R-T-B Sintered Magnet Grain Boundary Gradient for Coercivity
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Solution Overview
Problem
Sintered R-T-B based magnets face a challenge in maintaining high coercivity (HcJ) at high temperatures due to irreversible thermal demagnetization, and replacing light rare-earth elements with heavy rare-earth elements improves HcJ but decreases remanence, while heavy rare-earth elements are scarce and unstable in supply.
Innovation Solution
A sintered R-T-B based magnet with a specific composition and production method that includes a molar ratio of T to B greater than 14.0, a gradient of R and Ga content across the magnet's cross-section, and a heat treatment process using an R2-Cu—Ga—Fe alloy to enhance coercivity and remanence without relying on heavy rare-earth elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If light rare-earth elements (Nd, Pr) are replaced with heavy rare-earth elements (Dy, Tb) to improve coercivity, then coercivity HcJ is improved, but remanence Br decreases due to decreasing saturation magnetization
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of heavy rare-earth elements within the magnet structure. The R3T5B phase at grain boundaries contains higher concentrations of Dy or Tb compared to the main R2T14B phase, allowing localized enhancement of coercivity at critical interfaces while preserving the overall saturation magnetization of the bulk material.
Solution Approach 2:
The patent employs composite materials by forming a multi-phase structure consisting of R2T14B main phase and R3T5B grain boundary phase. This composite structure combines the high magnetization properties of the R2T14B phase with the high coercivity properties of the R3T5B phase containing heavy rare-earth elements, achieving both high Br and high HcJ simultaneously.
2Strength
If heavy rare-earth elements (Dy, Tb) are used to improve coercivity, then coercivity HcJ is improved, but supply stability deteriorates due to scarcity and price fluctuation
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration and distribution of heavy rare-earth elements within specific compositional ranges. By controlling the amount of Dy or Tb to 0.1-5.0 mass% and adjusting the R3T5B phase formation parameters, the patent achieves high coercivity while minimizing the total quantity of heavy rare-earth elements required, thereby improving supply stability.
Solution Approach 2:
The patent reduces overall heavy rare-earth element consumption by concentrating them locally at grain boundaries in the R3T5B phase rather than distributing them uniformly throughout the entire magnet. This localized approach achieves the necessary coercivity enhancement only where it is most needed for domain wall pinning, reducing the total amount of scarce heavy rare-earth elements required.
3Temperature
If coercivity is improved by heavy rare-earth element substitution, then high-temperature stability is improved, but manufacturing complexity increases due to precise composition control requirements
Solution Approach 1:
The patent simplifies manufacturing by establishing a clear two-phase composite structure (R2T14B + R3T5B) with defined compositional ranges. This structured approach provides manufacturers with clear guidance on phase formation and element distribution, making the precise control of heavy rare-earth element content more manageable through standardized processing parameters.
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 high remanence and coercivity similar to magnets with heavy rare-earth elements, while reducing the content of these scarce elements, thereby stabilizing the magnet's performance and supply chain.
Implementation Method 1
The R2T14B compound is a ferromagnetic phase having high magnetization, and provides a basis for the properties of a sintered R-T-B based magnet
Implementation Method 2
performing a heat treatment while an alloy containing R, Ga and Fe as its component elements is kept in contact with at least a portion of a surface of an R-T-B based sintered compact
Data Source
AI summary
A sintered R-T-B based magnet composition includes: R: not less than 27 mass % and not more than 37 mass % (R is at least one rare-earth element which always includes at least one of Nd and Pr), B: not less than 0.75 mass % and not more than 0.97 mass %, Ga: not less than 0.1 mass % and not more than 1.0 mass %, Cu: not less than 0 mass % and not more than 1.0 mass %, and T: 61.03 mass % or more (where T is at least one selected from Fe, Co, Al, Mn and Si and always includes Fe, such that the Fe content is 80 mass % or more in the entire T). [T]/[B] is greater than 14.0. An R amount is greater in the surface than in the center, and a Ga amount is greater in the surface than in the center. [T]/[B] in the surface is higher than [T]/[B] in the center.