R-T-B Magnet Grain Boundary XZ Phase Coercive Force

The patent applies local quality by introducing heavy rare earth elements (Dy, Tb) specifically into the grain boundary phase rather than uniformly substituting throughout the entire R2Fe14B compound. This localized approach allows the grain boundary phase to provide enhanced coercive force through the heavy rare earth elements, while the main phase grains maintain their high residual magnetic flux density characteristics. The composition is designed so that the grain boundary phase contains 0.1-5.0 at% heavy rare earth elements, creating a spatially differentiated structure where each region performs its optimal function.

The patent employs composite materials by creating a multi-phase structure consisting of R2Fe14B main phase grains embedded in a grain boundary phase containing heavy rare earth elements. This composite structure combines the high magnetic properties of the R2Fe14B compound with the coercive force enhancement from heavy rare earth elements, achieving both high Br and high HcJ simultaneously. The grain boundary phase acts as a matrix that binds the main phase grains while providing additional magnetic hardening.

The patent applies partial action by using small, controlled amounts of heavy rare earth elements (0.1-5.0 at% in the grain boundary phase) rather than large substitutions. This partial incorporation is sufficient to achieve the desired coercive force improvement while minimizing the cost impact. The grain boundary phase contains just enough heavy rare earth elements to provide the necessary magnetic hardening without the excessive cost that would result from bulk substitution.

By localizing heavy rare earth elements to the grain boundary phase rather than distributing them throughout the entire magnet, the patent reduces the total amount of expensive heavy rare earth materials needed. The grain boundary region serves as a cost-effective site for incorporating these elements, as it requires much smaller quantities compared to uniform substitution, thereby reducing overall manufacturing cost while maintaining HcJ improvement.

The grain boundary phase is designed to perform multiple functions simultaneously: it provides coercive force enhancement through heavy rare earth elements, ensures mechanical strength through adequate bonding between grains, and offers corrosion resistance through the protective nature of the grain boundary structure. The R-rich composition (60-95 at% rare earth elements) combined with controlled heavy rare earth content creates a multi-functional phase that addresses magnetic, mechanical, and chemical requirements in one integrated structure.

The patent optimizes multiple parameters of the grain boundary phase including rare earth element composition (60-95 at%), heavy rare earth content (0.1-5.0 at%), and phase distribution to achieve a balance between coercive force and other properties. By carefully controlling these compositional parameters, the grain boundary phase simultaneously achieves high HcJ through heavy rare earth elements while maintaining adequate strength and corrosion resistance through the R-rich matrix structure.