NdFeB Magnet Grain Boundary Diffusion for Coercive Force
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Solution Overview
Problem
Existing methods for improving coercive force in rare earth permanent magnets, such as grain boundary diffusion, face challenges including high production costs, limited coercive force improvement, and difficulties in mass production, while also struggling to maintain residual magnetic flux density and corrosion resistance.
Innovation Solution
A grain boundary diffusion method using a mixed powder containing rare earth elements and metal compounds like Cu, Zn, and Al, applied through heating and rapid cooling processes, to diffuse rare earth elements into the grain boundaries of NdFeB sintered magnets, enhancing coercive force and corrosion resistance while minimizing processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rare earth elements such as Dy and Tb are added to increase magnetic anisotropy energy to improve coercive force, then coercive force is improved, but the total price of the permanent magnet increases and price competitiveness decreases
Solution Approach 1:
The patent applies local quality by concentrating rare earth elements specifically at the grain boundaries of the NdFeB main phase rather than uniformly distributing them throughout the magnet. This localized approach at the grain boundary regions provides the necessary coercive force enhancement while using significantly less expensive rare earth content compared to bulk addition methods.
Solution Approach 2:
The patent employs composite materials by creating a multi-phase structure consisting of the NdFeB main phase combined with grain boundary phases containing rare earth elements. This composite approach allows the system to achieve high coercive force through the synergistic combination of the main phase (providing magnetic properties) and the grain boundary phase (providing magnetic anisotropy), while optimizing rare earth usage.
2Strength
If a binary alloy method is used to improve coercive force by mixing different alloy powders, then coercive force is improved, but the element of the alloy powder may diffuse into the particle when sintering, reducing the effect
Solution Approach 1:
The patent applies preliminary action by pre-forming the grain boundary diffusion layer with rare earth elements before the final sintering process. This preliminary preparation ensures that the rare earth elements are already positioned at the grain boundaries before sintering occurs, preventing unwanted diffusion into the particle interiors during the sintering process and maintaining stable element distribution.
3Strength
If evaporation or sputtering method is used for grain boundary diffusion in mass production, then grain boundary diffusion is achieved, but productivity decreases
Solution Approach 1:
The patent replaces the complex physical vapor deposition systems (evaporation or sputtering equipment) with a simpler mechanical powder coating method. By using a coating apparatus that applies rare earth-containing powder to the magnet surface followed by conventional heat treatment, the system achieves grain boundary diffusion without requiring sophisticated vacuum deposition equipment, thereby significantly improving productivity for mass production.
4Productivity
If rare earth inorganic compound powder is coated on sintered body surface followed by heating, then productivity is improved, but it is difficult to introduce rare earth elements into the magnet in a large quantity
Solution Approach 1:
The patent applies parameter changes by optimizing the heat treatment parameters (temperature, time, and atmosphere) to enhance the diffusion efficiency of rare earth elements from the coating into the grain boundaries. By carefully controlling these thermal parameters, the system achieves effective grain boundary diffusion with sufficient rare earth element content while maintaining the simple coating process and high 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 effectively improves coercive force and maintains residual magnetic flux density, providing corrosion resistance and reducing the need for expensive rare earth elements, thus lowering manufacturing costs and simplifying the production process.
Implementation Method 1
the grain boundary diffusion material is heated to diffuse at least one of Re1, Re2 and M into a grain boundary part inside the sintered magnet
Implementation Method 2
A grain boundary diffusion method using a mixed powder containing rare earth elements and metal compounds like Cu, Zn, and Al, applied through heating and rapid cooling processes
Data Source
AI summary
A method for manufacturing a rare earth permanent magnet includes manufacturing an NdFeB sintered magnet. A grain boundary diffusion material in the form of a mixed powder comprising an alloy powder containing Re1aMb or M; and Re2 hydride or Re2 fluoride is disposed on a surface of the NdFeB sintered magnet. The grain boundary diffusion material is heated to diffuse at least one of Re1, Re2 and M into a grain boundary part inside the sintered magnet or a grain boundary part region of a sintered magnet main phase grain. Re1 and Re2 are each rare earth elements selected from the group consisting of dysprosium, terbium, neodymium, praseodymium, and holmium, M is a metal compound consisting of copper, zinc, tin, and aluminum, 0.1<a<99.9, and a+b=100.