NdFeB Magnet Coercive Force via Dy Tb Grain Boundary Diffusion
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Solution Overview
Problem
Nd—Fe—B sintered magnets face challenges with low Curie temperature leading to demagnetization due to heat, defects during fabrication causing magnetic property deterioration, and limited coercive force, which are exacerbated by the scarcity and high cost of Dy and Tb resources.
Innovation Solution
A method involving the adherence and diffusion of Dy and/or Tb into the grain boundary phase of Nd—Fe—B sintered magnets using a two-alloy method, followed by vacuum vapor processing to enhance coercive force and magnetic properties, while maintaining high productivity and avoiding surface deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Dy and Tb are added to improve grain magnetic anisotropy and coercive force, then coercive force is improved, but maximum energy product is extremely reduced
Solution Approach 1:
The patent applies local quality by concentrating Dy and Tb diffusion specifically at the grain boundary phase rather than uniformly throughout the entire magnet. This localized approach allows the grain boundary regions to have high coercive force properties while the grain interiors maintain high magnetic moment properties, thus resolving the contradiction between improving coercive force and maintaining maximum energy product.
Solution Approach 2:
The patent segments the magnet into two distinct regions with different compositional characteristics: grain boundary phase enriched with Dy and Tb for high coercive force, and grain interior phase with high magnetic moment. This segmentation allows each region to optimize its function independently, resolving the contradiction between coercive force and maximum energy product.
2Strength
If Dy and Tb are deposited as a thick film (above 3 μm) to improve coercive force, then coercive force is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent changes the deposition parameters by using a thin film (1-3 μm) combined with controlled heat treatment temperature (900-1100°C) to achieve the desired diffusion effect. This parameter optimization reduces the required film thickness while maintaining coercive force improvement, thereby reducing manufacturing complexity and cost.
Solution Approach 2:
The patent applies preliminary action by depositing a thin film of Dy and Tb on the magnet surface before heat treatment. This preliminary deposition creates a controlled source of diffusing elements that, when combined with heat treatment, achieves uniform distribution in the grain boundary phase without requiring a thick initial film, thus reducing manufacturing complexity.
3Strength
If Dy and Tb are deposited as a thick film to improve coercive force, then coercive force is improved, but surface quality deteriorates
Solution Approach 1:
The patent changes the deposition parameters by using a thin film (1-3 μm) instead of a thick film, which prevents surface roughness and other quality issues. The combination of thin film deposition with controlled heat treatment achieves the desired coercive force improvement without compromising surface quality.
4Strength
If Dy and Tb are deposited as a thick film to improve coercive force, then coercive force is improved, but productivity decreases
Solution Approach 1:
The patent optimizes deposition parameters by using a thin film (1-3 μm) combined with controlled heat treatment, which achieves the desired coercive force improvement in a single integrated process step. This eliminates the need for multiple processing steps required by thick film deposition, thereby improving productivity.
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 significantly increases coercive force and magnetic properties, improves productivity by efficient diffusion of Dy and/or Tb, and maintains surface quality, reducing the need for additional finishing steps.
Implementation Method 1
a second step of diffusing, through heat-treatment at a predetermined temperature, at least one of Dy and Tb adhered to the surface of the sintered magnet into grain boundary phase of the sintered magnet
Implementation Method 2
vacuum vapor processing to enhance coercive force and magnetic properties
Implementation Method 3
through heat-treatment at a predetermined temperature
Data Source
AI summary
There is provided a method of manufacturing a permanent magnet which has an extremely high coercive force and high magnetic properties is manufactured at high productivity. There are executed: a first step of causing at least one of Dy and Tb to adhere to at least part of a surface of iron-boron-rare-earth based sintered magnet; and a second step of diffusing, through heat-treatment at a predetermined temperature, at least one of Dy and Tb adhered to the surface of the sintered magnet into grain boundary phase of the sintered magnet. As the sintered magnet, there is used one which is manufactured by: mixing each powder of principal phase alloy (constituted primarily by R2T14B phase, where R is at least one rare earth element primarily including Nd and where T is a transition metal primarily including Fe), and a liquid phase alloy (having a higher content of R than R2T14B phase and primarily constituted by R-rich phase) in a predetermined mixing ratio; press-forming in magnetic field a mixed powder thus obtained; and sintering a press-formed body in vacuum or inert gas atmosphere.