R-T-B Magnet Alloy Microstructure for Coercive Force
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Solution Overview
Problem
R-T-B-based sintered magnets face challenges in maintaining coercive force at elevated temperatures due to the presence of magnetically soft R2T17 phases, which are not fully transformed during the sintering process, especially when heavy rare earth elements are reduced or absent.
Innovation Solution
The development of an R-T-B-based magnet material alloy with a refined microstructure, featuring primary and secondary dendrite arms, and a specific inter-R-rich phase spacing, which allows for improved anisotropy field and reduced local demagnetizing factor, achieved through advanced pulverization and forming techniques, enabling the production of sintered magnets with enhanced coercive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth elements are added to improve coercive force, then magnetic properties are enhanced, but cost and material availability are worsened
Solution Approach 1:
The invention changes the microstructural parameters of the alloy by controlling the formation of secondary dendrite arms through specific cooling rates and compositional ratios. This creates a refined microstructure with smaller grain sizes and optimized phase distribution, which improves coercive force without requiring heavy rare earth elements. The parameter changes occur in the solidification process where cooling rates of 2000-4500°C/second produce the desired dendritic structure.
Solution Approach 2:
The invention creates a composite microstructure consisting of multiple phases (R2T14B principal phase, R-rich phases, and intermetallic compounds) with specific spatial arrangements. The secondary dendrite arms form a composite network that enhances magnetic properties by creating multiple magnetic domains and improving magnetic anisotropy, thereby achieving high coercive force without heavy rare earth additions.
2Ease of manufacture
If R2T17 phase is present in the alloy, then manufacturing is simplified, but coercive force deteriorates due to magnetic softness
Solution Approach 1:
The invention applies local quality by creating specific microstructural zones with secondary dendrite arms that have different magnetic properties from the bulk material. These localized regions with refined structure and specific phase composition provide enhanced coercive force, while the overall alloy composition remains simple and easy to manufacture. The local microstructural modification does not require changing the overall alloy formulation.
Solution Approach 2:
The invention segments the alloy microstructure into distinct regions separated by secondary dendrite arms, creating a multi-domain structure. This segmentation divides the magnetic material into smaller units with different magnetization directions, which prevents the formation of large magnetic domains that would reduce coercive force. The segmented structure maintains manufacturing simplicity while improving magnetic performance.
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 refined microstructure of the magnet material alloy results in improved coercive force and heat resistance of sintered magnets, even when the amount of heavy rare earth elements is reduced, ensuring excellent magnetic properties.
Implementation Method 1
The chill roll 3 is configured to have a coolant circulating therein, and therefore the molten alloy is rapidly cooled on the outer peripheral surface of the chill roll 3 to be solidified
Implementation Method 2
the molten alloy is rapidly cooled on the outer peripheral surface of the chill roll 3 to be solidified
Implementation Method 3
the raw materials are heated using an induction heating apparatus (not shown). Thus, the raw materials are melted to form a molten alloy
Implementation Method 4
improved anisotropy field and reduced local demagnetizing factor
Implementation Method 5
The principal phase is a ferromagnetic phase that contributes to magnetization
Data Source
AI summary
Provided is an R-T-B-based magnet material alloy including an R2T14B phase which is a principal phase and R-rich phases which are phases enriched with the R, wherein the principal phase has primary dendrite arms and secondary dendrite arms diverging from the primary dendrite arms, and regions where the secondary dendrite arms have been formed constitute a volume fraction of 2 to 60% of the alloy, whereby excellent coercive force can be ensured in R-T-B-based sintered magnets even when the amount of heavy rare earth elements added to the alloy is reduced. The inter-R-rich phase spacing is preferably at most 3.0 μm, and the volume fraction of chill crystals is preferably at most 1%. Furthermore, the secondary dendrite arm spacing is preferably 0.5 to 2.0 μm, and the ellipsoid aspect ratio of R-rich phase is preferably at most 0.5.