Multilayer-Coated NdFeB Powder for Deeper Grain Boundary Diffusion
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Solution Overview
Problem
Conventional magnetic powder surface diffusion methods for enhancing coercivity in sintered NdFeB magnets face limitations due to shallow diffusion depth and inability to form a uniform, continuous network of grain boundary phases, leading to weakened demagnetization coupling and limited improvement in coercivity.
Innovation Solution
A novel NdFeB alloy powder with a multi-layered coating comprising a first metal layer of Tb or Dy, a second metal layer of W, Mo, Ti, or Zr, and a third metal layer of Pr, Nd, La, or Ce, which prevents direct contact between grains and promotes liquid phase diffusion to form a networked grain boundary structure, thereby enhancing coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earth elements (Dy, Tb) are added to increase coercivity, then the coercive force of the magnet is improved, but the cost of the magnet alloy increases significantly
Solution Approach 1:
The patent applies local quality by concentrating heavy rare earth elements specifically at the grain boundaries through diffusion, rather than uniformly distributing them throughout the entire magnet alloy. This localized approach achieves the necessary coercivity enhancement at the critical grain boundary regions while minimizing the overall quantity of expensive heavy rare earth elements required in the alloy composition.
Solution Approach 2:
The patent introduces light rare earth elements (Pr, Nd, La, Ce) as intermediary elements that facilitate the diffusion and distribution of heavy rare earth elements at grain boundaries. These light rare earth elements act as mediators that enable controlled diffusion processes and help form the desired grain boundary structure, reducing direct dependence on large amounts of expensive heavy rare earth elements.
2Strength
If conventional grain boundary diffusion technology is used, then some coercivity improvement is achieved, but the diffusion depth is shallow and thicker products cannot be effectively treated
Solution Approach 1:
The patent applies parameter changes by optimizing multiple process parameters including diffusion temperature, time, and the composition ratios of light and heavy rare earth elements. By carefully controlling these parameters, the diffusion depth is extended to achieve effective treatment of thicker products while maintaining controlled diffusion that prevents excessive grain growth. The specific parameter range enables deeper diffusion compared to conventional methods.
3Strength
If conventional dual alloy technology is used, then grain boundary phase is formed, but the main phase grains cannot be completely separated, leading to limited coercivity increase
Solution Approach 1:
The patent employs composite materials by combining light rare earth elements (Pr, Nd, La, Ce) with heavy rare earth elements (Dy, Tb) to create a composite grain boundary phase. This composite approach leverages the beneficial properties of both light and heavy rare earth elements, achieving complete separation of main phase grains through the synergistic effect of the composite grain boundary phase, which enables significant coercivity enhancement that neither element alone could achieve.
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 multi-layered coating effectively increases the coercivity of sintered NdFeB magnets by preventing grain growth and ensuring a uniform network of grain boundary phases, resulting in higher coercivity compared to traditional methods.
Implementation Method 1
heat treatment at a temperature higher than its melting point, liquid diffusion occurs
Implementation Method 2
By grain boundary diffusion of the heavy rare earth element Dy/Tb, a (Nd, Dy, Tb)2Fe14B hard magnetized layer can be formed on the epitaxial layer of the grain surface
Implementation Method 3
magnetron sputtering method to deposit light rare earth alloy on NdFeB magnet powder
Implementation Method 4
thermal resistance evaporation deposition method to deposit Dy/Tb particles and Pr/Nd particles on the surface of NdFeB magnetic powder
Implementation Method 5
pressed and sintered to improve the coercivity of the NdFeB magnet
Data Source
AI summary
The disclosure refers to a NdFeB alloy powder for forming high-coercivity sintered NdFeB magnets. The NdFeB alloy powder includes NdFeB alloy core particles with a multi-layered coating, wherein the multi-layered coating comprises:a first metal layer directly disposed on the NdFeB alloy core particles, wherein the first metal layer consists of at least one of Tb and Dy;a second metal layer directly disposed on the first metal layer, wherein the second metal layer consists of at least one of W, Mo, Ti, Zr, and Nb; anda third metal layer directly disposed on the second metal layer, wherein the third metal layer consists of (i) at least one of Pr, Nd, La, and Ce; or (ii) a combination of one of the group consisting of Cu, Al, and Ga and at least one of the group consisting of Pr, Nd, La, and Ce.