R-Fe-B Magnet Grain Boundary Diffusion for Coercivity
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Solution Overview
Problem
Existing R-Fe-B based rare-earth sintered magnets with thicknesses of 3 mm or more face challenges in effectively increasing coercivity due to limited diffusion of heavy rare-earth elements, which are essential for maintaining high magnetic performance, especially in thicker magnets.
Innovation Solution
A method involving the deposition of a metallic element M layer, such as Al, and a heavy rare-earth element RH layer, like Dy, on the surface of the magnet, followed by heat treatment to promote grain boundary diffusion, allowing the heavy rare-earth element to penetrate deep inside the magnet, thereby increasing coercivity and remanence without significantly decreasing the magnet's performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the light rare-earth element RL is replaced with a heavy rare-earth element RH to increase coercivity, then the magnetocrystalline anisotropy improves, but the remanence Br decreases
Solution Approach 1:
The patent applies local quality by concentrating the heavy rare-earth element RH specifically at the grain boundaries of the R2Fe14B phase rather than uniformly distributing it throughout the crystal grains. This localized distribution at the periphery enhances magnetocrystalline anisotropy and coercivity while preserving the light rare-earth element RL in the core regions, thereby maintaining high remanence Br.
Solution Approach 2:
The patent uses partial action by replacing only a portion of the light rare-earth element RL with the heavy rare-earth element RH, specifically targeting the grain boundary regions. This partial replacement is sufficient to achieve the desired coercivity enhancement without the need for complete replacement, thus avoiding excessive loss of remanence.
2Force
If a lot of heavy rare-earth element RH is added to increase coercivity effectively, then the magnetocrystalline anisotropy improves, but the amount of rare natural resource consumed increases
Solution Approach 1:
The patent concentrates the heavy rare-earth element RH at the grain boundaries where it has the maximum effect on coercivity through enhanced magnetocrystalline anisotropy. This localized approach ensures that a minimal amount of RH is used to achieve the desired coercivity enhancement, avoiding unnecessary consumption of this rare natural resource in the core regions where it is not needed.
Solution Approach 2:
The grain boundary structure naturally serves as the optimal location for RH distribution, as this is where the element exerts its maximum influence on the magnetic properties. The system self-optimizes by utilizing the grain boundary architecture to achieve coercivity enhancement with minimal RH content.
3Force
If the heavy rare-earth element RH is diffused during sintering at high temperature to distribute it throughout the magnet, then the coercivity increases, but the RH may diffuse to the core of crystal grains causing excessive remanence loss
Solution Approach 1:
The patent employs local quality by restricting the RH distribution to grain boundary regions through controlled diffusion processes. The grain boundaries act as preferential diffusion paths and trapping sites, confining RH to the periphery where it enhances coercivity without penetrating into the core regions, thereby preserving remanence.
Solution Approach 2:
The patent applies preliminary action by establishing the grain boundary structure and composition before the diffusion process. The grain boundaries are prepared as preferential sites for RH accumulation, ensuring that during subsequent thermal treatment, RH preferentially accumulates at the boundaries rather than diffusing uniformly into the crystal grain cores.
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 enables efficient distribution of heavy rare-earth elements throughout the magnet, enhancing coercivity and remanence, even in thicker magnets, resulting in high-performance magnetic properties that withstand high temperatures without excessive resource consumption.
Implementation Method 1
a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb, has been introduced from its surface by grain boundary diffusion
Implementation Method 2
depositing an M layer, including a metallic element M that is at least one element selected from the group consisting of Al, Ga, In, Sn, Pb, Bi, Zn and Ag, on the surface of an R-Fe-B based rare-earth sintered magnet body
Data Source
Figure 1(a)~2(b)
Figure 3(a)~3(c)
Figure 4(a)~4(b)
AI summary
First, an R-Fe-B based rare-earth sintered magnet body including, as a main phase, crystal grains of an R2Fe14B type compound that includes a light rare-earth element RL, which is at least one of Nd and Pr, as a major rare-earth element R is provided. Next, an M layer, including a metallic element M that is at least one element selected from the group consisting of Al, Ga, In, Sn, Pb, Bi, Zn and Ag, is deposited on the surface of the sintered magnet body and then an RH layer, including a heavy rare-earth element RH that is at least one element selected from the group consisting of Dy, Ho and Tb, is deposited on the M layer. Thereafter, the sintered magnet body is heated, thereby diffusing the metallic element M and the heavy rare-earth element RH from the surface of the magnet body deeper inside the magnet.