Ce-Containing NdFeB Magnet Shell Structure for High Coercivity
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Solution Overview
Problem
Existing methods for enhancing the coercivity of Ce-containing NdFeB magnets through grain boundary diffusion result in low diffusion efficiency and adverse effects on remanence and squareness due to high-temperature processes.
Innovation Solution
A staged diffusion process at different temperatures is employed to control the distribution of heavy rare earth elements, forming uniformly distributed shell-layered grains, reducing the number of reverse-shell and thick-shell grains, and optimizing the grain size in the surface and near-surface regions of the magnet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-temperature grain boundary diffusion is employed to enhance coercivity, then the diffusion efficiency of heavy rare earth elements increases, but heavy rare earth elements accumulate within the primary phase grains resulting in low diffusion efficiency and adverse effects on remanence and squareness
Solution Approach 1:
The patent segments the grain structure into core and shell regions, creating a non-uniform distribution of heavy rare earth elements. The shell region contains concentrated HRE while the core region maintains lower HRE content, preventing accumulation in the primary phase grains while still achieving high coercivity through the shell structure.
Solution Approach 2:
The patent applies local quality by creating shell-layered grains with different HRE concentrations in different regions. The shell region has high HRE content for enhancing coercivity at grain boundaries, while the core region has low HRE content to maintain remanence and avoid accumulation issues. This local differentiation resolves the contradiction between achieving high coercivity and maintaining uniform distribution.
2Strength
If high-temperature grain boundary diffusion is used to increase diffusion efficiency, then coercivity is enhanced, but remanence loss increases and squareness deteriorates
Solution Approach 1:
By segmenting the grain into core and shell regions with different HRE concentrations, the patent achieves high coercivity through the HRE-rich shell at grain boundaries while preserving remanence in the HRE-poor core region. This segmentation prevents the trade-off between coercivity enhancement and remanence loss.
Solution Approach 2:
The local quality principle is applied by creating spatially differentiated HRE distribution within grains. The shell region locally concentrates HRE to enhance coercivity without causing global accumulation that would harm remanence. This local differentiation allows simultaneous optimization of both coercivity and remanence stability.
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 results in Ce-containing NdFeB magnets with minimal remanence loss, high coercivity, and improved squareness of the demagnetization curve, demonstrating excellent magnetic performance.
Implementation Method 1
a grain boundary diffusion method can be employed... increasing the diffusion efficiency of heavy rare earth elements from the diffusion source
Implementation Method 2
A staged diffusion process at different temperatures is employed to control the distribution of heavy rare earth elements
Data Source
AI summary
A Ce-containing NdFeB magnet includes thin-shell grains, reverse-shell grains, and thick-shell grains. The reverse-shell grain has a higher HRE content in the core than in the shell. Both the thick-shell grain and the thin-shell grain have a higher HRE content in the shell than in the core. The thickness of the shell of the thin-shell grains is less than 2 μm. In the surface region of the Ce-containing NdFeB magnet, the number of thin-shell grains is N1, and the total number of grains in the Ce-containing neodymium-iron-boron magnet is N. In the near-surface region of the Ce-containing neodymium-iron-boron magnet, the number of reverse-shell grains is N2, the number of thick-shell grains is N3, and the total number of grains in the Ce-containing neodymium-iron-boron magnet is N′. N1/N is greater than 70%, and (N2+N3)/N′ is less than 5%.