Corrosion resistance of the polymer matrix hard magnetic composite materials Nd–Fe–B

Abstract

The paper presents the characteristics of the protective polymer, lacquer, and metal coatings put down onto the hard magnetic composite substrate with the polymer matrix, reinforced with the Nd–Fe–B particles with additions of metal powders. Examinations of the coatings’ structures were made with the scanning electron microscopy method. Hardness, thickness, and adhesion tests of the deposited coatings were also made. It was found out that the protective coatings are characteristic of the uniform deposition on the entire surface and of the same thickness all over their area. These coatings are characterised by a compact structure with no visible delaminations and defects. Polymer coatings demonstrate higher hardness compared to the lacquer ones. The highest hardness of 350s is characteristic of the polyester polymer coating. It was found that the highest adherence of 8.4 MPa is characteristic of the polyester–epoxy coating, whereas, the lowest adherence is displayed by the phthal-urethane coating—5.0 MPa. The paper presents also the corrosive wear of the hard magnetic composite materials with the polymer matrix, reinforced with the Nd–Fe–B particles from the rapid quenched strip, sintered Nd–Fe–B magnets, and composite materials coated with the protective polymer, lacquer, and metal coatings. The corrosive resistance values in the water environment and in the 5% NaCl solution environment were determined. It was found out that the composite magnets with the polymer matrix demonstrate better corrosive resistance than the sintered magnets; whereas, the best protection from the corrosive environment is provided by the polymer coatings. The neural network model for evaluation of the rate of corrosive wear of the polymer matrix hard magnetic composite materials with addition of metallic powder was established based on the research results from the investigations carried out in two corrosive environments. Three types of input data were used in the investigation: the contribution of the added powder, the nominal variable that defined the corrosive environment and the time duration of the test. The percentage corrosive wear of the surface was the output produced from such input data.