R-T-B Magnet Coercivity via Grain Boundary C-Ga-M
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Solution Overview
Problem
R-T-B based permanent magnets used in high-temperature applications, such as hybrid vehicle motors, face challenges in achieving sufficient coercivity without relying heavily on expensive and rare heavy rare earth elements like Dy and Tb, which are also subject to supply instability.
Innovation Solution
The development of an R-T-B based permanent magnet composition that includes specific amounts of C, Ga, and M (Zr, Ti, or Nb) to form a thick two-grain boundary, optimizing the balance of elements such as B, C, and M to enhance coercivity, allowing for reduced usage of Dy and Tb.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earth elements (Dy, Tb) are used to improve coercivity, then coercivity increases, but cost increases and supply stability deteriorates
Solution Approach 1:
The patent replaces expensive heavy rare earth elements (Dy, Tb) with lighter rare earth elements (Nd, Pr) combined with specific amounts of B, C, Ga, and M elements. This substitution uses more abundant, cheaper materials to achieve the same coercivity improvement, directly addressing the cost and supply stability issues while maintaining the required magnetic strength
Solution Approach 2:
The patent optimizes the compositional parameters by precisely controlling the content ranges of B (0.60-0.95 mass%), C (0.10-0.35 mass%), Ga (0.30-1.50 mass%), and M (0.20-2.00 mass%). By adjusting these parameters within specific ranges, the patent achieves high coercivity without relying on heavy rare earth elements, resolving the contradiction between coercivity improvement and supply stability
2Strength
If B content is reduced to improve coercivity, then coercivity improves, but magnetic properties deteriorate
Solution Approach 1:
The patent creates a composite material system combining R2T14B main phase with R2T17 secondary phase and grain boundary phases containing Ga and M elements. This composite structure allows the R2T14B phase to provide high coercivity while the R2T17 phase and grain boundary phases contribute to magnetic properties, resolving the contradiction between improved coercivity and maintained magnetic properties
Solution Approach 2:
The patent distributes different elements to different regions: B and C are concentrated in the R2T14B main phase for coercivity, while Ga and M elements are localized in the grain boundary phases and R2T17 secondary phase. This spatial distribution allows each region to optimize its function, with the main phase providing coercivity and the grain boundary/secondary phases preserving magnetic properties
Data Source
AI summary
An R-T-B based permanent magnet includes main phase grains composed of R2T14B type compound. R is a rare earth element. T is iron group element(s) essentially including Fe or Fe and Co. B is boron. The magnet contains at least C, Ga, and M selected from Zr, Ti, and Nb in addition to R, T, and B. B is contained at 0.71 mass % to 0.88 mass %. C is contained at 0.15 mass % to 0.34 mass %. Ga is contained at 0.40 mass % to 1.40 mass %. M is contained at 0.25 mass % to 2.50 mass %. A formula (1) of 0.14≤[C]/([B]+[C])≤0.30 and a formula (2) of 5.0≤[B]+[C]−[M]≤5.6 are satisfied, where [B], [C], and [M] are respectively a content of B, C, and M by atom %.