NdFeB Magnet Coating with Low-Melting Metals for High Coercivity
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Solution Overview
Problem
Current methods for improving the coercive force of neodymium iron boron (NdFeB) magnets, such as grain boundary diffusion, suffer from low utilization of heavy rare earth elements, high costs, and poor consistency and uniformity in diffusion processes.
Innovation Solution
A coating material comprising alloy powder with heavy rare earth elements like Dysprosium (Dy) and/or Terbium (Tb) combined with low-melting-point metal powders like zinc (Zn), aluminum (Al), or gallium (Ga) is applied to the surface of NdFeB magnets, followed by a two-stage diffusion heat treatment and annealing, enhancing diffusion efficiency and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare earth elements (Dy or Tb) are added during smelting to increase coercive force, then the coercivity is improved, but the magnet magnetism is significantly reduced and product costs increase
Solution Approach 1:
The invention segments the heavy rare earth element distribution by confining Dy or Tb specifically to the grain boundary phase rather than allowing uniform distribution throughout the magnet. This is achieved through controlled addition during sintering, where the heavy rare earth elements preferentially segregate to grain boundaries, creating a segmented structure with distinct compositional regions that maintains bulk magnetism while providing boundary hardening.
Solution Approach 2:
The invention applies local quality by creating a non-uniform composition where the grain boundary phase has a different chemical composition (enriched with Dy or Tb) compared to the main phase. This localized modification of grain boundary regions provides magnetic hardening exactly where needed at the interfaces, while the bulk magnet retains its high magnetization properties.
2Force
If heavy rare earth elements (Dy or Tb) are added during smelting to increase coercive force, then the coercivity is improved, but product costs increase
Solution Approach 1:
The invention applies local quality by creating a non-uniform composition where the grain boundary phase has a different chemical composition (enriched with Dy or Tb) compared to the main phase. This localized modification of grain boundary regions provides magnetic hardening exactly where needed at the interfaces, while the bulk magnet retains its high magnetization properties.
Solution Approach 2:
The invention changes the processing parameters by controlling the sintering atmosphere and temperature profile to enable preferential segregation of heavy rare earth elements to grain boundaries. By adjusting the oxygen partial pressure and cooling rate during sintering, the distribution of Dy or Tb is controlled to concentrate at grain boundaries rather than distributing uniformly, optimizing both performance and cost.
3Force
If grain boundary diffusion method is used to improve coercive force, then the magnet magnetism is maintained, but the consistency and uniformity of diffusion process are poor
Solution Approach 1:
The invention applies preliminary action by pre-mixing the heavy rare earth elements with the powder compact before sintering, rather than attempting to diffuse them during or after sintering. This ensures uniform initial distribution of Dy or Tb throughout the compact, which then segregates to grain boundaries during controlled sintering, providing consistent and repeatable results across production batches.
Solution Approach 2:
The invention implements feedback control by monitoring and controlling the sintering atmosphere parameters (oxygen partial pressure, temperature profile, cooling rate) to ensure consistent segregation behavior of heavy rare earth elements to grain boundaries. This controlled atmosphere sintering process provides feedback mechanisms that maintain uniformity and consistency in the grain boundary composition across different production runs.
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 effectively increases the coercive force of NdFeB magnets while maintaining remnant magnetism and maximum magnetic energy capacity, reducing the cost of heavy rare earth element usage and improving the consistency and uniformity of the diffusion process.
Implementation Method 1
applying a high temperature to melt the grain boundary phase, and causing Tb or Dy to diffuse from the surface to the inside of the sintered magnet
Implementation Method 2
causing Tb or Dy to diffuse from the surface to the inside of the sintered magnet
Implementation Method 3
subject the sintered body to a high temperature heat treatment
Data Source
AI summary
The application discloses a coating material for fabricating rare earth magnets and a method using the coating material to prepare neodymium-iron-boron (NdFeB) magnets having high coercive force. The coating material includes: alloy powder A and low-melting-point metal powder B. The alloy powder A is heavy rare earth element R powder, or rare earth-metal alloy (RM) powder, or rare earth-metal-hydrogen alloy (RMH) powder. The heavy rare earth elements are Dy and/or Tb, metal is Fe or Co, or an alloy of Fe and Co, and H is hydrogen element. The low-melting-point metal powder B is one or two of Zn, Al, and Ga. The preparation method includes the following steps: the coating material is mixed into a slurry, and the slurry is coated on the surface of NdFeB magnet, and then apply a two-stage diffusion heat treatment to the magnet, followed by an annealing process to obtain a high-coercivity NdFeB magnet.