Process Optimization And Interfacial Control Of Selective Laser Melting Forming CuCrZr Alloy For 316L Stainless Steel Matrix

Complex parts in aerospace,mold and other fields often have complex structures locally,while other parts are simple structures with regular geometric characteristics,and the existing overall metal directly additive manufacturing technology is difficult to balance high efficiency and low cost,which restricts its promotion and application.The hybrid manufacturing technology based on the combination of traditional manufacturing and additive manufacturing is an effective way to solve the above bottleneck problem.Selective laser melting(SLM)is a kind of additive manufacturing technology for directly forming metal parts,which realizes the personalized customization and high quality forming of metal parts.Copper alloy radiator has some problems such as bulky structure design and long SLM process time.Based on this,this paper proposes the hybrid manufacturing scheme between traditional processing and additive manufacturing for steel instead of copper for basic load-bearing structures,and carries out the research on the SLM hybrid manufacturing technology of steel copper heterogeneous structure.The main research contents are as follows:(1)The effect of laser power and scanning speed on the surface morphology of the single track was investigated,and the forming process parameter intervals for CuCrZr alloys were preliminary determined.The effect of different scanning strategies on the relative density of CuCrZr alloy were investigated.Based on the above research results,the response surface method was used to optimize the relative density of CuCrZr alloy,and the mathematical model between the process parameters and the relative density was established.The optimal SLM process parameters were obtained,and the relative density of CuCrZr alloy was reached 99.57%.The microstructure of the CuCrZr samples consists of irregular columnar grains growing along the forming direction,and there is a preferred orientation of <110> grains parallel to the processing direction.(2)The effects of different heat treatment on the microstructure and mechanical properties of CuCrZr alloys fabricated by SLM were systematically studied.The strengthening mechanism of CuCrZr alloys by heat treatment was analyzed,and the effects of different strengthening mechanisms on mechanical properties were explored.With the increase of solution temperature,the number of particles dissolved into the matrix grains increases,and the precipitated phase inside the grains decreases obviously,but the precipitated phase at the grain boundary increases slightly.When the solution temperature reached 950℃,almost no precipitated phase was observed in the sample.After solution +aging treatment and aging treatment,the quantity of nanoscale precipitated phase was significantly increased,and the mechanical properties were improved.The direct ageing treatment can significantly improve the mechanical properties of the alloy.The tensile strength and hardness of the samples reached 569.7MPa and 160 HV at 470℃ with a holding time of 60 min.(3)The mechanism of element diffusion and metallurgical bonding at the 316L-CuCrZr interface was investigated.The strength of the 316L-CuCrZr interface was improved by using different processing processes to regulate the interface properties including the substrate surface state,substrate preheating temperature,number of remelting times,interface initial layer process parameters and heat treatment.Cracks and pores are the main defects at the interface.With the decrease of the surface roughness of the substrate,the macroscopic defects at the interface decrease.The interfacial remelting process and the increase of substrate temperature will degrade the performance of CuCrZr and lead to the fracture of 316L-CuCrZr samples on the copper side.The interfacial strength of 316L-CuCrZr is comparable to that of CuCrZr alloys by changing the interfacial process parameters of the initial layer.Heat treatment can significantly improve the interfacial tensile strength.Convection and element diffusion occurred in the 316L-CuCrZr interface under the action of Marangoni convection,which is conducive to improving the bonding strength of the interface.Due to metastable miscibility gap in Cu-Fe system,primary and secondary separation of the liquid phase occurs,forming two different forms of liquid phase present as spheres and matrix.(4)The effect of IN718 alloy transition layer on the microstructure,phase composition,and mechanical properties of 316L-CuCrZr interface was studied.The steel and nickel have good suitability and bonding compatibility,and the IN718-316L interface is free of defects such as pores and cracks,achieving a good metallurgical bond.The width of the interfacial fusion region is about 500 μm,and the interface is mainly composed of fine Fe-Ni-based dendrites,which are perpendicular to the boundary of the molten pool and extend to the center of the molten pool.IN718-CuCrZr samples have round keyholes and smaller pores at the interface and copper side.In the solidification process,IN718 preferred to solidify in the shape of fine particles,which provided nucleation points for copper grains.Due to the high cooling rate at the interface,equiaxed grains were formed.There are no macroscopic defects such as pores and cracks in the binding position of 316L-IN718-CuCrZr samples,and the elements at the interface have sufficient mutual diffusion.The interfacial tensile strength of the 316L-IN718-CuCrZr samples reached 403 MPa.The addition of the transition layer significantly improved the interfacial strength,which realized the hybrid manufacturing without reducing the properties of the two materials.