First-principles Study On The Interface Of Selective Laser Melting Forming（TiC,TiB₂）/316L Stainless Steel Composite

316L stainless steel is a widely used structural material.Due to its good plasticity,wear resistance,weldability,corrosion resistance and biocompatibility,316L stainless steel is largely used in aerospace,biomedical and petrochemical fields.A single alloy is difficult to meet the needs of extreme environments such as high strength and high temperature.In this study,selective laser melting（SLM）was used to form ceramic particles（TiC,TiB₂）reinforced 316L stainless steel composites,exploring the microstructure and morphology characteristics,crystal phase relationship and interface bonding strength between ceramic particles and the 316L stainless steel matrix.Based on the experimental results,the interface bonding strength between TiC,TiB₂ andγ-Fe in 316L matrix（TiC/γ-Fe,TiB₂/γ-Fe）and the interface stability between TiC,TiB₂ and alloying element doping model were simulated by first principle calculations,and the heterogeneous nucleation was analyzed.The main research contents and conclusions are as follows:（1）The ball milling process of SLM forming（TiC,TiB₂）/316L stainless steel composite powder was studied,and 316L stainless steel composite material with uniform ceramic particle distribution was prepared.When the ball-to-material ratio is 8:1,the ball milling speed is 240r/min,and the ball milling time is 4h,the stainless steel composite powder with good sphericity and uniform distribution can be obtained and（TiC,TiB₂）/316L stainless steel composite was formed by SLM.（2）The interfacial bonding strength between TiC and 316L stainless steel,alloying elements（Cr,Mn,Mo,Ni,Si）in 316L stainless steel doped withγ-Fe and TiC were studied.The interfacial adhesion work,interfacial energy,bond length,interlayer distance,charge density and density of states of the interface structure were calculated,and the heterogeneous nucleation of TiC/γ-Fe interface was analyzed.The results show that the TiC（001）/γ-Fe（001）interface model has a smaller mismatch and the highest interface bonding strength.Among them,the Fe-on-Ti center interface structure has the largest interface adhesion work,the smallest interfacial distance,and the smallest interface energy.The Fe and C atoms at the interface have obvious charge transfer and orbital hybridization,forming a stable Fe-C covalent bond.At the same time,Cr,Mn,Mo,Ni and Si are easy to replace the Fe atoms at the interface in the doping system,and it is found that Cr4,Mn4,Mo4,Ni1 and Si1 doping models are more conducive to improving the bonding strength of the interface.It indicates that TiC can be used as an effective heterogeneous nucleation substrate forγ-Fe.（3）The interfacial bonding strength between TiB₂ and 316L stainless steel,alloying elements（Cr,Mn,Mo,Ni,Si）in 316L stainless steel doped withγ-Fe and TiB₂ were studied.The interface bonding work,interface energy,bond length,interlayer distance,charge density,density of states of the interface structure were calculated,and the heterogeneous nucleation of TiB₂/γ-Fe interface was analyzed.The study found that the TiB₂（0001）/γ-Fe（111）interface model has the smallest mismatch and the highest interface bonding strength.The B-HCP interface structure has the largest interface bonding work and the smallest interfacial spacing.The charge exchange and orbital hybridization between the Fe atoms and B atoms at the interface are obvious,and a large number of stable Fe-B covalent bonds are formed,which is conducive to the enhancement of interface stability.The tensile test showed that the interface between TiB₂ andγ-Fe and the inside of TiB₂ are not easy to fracture,and the bonding strength at the interface is higher.In the doped atom system,in addition to doping Mn and Si atoms,the interface models doped with Cr,Mo,and Ni are all conducive to improving the interface stability,which indicates that TiB₂ can be used as an effective heterogeneous nucleation substrate ofγ-Fe.In this paper,the interfacial bonding strength between TiC,TiB₂ and 316L stainless steel were studied in detail from the perspective of first principle calculations,and the interfacial bonding mechanism was revealed,which laid a solid foundation for the preparation of high-performance 316L stainless steel matrix composites.