R-T-B Sintered Magnet Core-Shell Structure for Coercivity and Weight
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Solution Overview
Problem
The existing R-T-B based permanent magnets, particularly those with Nd as the rare earth element, face challenges in achieving a balance between high coercivity and low weight, which is essential for efficient operation in permanent-magnet synchronous motors, as they tend to have increased inertia momentum due to the elevated weight of the rotor, affecting controllability and efficiency.
Innovation Solution
A R-T-B based sintered magnet with a core-shell structure is developed, where Yttrium (Y) is concentrated in the core portion and other rare earth elements like Nd in the grain boundary, maintaining high coercivity while reducing the overall weight by optimizing the mass concentration ratios of Y in the core and shell portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Nd-Fe-B based magnet is used to achieve high coercivity, then magnetic performance is improved, but rotor weight increases causing increased inertia momentum
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the core region contains high concentrations of heavy rare earth elements (Nd, Dy, Tb) for high coercivity, while the shell region contains lighter rare earth elements (Pr, Y) for weight reduction. This spatial differentiation of composition allows simultaneous optimization of magnetic performance and weight, directly resolving the contradiction between coercivity and rotor weight.
Solution Approach 2:
The patent uses composite materials by combining multiple rare earth elements (Nd, Pr, Dy, Tb, Y) in a core-shell structured R2Fe14B phase. The composite composition allows the magnet to achieve high coercivity through heavy rare earth elements in the core while reducing overall weight through lighter rare earth elements in the shell, thereby resolving the weight-coercivity trade-off.
2Weight of moving object
If Y-T-B based magnet is used to reduce weight, then rotor weight decreases, but coercivity deteriorates significantly
Solution Approach 1:
The patent overcomes the limitation of Y-T-B magnets by using local quality differentiation: Y is concentrated in the shell region where it contributes to weight reduction, while heavy rare earth elements (Nd, Dy, Tb) are concentrated in the core region where they provide high coercivity. This spatial separation allows Y to reduce weight without sacrificing coercivity, as the core maintains high magnetic anisotropy field.
Solution Approach 2:
The patent creates a composite rare earth system combining Y with heavy rare earth elements in a core-shell structure. This composite approach allows Y to provide weight reduction benefits while the heavy rare earth elements in the core compensate for Y's low magnetic anisotropy, achieving both low weight and high coercivity simultaneously.
3Reliability
If heavy rare earth elements are uniformly distributed to maximize coercivity, then magnetic performance is improved, but weight increases
Solution Approach 1:
The patent resolves this contradiction by applying local quality through non-uniform distribution of rare earth elements. Heavy rare earth elements (Nd, Dy, Tb) are concentrated in the core region to maximize coercivity where it is most needed, while lighter rare earth elements (Pr, Y) are placed in the shell region to reduce weight. This spatial differentiation achieves high coercivity without uniform weight increase throughout the entire magnet.
Data Source
AI summary
The present invention provides a permanent magnet with a coercivity that will not be significantly decreased and a light weight compared to conventional R-T-B based permanent magnets. A core-shell structure is formed for the major phase grain by adding Cu to the R-T-B based magnet which is the raw material. When the mass concentration of Y in the core portion is set as EY, the mass concentration of Y in the shell portion is set as LY and the mass concentration of Y in the R2—Fe14—B crystal grain calculated from the ratio R1:Y in the total composition is set as SY, the ratio α of EY to SY (EY/SY) is 1.1 or more. Thus, the magnetic insulation among the crystal grains becomes better which prevents the coercivity from decreasing due to the addition of Y. Further, the addition of Y makes the magnet lighter in weight.