Investigation On Microstructure And Corrosion Resistance Of CoCrFeNiTiMo High Entropy Alloy Coating

Erosion and cavitation are common causes of hydro-mechanical damage to over-current components in the marine environment.The damage caused by the corrosion of material is far more than the material itself,but also includes major accidents and casualties caused by the destruction of important metal components,and there is a huge potential safety hazard.The use of advanced surface modification technology to prepare a kind of new material coating with excellent corrosion resistance on the surface of the flow-passing component can not only improve their service life but also save costs,which has profound theoretical significance and great practical significance.In this paper,the theoretical calculation of the phase composition of the CoCrFeNiTiMo high-entropy alloy is carried out.The results show that the high-entropy alloy is dominated by the FCC phase.Then,the double-cathode plasma sputtering deposition technique is used to prepare a kind of 10μm thick CoCrFeNiTiMo high entropy alloy coating on Ti-6Al-4V.XRD,SEM and TEM were used to study the microstructure and phase structure of the coating.The coating was composed of FCC high entropy phases and（CoCrFeNi）₂（Ti Mo）₃ compounds.Nanoindentation,Vikers indentation and scratch instruments were used to study the hardness,elastic modulus,toughness and binding force of the coating.The hardness and elastic modulus of the coating reached 12.37±0.21 GPa and 179.25±2.13 GPa respectively.The substrate is 2.2 times and 1.5 times,and has strong resistance to plastic deformation and high indentation toughness;the bonding force between the coating and the substrate is 70N,which meets the requirements of engineering applications.AFM and contact angle measuring instruments were used to study the surface morphology and hydrophilic/hydrophobic characteristics of the coating.The results showed that the coating surface was flat and hydrophobic.The erosion corrosion tests and cavitation corrosion tests were carried out in 3.5wt.%NaCl+10wt.% quartz sand and 3.5wt% NaCl solution respectively.The erosion and cavitation performance of the high entropy alloy coating and substrates in the solution were studied by using a variety of electrochemical testing techniques（time current response,open circuit potential,potentiodynamic polarization,electrochemical impedance,low frequency impedance,zero charge potential）,weightless methods and SEM.The results show that the corrosion resistance and cavitation resistance of CoCrFeNiTiMo high entropy coating are significantly improved compared with those of Ti-6Al-4V alloy because of its high hardness,strong ability to repair passive film and ability to repel chloride ions.XPS results show that the passive film of CoCrFeNiTiMo high entropy coating in 3.5wt% Na Cl solution is mainly composed of CO,Cr,Fe,Ni,Ti and Mo oxides（Co₃O₄,Cr₂O₃,Fe₂O₃,TiO₂,MoO₃）and hydroxides（Cr（OH）₃,Ni（OH）₂）.