| Aero-engine plays a key role in aircraft,while the turbine disk and blade are core components of aero-engine.The service condition of the turbine disk and blade are distinctly different,and the working temperature of the blade is much higher than that of the turbine disk.The blisk made of two kinds of superalloys can not only meet the requirements of different performances of disk and blade,but also has the advantages of weight reduction,efficiency enhancement and high reliability.It has become the preferred structure of the new generation of high thrust-weight ratio aero-engine.Traditionally,the blisk can be manufactured by high speed cutting,electrochemical machining and linear friction welding.Laser melting deposition(LMD)is a new additive manufacturing technology.Compared to the conventional processes,LMD has shorter processing cycle and higher dimensional accuracy.In recent years,combining the technology of laser melting deposition with the concept of functionally gradient material(FGM)has been proposed,and this will not only make sure the excellent performance of deposited components,but also release the thermal stress concentration between different materials.Therefore,LMD technique provides a new way to form the graded structure of the blisk.In this paper,the laser power,scanning speed,overlap ratio,hatch distance and some main process parameters were used as variables and optimized according to their effect on the morphology of cladding layers.GH4169/K417G gradient composition material was formed under the best process parameters.The optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD)differential scanning calorimetry(DSC)were used in order to evaluate the microstructure and phase composition of the deposited layer.The tensile property and hardness of the deposited layer was tested by the electronic universal testing machine and Vickers hardness tester.The results show that the optimum process parameters for laser forming are laser power 600 W,powder feeding speed 5 g/min,scanning speed 5.4 mm/s,powder gas flow 3.5 L/min,overlap rate 40%and hatch distance 0.4mm.With optimized process parameters,a compact structure with no macro defects can be obtained,the thin wall structure obtained is a columnar crystal that tends to extend continuously through multiple layers along the depositional height.The microstructure of the bulk material is interlaced with different orientation columnar crystals in the layer and the coarse equiaxed grains.Set five gradient materials,containing 100%,75%,50%,25%and 0%of GH4169 in the raw powder.Materials prepared by laser melting deposition were named M100,M75,M50,M25 and M0,respectively.M100,M75,M50 Gradient layer matrix is nickel-based austenite ?-phase,precipitates are Laves phase and MC carbide,however,with GH4169 composition decreased Laves phase segregation to reduce.When the Laves phase of M25 and MO gradient components disappear,dendrites appeared between the y' precipitation strengthening phase and y+y'eutectic.Cracking of pure K417G gradient material during laser melting and deposition forming was studied.Found that the first solidification process formed? matrices,follow-up due to the formation of partial melting of low-melting point?+?' eutectic,in the process of laser forming,the eutectic structure melts and forms liquefied cracks,and then expands along the columnar grain boundaries to form macroscopic cracks finally.The five gradient layer materials hardness and thermal expansion coefficient of two physical performance tests,from M100,M75,M50,M25 to M0 material,microhardness gradually increased,Rising from 220 HV0.2 to 430 HV0.2,different gradient materials thermal expansion coefficient is close.The mechanical properties of each gradient layer material testing,test results show,from M100 to M25,the yield strength and tensile strength gradually increase,the elongation decreases,and the strength along the deposition direction is the highest,and the performance of scanning and lap direction are close.After laser remelting,the surface quality is improved and the microstructure is refined and transformed from columnar crystals into equiaxed grains.The segregation of elements in the interdendritic grains is alleviated.The hardness of each graded material is enhanced compared with that in the as-deposited state.The yield and tensile strength the intensity exceeds the deposition direction of the scanning direction and close to the deposition direction,but the elongation decreased,the overall performance of the performance. |
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