R-T-B Permanent Magnet Surface R-O-C Phase Distribution
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Solution Overview
Problem
R-T-B based permanent magnets face a trade-off between corrosion resistance and coercivity due to the formation of an R—O—C concentrated phase, which enhances corrosion resistance but decreases coercivity.
Innovation Solution
A surface layer portion with a higher proportion of R′—O—C phase and a central portion with a lower proportion, where the R′—O—C phase is localized on the surface to prevent corrosion while maintaining high coercivity, by controlling the concentration and distribution of R′—O—C phase in the grain boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an R-O-C concentrated part is formed in the grain boundaries to enhance corrosion resistance, then corrosion resistance is improved, but coercivity decreases due to reduction of R-rich phase
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of R-O-C phase within the magnet structure. Specifically, the surface layer portion contains a higher proportion of R-O-C phase (S1%) compared to the central portion (S2%), with S1-S2 ranging from 1.0 to 80. This localized concentration of corrosion-resistant phase at the surface while maintaining lower concentrations in the interior resolves the contradiction by providing enhanced corrosion resistance where it is most needed (at the surface exposed to environment) while preserving coercivity in the bulk material through adequate R-rich phase content.
2Reliability
If a certain amount of R-O-C concentrated part is formed over the entire magnet to achieve excellent corrosion resistance, then corrosion resistance is improved, but coercivity decreases due to R-rich phase reduction
Solution Approach 1:
The patent segments the magnet into two distinct regions: a surface layer portion and a central portion, each with different R-O-C phase concentrations. The surface layer portion (positioned on the surface side) contains a higher proportion of R-O-C phase (S1%), while the central portion (positioned on the inner side) contains a lower proportion (S2%). This segmentation allows the surface region to provide corrosion protection while the interior region maintains the magnetic properties and coercivity required for functional performance.
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 effectively suppresses corrosion and maintains high coercivity by localizing the R′—O—C phase on the surface, preventing hydrogen production and oxidation in the grain boundaries, thereby reducing corrosion progression and minimizing coercivity loss.
Implementation Method 1
rare earth elements, which constitute a main component of the R-T-B based permanent magnets, are easily oxidized, the R-T-B based permanent magnets tend to be susceptible to corrosion
Implementation Method 2
when a magnet body contains an R—O—C concentrated part, corrosion resistance of the magnet body itself is enhanced
Data Source
AI summary
A permanent magnet 2 includes Nd, Fe, and B, the permanent magnet 2 contains a plurality of main phase grains; and grain boundaries positioned between the main phase grains, the main phase grains include Nd, Fe, and B, at least a portion of the grain boundaries contains an R′—O—C phase, the R′—O—C phase includes a rare earth element R′, O, and C, the concentration of each of R′, O, and C in the R′—O—C phase is higher compared to the main phase grains, the permanent magnet 2 comprises a surface layer portion 21 and a central portion 22, the surface layer portion 21 is positioned on the surface side of the permanent magnet 2, the central portion 22 is positioned on the inner side of the permanent magnet 2, the proportion of the area of the R′—O—C phase occupying in a cross-section of the surface layer portion 21 is S1 %, the proportion of the area of the R′—O—C phase occupying in a cross-section of the central portion 22 is S2%, and S1 is higher than S2.