| Leaf discs and blades are the main components of the aero engine and play an important role in the performance of the engine.Compared with the traditional leaf disc,the overall leaf disc has the advantages of light weight.simple structure and high aerodynamic efficiency,which has become a mandatory structure for the high thrust-to-weight ratio engine.Due to the low cost and short cycle of the additive manufacturing technology,it is suitable for the direct near-final forming of complex parts,and can realize the preparation of the double alloy whole leaf disc.According to the different service performance requirements of the leaf disc and the blade,different materials are used to prepare the whole leaf disk.The transition zone between the two materials of the leaf disc and the blade requires uniform and smooth transition of the tissue properties to achieve the service performance of the overall leaf disc.In this paper,the micro structure and properties of the transition zone composition of the nickel-based alloy and the corresponding composition of the laser melt deposition were studied.This experiment designed three transition components intended to be used to prepare transition zone materials that connect GH4169(lea disc material)and K465(blade material)in the mintegral leaf disc.The bulk samples of these three components were prepared by laser melting deposition.The transition components were calculated according to the gradient of 25%of the original components of the leaf disc and the original components of the leaves,named M25,M50 and M75.The K465 material and the GH4169 material prepared by laser melting deposition were named M0 and M100,respectively.Laser melting deposition prepared two sample gradient samples from M50 to M75 and M75 to M100 were named T1 and T2.respectively.Through macroscopic analysis and metallographic characterization,the process parameters were successfully optimized to be laser power 1800w,scanning speed 8 mm/s.and lap rate 45%.Under the optimized parameters,the density of the prepared transition zone material is about 94.71%～98.31%,and the density of the sample increases gradually with the decrease of the proportion of elements such as Al and Ti.Macroscopic cracking(10～90 μm)on the surface of K465 material(M0)prepared by laser melting deposition is poor.The formation of laser melting deposition is poor.By adding a small amount(～15%)of GH4169 alloy powder.the percentage of elements such as Al and Ti can be reduced.The crack of the sam,ple is effectively controlled.The phase analysis of the samples by XRD,SEM and EDS showed that the phase composition mainly consisted of the fragile phase Laves phase,the carbide and the reinforcing phase γ’ phase.In the M0 and M25 samples,the main elements γ’ were composed of a large content of Al and Ti,and precipitation of γ’ was observed.In other samples,the Laves phase occupied a large amount of γ’ constituent elements,and due to rapid solidification by laser melting deposition,no γ’ phase precipitated.The micro structure of the nickel-based alloy prepared by laser melting deposition is mainly composed of dendrites and equiaxed crystals,and there is a "leucorrhea" between the deposited layers due to remelting.The growth direction of dendrites has a tendency to deflect horizontally with the increase of the sedimentary layer.The angle between the dendrites at the bottom and the deposition direction is 12°,and the angle between the dendrites near the top region and the deposition direction is 47°.Due to the rapid cooling in the 5 mm height region from the top of the sample,the structure is mainly composed of equiaxed crystals.When the orientation was studied by EBSD.the micro structure of the sample was found to be disordered,and the large-angle grain boundaries were significantly more than the small-angle grain boundaries.The dendritic spacing of M0,M25,M50,M75 and M100 samples prepared by laser melting deposition is usually about 10 μm.With the increase of the proportion of GH4169 alloy powder in the designed transitional component powder,the dendrite spacing has a tendency to increase gradually.10.67～12.57 μm).The micro hardness of M0,M25,M50,M75 and M100 samples showed that the micro hardness decreased with the increase of the proportion of GH4169 alloy powder in the designed transition zone powder(M0 hardness 441 HV,M100 hardness 277 HV).The tensile strength and yield strength tend to increase gradually(the laser melt deposition M100 sample has the highest tensile strength of 768.56 MPa and the M25 tensile strength of 717.54 MPa).By comprehensively analyzing the micro structure and properties of the material,the comprehensive properties of M75(the tensile strength is 736.47 MPa and the elongation is 42%)is the most excellent.The tensile strength,yield strength and elongation of the two component gradient samples T1 and T2 were 744 MPa,395 MPa and 42.31%and 685 MPa.392 MPa and 37.54%,respectively.Heat treatment of T1 with better comprehensive performance,in the optimization process is solid solution+double aging:980 ℃.1 h/air cooling+720℃,8 h/furnace cooling(cooling rate 55℃/h)to 620℃,8 h/air cooling Under the conditions.the Laves phase in the micro structure of the T1 sample was significantly reduced,and the enhancement phase γ’ was significantly increased.The micro hardness increased from 246.48 HV to 434.38 HV,which increased by nearly 50%.The tensile strength and yield strength were 974.09 MPa and 702.10 MPa,respectively,which were 31%and 79%higher than those without heat treatment.The elongation was improved by 3 1%and 79%,respectively.42.31%was reduced to 22.5%,but still meet the performance requirements of the transition zone.Good comprehensive mechanical properties were obtained by laser melting and post-heat treatment. |
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