Rare Earth Permanent Magnet Grain-Boundary Diffusion for Uniform Coercivity
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Solution Overview
Problem
The challenge lies in selecting a suitable diffusion source and diffusion temperature process to reduce the reaction of diffusion sources with crystal grains on the surface of neodymium-iron-boron magnets, thereby minimizing the coercivity difference between the magnet surface and core, and enhancing the utilization and diffusion depth of heavy rare earth elements.
Innovation Solution
A rare earth permanent magnet with a main phase structure of R2T14B crystal grains, where R is a rare earth element, T includes Mn and Fe, and B is boron, with Mn and a heavy rare earth element (Dy, Ho, or Tb) diffused in the grain boundary, using a two-stage heat treatment process and controlling oxygen content below 2000 ppm to improve diffusion depth and coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If low melting point elements (Cu, Ga, Al, Ag) are added as auxiliary diffusion sources, then grain boundary infiltration and Hcj are improved, but the diffusion source elements excessively permeate into crystal grains on the surface, increasing consumption and Hcj difference between surface and core
Solution Approach 1:
The patent changes the melting point parameter of the diffusion source by selecting high melting point elements (Zr, Ti, Nb, W) instead of low melting point elements, thereby reducing excessive permeation into surface crystal grains and lowering consumption of diffusion source elements while maintaining coercivity improvement
2Loss of substance
If diffusion temperature is reduced to decrease consumption of diffusion sources, then consumption is reduced, but migration speed of heavy rare earth element in grain boundary phase is reduced, greatly reducing diffusible depth
Solution Approach 1:
The patent changes the temperature parameter by adopting high diffusion temperatures (1000-1200°C) that enable sufficient migration speed of heavy rare earth elements in the grain boundary phase, achieving both reduced consumption and adequate diffusion depth in thick magnets
3Length of stationary object
If diffusion temperature is increased to improve diffusion depth, then diffusible depth is improved, but liquid phase ratio increases and reaction of diffusion sources with crystal grains on surface is accelerated
Solution Approach 1:
The patent changes the chemical composition parameter by selecting high melting point elements (Zr, Ti, Nb, W) as diffusion sources, which remain stable at high diffusion temperatures and do not excessively react with surface crystal grains, enabling deep diffusion without excessive surface consumption
Solution Approach 2:
The patent uses composite diffusion sources containing heavy rare earth elements combined with high melting point elements, creating a material system that achieves both deep diffusion and reduced surface reaction at elevated temperatures
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 solution results in a more uniform distribution of heavy rare earth elements, reducing the coercivity difference between the surface and core, improving the magnetic properties and mechanical properties of the magnet, while also enhancing corrosion resistance.
Implementation Method 1
a heavy rare earth element diffused and distributed in a grain boundary
Implementation Method 2
using a two-stage heat treatment process
Data Source
AI summary
The permanent magnet comprises a main phase structure of R2T14B crystal grains, and R is a rare earth element; T comprises at least Mn, Fe, and optionally a transition metal comprising Co; B is boron; the permanent magnet further comprises Mn and heavy rare earth elements which are distributed in a grain boundary in a diffusion mode. The heavy rare earth element is selected from at least one selected from Dy, Ho and Tb. According to the rare earth permanent magnet prepared through the preparation method, more heavy rare earth elements can be diffused into the magnet core along the grain boundary, Hcj distribution of the permanent magnet is improved, and meanwhile the corrosion resistance and the mechanical property of the permanent magnet are improved.