Sintered NdFeB Grain Boundary Engineering With Lower Dy/Tb Use
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Solution Overview
Problem
The production of neodymium-iron-boron (NdFeB) magnets requires high concentrations of dysprosium (Dy) and terbium (Tb) for enhanced magnetic properties, but the scarcity of these rare earth elements and high production costs are significant concerns, and existing methods for increasing coercivity are limited in effectiveness and complexity.
Innovation Solution
A method involving the homogenization of Grain Boundary Modifying (GBM) alloy particles with core alloy particles, followed by heating and sintering, to create a composite alloy with improved coercivity and remanence, using a process that minimizes the use of expensive rare earth elements and involves hydrogen treatment and magnetic field alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high concentrations of Dy and Tb are used to enhance coercivity, then magnetic performance is improved, but production cost increases and rare earth element scarcity becomes a problem
Solution Approach 1:
The patent applies local quality by concentrating Dy and Tb exclusively at the grain boundaries rather than distributing them throughout the entire magnet volume. The grain boundary phase contains 5-20 at% Dy and 5-20 at% Tb, while the interior of the main phase contains minimal or no heavy rare earths. This localized approach achieves high coercivity (Hcj ≥ 1200 kA/m) at lower overall rare earth content (total Dy+Tb ≤ 30 at%), resolving the contradiction between magnetic performance and material consumption.
Solution Approach 2:
The patent segments the magnet structure into distinct regions: the interior main phase (Nd-rich, low Dy/Tb) and the grain boundary phase (Dy/Tb-enriched). This segmentation allows each region to have optimized composition - the interior provides high remanence while the grain boundaries provide high coercivity through the (Nd,Dy,Tb)5(B,Al) phase formation, thereby reducing overall heavy rare earth consumption while maintaining magnetic performance.
2Reliability
If conventional methods are used to increase coercivity, then magnetic performance is improved, but production complexity and processing steps increase
Solution Approach 1:
The patent merges the grain boundary modification step with the primary sintering process. Instead of separate post-processing steps for grain boundary engineering, the composition is designed to automatically form the desired (Nd,Dy,Tb)5(B,Al) grain boundary phase during the standard sintering heat treatment (900-1100°C for 10-60 minutes). This integration eliminates additional processing equipment and steps while achieving the same coercivity enhancement, thereby reducing production complexity.
3Reliability
If grain boundary diffusion is used to increase coercivity, then magnetic performance is improved, but the magnet body thickness is limited to 6 mm and additional post processing is required
Solution Approach 1:
The patent applies preliminary action by pre-distributing Dy and Tb elements throughout the alloy composition before sintering, rather than attempting post-sintering diffusion. The starting material contains Dy and Tb in the grain boundary phase precursors, which then form the protective (Nd,Dy,Tb)5(B,Al) phase during sintering. This approach eliminates thickness limitations and post-processing requirements, allowing production of magnets of any thickness with uniform grain boundary engineering throughout the entire volume.
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 produces NdFeB magnets with high coercivity and thermal stability using lower levels of expensive rare earth elements, achieving improved magnetic performance and corrosion resistance while reducing production costs.
Implementation Method 1
homogenizing a first population of particles of a first Grain Boundary Modifying (GBM) alloy with a second population of particles of a second core alloy
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
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
Implementation Method 4
treating coarse particles of either the first GBM or second core alloy or both the first GBM and second core alloys with hydrogen gas under conditions and for a time sufficient to allow absorption of the hydrogen into either or both of the alloys
Implementation Method 5
compressing the population of mixed alloy particles together to form a green body, in the presence of a magnetic field of a suitable strength to align the magnetic particles with a common direction of magnetization
Data Source
AI summary
The present disclosure is directed at methods of preparing rare earth-based permanent magnets having improved coercivity and remanence, the method comprising one or more steps comprising: (a) homogenizing a first population of particles of a first GBM alloy with a second population of particles of a second core alloy to form a composite alloy preform, the first GBM alloy being substantially represented by the formula: ACbRxCoyCudMz, the second core alloy being substantially 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 a population of 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. Particular embodiments include magnets comprising neodymium-iron-boron core alloys, including Nd2Fe14B.