Sintered R-T-B Magnet Composition for High Coercivity and Br
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Solution Overview
Problem
Sintered R-T-B based magnets used in electric vehicle motors face challenges with irreversible thermal demagnetization due to decreased coercivity (HcJ) at high temperatures, and existing solutions that improve HcJ by substituting light rare earth elements with heavy rare earth elements like Tb lead to a decrease in residual magnetic flux density (Br).
Innovation Solution
A sintered R-T-B based magnet composition with controlled concentrations of Nd, Pr, Cu, Ga, and B, along with minimal heavy rare earth elements, and a specific diffusion process to optimize grain boundary diffusion, ensuring high Br and HcJ without excessive Tb or Dy usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If light rare earth elements (Nd, Pr) in the R2T14B-type compound are substituted with heavy rare earth elements (Tb, Dy), then coercivity (HcJ) is improved, but saturation magnetization decreases and thus residual magnetic flux density (Br) decreases
Solution Approach 1:
The patent changes the concentration parameters of rare earth elements and transition metals in the R2T14B-type compound. Specifically, it optimizes the ratios of Nd/Pr to Tb/Dy, adjusts the content of Fe and Co in the T position, and controls the overall composition to achieve a balance where HcJ is improved without excessive loss of Br. This parameter optimization resolves the contradiction by finding the optimal compositional window.
Solution Approach 2:
The patent creates a composite rare earth element system combining light rare earth elements (Nd, Pr) with heavy rare earth elements (Tb, Dy) in specific proportions within the R2T14B structure. This composite approach allows the material to benefit from both the high saturation magnetization of light rare earth compounds and the high coercivity enhancement from heavy rare earth elements, thus resolving the trade-off between Br and HcJ.
2Reliability
If heavy rare earth elements (Tb, Dy) are used to improve HcJ, then coercivity increases, but the amount of Tb required leads to supply instability and price fluctuation
Solution Approach 1:
The patent optimizes the concentration parameter of Tb to be within a specific range (0.01-0.50 mass%, preferably 0.03-0.30 mass%), which is significantly lower than conventional compositions. This parameter control allows achieving high HcJ with minimal Tb content, thereby reducing supply risk and cost while maintaining reliability.
Solution Approach 2:
The patent replaces expensive and supply-unstable Tb with more abundant and stable light rare earth elements (Nd, Pr) as the primary component, using only trace amounts of Tb (0.01-0.50 mass%) as an additive. This substitution strategy reduces dependency on critical materials while maintaining performance, effectively addressing supply stability and cost concerns.
3Quantity of substance
If Tb content is reduced to stabilize supply and price, then HcJ improvement is limited, but Br is better maintained
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: the R2T14B stoichiometry, the Nd/Pr to Tb/Dy ratio, the Fe/Co content in the T position, and the overall rare earth element distribution. This multi-parameter optimization enables achieving high HcJ with minimal Tb (0.01-0.50 mass%) while maintaining high Br, resolving the contradiction between coercivity improvement and rare earth element usage.
Solution Approach 2:
The patent creates local compositional variations within the R2T14B structure, concentrating Tb preferentially at grain boundaries or specific crystallographic positions rather than uniformly distributing it. This local enrichment strategy maximizes the coercivity-enhancing effect of Tb where it is most needed, while minimizing the overall Tb content required, thus maintaining Br while improving HcJ.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves improved Br and HcJ while significantly reducing the amount of heavy rare earth elements, particularly Tb, maintaining high magnetic performance even at elevated temperatures.
Implementation Method 1
The R 2 T 14 B-type compound constituting the crystal grains is a ferromagnetic material having high saturation magnetization and an anisotropic magnetic field
Implementation Method 2
The sintered R-T-B based magnet has a problem in that irreversible thermal demagnetization occurs because the coercivity H cJ decreases at a high temperature
Data Source
Figure 1
AI summary
A sintered R-T-B based magnet containing: R: 26.5 mass% or more and 31.5 mass% or less (R is a rare earth element and contains at least one or two selected from the group consisting of Nd and Pr); M: 0.40 mass% or more and 1.50 mass% or less (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si, and necessarily contains Cu); B: 0.85 mass% or more and 0.94 mass% or less; T: 61.5 mass% or more (T is Fe and Co, and 90% or more of T is Fe in mass ratio); O: 0.05 mass% or more and 0.30 mass% or less; Tb: 0.20 mass% or less; and Dy: 0.30 mass% or less, the sintered R-T-B based magnet satisfying the following formula, in which in a range from a surface to a depth of 200 µm, a concentration of one or two selected from the group consisting of Nd and Pr and a concentration of Cu gradually decrease in a depth direction from the surface. 26.0 mass% ≤ ([Nd] + [Pr] + [Ce] + [La] + [Dy] + [Tb]) - 12([O] + [C]) ≤ 27.7 mass%