Sintered R-Fe-B Magnet Core-Shell Structure for Coercivity Retention
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Solution Overview
Problem
Current methods for incorporating La and Ce into neodymium-iron-boron magnets to enhance coercivity are limited by complex processes, low addition amounts, and reduced magnetic properties, leading to poor cost performance and limited application development.
Innovation Solution
A sintered R—Fe—B permanent magnet with a core-shell structure and grain boundary diffusion, where the grain boundary contains a heavy rare earth-rich phase and the composite main phase grains have a Ce-rich and Ce-poor core-shell structure, achieved through mixing low-Ce and high-Ce alloy powders, press molding, sintering, and composite diffusion treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If La and Ce are added by alloying during smelting, then the addition amount can be large, but La and Ce enter main phase grains and reduce saturation magnetic polarization intensity, Curie temperature, and magnetocrystalline anisotropy field, thereby reducing initial magnetic properties
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the grain boundary region has different composition (enriched with La and Ce) compared to the main phase grains. This localized addition prevents La and Ce from entering the main phase grains while still achieving sufficient addition amounts, thereby maintaining the initial magnetic properties of the main phase while incorporating the cost-effective rare earth elements at the grain boundaries.
Solution Approach 2:
The patent segments the magnet structure into distinct regions: main phase grains and grain boundary phases. By separating the addition location of La and Ce to specifically the grain boundary regions rather than uniformly throughout, the patent avoids contamination of the main phase grains while achieving the desired addition amounts, thus resolving the contradiction between quantity added and property maintenance.
2Reliability
If heavy rare earth elements such as Dy and Tb are added to improve magnetic properties, then coercivity increases, but the grain boundary phase component and structure play a decisive role in permeation, and the process becomes complex with limited effectiveness
Solution Approach 1:
The patent changes the compositional parameters of the grain boundary phase by enriching it with La and Ce elements, which modifies the diffusion characteristics and enables effective heavy rare earth element incorporation. This parameter change in grain boundary composition creates favorable conditions for coercivity enhancement without requiring complex processing steps, as the compositional modification itself facilitates the desired element distribution and magnetic property improvement.
3Ease of manufacture
If La and Ce are added by diffusion to increase usage of abundant rare earth elements, then cost performance improves, but the process is complicated, addition amounts are insufficient, and difficulty in increasing coercivity remains
Solution Approach 1:
The patent applies local quality by concentrating La and Ce enrichment specifically at the grain boundary regions rather than attempting uniform diffusion throughout the entire magnet. This localized approach achieves sufficient effective addition amounts at the critical grain boundary locations, enhances coercivity through proper element distribution, and maintains cost performance by using abundant rare earth elements, thereby resolving all three issues simultaneously.
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 significantly improves coercivity and squareness of the magnet, ensuring deep diffusion of heavy rare earth elements and uniform distribution, thereby enhancing the magnet's resistance to demagnetization at high temperatures and achieving high coercivity.
Implementation Method 1
perform a composite diffusion treatment on the blank to obtain the sintered R—Fe—B permanent magnet
Implementation Method 2
press molding
Implementation Method 3
sintering
Data Source
AI summary
A sintered R—Fe—B permanent magnet has at least a grain boundary and composite main phase grains. The grain boundary has an RH-rich phase distributed in the form of an agglomerate within the grain boundary between the composite main phase grains, preferably at the intersection of any adjacent three or more composite main phase grains. The RH-rich phase is continuously distributed along the grain boundary in the form of a thin-layer stripe. The composite main phase grain has a core-shell structure, which includes a core structure having an R-T-B type phase structure and a shell structure on the outer layer of the core structure. The core structure contains Ce-rich main phase grains and Ce-poor main phase grains.