NdFeB Magnet Grain Size Control for Coercive Force
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Solution Overview
Problem
NdFeB system sintered magnets face a challenge in maintaining high magnetization characteristics while reducing crystal grain size to enhance coercive force, as the magnetization process is affected by the nucleation type coercivity mechanism and handling difficulties.
Innovation Solution
The development of a NdFeB system sintered magnet with a grain size median of 4.5 μm or smaller and an area ratio of crystal grains ≤1.8 μm of 5% or lower, achieved by regulating the rare-earth element content and sintering conditions, ensures improved magnetization characteristics and coercive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the particle size of the alloy powder is reduced to decrease crystal grain size, then the coercive force HcJ is enhanced, but the total surface area of the particles increases making the powder easier to be oxidized
Solution Approach 1:
The patent applies inert atmosphere protection throughout the manufacturing process, including using inert gas (nitrogen or argon) in the atomization process, during powder handling, and in the sintering atmosphere. This prevents oxidation of the fine alloy powder particles while maintaining the reduced grain size structure that provides high coercive force.
2Strength
If the crystal grain size is reduced to enhance coercive force HcJ, then the magnetization characteristic deteriorates due to the nucleation type coercivity mechanism
Solution Approach 1:
The patent creates local quality differences by forming a rare-earth element rich phase specifically at the grain boundaries while maintaining the interior grain structure. This localized rare-earth enrichment at boundaries provides nucleation sites that improve magnetization characteristics without compromising the overall fine grain size structure needed for high coercive force.
Solution Approach 2:
The patent creates a composite microstructure consisting of fine NdFeB main phase grains (5-20 μm) combined with a rare-earth element rich grain boundary phase. This composite structure at the micrometer scale provides both the fine grain size needed for high coercive force and the rare-earth enriched regions needed for improved magnetization characteristics.
3Strength
If heavy rare-earth element RH is added to improve crystalline magnetic anisotropy, then the coercive force HcJ is enhanced, but the residual magnetic flux density Br is lowered
Solution Approach 1:
The patent concentrates rare-earth elements (including heavy rare-earth elements) specifically at the grain boundaries rather than distributing them uniformly throughout the material. This localized enrichment provides the magnetic anisotropy enhancement needed for high coercive force while minimizing the overall rare-earth content that would reduce residual magnetic flux density.
Solution Approach 2:
The patent optimizes the concentration and distribution parameters of rare-earth elements by controlling the atomic percentage (0.1-5.0 at%) and creating spatial distribution gradients with higher concentration at grain boundaries. This parameter optimization achieves enhanced coercive force while maintaining adequate residual magnetic flux density.
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 results in a NdFeB system sintered magnet with high coercive force and magnetization characteristics, allowing for effective magnetization using a weaker external magnetic field and maintaining a high magnetization ratio of 90% at 20 kOe.
Implementation Method 1
the temperature is raised to roughly 1000° C. in the sintering process
Implementation Method 2
a process of magnetizing the obtained sintered body is performed by applying a magnetic field to the sintered body
Implementation Method 3
NdFeB system alloy is extremely reactive with oxygen and may possibly ignite
Data Source
AI summary
The present invention aims to provide a NdFeB system sintered magnet capable of improving the magnetization characteristic. The NdFeB system sintered magnet is a NdFeB system sintered magnet with the c axis oriented in one direction, characterized in that: the median of the grain size of the crystal grains at a section perpendicular to the c axis is 4.5 μm or less, and the area ratio of the crystal grains having grain sizes of 1.8 μm or smaller on the aforementioned section is 5% or lower. The median of the grain size is decreased (to 4.5 μm or less), whereby improve the coercive force is improved. Simultaneously, the area ratio of the crystal grains having grain sizes of 1.8 μm or smaller is decreased (to 5% or lower) to reduce the number of crystal grains having no magnetic wall formed, whereby the magnetization characteristic is improved.