NdFeB Magnet Composition for High Coercivity Without Dy or Tb
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Solution Overview
Problem
Sintered NdFeB magnets face challenges in achieving high remanence and coercivity while reducing the use of scarce and expensive heavy rare earth elements like Dy and Tb, which also leads to performance inconsistencies and cost fluctuations due to unstable prices and limited reserves.
Innovation Solution
A dual-alloy method is employed to prepare rare earth magnets by controlling the contents of Ga and B elements in main and auxiliary alloys, reducing the reliance on heavy rare earth elements and ensuring consistent performance, combined with sputtering and thermal diffusion treatments to enhance coercivity and remanence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Dy and Tb are used to partially replace Nd to increase coercivity, then the coercivity is improved, but the remanence is reduced and the cost fluctuates significantly
Solution Approach 1:
The patent changes the chemical composition parameters by introducing Ga and B elements to replace traditional Dy/Tb additions. Specifically, Ga content is controlled at 0.3-0.8 wt% and B content at 0.97-1.0 wt%, which modifies the phase structure to form Nd6Fe13Ga phase that enhances coercivity without sacrificing remanence. This parameter change resolves the contradiction by achieving high coercivity through a different compositional pathway.
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases: the primary Nd2Fe17 phase combined with Nd6Fe13Ga phase formed through Ga-B interaction. This composite structure leverages the high remanence of Nd2Fe17 while the Nd6Fe13Ga phase provides enhanced coercivity, thus simultaneously achieving both high remanence and high coercivity without relying on heavy rare earth elements.
2Strength
If the content of B in the raw material is reduced and Ga, Al, or Cu are added to form Nd6Fe13Ga phase, then the remanence and coercivity are improved, but the consistency of performance in mass production deteriorates
Solution Approach 1:
The patent optimizes the B content parameter to a specific range (0.97-1.0 wt%) that is sufficient to form the desired Nd6Fe13Ga phase but not excessive. This precise parameter control, combined with Ga content control (0.3-0.8 wt%), ensures consistent phase formation and performance in mass production, resolving the inconsistency issue while maintaining high coercivity.
Solution Approach 2:
The patent implements a feedback mechanism through controlled tempering treatment parameters (temperature and time) that ensure the Nd6Fe13Ga phase forms consistently. The tempering process is optimized to promote the transformation of excess B into the Nd6Fe13Ga phase structure, providing a self-regulating mechanism that ensures performance consistency across production batches.
3Strength
If heavy rare earth Dy and Tb are diffused in the low B content magnets, then the coercivity increases slightly, but the demagnetization curve squareness deteriorates
Solution Approach 1:
The patent replaces expensive and problematic heavy rare earth elements (Dy, Tb) with lighter, more abundant elements (Ga, B) that achieve the same coercivity enhancement without the negative side effects. This substitution eliminates the need for diffusion processes that compromise demagnetization curve squareness, thereby maintaining both high coercivity and good squareness.
Solution Approach 2:
The patent changes the compositional parameters by incorporating Ga (0.3-0.8 wt%) and B (0.97-1.0 wt%) to form Nd6Fe13Ga phase, which provides coercivity enhancement through a different mechanism than heavy rare earth diffusion. This parameter change avoids the formation of detrimental phases that would reduce demagnetization curve squareness, thus simultaneously achieving high coercivity and good squareness.
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 high-performance magnets with improved coercivity and remanence consistency, suitable for mass production, and reduces the reliance on expensive heavy rare earth elements, leading to more stable and cost-effective production.
Implementation Method 1
Mixing the main alloy powder and the auxiliary alloy powder in the mass ratio of 95～99:1～5 to obtain the mixed alloy powder
Implementation Method 2
Orienting and pressing the mixed alloy powder under a magnetic field to form a compact
Implementation Method 3
Placing the compact in a vacuum sintering furnace for sintering, so as to obtain sintered magnets
Implementation Method 4
Tempering the sintered magnet to obtain the rare earth magnet
Implementation Method 5
The one or more metal elements of Ga, Al, and Cu added during the tempering treatment react with Nd2Fe17 phase (2:17 phase) generated by rare earth and transition metals such as Fe, forming the Nd6Fe13Ga phase (6:13:1 phase)
Data Source
AI summary
A NdFeB rare earth magnet includes a main phase and a grain boundary phase including a white grain boundary phase and a gray grain boundary phase. In a microstructure observation area of the rare earth magnet, an area of the white grain accounts for 1˜3% of a total area of the microstructure observation area, and an area of the gray grain boundary phase accounts for 2˜10% of the total area of the microstructure observation area.