R-T-B Permanent Magnet Grain Structure for Higher Coercivity
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Solution Overview
Problem
R-T-B based permanent magnets, particularly hot deformed magnets, do not achieve the anticipated high coercivity due to the distribution of R-rich phases parallel to the easy magnetization axis, which affects their magnetic properties.
Innovation Solution
The magnets are designed with R-rich phases located between main phase grains, where the average interval of these phases in the easy magnetization axis direction is controlled between 5 μm to the width of the magnet, and the main phase grains have flat, platelet shapes stacked along this direction, with R-oxides present, to enhance coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the crystal grain size is reduced to increase coercivity, then the theoretical coercivity should increase according to the Kronmuller Formular, but the actual coercivity remains equivalent to sintered magnets due to the distribution of R-rich phases
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of R-rich phases specifically at grain boundaries while maintaining uniform composition within grains. The R-rich phase concentration is locally enhanced at boundaries (forming a shell structure) rather than being uniformly distributed, which selectively improves coercivity without compromising overall magnetic properties. This localized modification resolves the contradiction by making the harmful R-rich phases beneficial when confined to specific regions.
Solution Approach 2:
The patent changes the concentration parameter of R-rich phases from uniform distribution to gradient distribution. Specifically, the R-rich phase concentration is increased at grain boundaries (forming a shell with higher concentration) while the core maintains lower concentration. This parameter change transforms the harmful effect of R-rich phases into a beneficial structure that enhances coercivity while maintaining compositional stability.
2Ease of manufacture
If R-rich phases are present in the magnet, then they can form during manufacturing, but they reduce coercivity by facilitating reverse magnetic domain generation
Solution Approach 1:
The patent converts the harmful effect of R-rich phases into a beneficial one by strategically locating them at grain boundaries. Instead of trying to eliminate R-rich phases entirely (which would be difficult during manufacturing), the invention utilizes their presence but confines them to boundary regions where they form a protective shell. This shell structure actually prevents reverse domain propagation, thereby converting the originally harmful R-rich phases into coercivity-enhancing features.
Solution Approach 2:
The patent segments the magnet structure into core and shell regions at the grain level. Each grain consists of an inner core (main phase) and an outer shell (R-rich phase). This segmentation allows the R-rich phases to be isolated to specific regions (boundaries) rather than being uniformly distributed, thereby preventing them from acting as continuous pathways for reverse domain generation while still allowing their formation during manufacturing.
3Manufacturing precision
If the magnet is hot deformed to achieve fine crystal grains, then the grain size is reduced, but the coercivity does not increase as expected due to R-rich phase distribution
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of R-rich phases specifically at grain boundaries while maintaining uniform composition within grains. The R-rich phase concentration is locally enhanced at boundaries (forming a shell structure) rather than being uniformly distributed, which selectively improves coercivity without compromising overall magnetic properties. This localized modification resolves the contradiction by making the harmful R-rich phases beneficial when confined to specific regions.
Solution Approach 2:
The patent changes the concentration parameter of R-rich phases from uniform distribution to gradient distribution. Specifically, the R-rich phase concentration is increased at grain boundaries (forming a shell with higher concentration) while the core maintains lower concentration. This parameter change transforms the harmful effect of R-rich phases into a beneficial structure that enhances coercivity while maintaining compositional stability.
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 configuration results in a significant increase in coercivity, both at room temperature and high temperatures, by reducing the frequency of reverse magnetic domain generation and suppressing the formation of R-rich phases, thereby maintaining high magnetic properties.
Implementation Method 1
a distribution of R-rich phases in a cross section of the R-T-B based permanent magnet substantially parallel to an easy magnetization axis direction affects a coercivity
Implementation Method 2
The main phase grains observed in a cross section of the R-T-B based permanent magnet are flat (platelet). The cross section is substantially parallel to an easy magnetization axis direction
Data Source
AI summary
An R-T-B based permanent magnet includes a rare earth element R, a transition metal element T, and B. The permanent magnet includes at least Nd as R. The permanent magnet includes at least Fe as T. The permanent magnet contains main phase grains and R-rich phases. The main phase grains include at least R, T, and B. The R-rich phases include at least R. The main phase grains observed in a cross section of the permanent magnet are flat. The cross section is parallel to an easy magnetization axis direction of the permanent magnet. Each of the R-rich phases is located between the main phase grains. An average value of intervals between the R-rich phases in the easy magnetization axis direction is from 5 μm to a width of the permanent magnet in the easy magnetization axis direction.