Microstructure And Properties Analysis Of CoCrFeNiTi/Si High Entropy Alloy By Additive Manufacturing

Metal materials are irreplaceable in some key components such as hulls,offshore oil platforms,and submarine pipeline facilities.In practical applications,metal materials are often faced with the challenge of complex environmental impacts.Corrosion and wear are the most common failure modes.Therefore,strengthening the metal surface and developing new high-performance materials are of great significance for improving the surface protection ability of marine steel structure materials and prolonging their service life in harsh environments such as corrosion and wear.In this paper,CoCrFeNiTi and CoCrFeNiTiSi high-entropy alloy coatings and CoCrFeNiTi Si high-entropy alloy blocks were prepared by laser cladding technology.For the high-entropy alloy coating,the effects of Si element on the macroscopic morphology,microstructure,corrosion resistance and wear resistance of CoCrFeNiTi high-entropy alloy were investigated.For the bulk alloy,the corrosion resistance and wear resistance of the alloy in different parts of the printing process were investigated,and the corrosion resistance and friction mechanism were revealed.The main conclusions of this paper are as follows:（1）After adding Si element to CoCrFeNiTi alloy system,the grain morphology of the coating is transformed from large equiaxed crystal to fine equiaxed crystal.The phase composition is composed of a solid solution phase with a single FCC lattice transformed into a mixed solid solution phase of FCC+BCC lattice and a small amount of CoSi₂ phase.The average grain size of the coating decreased from 34.37μm to 3.55μm after adding Si element,indicating that the addition of Si element is beneficial to grain refinement.The CoCrFeNiTi Si high entropy alloy block is mainly composed of solid solution phase with FCC+BCC lattice,and the increase of alloy thickness does not change its phase composition.The interdendritic region is rich in Fe,Crand Ti,while the dendritic region is rich in Co,Niand Si.（2）In 3.5 wt.%NaCl solution,the corrosion current densities of 316L stainless steel substrate,CoCrFeNiTi and CoCrFeNiTi Si high-entropy alloy coatings are 0.56×10^-6,0.35×10^-6 and 0.18×10^-6 A/cm²,respectively,indicating that CoCrFeNiTi Si coating has the best corrosion resistance.For CoCrFeNiTi Si bulk alloy,the current densities of the top,middle and bottom alloys are 1.73×10^-7,0.80×10^-7 and 0.96×10^-7 A/cm²,respectively,indicating that the middle alloy surface has better corrosion resistance.The passivation film formed on the surface of CoCrFeNiTi coating has higher Fe₂O₃ content,while the passivation film formed on the surface of CoCrFeNiTi Si coating has higher Cr₂O₃,Cr（OH）₃,FeO and Ti O₂ content.Among them,the higher Cr₂O₃ content will form a dense oxide film on the surface of the alloy,which can effectively improve the corrosion resistance.（3）The average hardness of 316 L stainless steel substrate,CoCrFeNiTi and CoCrFeNiTi Si coatings are 220 HV_0.2,550 HV_0.2 and 650 HV_0.2,respectively.The hardness of the two coatings is 2.50 times and 2.95 times that of the substrate,respectively.At room temperature,the main wear mechanisms of the matrix are typical abrasive wear,oxidation wear and plastic deformation.The main wear mechanism of CoCrFeNiTi coating is abrasive wear.The CoCrFeNiTi Si coating has the best wear resistance,and its main wear mechanism is slight abrasive wear.For bulk alloys,the average hardness of the upper,middle and bottom alloys is1200 HV_0.2,1236.4 HV_0.2 and 1342.6 HV_0.2,respectively.The main wear mechanisms of the top alloy are abrasive wear and delamination wear,accompanied by oxidation wear.The wear mechanism of the middle alloy is abrasive wear and fatigue wear during dry sliding.The wear mechanism of the bottom alloy is adhesive wear and abrasive wear.