Surface Protection Of NdFeB Material Coated With SiC Thin Films By Magnetron Sputtering

SiC and AIN/SiC thin films were prepared on sintered NdFeB by RF magnetron sputtering, and then they were annealed at different temperature under argon atmosphere. The samples were characterized by XRD, AFM, SEM, electrochemical analyzer, ultra-high coercivity, permanent magnet pulse tester,60Co irradiation source, etc. The effects of annealing temperature on the structures and properties of NdFeB specimen coated with thin films were given, and the corrosion resistance of thin films was studied under acidic, alkaline and neutral solutions. Finally, properties of NdFeB coated with thin films were studied under the different irradiation intensity. The main contents are as follows:The first chapter outlines the development developing history, composition structure, and preparation preparaing and protection protectective method of NdFeB permanent magnetic materials.In addition, the research status, main content and innovation point are introduced.The second chapter introduces the principle of RF magnetron sputtering, and describes the preparation and growth of thin films. Furthermore, the testing techniques of X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscope (SEM), electrochemcial measurement are simply introduced.The third chapter discusses the preparation and annealing parameters of SiC thin films deposited on NdFeB substrates. The XRD, AFM, SEM are used to characterize the structures and properties of the films. Besides, the relationships of annealing temperature with the structures and properties of SiC films are analyzed. The corrosion resistance of the NdFeB specimen coated with SiC layer in 3.5%NaCl solution is studied too. The corrosion current density of NdFeB is approximately 1.37×10-6A·cm-2, however this is approximately 1.54×10-8 A·cm-2 on the NdFeB specimen coated SiC layer. The result shows that the NdFeB coated SiC layer presents better resistance to the fast and destructive corrosion than the bare NdFeB.The forth chapter studies AlN buffer layer prepared on the NdFeB substrates, in order to solve the mismatch problems between SiC films and NdFeB substrates. The structures, morphologies, magnetic properties and corrosion resistance of specimens are compared between SiC monolayer and AIN/SiC bilayer thin films.The corrosion behaviors of AIN/SiC and SiC-coated NdFeB in 3.5%NaCl,20%NaOH and 0.1mol/LH2SO4 solutions are characterized with potentiodynamic polarization curves. The results show that AIN/SiC and SiC thin films can evidently improve the corrosion resistance of NdFeB, and the AIN/SiC films have the better resistance than the SiC film.In the fifth chapter, the specimens are irradiated by y-ray using 60Co irradiation source.The effects of irradiation doses at 200KGy,2MGy on magnetic properties and corrosion resistance of samples are studied.The chapter six summarizes the whole paper and makes prediction in this area.