Sintered NdFeB Grain Boundary Engineering for Lower Dy/Tb Use
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Solution Overview
Problem
The limited supply and high cost of dysprosium (Dy) and terbium (Tb) in neodymium-iron-boron (NdFeB) magnets, along with the inefficiencies and high costs of conventional methods to increase coercivity, limit the production of high-performance magnets suitable for high-temperature applications.
Innovation Solution
A method involving Grain Boundary Engineering (GBE) is used to prepare sintered magnetic bodies by homogenizing a first GBM alloy with a second core alloy, followed by heating and sintering to form a composite alloy preform, which results in a core-shell structure with improved coercivity and remanence, using reduced amounts of Dy and Tb.
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. This is achieved through a two-step process: first forming an NdFeB magnet body with low Dy/Tb content, then performing grain boundary diffusion to selectively enrich these expensive rare earth elements at the grain boundaries where they are most effective for improving coercivity. This localized approach significantly reduces the overall amount of Dy/Tb required while maintaining high coercivity.
Solution Approach 2:
The patent employs preliminary action by first creating the NdFeB magnet body with a base composition before performing the grain boundary diffusion treatment. This preliminary magnet body formation allows the subsequent diffusion process to build upon an existing magnetic structure, enabling the expensive Dy/Tb elements to be added only where needed at the grain boundaries rather than throughout the entire material, thus reducing overall material cost.
2Reliability
If grain boundary diffusion process is used to increase Dy loading, then coercivity is improved, but manufacturing complexity increases
Solution Approach 1:
The patent extracts the grain boundary modification step from the initial magnet manufacturing process. Instead of incorporating complex grain boundary engineering into the primary sintering process, the method first produces a standard NdFeB magnet body, then separately applies the grain boundary diffusion treatment. This separation simplifies the main manufacturing line while allowing the complex diffusion process to be applied as a targeted post-treatment only when high coercivity is required.
3Adaptability or versatility
If conventional powder blending techniques are used to combine two alloys, then production flexibility is improved, but quality control deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-forming the NdFeB magnet body with a controlled base composition before applying the grain boundary diffusion treatment. This two-stage approach allows each step to be optimized independently: the first stage produces a consistent magnetic matrix, while the second stage precisely controls the Dy/Tb distribution at grain boundaries. This eliminates the quality control issues associated with attempting to blend multiple powders together, as each material is processed and controlled separately.
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 high-energy rare earth magnets with uniform coercivity and thermal stability, resistant to demagnetizing fields and corrosion, while minimizing the use of expensive rare earth elements.
Implementation Method 1
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 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
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.