R-T-B Sintered Magnet Coercivity Gradient Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Sintered R-T-B based magnets face challenges in maintaining coercivity at high temperatures without decreasing remanence, and existing methods for diffusing heavy rare-earth elements often result in property alterations, contamination, and reduced weather resistance due to excessive rare-earth element diffusion or surface layer formation.
Innovation Solution
A sintered R-T-B based magnet with R2Fe14B type compound crystal grains, where a heavy rare-earth element like Dy or Tb is diffused inside the magnet without forming a high-concentration surface layer, maintaining a gradual decrease in coercivity from the surface to the core, and using a movable processing chamber to prevent adhesion and excessive rare-earth element supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heavy rare-earth element RH is added to increase coercivity, then coercivity increases, but remanence decreases
Solution Approach 1:
The heavy rare-earth element RH is selectively concentrated at the grain boundaries of the R2Fe14B type compound crystal grains rather than being uniformly distributed throughout the magnet. This local concentration at grain boundaries enhances coercivity by strengthening the magnetic anisotropy at these critical regions, while the bulk material maintains its light rare-earth element composition and high remanence properties.
Solution Approach 2:
The magnet structure is segmented into distinct regions: grain boundary phases containing heavy rare-earth elements RH and light rare-earth elements RL, and interior phases of R2Fe14B type compound crystal grains with light rare-earth elements RL. This segmentation allows different functional requirements to be met in different regions - high coercivity at grain boundaries and high remanence in the bulk.
2Reliability
If a heavy rare-earth element RH is added to increase coercivity at high temperature, then coercivity at high temperature increases, but the amount of rare-earth resources consumed increases
Solution Approach 1:
The heavy rare-earth element RH is selectively concentrated at the grain boundaries of the R2Fe14B type compound crystal grains rather than being uniformly distributed throughout the magnet. This local concentration at grain boundaries enhances coercivity by strengthening the magnetic anisotropy at these critical regions, while the bulk material maintains its light rare-earth element composition and high remanence properties.
Solution Approach 2:
Instead of uniformly distributing heavy rare-earth elements throughout the entire magnet volume, the invention applies partial action by concentrating RH only at the grain boundaries where it is most needed for maintaining coercivity. This reduces the total amount of heavy rare-earth elements required while achieving the desired high-temperature coercivity performance.
3Reliability
If heavy rare-earth element RH is diffused inside the magnet body, then coercivity increases, but the surface region may form a high-concentration layer that reduces weather resistance
Solution Approach 1:
The heavy rare-earth element RH is selectively concentrated at the grain boundaries of the R2Fe14B type compound crystal grains rather than being uniformly distributed throughout the magnet. This local concentration at grain boundaries enhances coercivity by strengthening the magnetic anisotropy at these critical regions, while the bulk material maintains its light rare-earth element composition and high remanence properties.
Solution Approach 2:
The diffusion process is controlled to achieve preliminary concentration of heavy rare-earth elements RH at the grain boundaries before they can migrate to the surface and form high-concentration layers. This preliminary positioning at grain boundaries ensures coercivity enhancement while preventing surface degradation that would compromise weather resistance.
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 approach effectively increases coercivity while minimizing remanence loss and improving weather resistance by ensuring a uniform distribution of rare-earth elements within the magnet, reducing grain boundary corrosion, and preventing surface oxidation.
Implementation Method 1
a heavy rare-earth element RH (which includes at least one of Dy and Tb) has been diffused inside from the surface region of the sintered R-T-B based magnet body
Implementation Method 2
the sintered magnet body and the RH diffusion source are movable relative to each other and are brought close to, or in contact with, each other
Implementation Method 3
heating to, and maintaining at, a temperature (processing temperature) of 500° C. through 850° C.
Data Source
AI summary
This sintered R-T-B based rare-earth magnet includes: R2Fe14B type compound crystal grains, including a light rare-earth element RL (which includes at least one of Nd and Pr) as a major rare-earth element R, as main phases; and a heavy rare-earth element RH (which includes at least one of Dy and Tb). Before its surface region is removed, the sintered R-T-B based rare-earth magnet has no layer including the rare-earth element R at a high concentration in that surface region. The sintered R-T-B based rare-earth magnet has a portion in which coercivity decreases gradually from its surface region toward its core portion. The difference in the amount of TRE between a portion of the sintered R-T-B based rare-earth magnet that reaches a depth of 500 μm as measured from its surface region toward its core portion and the core portion of the sintered R-T-B based rare-earth magnet is 0.1 through 1.0.