basis of the original turbine disks and blades is explored.In order to further use laser additive manufacturing K417G/GH4169 nickel-based superalloy gradient transition lays the foundation for the turbine disc and the blade.The research results show that the temperature field simulation during the laser melting forming process shows that the initial stage,the molten pool is small,the cooling rate is about 2.6 × 103 K/s,and the temperature gradient is about 4.8 × 105 K/m.Large,as the forming layer increases,the molten pool expands,the cooling rate in the molten pool decreases,and the temperature gradient decreases.The cooling rate of the last layer is about 1.3 × 103 K/s,and the temperature gradient of the molten pool is 2.9 × 105 K/m.Generally speaking,with the increase of the forming layer,the heat transfer effect on the surface of the sample is enhanced,but the overall heat dissipation direction has not changed,mainly from the top to the bottom,and the heat is radiated from the molten pool to the base in one direction.feature.The microstructure of the forming material is mainly columnar crystals,and local equiaxed crystals are generated.Three gradient composition materials are set,namely,the raw material powder contains 30%,50%and 70%of K417G(the remaining components are GH4169).The materials prepared by the laser preset powder layer melting forming are named M30,M50 and M70,respectively.The matrix of M30 gradient component material is nickel-based austenite ? phase,and the precipitates are Laves phase and a small amount of MC carbide.Laves phase began to disappear in M50 and M70 gradient composition materials,and y' precipitation strengthening phase appeared between dendrites.Due to the higher cooling rate and temperature gradient,the?' phase is mainly coherently precipitated in the shape of nano-sized spherical particles.The mechanical properties of three gradient composition materials were tested.From M30,M50 to M70 materials,the micro hardness gradually increased,from about 184 HV0.2 to 352 HV0.2,and the yield and tensile strength gradually increased.After increasing,it decreases,and the elongation of M50 material reaches a maximum of 37.2%.The heat treatment uses a hightemperature homogenizing material with a temperature of 1220? for 1 h for better homogenization and higher solid solution.M70,M50 and M30 three gradient component materials are respectively formed on the two substrates.The causes of crack formation on the joints of K417G casting plate were analyzed.It is thought that the ? and ?' eutectic phases between the heated dendrites of the K417G substrate liquefy to form crack sources,and propagate in the form of solidified cracks in the forming layer.The formation of a grown grain layer at the junction of the sample prepared on the hot-rolled GH4169 substrate is discussed.The coarsened grain layer is mainly due to the small size of the original hot-rolled structure and the heat input of the laser Under the continuous growth,a grown grain layer is formed,and the thickness of the grown grain layer is related to the energy density of the laser on the substrate.The laser scanning speed has the greatest effect on the thickness of the grain growth layer.