Study On Fabrication And Performance Of Nickel-based Alloy By Indirect Metal Additive Manufacturing

At present,metal additive manufacturing is one of the most widely used technology in additive manufacturing.However,because its method of fabrication is relying on laser to melt metal powder,there is excessively high cooling rate which causes huge residual stress to generate crack in metal part.It would critically impact and reduce the service life of metal part.Metal Fused Filament Fabrication（MF³）,as a technology based on Fused Filament Fabrication,provides a new method for metal additive manufacturing due to its method that fabricates metal part without melting and possibility of crack.The application and development of MF³are limited by the problems of difficulty to achieve high relative density and high performance simultaneously and asymmetric shrinkage along each direction.Herein,the process parameters of MF³based on Ni60 alloy as the research object were optimized.In order to solve above problems,this study proposed a printing method of optimizing,called pressing after printing per several layers or pressing per several layers,and fabricated metal part with low shrinkage rate,high relative density and high performance simultaneously through pressing per several layers.The influence of key parameters on the relative density of green part was investigated by orthogonal experiment and range analysis.Results of orthogonal experiment and range analysis illustrated that relative density of green part was the highest under the layer thickness of 0.1 mm,extrusion multiplier of 1.2 and overlap of 15%and pointed out the influence degree（from high to low）on the relative density of green part was extrusion multiplier,layer thickness and overlap.Study of influence of sintering time on the relative density of metal part illustrated that the relative density of metal part was the highest（95.68%）under sintering time of 3 h,and the shrinkage rate in each direction（X,Y and Z）was23.57%,23.04%and 29.03%,respectively.The results of influence of sintering time on the properties of the metal part showed the hardness increased from 537.51 HV_0.2to 564.21 HV_0.2（from 1 h to 2 h）and then decreased to 550.09 HV_0.2（to 3 h）with the extension of sintering time.Phase of metal part was not influenced by variation of sintering time.After sintering,phase of metal part was composed of nickel-based solid solution,its compounds,borides and carbides of CrBased on the optimization results of the above process,green part with pressing per 10 layers and pressing per 5 layers were fabricated,using the printing method of optimizing,pressing per several layers.Based on the optimal printing process parameters of above process,compared with the green part under no pressing,the relative density of the green parts prepared by pressing per 10 layers and pressing per 5layers was increased 94.46%and 96.03%,respectively,which demonstrated pressing per several layers could increase relative density of green part and relative density could be further improved by increasing the pressing frequency.It is found that the relative density of metal part could be further improved and shrinkage rate could be reduced by pressing per several layers.In particular,for pressing per 5 layers,the relative density of the metal part at sintering time of 2 h（96.57%）exceeded that of the metal part with no pressing at sintering time of 3 h（95.68%）,and the shrinkage rate in each direction（X,Y,Z）were19.24%,19.69%and 16.67%,respectively.By analyzing the micro-structure of the metal part under different pressing frequency,the compositions of phase of metal parts with no pressing,pressing per 10layers and pressing per 5 layers were the same,and the precipitation of hard phase increased with the increase of the pressing frequency.With the increase of hard phase,the micro-hardness and wear resistance of metal part could be effectively improved.The micro-hardness of pressing per10 layers and pressing per 5 layers were increased to 612.16 HV_0.2and640.42 HV_0.2,respectively,and the coefficient of friction decreased to0.59 and 0.49.Thus the problem of difficulty to achieve high relative density and high performance simultaneously could be solved effectively through pressing per several layers.High performance metal parts could be fabricated effectively by pressing per several layers each layer based on MF³technology.It could promote the application and development of MF³,and provides more options of application of fabricating high performance metal part using metal additive manufacturing.