Sintered R-T-B Magnet With Grain-Boundary Tb Dy Gradients
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Solution Overview
Problem
Sintered R-T-B based magnets experience a decrease in coercivity (HcJ) at high temperatures, leading to irreversible thermal demagnetization, and the replacement of light rare-earth elements with heavy rare-earth elements improves HcJ but decreases saturation magnetization and remanence (Br), particularly with limited and unstable supply of elements like Tb.
Innovation Solution
A sintered R-T-B based magnet with a specific composition and structure, including a main phase of R2T14B compound and a grain boundary phase, where the atomic ratio of B to T is lower than in the stoichiometric composition, and the concentrations of elements like Nd, Pr, Ce, Dy, Tb, O, and C are optimized to promote the diffusion of heavy rare-earth elements while maintaining high Br and HcJ, with a gradual decrease in Tb and Dy concentration from the surface to the interior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare-earth elements (Tb, Dy) are used to improve coercivity, then HcJ increases, but saturation magnetization and remanence Br decrease
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of heavy rare-earth elements within the magnet structure. Specifically, Tb and Dy are concentrated at the grain boundaries of the main phase rather than being uniformly distributed throughout. This localized placement allows the heavy rare-earth elements to exert their maximum effect on coercivity at the critical grain boundary regions where magnetic domain wall pinning occurs, while minimizing their overall quantity to preserve bulk saturation magnetization and remanence.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the composition ratios and concentration gradients of rare-earth elements. The formula specifies exact ranges for light rare-earth elements (Nd, Pr, Ce) and heavy rare-earth elements (Tb, Dy), along with their optimal ratios. By adjusting these compositional parameters and creating controlled concentration gradients from grain interior to boundary, the patent optimizes the balance between coercivity enhancement and magnetization preservation.
2Reliability
If Tb is used to improve HcJ, then coercivity increases, but resource stability and cost control deteriorate
Solution Approach 1:
The patent applies this principle by replacing the expensive and scarce Tb element with more abundant and cost-effective alternatives. Specifically, the patent uses Dy as a substitute for Tb, and also utilizes light rare-earth elements (Nd, Pr, Ce) in optimized combinations. This substitution strategy maintains the required coercivity performance while significantly reducing dependence on critically sourced materials, thereby improving resource stability and cost-effectiveness.
Solution Approach 2:
The patent employs composite material strategy by creating a multi-element rare-earth system rather than relying on a single heavy rare-earth element. The magnet comprises a composite of light rare-earth elements (Nd, Pr, Ce) and heavy rare-earth elements (Dy, Tb) in specific ratios, forming a synergistic combination where each element contributes its unique properties. This composite approach reduces reliance on any single scarce element like Tb while achieving the desired magnetic performance.
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 (Br) and coercivity (HcJ) while minimizing the use of heavy rare-earth elements like Tb, ensuring stability and performance at high temperatures, particularly suitable for motors in electric vehicles.
Implementation Method 1
allowing the heavy rare-earth element RH to diffuse into an interior of the sintered magnet... the heavy rare-earth element RH is diffused from the surface of the sintered R-T-B based magnet into the interior thereof
Data Source
AI summary
The present disclosure includes a main phase comprising an R2T14B compound, and a grain boundary phase. The atom number ratio of B to T in this R-T-B sintered magnet is less than the atom number ratio of B to T in the stoichiometric composition of the R2T14B compound, and the relationships 26.0 mass %≤([Nd]+[Pr]+[Ce]+[Dy]+[Tb])−(9×[O]+12×[C])≤27.5 mass %, 0.15 mass %≤[O]≤0.30 mass %, and 0.05 mass %<[Tb]≤0.35 mass % are satisfied, where [Nd] is the Nd content (mass %), [Pr] is the Pr content (mass %), [Ce] is the Ce content (mass %), [Dy] is the Dy content (mass %), [O] is the O content (mass %), and [C] is the C content (mass %). Tb concentration and/or the Dy concentration gradually decreases from the magnet surface toward the magnet interior, at least in part.