Microstructure And Electromagnetic Properties Of Ferrite Composite Coatings Prepared By Plasma Spraying

CoFe₂O₄ has excellent electromagnetic properties,which can be utilized in the fields of biomedical,information storage,microwave equipment,sensors and so on.Meanwhile,the electronic components were tending to miniaturization and lamination.How to use a simple and economical method to fabricate two-dimensional ferrite devices with excellent performance is the focus of current research.Comparing with other preparation technology of two-dimensional materials,plasma spray has the advantages of high spraying temperature,deposition efficiency and less impurity.However,for the plasma spraying coating,the matching of the thermal expansion coefficient between the coating and substrate was a key factor affecting the performance of coatings,which can be effectively reduced by adjusting the spraying parameters or adding a transition layer.In this study,CoFe₂O₄ and NiFe-CoFe₂O₄ composite coatings were prepared by atmospheric plasma spraying technique.The microstructure,composition,mechanical properties,electro-magnetic properties and magnetic domain structure of the coatings were characterized and analyzed.Both the effects of spraying parameters and the content of Ni-Fe on the structure and properties of the coatings were systematically studied.The main conclusions are drawn as following:(1)Based on the orthogonal experimental results of three factors and three levels of spraying progress parameters,it is found that the main gas flow rate has the greatest influence on the structure and performance of the coating,followed by the spraying distance and spraying power.The optimal spraying process parameters are as follows:main gas flow of 30 L/min,spraying distance of 80 mm,spraying power of 25 k W.The saturation magnetization is directly proportional to the content of magnetic phase in the coating,while the content of magnetic phase is inversely proportional to the spraying power and distance,and directly proportional to the main gas flow.The coercivity of the coating is mainly affected by the microstructure,residual stress and the easy magnetization orientation of the crystals.With the increase of frequency,the real part of the dielectric constant increases and the imaginary part decreases.(2)The addition of Ni-Fe alloy can effectively reduce the pore size and porosity of the coating,and enhance the bonding strength of the coating.The hardness of the coating increases first and then decreases with the increase of the addition of alloy.In addition,the magnetization of NiFe-CoFe₂O₄ composite coating has a nonlinear relationship with the content of the alloy due to the interface interaction between CoFe₂O₄ and Ni-Fe alloy and the influence of impurity phases in the alloy.The dielectric constant changes non-monotone with the increase of the content of alloy,and the dielectric constant gradually decreases with the increase of the frequency.(3)The magnetic domain morphology of CoFe₂O₄ and its composite coating surface is dot-like or island-like.With the content of Ni-Fe alloy increasing,the magnetic domain changed from island-like to dot-like.The magnetic domain structure of Ni-Fe alloy was not observed under magnetic microscope.With the change of spraying parameters,the changing law of magnetic domain brightness and darkness is consistent with the changing law of magnetization velocity,but contrary to the changing law of coercivity.With the addition ofFe-Ni alloy,the change law of the light and dark contrast of the magnetic domain is consistent with the change law of saturation magnetization and magnetization velocity of NiFe-CoFe₂O₄ composite coating.