NdFeB Grain Boundary Diffusion Alloy for High-Coercivity Magnets
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Solution Overview
Problem
Current grain boundary diffusion methods for NdFeB magnets face challenges such as high costs due to the use of heavy rare earth elements and limited improvement in coercivity and residual magnetism, especially with rising prices of Dy and Tb, and inefficiencies in diffusion processes.
Innovation Solution
A method involving a diffusion source alloy with a chemical formula RαMβBγFe100-α-β-γ, where R is Nd or Pr, M is Al, Cu, or Ga, and B is present in lower content, facilitating high diffusion efficiency and forming μ and δ phases that enhance coercivity and residual magnetism, while reducing production costs through efficient utilization of light rare earths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare earth elements Dy, Tb are added in large quantities to the base metal, 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 boundary phase rather than uniformly distributing them throughout the base metal. The grain boundary phase contains 2-20 wt% heavy rare earth elements while the main phase contains less than 0.5 wt%, creating localized high-coercivity regions at grain boundaries that improve overall magnet performance without sacrificing the residual magnetism of the main phase.
Solution Approach 2:
The patent segments the magnet structure into distinct main phase and grain boundary phase regions with different compositions. The main phase (NdFeB) provides high residual magnetism while the grain boundary phase (containing heavy rare earths) provides enhanced coercivity. This segmentation allows each phase to optimize its function independently, resolving the contradiction between coercivity and residual magnetism.
2Force
If heavy rare earth elements Dy, Tb are added in large quantities to the base metal, then the coercivity of the magnet is improved, but the production cost increases significantly due to skyrocketing raw material prices
Solution Approach 1:
By localizing heavy rare earth elements to the grain boundary phase (2-20 wt%) rather than distributing them throughout the entire magnet, the patent achieves high coercivity with significantly reduced overall heavy rare earth content. This localized approach minimizes raw material consumption and production cost while maintaining effective coercivity enhancement at critical grain boundary regions.
Solution Approach 2:
The patent replaces expensive heavy rare earth elements in the main phase with a cost-effective grain boundary diffusion approach. By using a diffusion source layer containing heavy rare earths that is applied only to the surface and then diffused during heat treatment, the patent achieves coercivity enhancement at much lower material cost compared to bulk addition of heavy rare earths.
3Temperature
If the B content in the diffusion source is too high, then the melting point becomes relatively high and it is not easy to diffuse into the magnet, but reducing B content may affect the diffusion efficiency
Solution Approach 1:
The patent optimizes the B content parameter in the diffusion source to a specific range (0.1-5 wt%) that balances melting point and diffusion efficiency. This parameter optimization ensures the diffusion source has sufficiently low melting point for effective diffusion while maintaining adequate diffusion efficiency. The patent also optimizes the Fe content (5-20 wt%) to further regulate the melting characteristics and diffusion behavior of the source alloy.
Solution Approach 2:
The patent creates a composite diffusion source material containing multiple elements (heavy rare earths, light rare earths, Fe, B, and other additives) that work synergistically. The composite composition allows the material to achieve both low enough melting point for diffusion and sufficient diffusion efficiency, resolving the contradiction between these two properties through compositional design.
4Length of stationary object
If light rare earths are used to improve the diffusion depth of heavy rare earths, then the diffusion process is enhanced, but the coercivity improvement is limited and heavy rare earths are still consumed
Solution Approach 1:
The patent uses light rare earths (La, Ce, Pr) specifically in the grain boundary phase (0.1-5 wt%) to create local regions that facilitate heavy rare earth diffusion. These light rare earths form low-melting-point eutectic phases at grain boundaries that act as diffusion channels, enabling deep penetration of heavy rare earth elements without requiring large quantities of heavy rare earths themselves, thus maintaining high coercivity with reduced consumption.
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 significantly improves coercivity and residual magnetism of NdFeB magnets, reduces production costs, and achieves nearly 100% utilization efficiency of the diffusion source, addressing the limitations of prior art by effectively transporting heavy rare earths into the magnet structure.
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. The diffusion source alloy, which is RLuRHvFe100-u-v-w-zBwMz rare earth alloys, contains not only element of light rare earths, but also heavy rare earths
Data Source
AI summary
The present disclosure provides a rare earth magnet and manufacturing method thereof, which belongs to the field of rare earth magnet technology. The diffusion source is coated on the NdFeB base material, which is diffused and aged to obtain NdFeB magnet. The diffusion source alloy is RαMβBγFe100-α-β-γ, wherein R refers to at least one of Nd and Pr, and M Refers to at least one of Al, Cu, Ga. The Br reduction range is lower than 0.03 T, and Hcj growth is more than 318 kA/m.