Pr-Ga Diffusion Source for Sintered R-T-B Magnet Coercivity
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Solution Overview
Problem
Sintered R-T-B based magnets face challenges in maintaining high coercivity (HcJ) and remanence (Br) at high temperatures, particularly in electric vehicle motors, due to the scarcity and price volatility of heavy rare-earth elements like Dy, which are used to enhance HcJ but reduce Br when substituted into the R2T14B compound.
Innovation Solution
A method involving a sintered R-T-B based magnet work with specific composition and a Pr—Ga alloy diffusion source, where the Pr—Ga alloy is heat-treated to produce particles with uniform texture and large crystal grain size, allowing Pr and Ga to diffuse into the magnet, thereby enhancing Br and HcJ while reducing the need for heavy rare-earth elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light rare-earth element RL (e.g., Nd or Pr) contained in the R2T14B compound is partially replaced with a heavy rare-earth element RH (e.g., Dy or Tb), then HcJ is improved, but Br is decreased
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of rare-earth elements through diffusion treatment. The surface layer contains a higher concentration of heavy rare-earth elements (Dy, Tb) for enhanced coercivity, while the interior maintains light rare-earth elements for high remanence. This spatial differentiation resolves the contradiction by allowing both high HcJ and high Br in different regions of the magnet.
Solution Approach 2:
The magnet is segmented into functionally distinct zones: a surface layer optimized for coercivity with heavy rare-earth element enrichment, and an interior region optimized for remanence with light rare-earth element dominance. This segmentation allows each region to perform its specific function optimally, resolving the trade-off between HcJ and Br.
2Reliability
If the amount of substituted RH increases, then HcJ is more improved, but Br is decreased and RH consumption increases
Solution Approach 1:
The patent applies partial action by introducing heavy rare-earth elements only into the surface layer through diffusion treatment, rather than uniformly throughout the entire magnet. This partial enrichment provides sufficient coercivity enhancement at the critical grain boundary regions while minimizing overall RH consumption and preserving bulk remanence properties.
Solution Approach 2:
The patent changes the concentration parameter of heavy rare-earth elements from uniform distribution to gradient distribution. The surface layer achieves high RH concentration (0.1-5.0 mass%) for improved HcJ, while the interior maintains low or zero RH content to preserve Br, thus resolving the contradiction through parameter optimization.
3Reliability
If B amount is made comparatively smaller than conventional R-T-B based alloy, then HcJ is improved through R2T17 phase formation, but Br is greatly lowered
Solution Approach 1:
The patent applies local quality by forming R2T17 phase selectively at grain boundaries through controlled B content (0.80-0.99 mass%) and diffusion treatment, rather than uniformly throughout the magnet. This localized phase formation provides coercivity enhancement at critical regions while maintaining adequate B content in the bulk to preserve remanence.
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
This approach achieves high Br and HcJ with reduced variations in magnetic characteristics, ensuring stable performance in high-temperature applications without relying heavily on scarce and expensive heavy rare-earth elements.
Implementation Method 1
subjecting the Pr—Ga alloy powder to a heat treatment at a temperature which is not lower than a temperature that is 250° C. below a melting point of the Pr—Ga alloy powder and which is not higher than the melting point
Implementation Method 2
heating the sintered R-T-B based magnet work and the diffusion source to a temperature which is above 600° C. but not higher than 950° C., thereby allowing Pr and Ga contained in the diffusion source to diffuse from the surface into the interior
Data Source
AI summary
A method for producing a sintered R-T-B based magnet includes the steps of: providing a sintered R-T-B based magnet work; providing a Pr—Ga alloy powder produced through atomization; subjecting the Pr—Ga alloy powder to a heat treatment at a temperature which is not lower than a temperature that is 250° C. below a melting point of the Pr—Ga alloy powder and which is not higher than the melting point, to obtain a diffusion source from the Pr—Ga alloy powder; and placing the sintered R-T-B based magnet work and the diffusion source in a process chamber, and heating the sintered R-T-B based magnet work and the diffusion source in a vacuum or an inert gas ambient, thereby allowing Pr and Ga to diffuse from the diffusion source into the interior of sintered R-T-B based magnet work.