NdFeB Magnet Grain Boundary Diffusion for Higher Coercivity
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Solution Overview
Problem
Current methods for enhancing the coercivity of NdFeB rare earth magnets, such as grain boundary diffusion and the use of heavy rare earth alloys, face challenges including high costs due to the high price of Dy and Tb raw materials, uneven magnet performance, and limited coercivity improvement, along with issues related to high melting points and reduced residual magnetism.
Innovation Solution
The development of an NdFeB rare earth magnet with a main phase, heavy rare earth shells, and a grain boundary phase comprising μ and δ phases, where the μ phase is R36.5Fe63.5-xMx and the δ phase is R32.5Fe67.5-yMy, with specific atomic percentages, and a diffusion source alloy RαRHδMβBγFe100-α-β-γ-δ coated with a non-heavy rare earth alloy film, which reduces Fe content and increases M content, facilitating efficient diffusion and reducing oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare earth elements Dy or Tb are added to the NdFeB base material in large quantities, then the coercivity of the magnet is improved, but the residual magnetism and magnetic energy product are reduced and the cost 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 magnet. This localized enrichment at critical regions (grain boundaries) provides effective coercivity enhancement while minimizing overall heavy rare earth content and preserving bulk residual magnetism.
Solution Approach 2:
The patent uses an alloying element (such as Al, Ga, or In) as an intermediary to facilitate the diffusion of heavy rare earth elements along grain boundaries. This intermediary element creates a diffusion pathway that enables controlled transport of heavy rare earths, achieving uniform grain boundary enrichment without requiring large quantities of expensive materials.
2Force
If heavy rare earth elements Dy or Tb are added to the NdFeB base material in large quantities, then the coercivity of the magnet is improved, but the cost 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 magnet. This localized enrichment at critical regions (grain boundaries) provides effective coercivity enhancement while minimizing overall heavy rare earth content and preserving bulk residual magnetism.
Solution Approach 2:
The patent uses an alloying element (such as Al, Ga, or In) as an intermediary to facilitate the diffusion of heavy rare earth elements along grain boundaries. This intermediary element creates a diffusion pathway that enables controlled transport of heavy rare earths, achieving uniform grain boundary enrichment without requiring large quantities of expensive materials.
3Force
If grain boundary diffusion technology using pure Dy and Tb is used, then the coercivity of the magnet is improved, but the cost remains high due to skyrocketing raw material prices
Solution Approach 1:
The patent replaces expensive pure heavy rare earth elements (Dy, Tb) with a cost-effective alloy composition containing lighter rare earth elements (Pr, Nd) combined with alloying elements (Al, Ga, In). This substitution uses more abundant, cheaper materials to achieve the same diffusion effect, dramatically reducing raw material costs while maintaining coercivity improvement.
Solution Approach 2:
The patent employs a composite diffusion source material consisting of multiple elements (rare earth elements + alloying elements) that work synergistically. The alloying elements enhance diffusion capability and control the distribution pattern, allowing effective grain boundary enrichment using a composite material that is both cheaper and more controllable than pure heavy rare earths.
4Speed
If the diffusion source contains high Fe content, then the diffusion process can proceed, but excessive ferromagnetic phases are formed reducing the Hcj and Br of the magnet
Solution Approach 1:
The patent optimizes the compositional parameters of the diffusion source by precisely controlling the Fe content within a specific range (5-15 wt%). This parameter optimization balances diffusion kinetics with phase formation control, ensuring sufficient diffusion rate while preventing excessive ferromagnetic phase precipitation that would harm magnetic properties.
Solution Approach 2:
The patent ensures that Fe in the diffusion source is selectively consumed at the grain boundaries during diffusion, creating local enrichment of heavy rare earths at grain boundaries while the bulk material maintains its optimal composition. This localized consumption pattern prevents bulk ferromagnetic phase formation and preserves overall magnetic performance.
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 effectively increases coercivity, improves diffusion speed, reduces production costs, and minimizes the decline in residual magnetism, achieving significant enhancements in magnetic performance while lowering production expenses and improving the utilization efficiency of heavy rare earth elements.
Implementation Method 1
grain boundary diffusion, which is a technology that the diffusion source is diffused into the magnet along the grain boundary to improve the coercivity of the magnet
Implementation Method 2
The alloy powders are loaded into a rotary diffusion device with an R-T-B magnet for thermal diffusion, with temperature range of 750-950° C. and a time range of 4-72 h
Implementation Method 3
Aging treatment
Data Source
AI summary
The present disclosure provides an NdFeB rare earth magnet and manufacturing method thereof, which belongs to the field of rare earth magnet technology. The production method of diffusion source is to coat a layer of non-heavy rare earth alloy film on the diffusion source sheet, and aging treatment are carried out to form diffusion source. The diffusion source is RαRHδMβBγFe100-α-β-γ-δ. The chemical formula of the non-heavy rare earth alloy film is RnMm. The chemical formula of NdFeB magnet base material is RaM1bM2cBdFe100-a-b-c-d. The performance NdFeB by diffusion source containing Dy have ΔHcj>636.8 kA/m and containing Tb have ΔHcj>875.6 kA/m, containing DyTb have ΔHcj>716.4 kA/m.