Grain Boundary Diffusion in NdFeB Magnets
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Solution Overview
Problem
Nd—Fe—B permanent magnets face a challenge in achieving high coercive force while maintaining high remanence, as the addition of expensive rare earth elements like Dy and Tb leads to a loss in remanence, and existing grain boundary diffusion processes are not optimized for incidental impurities such as oxygen, carbon, and nitrogen.
Innovation Solution
A method involving a grain boundary diffusion process where a powder with specific rare earth elements is applied to a sintered magnet body, optimizing the amount of Nd-rich phase based on incidental impurities, and heat treating at a temperature below the sintering temperature to minimize the use of Dy and Tb while enhancing coercive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If Dy or Tb is added to increase coercive force, then coercive force is improved, but remanence is reduced
Solution Approach 1:
The patent applies local quality by concentrating Dy or Tb at grain boundaries rather than uniformly distributing them throughout the magnet. The grain boundary phase serves as a localized region where these rare earth elements are preferentially positioned, creating a non-uniform composition that enhances coercive force at the grain boundaries while preserving the magnetic properties of the crystal grains interior.
Solution Approach 2:
The patent segments the magnet structure into distinct regions: grain boundaries and crystal grains interior. By targeting the grain boundary phase specifically for Dy/Tb enrichment, the invention separates the functional roles of different regions - grain boundaries provide coercive force enhancement while crystal grains maintain saturation magnetic polarization.
2Force
If Dy or Tb is uniformly distributed throughout the magnet, then coercive force is improved, but the amount of expensive rare earth elements increases
Solution Approach 1:
The patent makes the composition non-uniform by concentrating Dy or Tb specifically in the grain boundary phase rather than distributing them uniformly. This localized enrichment achieves the necessary coercive force enhancement only where needed at grain boundaries, minimizing the overall amount of expensive rare earth elements required in the magnet.
3Quantity of substance
If the sintering temperature is reduced to preserve remanence, then remanence is maintained, but diffusion of Dy or Tb is insufficient
Solution Approach 1:
The patent changes the chemical composition parameters of the grain boundary phase by adjusting the ratio of Nd-rich phase to oxide phase. By optimizing this composition, the invention enables effective Dy/Tb diffusion at lower temperatures, as the specific grain boundary composition facilitates element transport without requiring high thermal energy that would compromise remanence.
4Manufacturing precision
If the amount of Nd-rich phase is increased to facilitate diffusion, then diffusion medium is sufficient, but the amount of Nd2Fe14B compound is reduced
Solution Approach 1:
The patent optimizes the compositional parameters of the grain boundary phase, specifically the ratio of Nd-rich phase to oxide phase. By fine-tuning this ratio, the invention achieves sufficient diffusion capability without excessively increasing the Nd-rich phase content, thereby maintaining an optimal balance between diffusion medium availability and the volume of the magnetic Nd2Fe14B compound.
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 a rare earth permanent magnet with high performance and minimal use of expensive rare earth elements, achieving increased coercive force without significant loss in remanence.
Implementation Method 1
Dy or Tb is incorporated into the sintered magnet body from the rare earth compound present on the sintered magnet body surface and diffused into the magnet body along grain boundaries
Implementation Method 2
the Nd-rich phase becomes a liquid phase during the heat treatment, and Dy or Tb is dissolved in this liquid phase and diffused into the interior
Data Source
AI summary
A rare earth permanent magnet is prepared by providing a sintered magnet body consisting of 12-17 at % of rare earth, 3-15 at % of B, 0.01-11 at % of metal element, 0.1-4 at % of O, 0.05-3 at % of C, 0.01-1 at % of N, and the balance of Fe, disposing on a surface of the magnet body a powder comprising an oxide, fluoride and/or oxyfluoride of another rare earth, and heat treating the powder-covered magnet body at a temperature below the sintering temperature in vacuum or in an inert gas, for causing the other rare earth to be absorbed in the magnet body.