| NdFeB rare earth permanent magnet material is the third generation permanent magnet material developed after metal system and ferrite system.It has become a key core material for supporting and guaranteeing high-end applications in marine engineering,aerospace engineering and rail transit.It is also a key safeguard material for major strategic needs such as smart technology,information technology and cutting-edge defense technologies.New technologies and new equipment put forward higher requirements for NdFeB permanent magnets,but NdFeB permanent magnets are easy to corrode under certain circumstances due to their own material characteristics and manufacturing processes,which affects the service life of existing products.Severely block the further expansion of NdFeB in marine engineering,aerospace,defense and military industries.The use of surface protection barrier NdFeB magnets and corrosive environment is the main means of corrosion protection of NdFeB permanent magnets at present,with significant effects and no harm to magnetic properties.Compared with other surface protection methods,physical vapor deposition technology has the advantages of simple operation,stable process,no pollution,no secondary corrosion,etc.,and has become a hot spot in the research of NdFeB corrosion protection at this stage.In this study,a single layer of TiN film,TiN/Al2O3 double layer film and(TiN/Al2O3)n multilayer film were deposited on the NdFeB permanent magnet material substrate by physical vapor deposition technique.The coating process,film structure and film were studied.The layer sequence has a corrosive protective effect on the NdFeB substrate.Firstly,a single TiN film was deposited on the NdFeB substrate.The surface parameters,phase structure,corrosion resistance and the magnetic properties of the film on the substrate were investigated by different process parameters(base temperature,deposition time).The experimental results show that as the substrate temperature increases from normal temperature to 300℃,the surface of the film is flatter,the grain size increases continuously,and the self-corrosion current density decreases to 7.68467×10-5 A/cm2,but the substrate temperature is too high.Reduce the magnetic properties of NdFeB.As the deposition time increases from 0.5 h to 2 h,the thickness of the film layer increases continuously,and the surface of the film layer tends to be flat.However,if the film layer is too thick,it will cause large internal stress,and more cracks or even shedding will appear on the surface of the film layer,which is aggravated.Corrosion of the substrate.Considering the properties of the film,the optimal preparation parameters of the TiN protective film were as follows:sputtering power 115 W,N2/Ar flow rate 2sccm/30sccm,substrate temperature 100℃,deposition time 2 h.To solve the problem of film peeling caused by lattice mismatch and thermal expansion coefficient mismatch between TiN film layer and substrate,and to improve the quality of protective film layer and the bonding force between film layer and substrate,Al2O3 was added as the buffer layer to prepare TiN/Al2O3 bilayer.The effect of different Al2O3 buffer layer thickness on the quality and corrosion resistance of the upper TiN film layer was studyed.At the same time,the protective effect of the single-layer Al2O3 film on the substrate was studied for comparison.The experimental results show that when the thickness of the buffer layer increases from 200 nm to 800 nm,the number and size of large particles on the surface of the TiN film layer are significantly reduced,and the surface of the film layer tends to be flat.The grain size of the TiN film layer is also gradually reduced.The grain size is uniform,the grain gap is reduced,and the film layer is denser.The self-corrosion current density first increases and then decreases.When the thickness of alumina in the TiN/Al2O3 double-layer film is 800 nm,the self-corrosion density of the composite film layer is at least 3.1548×10-5 A/cm2,and the protective effect of the composite film layer on the substrate is 85.5%,and the single-layer Al2O3 film pair of the same thickness The protection of the base reached 82.4%,and the protective performance was lower than that of the composite film.In order to further reduce the internal stress between the layers,reduce the surface cracks and other defects of the TiN film layer,deposit a(TiN/Al2O3)n multilayer film on the surface of NdFeB to study the number of layers(TiN/Al2O3)n under different film periods.Corrosion protection of the membrane to the substrate.The experimental results show that with the increase of the number of cycles,the grains of the multilayer film are gradually refined and smooth,and the density is continuously enhanced and has a tendency to form a sheet.The surface of the TiN/Al2O3 multilayer film is the most dense when the number of cycles is n=20.The sample self-corrosion current density is 1.7658 × 10-5A/cm2,which is reduced by an order of magnitude,and the protection efficiency for the NdFeB substrate is 91.9%.In summary,by controlling the process parameters of the magnetron sputtering method in this study,a single-layer TiN film,a TiN/Al2O3 double-layer film,and a(TiN/Al2O3)n multilayer film were prepared on a neodymium-iron-boron substrate.Characterization methods such as appearance,phase analysis,electrochemical corrosion,salt spray,show that(TiN/Al2O3)n multilayer films are generally more effective in protecting the substrate than single-layer and double-layer films.The(TiN/Al2O3)n multilayer film with a layer number of 20 has a better protection effect on the NdFeB substrate.This study provides a new method for the design and structure improvement of NdFeB surface protective film system. |
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