R-T-B Magnet Core-Shell Diffusion for High Coercivity
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Solution Overview
Problem
Conventional methods for enhancing coercivity in NdFeB magnets using heavy rare earth elements like dysprosium and terbium result in a significant concentration gradient, leading to shallow diffusion and limited performance enhancement, while high market prices of these elements increase manufacturing costs.
Innovation Solution
An R-T-B based magnet with a core-shell structure and controlled diffusion of heavy rare earth elements, where RH1−RH2≥2.6 wt % and/or RH1/RH2≥1.5, ensuring deep diffusion and high magnetic performance with reduced heavy rare earth content, achieved through a three-stage heat treatment and tempering process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth elements Dy and Tb are deposited and diffused onto the substrate surface to enhance coercivity, then coercivity is improved, but the concentration of heavy rare earth elements decreases markedly from the surface to the interior, resulting in shallow diffusion depth and limited performance enhancement
Solution Approach 1:
The patent creates a core-shell structure where the shell region contains high concentration of heavy rare earth elements (Rh1) and the core contains low concentration (Rh2), with Rh1-Rh2≥2.6 wt% and Rh1/Rh2≥1.5. This local quality differentiation ensures that heavy rare earth elements are concentrated where they are most needed (at grain boundaries and shell regions) rather than being uniformly distributed, thereby achieving deep effective diffusion and enhanced coercivity.
2Reliability
If heavy rare earth elements Dy and Tb are used to enhance coercivity, then magnetic performance is improved, but manufacturing costs increase due to high market prices of these elements
Solution Approach 1:
The patent applies heavy rare earth elements locally at the shell region with high concentration (Rh1≥2.0 wt%) rather than uniformly throughout the entire magnet. This localized application reduces the overall amount of expensive heavy rare earth elements needed while maintaining high coercivity performance, thereby lowering manufacturing costs.
Solution Approach 2:
The patent uses a relatively small amount of heavy rare earth elements (total content of 0.65-1.2 wt%) but concentrates them excessively in the shell region (Rh1/Rh2≥1.5). This partial application with excessive local concentration achieves the desired coercivity enhancement without requiring large amounts of expensive materials throughout the entire magnet.
3Reliability
If the concentration of heavy rare earth elements is increased to enhance coercivity, then magnetic performance is improved, but the squareness and residual induction are compromised
Solution Approach 1:
The patent confines high heavy rare earth element concentration to the shell region (Rh1) while keeping the core region (Rh2) at low concentration. This spatial separation allows the shell to provide high coercivity through heavy rare earth elements, while the core maintains its original composition and magnetic properties, preserving squareness and residual induction.
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 method results in R-T-B magnets with enhanced remanence (Br) of at least 14.2 kGs, intrinsic coercivity (HcJ) of at least 27 kOe, and a high Hk/HcJ ratio of 94%, despite low overall heavy rare earth element content.
Implementation Method 1
heavy rare earth elements diffuse from the surface into the interior of the R-T-B based magnet
Implementation Method 2
The subject formula (1) undergoes heat treatment to facilitate the diffusion of heavy rare earth elements
Data Source
AI summary
An R-T-B based magnet includes R, Fe, and B. R includes light and heavy rare earth elements. The heavy rare earth element includes terbium and/or dysprosium. The R-T-B based magnet includes main phase grains and an intergranular phase situated between the main phase grains. The main phase grains include grains that exhibit a core-shell structure. Along a diffusion direction of the heavy rare earth element from a surface to an interior of the R-T-B based magnet, in a microstructure observation surface within a region extending 200 μm inward from the surface of the R-T-B based magnet, an average heavy rare earth element content RH1 in the shell of the core-shell structure and an average heavy rare earth element content RH2 in the intergranular phase satisfy: RH1−RH2≥2.6 wt % and/or RH1/RH2≥21.5. The microstructure observation surface is perpendicular to the diffusion direction of the heavy rare earth element.