Cladded NdFeB Magnets With Grain-Boundary Pinning for Thermal Stability

The patent applies composite materials by combining NdFeB magnetic microparticles with metal-containing inoculant nanoparticles (such as Zr, ZrB2, ZrC, Hf, HfB2, HfC) to form a composite structure. The inoculant nanoparticles serve as grain boundary phases that pin domain walls and prevent magnetic domain reversal at elevated temperatures, thereby maintaining magnetic coercivity while improving thermal stability. This composite approach allows the magnet to achieve both high magnetic strength and thermal resistance simultaneously.

The patent implements local quality by concentrating the metal-containing inoculant nanoparticles specifically at the grain boundaries of the NdFeB magnetic grains. This localized distribution ensures that the grain boundary regions have enhanced thermal stability and domain wall pinning capability, while the interior of the magnetic grains maintains high magnetization. The selective placement of functional material at critical locations (grain boundaries) resolves the contradiction between overall magnetic strength and localized thermal resistance.

The patent replaces expensive heavy rare earth elements (Dy, Tb) with cheaper alternative materials such as Zr, Hf, and their borides and carbides. These inoculant nanoparticles provide similar or superior grain boundary pinning effects at lower cost. The use of non-rare-earth or less-critical materials substitutes the expensive rare earth additives, thereby reducing material cost while maintaining or improving demagnetization resistance.

The patent changes the chemical composition parameters by introducing metal-containing inoculant nanoparticles with different elemental compositions (Zr-based, Hf-based, borides, carbides) instead of relying on heavy rare earth elements. This parameter change in the grain boundary phase composition achieves the same functional effect (domain wall pinning) through alternative chemical mechanisms, reducing dependence on expensive rare earth elements and lowering overall material cost.

The patent segments the manufacturing process into two distinct stages: (1) conventional die-press and sintering to efficiently produce the bulk magnet with high manufacturing efficiency, and (2) subsequent surface modification or coating with metal-containing inoculant nanoparticles to achieve geometric flexibility and tailored surface properties. This segmentation allows each process to optimize for its specific function, combining the advantages of both conventional efficiency and advanced geometric control.

The patent applies preliminary action by pre-dispersing metal-containing inoculant nanoparticles into the NdFeB magnetic powder feedstock before the die-press and sintering process. This preliminary incorporation ensures that the inoculant particles are already positioned at grain boundaries during sintering, eliminating the need for post-processing steps to achieve the desired microstructure and geometric properties. The preliminary preparation enables conventional manufacturing methods to produce magnets with enhanced geometric flexibility and tailored microstructures.