Bulk Rare Earth Magnet Diffusion Using SPS for Deep Coercivity Gain
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Solution Overview
Problem
Conventional grain boundary diffusion methods are limited to magnets with a thickness of less than 5 mm, restricting the large-scale application of bulk rare earth permanent magnets due to limited diffusion depth, and existing methods to enhance coercivity, such as adding heavy rare earths or grain refinement, are costly or ineffective.
Innovation Solution
A grain boundary diffusion method using spark plasma sintering (SPS) with controlled heating, pressure, and vacuum conditions to enhance elemental diffusion, allowing high-abundance rare earth elements like La, Ce, and Y to penetrate deeper into the magnet, improving coercivity and magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional grain boundary diffusion method is used, then coercivity is improved, but diffusion depth is limited to less than 5 mm
Solution Approach 1:
The patent applies spark plasma sintering (SPS) technology to change the processing parameters (heating rate, pressure, atmosphere) to enhance element diffusion depth from less than 5 mm to over 10 mm while maintaining improved coercivity. The SPS process parameters including heating rate of 20-400°C/min, pressure of 2-50 MPa, and vacuum degree less than 10^-3 Pa enable deeper diffusion without sacrificing magnetic performance.
2Strength
If heavy rare earths (Dy/Tb) are added through smelting to improve coercivity, then coercivity increases, but raw material cost increases significantly
Solution Approach 1:
The patent replaces expensive heavy rare earths (Dy/Tb) with cheap and high-abundance rare earths (La/Ce/Y) as the diffusion source. The grain boundary diffusion process enables these abundant rare earths to effectively improve coercivity without the high material cost, achieving a substitute that is both economically viable and performance-effective.
Solution Approach 2:
The patent uses a grain boundary diffusion alloy source (containing La/Ce/Y and other elements) as an intermediary to deliver rare earth elements to the magnet's grain boundaries through controlled diffusion. This intermediary approach allows efficient utilization of abundant rare earths to improve coercivity without directly adding expensive heavy rare earths to the main phase.
3Strength
If grain size is reduced to 3 μm or smaller to improve coercivity through grain refinement, then coercivity increases, but magnetic powders are easily oxidized
Solution Approach 1:
The patent employs spark plasma sintering in a vacuum environment (vacuum degree less than 10^-3 Pa) to protect the fine-grained magnetic powders from oxidation during the diffusion process. This inert atmosphere protection allows grain refinement to 3 μm or smaller to be achieved without the harmful oxidation that would otherwise occur.
4Length of moving object
If SPS parameters (heating rate, pressure, temperature) are optimized to increase diffusion depth, then diffusion depth increases, but process complexity increases
Solution Approach 1:
The patent uses spark plasma sintering (SPS) technology which serves multiple functions simultaneously: it provides rapid heating, applies pressure, maintains vacuum atmosphere, and enables element diffusion all in one process. This multi-functionality achieves deep diffusion (over 10 mm) without requiring multiple separate processing steps, thereby limiting the increase in process complexity.
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 achieves a significant increase in diffusion depth and coercivity, enabling the production of bulk rare earth permanent magnets with enhanced magnetic properties, utilizing abundant rare earth elements efficiently and suppressing grain growth.
Implementation Method 1
heating the initial magnet loaded with the alloy source at a heating rate of 20° C./min to 400° C./min in the SPS device to allow grain boundary diffusion for 20 min to 180 min at a diffusion temperature of 400° C. to 900° C.
Implementation Method 2
a pressure of 2 MPa to 50 MPa
Data Source
AI summary
A grain boundary diffusion method for a bulk rare earth permanent magnetic material includes the following steps: (1) fabricating an initial magnet by a sintering, hot pressing, or hot deformation process; (2) loading a grain boundary diffusion alloy source on a surface of the magnet through electrodeposition, chemical vapor deposition (CVD), physical vapor deposition (PVD), direct physical contact, or adhesive bonding; and (3) placing the initial magnet loaded with the grain boundary diffusion alloy source in a SPS device, and heating to obtain a final magnet. The current, plasma, and pressure in an SPS process can be controlled to significantly improve elemental diffusion coefficient and enhance the diffusion depth. The bulk rare earth permanent magnetic material undergoing grain boundary diffusion fabricated in the present disclosure has a significant increase in magnetic properties that catering to commercial demands for industrial production.