Study On The Process,Microstructure And Properties Of 316L Stainless Steel/(Copper,Nickel,Tungsten) Multi-material Fabricated By Selective Laser Melting

Multi-material integrates the excellent performance of multiple single metal materials to realize the special functions of components,which can greatly improve the flexibility of design and manufacturing,and is widely used in aerospace,defense,chemical and automotive fields.However,the traditional forming method is difficult to meet the requirements of the structure complexity of the multi-material component and the degree of design freedom.Selective laser melting(SLM)technology,as a metal additive manufacturing method that has attracted much attention in recent years,has advantages in forming complex structures and multiple materials.Based on this,this article takes 316L SS stainless steel alloy and CuSn10 tin bronze alloy,Inconel 718 nickel-based alloy,and pure tungsten as the research objects,and carries out the SLM multi-material combination of"steel/copper","steel/nickel",and"steel/tungsten"forming experiments,exploring the effects of SLM process parameters optimization for 316L/CuSn10,316L/Inconel 718,and heat treatment for 316L/W multi-material on interface metallurgical defect initiation and expansion,transition element and phase diffusion,microstructure texture evolution,intermetallic compound formation,tensile strength and shear strength values,etc.and its internal mechanism.The specific research content and conclusions are as follows:(1)The 316L/CuSn10 sample with good interface bonding was formed by optimizing the process parameters.According to the element and phase distribution,the interface of the multi-material sample can be divided into three typical regions:316L zone,interface fusion zone and CuSn10 zone.The tensile strengths of the 316L/CuSn10 specimens formed by the horizontal and vertical bonding of the two materials are 617.9±43.4 MPa and 418.9±13.5MPa,respectively,which are higher than the 392.7±20.4 MPa of the single CuSn10 tensile specimen.The average shear strength of 316L/CuSn10 sample is 210 MPa,which is better than spark plasma sintering,rolling and other forming processes.The high interfacial bonding strength of 316L/CuSn10 multi-material benefits from the solid solution and diffusion effects of Fe and Cu to form a good metallurgical bond fusion zone,and the fusion zone is heated by the heat-affected zone and the grain refinement effect caused by remelting and recrystallization.(2)Optimizing the process parameters to form a 316L/Inconel 718 sample with good interface bonding,the interface of the multi-material sample can be divided into three typical areas:316L zone,interface fusion zone,and Inconel 718 zone.The width of the interface fusion zone is about 150?m,and the structure is mainly Laves phase and??phase and?phase precipitates dispersed in the columnar crystal area.At the same time,there is an obvious grain coarsening zone in the Inconel 718 zone,which has a strong<001>//Z(BD)orientation texture.The average tensile strength of the horizontally bonded 316L/Inconel 718specimens is 795.4±2.3 MPa.Compared with the single 316L(1007.5±21.3 MPa)and Inconel 718(986.2±33.5 MPa)alloy specimens,the average tensile strength is reduced by21.1%and 19.3%,respectively.The average shear strength of 316L/Inconel 718 is 449.5MPa,and the bonding strength is equivalent to forming processes such as argon arc welding and brazing.The higher interface bonding strength of 316L/Inconel 718 multi-material is due to the similarity of the main elements of 316L and Inconel 718 alloy,which can form a better metallurgical bonding zone,but the grain coarsening effect and the brittle Laves harmful phase produced in the bonding zone And the lack of??strengthened precipitates is an important reason that restricts the further improvement of interface bonding strength.(3)The optimized process parameters formed a 316L/W multi-material sample with good interface bonding.The multi-material sample was solution heat treated at 1200?for1 hour and then cooled in the furnace.The interface of 316L/W sample before and after heat treatment is divided into three typical areas:316L zone,interface fusion zone and W zone.SLM forming 316L/W multi-material is accompanied by the formation of Fe₇W₆and metastable Fe₂W phases,and heat treatment further introduces secondary Fe₂W,Fe₃W₃C and Fe₆W₆C phases.After heat treatment,the microhardness value of the bonding area of the sample is 661.4±6.1 HV₃,which is an increase of nearly 22%compared with 543.4±3.7 HV₃before heat treatment.At the same time,the elongation at break increased from 2.5%to23.0%.The tensile strength of the samples before and after heat treatment did not change significantly,and they were 245 MPa and 257 MPa,respectively.The increase in hardness is due to the precipitation of more brittle and hard secondary Fe₂W,Fe₃W₃C,Fe₆W₆ phase particles after heat treatment,introducing more nucleation sites and fine-grain strengthening effects while limiting the slip of dislocations,thereby achieving the effect of dispersion precipitation strengthening.However,the dispersed Fe₂W phase and its replacement solid solution phase Fe₆W₆C hinder dislocation slippage and the irregular block Fe₇W₆ phase further causes dislocation blockage and weakens the tensile strength.Based on the above research results,SLM forming 316L and CuSn10,Inconel 718,W multi-materials need to meet the characteristics of large lattice matching,large solid solubility,small thermal expansion coefficient difference,and not easy to generate intermetallic compounds.This research explores and clarifies the possibility,difficulty,internal mechanism and improvement methods of combining steel and copper,nickel,tungsten and other alloys or metals into multiple materials,and provides factual and theoretical guidance for the development,application and expansion of SLM forming multiple materials.