Electrodeposited Rare Earth Coating for Nd-Fe-B Magnet Coercivity
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Solution Overview
Problem
Current methods for enhancing the coercive force of sintered Nd-Fe-B base permanent magnets while maintaining remanence are limited by diffusion issues during high-temperature sintering and inefficiencies in powder coating processes, leading to productivity and cost challenges.
Innovation Solution
A method involving electrodeposition of rare earth elements like Dy or Tb onto the surface of sintered magnet bodies, using a powder dispersed in a solvent, followed by heat treatment, to create a uniform and dense coating that increases coercive force without sacrificing remanence, with the option to locally apply the coating for specific areas of high demand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If Dy or Tb is substituted for Nd in the Nd2Fe14B compound to increase coercive force, then the anisotropic magnetic field and coercive force increase, but the saturation magnetic polarization and remanence decrease
Solution Approach 1:
The patent applies local quality by concentrating Dy or Tb substitution specifically at the grain boundary regions rather than uniformly throughout the crystal grains. This localized substitution increases the anisotropic magnetic field and coercive force at the grain boundaries where reverse magnetic domain nuclei form, while preserving the saturation magnetic polarization and remanence in the interior of the crystal grains.
2Manufacturing precision
If sintering is performed at high temperature (1000-1100°C) to achieve densification, then the magnet achieves good density, but Dy or Tb diffuses excessively into the crystal grain interior, reducing the concentration at grain boundaries
Solution Approach 1:
The patent applies preliminary action by pre-forming the magnet body with a specific composition and structure before the final sintering treatment. The magnet body is prepared with conditions that enable controlled diffusion of Dy or Tb during sintering, ensuring that the elements concentrate at grain boundaries rather than diffusing uniformly into the grain interiors, thus achieving both densification and proper composition distribution.
3Stability of the object's composition
If low temperature sintering is used to minimize diffusion of Dy or Tb into crystal grains, then the concentration at grain boundaries is maintained, but densification by sintering is retarded
Solution Approach 1:
The patent applies parameter changes by optimizing the sintering temperature to a specific range (900-1100°C) that balances two competing requirements: achieving sufficient densification while controlling the diffusion of Dy or Tb. This temperature parameter is carefully selected to enable controlled diffusion that concentrates rare earth elements at grain boundaries without excessive diffusion into the grain interiors, thus achieving both good density and proper composition distribution.
4Ease of manufacture
If powder coating methods are used to apply rare earth-containing powder to the magnet surface, then the coating process is simple, but the coating is not uniform and adhesion is poor
Solution Approach 1:
The patent replaces the mechanical powder coating method with an electrochemical deposition process. Instead of mechanically applying powder to the surface, the rare earth-containing powder is deposited onto the magnet body surface through electrochemical reactions during sintering. This substitution achieves uniform coating with excellent adhesion because the deposition is controlled by electrochemical fields rather than mechanical forces, ensuring consistent distribution and strong bonding to the substrate.
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 increases coercive force while maintaining high remanence, reduces powder consumption, and improves process efficiency by ensuring a uniform and adherent coating, making the production of high-performance magnets more economical and productive.
Implementation Method 1
immersing a portion of a sintered magnet body having a R1Fe2B-based permanent magnet structure in an electrodepositing bath of dispersion of rare earth-containing powder in solvent, and electrodepositing the powder on the magnet body surface
Implementation Method 2
heating a R1Fe2B-based permanent magnet with a magnetization direction along a rolling direction or transverse direction of the permanent magnet, wherein the permanent magnet is produced by a method comprising: disposing rare earth-containing powder on a surface of a sintered magnet body; and heat treating the sintered magnet body
Data Source
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AI summary
A rare earth permanent magnet is prepared by immersing a portion of a sintered magnet body of R1-Fe-B composition (wherein R1 is a rare earth element) in an electrodepositing bath of a powder dispersed in a solvent, the powder comprising an oxide, fluoride, oxyfluoride, hydride or rare earth alloy of a rare earth element, effecting electrodeposition for letting the powder deposit on a region of the surface of the magnet body, and heat treating the magnet body with the powder deposited thereon at a temperature below the sintering temperature in vacuum or in an inert gas.