R-T-B Magnet Coercivity via RLM-RH Surface Diffusion
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Solution Overview
Problem
Existing methods for improving the intrinsic coercivity (HcJ) of sintered R-T-B based magnets at high temperatures are inefficient, particularly in reducing heavy rare-earth elements (RH) on the magnet surface while maintaining remanence (Br), and require excessive RH usage due to limited diffusion effectiveness.
Innovation Solution
A method involving a heat treatment process with a powder mixture of an RLM alloy and an RH compound on the surface of sintered R-T-B based magnets, where the RLM alloy contains 50 at % or more of light rare-earth elements (RL) like Nd or Pr, and the RH compound is an oxide, fluoride, or oxyfluoride, with a mass ratio of RLM alloy:RH compound ranging from 9.6:0.4 to 5:5, allowing efficient diffusion of RH into the magnet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heavy rare-earth element RH is profusely added to replace light rare-earth element RL in the sintered R-T-B based magnet, then intrinsic coercivity HcJ increases, but remanence Br decreases
Solution Approach 1:
The patent applies preliminary action by coating the magnet surface with RH compound powder before heat treatment, preparing the heavy rare-earth element in advance for controlled diffusion into the magnet body during subsequent heating, thereby achieving HcJ improvement without excessive RH addition that would lower Br
Solution Approach 2:
The patent implements local quality by concentrating RH compound coating only on the magnet surface rather than uniformly distributing RH throughout the entire magnet, allowing HcJ enhancement at the critical surface region while preserving the overall magnetic properties and remanence Br of the bulk material
2Reliability
If existing methods using powder mixture of RH oxide or RH fluoride and metal M are used to improve HcJ, then some HcJ enhancement is achieved, but the methods cannot effectively exploit the RH present on the magnet surface and require excessive RH usage
Solution Approach 1:
The patent applies parameter changes by optimizing the heat treatment temperature range (900-1100°C) to match the melting point of the RLM alloy, enabling the alloy to become liquid and effectively reduce the RH oxide, thereby maximizing RH utilization efficiency and reducing the total amount of RH compound needed compared to conventional methods
Solution Approach 2:
The patent introduces RLM alloy as an intermediary substance that mediates between the RH oxide coating and the magnet body. The RLM alloy reduces the RH oxide to metallic RH during heat treatment, facilitating controlled diffusion of RH into the magnet while improving HcJ with less RH consumption than direct RH compound application
3Reliability
If heat treatment is performed at high temperature to diffuse RH into the magnet, then HcJ improves, but excessive heat treatment may cause unwanted side effects and the RH diffusion efficiency remains limited
Solution Approach 1:
The patent exploits phase transitions by heating the RLM alloy to its melting point during heat treatment, transforming it from solid to liquid state. This phase change enables the RLM alloy to effectively reduce the RH oxide and facilitates rapid, efficient diffusion of RH into the magnet, significantly improving diffusion efficiency compared to solid-state diffusion in conventional methods
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 method enhances HcJ to levels comparable to conventional techniques using less RH, ensuring high coercivity without significantly lowering remanence, and effectively reduces RH compounds on the surface, preventing excess fluorine from diffusing into the magnet.
Implementation Method 1
by using a powder mixture including a powder of an RM alloy (where M is one, or two or more, selected from among Al, C, P, Ti, and the like) and a powder of an M1M2 alloy (M1 and M2 are one, or two or more, selected from among Al, Si, C, P, Ti, and the like), and an RH oxide, it is possible to partially reduce the RH oxide with the RM alloy or the M1M2 alloy during the heat treatment
Implementation Method 2
allowing the RH and M to be efficiently absorbed to the sintered R-T-B based magnet, thereby enhancing HcJ of the sintered R-T-B based magnet
Implementation Method 3
allowing the RH and M to be efficiently absorbed to the sintered R-T-B based magnet
Data Source
AI summary
A step of, while a powder of an RLM alloy (where RL is Nd and/or Pr; M is one or more elements selected from among Cu, Fe, Ga, Co, Ni and Al) which is produced through atomization and a powder of an RH compound (where RH is Dy and/or Tb) are present on the surface of a sintered R-T-B based magnet, performing a heat treatment at a sintering temperature of the sintered R-T-B based magnet or lower is included. The RLM alloy contains RL in an amount of 65 at % or more, and the melting point of the RLM alloy is equal to or less than the temperature of the heat treatment. The heat treatment is performed while the RLM alloy powder and the RH compound powder are present on the surface of the sintered R-T-B based magnet at a mass ratio of RLM alloy:RH compound=9.6:0.4 to 5:5.