Sintered R-T-B Magnet Diffusion for High Coercivity and Remanence
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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 substituting light rare-earth elements with heavy rare-earth elements improves HcJ but decreases saturation magnetization and remanence (Br).
Innovation Solution
A method involving the preparation of a sintered R-T-B based magnet work and an RL-RH-B-M alloy, with specific compositions and heating processes, where the RL-RH-B-M alloy is diffused onto the magnet work at temperatures between 700°C and 1100°C in a vacuum or inert gas atmosphere, optimizing the molar ratios and concentrations of elements to balance HcJ and Br while reducing heavy rare-earth element usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare-earth elements (Dy, Tb) are used to substitute light rare-earth elements in R2T14B compound phase, then coercivity HcJ is improved, but saturation magnetization decreases and remanence Br decreases
Solution Approach 1:
The patent applies local quality by creating a concentration gradient of heavy rare-earth elements (Dy/Tb) where the content is highest at the outer crust of main phase crystal grains and decreases toward the center. This localized distribution allows the outer regions to provide high coercivity while the inner regions maintain high saturation magnetization, thus resolving the contradiction between improving HcJ and maintaining Br.
Solution Approach 2:
The patent segments the main phase crystal grains into different regions with different compositional characteristics: an outer crust region enriched with heavy rare-earth elements for high coercivity, and an inner region with light rare-earth elements for high saturation magnetization. This segmentation allows each region to contribute its optimal properties to the overall magnet performance.
2Stability of the object's composition
If heavy rare-earth elements are increased to maintain high HcJ at high temperatures, then thermal stability is improved, but cost increases due to heavy rare-earth element price
Solution Approach 1:
The patent changes the compositional parameters by creating a gradient distribution of heavy rare-earth elements rather than uniform distribution. The heavy rare-earth content varies from the outer crust to the center, allowing optimization of thermal stability where it is most needed (at grain boundaries and outer regions) while reducing overall heavy rare-earth content to lower cost.
3Reliability
If uniform distribution of heavy rare-earth elements is used throughout the magnet, then HcJ is improved, but Br decreases significantly
Solution Approach 1:
The patent implements local quality by creating a non-uniform distribution of heavy rare-earth elements concentrated at the outer crust of main phase crystal grains. This localized enrichment provides the necessary coercivity enhancement at critical regions (grain boundaries and surfaces) while preserving the light rare-earth element composition in the bulk, thereby maintaining high 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
The method achieves a good balance between coercivity and remanence with reduced heavy rare-earth element usage, maintaining high HcJ and suppressing the decrease in Br, thereby enhancing the thermal stability of sintered R-T-B based magnets.
Implementation Method 1
a diffusion step of heating the sintered R-T-B based magnet work and the RL-RH-B-M based alloy at a temperature not lower than 700° C. and not higher than 1100° C. in a vacuum or an inert gas atmosphere while at least a portion of the RL-RH-B-M based alloy is attached to at least a portion of a surface of the sintered R-T-B based magnet work
Implementation Method 2
heating the sintered R-T-B based magnet work and the RL-RH-B-M based alloy at a temperature not lower than 700° C. and not higher than 1100° C. in a vacuum or an inert gas atmosphere
Data Source
AI summary
A method for producing a sintered R-T-B based magnet includes: preparing a sintered R-T-B based magnet work (R is a rare-earth element; and T is at least one selected from the group consisting of Fe, Co, Al, Mn and Si, and contains Fe with no exception); preparing an RL-RH-B-M based alloy; and a diffusion step of performing heat treatment while at least a portion of the RL-RH-B-M based alloy is attached to at least a portion of a surface of the sintered R-T-B based magnet work. In the RL-RH-B-M based alloy, the content of RL is 50 mass % or higher and 95 mass % or lower, the content of RH is 45 mass % or lower (including 0 mass %), the content of B is 0.1 mass % or higher and 3.0 mass % is lower; and the content of M is 4 mass % or higher and 49.9 mass % or lower.