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Abstract

This doctoral dissertation present research aimed into enhancing polymer-bonded Nd–Fe–B magnets through innovative surface treatments and additive manufacturing techniques, focusing on improving their mechanical strength, magnetic characteristics, and environmental stability. This research is critical for broadening the applicability of these magnets in sectors like green technologies and motion control systems. The dissertation presents findings from three pivotal studies, each addressing different aspects of magnet production and treatment.
The first study explores surface modifications using a sequence of phosphatisation, tetraethyl orthosilicate (TEOS), and 3-aminopropyltriethoxysilane (APTES). This treatment significantly improved the mechanical properties and corrosion resistance of the magnets. Magnets subjected to these modifications showed enhancements in tensile strength by 62%, elongation at the break by 16.7%, and an elastic modulus increase of 19.9%. They also exhibited a remarkable corrosion resistance with less than 5% flux loss after exposure to harsh conditions.
The second study investigated the use of fused deposition modelling (FDM) for manufacturing polymer-bonded magnets with both melt-spun and gas-atomized Nd−Fe−B powders. It was found that using gas-atomized powders, which facilitated better flow and lower porosity, significantly improved the quality of printed magnets. These magnets demonstrated higher densities and enhanced magnetic properties with a remanence (Br) of 426 mT, coercivity (Hci) of 721 kA/m, and an energy product (BHmax) of 29 kJ/m3, compared to their melt-spun counterparts. Additionally, these FDM-printed magnets exhibited excellent thermal stability and corrosion resistance, maintaining performance integrity after prolonged exposure to 85°C in air and water.
The third study details the application of plasma treatments to enhance the interface adhesion between Nd–Fe–B magnetic powders and the polymer matrix within FDM-printed magnets. The application of both radio frequency and low-pressure microwave plasma treatments significantly enhanced the mechanical properties and environmental stability of the magnets. Results showed that plasma-treated magnets achieved high densities (92-94% of theoretical values), optimal mechanical profiles with elastic modulus up to 578 MPa, and the highest ductility at 21%. The flexural strength reached up to 15 MPa with minimal flux loss, confirming the effectiveness of plasma treatments in maintaining the magnet's integrity under various conditions.
Together, these studies validate the dissertation’s hypotheses and demonstrate that specialized surface treatments and additive manufacturing adjustments can substantially enhance the performance of Nd−Fe−B polymer-bonded magnets. The findings contribute to both the academic research and practical applications, promoting more sustainable and efficient use of rare earth magnets and fostering broader applications in essential technological fields.