Research On Microstructure And Properties Of Ceramic Particles Reinforced Steel-based Composites By Laser Cladding Additive Manufacturing

The key to the lightweight design of the structure is to increase stiffness and reduce density.High structural stiffness and lightweight design are often not available at the same time,which is the main bottleneck restricting the development of lightweight structure.Current research shows that ceramic particle reinforced metal matrix composites are an effective means to solve the dual contradiction between high structural rigidity and lightweight.Laser cladding additive manufacturing has a short production cycle and is suitable for components with more complex shapes.It can freely design the volume fraction of the reinforcement,the geometric dimensions of the deposited parts and the microstructure properties.It has unique advantages in the preparation of ceramic particle reinforced composites.This article uses laser cladding additive manufacturing to prepare TiB₂ particle reinforced steel matrix composites,explores the internal relationship between the laser cladding process,TiB₂ particle reinforced steel matrix composites structure and properties,and reveals its structure evolution law and performance response mechanism,provides theoretical basis and process reference for the preparation of high stiffness,lightweight ceramic particle reinforced metal matrix composites.In this paper,firstly,by means of low-energy ball milling,small irregular TiB₂ particles with a size of about 2?m are embedded on the surface of Fe-based powder.The final prepared composite powder consists of a steel matrix and fine TiB₂ particles embedded on the surface.meanwhile,because the composite powder maintains a spherical morphology,the composite powder still has good fluidity.Laser cladding additive manufacturing with coaxial powder feeding was used to successfully prepare TiB₂ reinforced 316L matrix composites with different contents.Through metallographic observation,its microstructure showed a cellular subcrystalline structure.The addition of TiB₂ resulted in the formation of a network-like reinforcing phase at the boundary of the cell structure.According to the results of XRD and TEM,it is judged that the matrix phase is?-austenite phase,and the phases on the grain boundary are(Fe,Cr)₂B and M₃B₂(M is Cr,Fe,Mo,Ni,Ti).Under the action of rapid laser cooling and multiple thermal cycles,the composite material exhibits an obvious preferred orientation.The elongated columnar sub-crystal grains grow along the direction of heat flow,and the structure of the top of the deposit is dendritic sub-crystals.With the addition of TiB₂increasing from 0wt%to 6wt%,the microhardness of the composite material increased from148HV to 186HV.Compared with 316L powder laser cladding additive manufacturing components,the addition of 3wt%and 6wt%TiB₂ increases the yield strength of the composite material by 22%and 29%,respectively,the tensile strength is slightly increased,and the elastic modulus is increased by 8%and 13%,but the elongation of the material decreased by 36%and47%,respectively.In order to explore the influence of alloying elements on TiB₂ particle reinforced steel matrix composites,TiB₂ reinforced 18Ni300 matrix composites with different contents were prepared by Laser cladding additive manufacturing with coaxial powder feeding.Observation of metallographic structure The morphology of the sample prepared by 18Ni300 powder is a cell structure.According to the element distribution and XRD results,there is a martensite structure within the cell,and the cell boundary is an austenite structure.After adding TiB₂,a reinforcing phase((Mo,Fe)₃B₂)is distributed at the boundary of the cell structure.The EBSD test results show that the grain size is mainly distributed in the range of 2.5-4.5?m,and high-density small-angle grain boundaries are found inside the three TiB₂ ratio materials,which indicates that there are a lot of substructures in the structure,and the existence of Twin structure.The non-uniform age hardening brought about by multiple thermal cycles makes the specimens prepared with 18Ni300 powder appear unevenly distributed in microhardness.The microhardness of 18Ni300 and the three additive samples with 3wt%and 6wt%TiB₂ are 354HV,371HV and 410HV,respectively.The high hardness of boride increases the microhardness of the composite material.The yield strength,modulus and elongation of the samples prepared with 18Ni300 powder are lower than that of forged 18Ni300,but the tensile strength reaches1134MPa.The addition of TiB₂ makes the yield strength and elastic modulus of the composite material increase significantly,and the plasticity becomes worse.Due to the 18Ni300 matrix's own characteristics,pore inclusions,reinforcement morphology,etc.,the plasticity of the material is poorer than that of 316L-based composites.In summary,this article uses the laser cladding additive manufacturing method to successfully prepare TiB₂-reinforced 316L-based and 18Ni300-based composite materials.The addition of the reinforcement phase is beneficial to improve the elastic modulus and yield strength of the material,provide certain theoretical support for the lightweight design of structural parts.