Rare Earth Permanent Magnet Diffusion with Mn for Core Coercivity Uniformity
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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, while improving the utilization and diffusion depth of heavy rare earth elements.
Innovation Solution
A rare earth permanent magnet with a main phase structure of R2T14B, 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 diffusion source containing Mn and a heavy rare earth, subjected to a two-stage heat treatment process to optimize diffusion, and controlling oxygen content below 2000 ppm to enhance infiltration and coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If elements with low melting points (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 of the magnet, increasing the Hcj difference between diffusion magnet surface and magnet core
Solution Approach 1:
The patent changes the melting point parameter of the diffusion source by selecting elements with high melting points (Zr, Ti, Nb, W) instead of low melting point elements. This parameter change prevents excessive permeation into surface crystal grains while maintaining grain boundary infiltration capability, thereby improving coercivity uniformity between surface and core.
Solution Approach 2:
The patent utilizes the phase transition behavior of high melting point elements that remain solid at conventional diffusion temperatures, preventing them from rapidly melting and excessively permeating into surface grains. The solid phase state controls the diffusion rate and prevents harmful over-diffusion while still achieving effective grain boundary infiltration.
2Manufacturing precision
If diffusion temperature is reduced to decrease consumption of diffusion source elements, then Hcj difference between surface and core is reduced, but the 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 conventional heavy rare earth diffusion temperatures (900-1100°C) combined with high melting point diffusion source elements. This temperature parameter change enables sufficient diffusion depth while the high melting point elements prevent excessive surface permeation, achieving both deep diffusion and uniform coercivity distribution.
3Manufacturing precision
If elements with high melting points (Zr, Ti, Nb, W) are added as auxiliary diffusion sources, then the melting point of diffusion sources is increased and heavy rare earth diffusion sources are more difficult to rapidly permeate into the magnet, but the liquid phase ratio of the magnet at high temperature is increased and the reaction of diffusion sources with crystal grains on the surface is accelerated
Solution Approach 1:
The patent optimizes the composition parameters of the diffusion source by using specific high melting point elements (Zr, Ti, Nb, W) in controlled amounts. These elements increase the overall melting point of the diffusion source mixture, preventing rapid melting and excessive surface permeation, while the controlled composition limits harmful surface reactions despite increased liquid phase ratio at diffusion 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
This approach results in improved coercivity uniformity and increased diffusion depth of heavy rare earth elements, reducing the coercivity difference between the surface and core, and enhancing the mechanical and corrosion resistance properties of the magnet.
Implementation Method 1
more diffusion sources permeate into the magnet, the Hcj difference between the magnet surface and the core is reduced, and the improvement of the utilization rate and the diffusion depth of the heavy rare earth is achieved
Implementation Method 2
subjected to a two-stage heat treatment process to optimize diffusion
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.