Study On Preparation Of Ceramic Matrix Composite Coatings By Thermal Spraying And Its Properties

The increasing shortage of land resources has led countries around the world to gradually shift their attention to the marine environment.Marine equipment in the development of marine resources is accompanied by major challenges such as seawater corrosion and biological pollution.In addition,the military strategic significance of the ocean also requires low detectability of marine equipment.Therefore,the development of composite materials with anti-corrosion and electromagnetic wave absorption has important research significance and value.Ceramics have unique advantages in wear,high temperature,corrosion and other applications.To improve the performance of equipment in harsh environments and extend the service life of marine equipment,the preparation of ceramic coating coated on the surface of equipment by thermal spraying and vapor deposition has been widely studied.In this dissertation,based on Fe-Al spinel ceramic materials with both anti-corrosion and electromagnetic wave absorption,Cu/RGO composite powder was prepared by spray granulation and thermal reduction,and mixed with spinel in proportion.The influence mechanism of graphene and metal copper particles on the corrosion resistance and electromagnetic wave absorption of composite materials was studied by scanning electron microscopy,X-ray diffractometer,electrochemical workstation and vector network analyzer.With the purpose of obtaining spinel ceramic coatings with excellent corrosion resistance,the Al₂O₃/Fe₃O₄ and Al₂O₃/Fe₃O₄/Fe prepared by spray granulation technology and fused iron aluminum spinel were used as spray powder for plasma spraying.After thermal spraying with Al₂O₃/Fe₃O₄ composite powders,the phase composition of coatings prepared under different powers did not change significantly,mainly Al₂O₃ and Fe₃O₄.When the iron powders were introduced into the system,the part of Fe₃O₄ was transformed into iron,and a small amount of ferrous oxide was generated.Fused hercynite with Fe Al₂O₄ as the main phase was used as the raw material.After plasma spraying,the phase structure was still dominated by Fe Al₂O₄ spinel phase.Fused hercynite can successfully prepare spinel ceramic coating.The two kinds of spray granulation powder can not effectively generate ceramic coating with spinel phase after plasma spraying.The difficulty lies in the instability of ferrous oxide under high oxygen partial pressure.Single ceramic coating has the disadvantages of high density,poor toughness and more pores.In this study,on the basis of Fe-Al spinel ceramic coating,Cu/RGO composite powders were prepared by spray granulation,and a series of coatings were prepared by doping different proportions of Cu/RGO composite powders.With the increase of Cu/RGO composite powder ratio,the porosity of the coating decreases first and then increases.The porosity of the composite coating doped with 10 wt.%Cu/RGO composite powder is the lowest,only 1.2%.More composite powder doping increases the porosity of the coating,which makes the coating quality worse.The corrosion resistance of the coating in simulated seawater and sulphate-reducing bacteria（SRB）solution was studied by open circuit potential and potentiodynamic polarization curve.The composite coating has better corrosion resistance in SRB solution.Compared with the single spinel ceramic coating,the corrosion resistance of the composite coating was greatly improved under two kinds of corrosion medium.The corrosion resistance of the composite coating doped with 10wt.%Cu/RGO powder was the best.The long-term immersion test of the composite coating doped with 10wt.%Cu/RGO powder was carried out by electrochemical impedance spectroscopy.The immersion results show that the corrosion resistance of the composite coating is mainly physical shielding.The introduction of Cu/RGO can reduce the porosity of the coating and enhance the physical shielding performance of the coating.The corrosion of the composite coating can be divided into early corrosion and late corrosion.R（Q（R（QR）））and R（Q（RW（QR）））equivalent circuits correspond to the early and late corrosion respectively.The immersion results of the composite coating in SRB solution show that the composite coating containing more Cu/RGO is beneficial to reduce the adhesion of SRB,and the antifouling effect increases with the increase of Cu/RGO doping ratio.The antifouling effect of the composite coating comes from the toxic effect of Cu⁺and Cu²⁺and the physical shielding effect of reduced graphene oxide.Spinel ferrite as electromagnetic wave absorbing material has been studied for a long time,but it has the disadvantages of poor impedance matching and high density.In this dissertation,Cu/RGO is introduced to improve the electromagnetic wave absorption effect of spinel,and the experiment proves that the spinel composite material exhibits soft magnetism.The doping ratio of different absorbents has obvious influence on the electromagnetic properties of the material,and the electromagnetic wave loss is strong when 50 wt.%is doped.The introduction of Cu/RGO composite powder with complex surface prepared by spray granulation drying technology can effectively optimize the impedance matching of Fe Al₂O₄ ferrite and improve the electromagnetic wave absorption performance.Under the synergistic effect of multiple reflection/scattering,natural resonance,interfacial polarization and conduction loss,the Fe Al₂O₄ composite doped with 10wt.%Cu/RGO composite powder has the best absorption effect.When the absorbent content is 50wt.%and the thickness is 3.0 mm,the reflection loss of the composite is-16 d B at 15 GHz and the effective bandwidth is 2 GHz.