Grain Boundary NdFeB Magnets With Lower Dy/Tb Material Cost
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Solution Overview
Problem
The supply of rare earth elements like dysprosium (Dy) and terbium (Tb) is scarce, leading to high costs and limited availability for manufacturing high-performance neodymium-iron-boron (NdFeB) magnets used in various applications, including electric motors.
Innovation Solution
A method of preparing sintered magnetic bodies with improved coercivity and remanence by homogenizing a first population of particles of a Grain Boundary Modifying (GBM) alloy with a second population of particles of a core alloy, followed by heating to form discrete mixed alloy particles, and then sintering these particles under controlled conditions to achieve a core-shell structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high concentration of Dy or Tb elements is used to form highly coercive sintered NdFeB magnet bodies, then coercivity is improved, but material cost increases
Solution Approach 1:
The patent applies local quality by concentrating Dy/Tb elements specifically at the grain boundaries rather than uniformly distributing them throughout the magnet body. The grain boundary region serves as a localized zone where heavy rare earth elements are preferentially positioned to maximize their coercivity-enhancing effect while minimizing overall material usage. This is achieved through controlled diffusion processes that deposit Dy/Tb at grain boundaries during sintering or post-sintering heat treatments.
Solution Approach 2:
The patent creates a composite structure where the magnet body consists of NdFeB grains embedded in a grain boundary phase enriched with Dy/Tb elements. This composite approach combines the high remanence properties of NdFeB with the high coercivity contribution from Dy/Tb at the grain boundaries, achieving optimized magnetic performance with reduced overall heavy rare earth content compared to conventional uniform alloying.
2Reliability
If grain boundary diffusion process is used to increase Dy loading, then coercivity is improved, but device complexity increases
Solution Approach 1:
The patent incorporates Dy/Tb-containing materials into the magnet precursor structure before the final sintering process. By pre-positioning the heavy rare earth elements in the grain boundary regions of the green compact or precursor alloy, the subsequent sintering process naturally facilitates their diffusion and concentration at grain boundaries without requiring separate post-sintering diffusion steps. This preliminary action simplifies the overall manufacturing process while achieving the desired grain boundary engineering.
3Adaptability or versatility
If two alloys are combined using powder blending techniques, then production flexibility is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent merges the advantages of powder blending with controlled metallurgical processing by first combining alloys in flexible powder forms and then using sintering to achieve homogeneous integration. The sintering process facilitates diffusion and uniform distribution of elements at the microstructural level, compensating for any inhomogeneities introduced during powder blending. This combination approach maintains production flexibility while achieving the manufacturing precision needed for consistent magnetic properties.
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 enables the production of high-energy rare earth magnets with uniform coercivity and thermal stability, while reducing the reliance on expensive rare earth elements, thereby lowering production costs and ensuring consistent magnetic performance.
Implementation Method 1
During the subsequent heating steps these heavy elements diffuse into the magnet body from one side/edge of the body through the grain boundaries
Implementation Method 2
heating the composite alloy preform to a temperature greater than the solidus temperature of the first alloy but less than the melting temperature of the second core alloy to form a population of discrete mixed alloy particles
Implementation Method 3
heating the green body to at least one temperature in a range of from about 800° C. to about 1500° C. for a time sufficient to sinter the green body into a sintered body
Data Source
AI summary
The present disclosure is directed to methods of preparing permanent magnets having improved coercivity and remanence, the method comprising: (a) homogenizing a first population of particles of a first GBM alloy with a second population of particles of a second alloy to form a composite alloy preform, the first GBM alloy being represented by the formula: ACbRxCoyCudMz, the second alloy being represented by the formula G2Fe14B, where AC, R, M, G, b, x, y, and z are defined; (b) heating the composite alloy preform particles to form mixed alloy particles; (c) compressing the mixed alloy particles, under a magnetic field of a suitable strength to align the magnetic particles with a common direction of magnetization and inert atmosphere, to form a green body; (d) sintering the green body; and (e) annealing the sintered body. Embodiments include magnets comprising neodymium-iron-boron core alloys, including Nd2Fe14B.