NdFeB Magnet Grain Boundary Diffusion for Coercive Force
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Solution Overview
Problem
Current methods for improving the intrinsic coercive force of sintered NdFeB magnets, such as adding heavy rare earth elements, often result in reduced remanence and increased production costs due to inefficient heating processes and energy wastage.
Innovation Solution
A method involving microwave heat treatment and grain boundary diffusion to create a volume diffusion layer of heavy rare earth elements within the magnet, optimizing the magnetocrystalline anisotropy field and coercive force while minimizing remanence loss, using a two-stage heat treatment process with microwave heating followed by conventional heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare earth elements (Dy, Tb) are added to substitute Nd in the main phase to improve coercive force, then the magnetocrystalline anisotropy field increases and coercive force improves, but the saturation magnetization significantly decreases, reducing remanence and maximum magnetic energy product
Solution Approach 1:
The patent applies local quality by concentrating heavy rare earth elements specifically at the grain boundary regions rather than uniformly distributing them throughout the main phase. This localized enrichment creates a high-anisotropy shell layer at grain boundaries that improves coercive force through magnetic decoupling, while the bulk main phase retains its high saturation magnetization properties, thus resolving the contradiction between improving coercive force and maintaining remanence.
Solution Approach 2:
The patent segments the magnet structure into distinct regions: a main phase core with high saturation magnetization and a grain boundary shell layer enriched with heavy rare earth elements for high anisotropy. This segmentation allows each region to fulfill its specific function - the core provides magnetic moment while the shell provides anisotropy - thereby simultaneously achieving high coercive force and high remanence.
2Stability of the object's composition
If conventional heating methods are used for grain boundary diffusion, then heavy rare earth elements can diffuse into the magnet, but the heating time is long and energy consumption is high
Solution Approach 1:
The patent replaces conventional thermal conduction heating with microwave heating technology. Microwave heating directly couples electromagnetic energy with the material, enabling rapid and uniform heating throughout the magnet body. This substitution dramatically reduces heating time and energy consumption while achieving the same or better diffusion效果, as microwaves can penetrate and heat the entire sample volume simultaneously rather than requiring slow heat conduction from the surface.
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
Enhances the intrinsic coercive force of sintered NdFeB magnets without significantly reducing remanence or magnetic energy product, while reducing heat treatment time and energy consumption, thus lowering production costs.
Implementation Method 1
a method involving microwave heat treatment and grain boundary diffusion
Implementation Method 2
the heavy rare earth elements are caused to diffuse into the interior of the magnet along an Nd-rich liquid grain boundary phase
Implementation Method 3
Dy2Fe14B or Tb2Fe14B crystal has a higher magnetocrystalline anisotropy field than Nd2Fe14B crystal, that is, has higher theoretical intrinsic coercive force
Data Source
AI summary
The present invention discloses a rare earth permanent magnet and a method for preparing same. The material of the rare earth permanent magnet has a heavy rare earth element volume diffusion phenomenon at a depth of 5 μm to 100 μm from the surface of the magnet to the interior of the magnet along the magnetic field orientation direction, thereby forming a volume diffusion layer region; the volume diffusion layer region is divided into magnet units having a volume of 10*100*5 μm, and the concentration difference of the heavy rare earth elements of the magnet units at different positions in the volume diffusion layer is below 0.5 at %. The present invention provides a sintered NdFeB magnet of high intrinsic coercive force Hcj on the premise of not influencing the remanence Br and the maximum magnetic energy product (BH)max of products. In the method for preparing the rare earth permanent magnet, microwave heat treatment is performed on a blank magnet coated with heavy rare earth source slurry in a vacuum condition. This method can effectively improve the heating efficiency, reduce the heat treatment time, lower the energy consumption, and reduce the production cost of the magnet.