R-T-B Permanent Magnet Grain Boundary Control
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Solution Overview
Problem
Conventional R-T-B based permanent magnets face challenges in achieving favorable coercivity and magnetization properties when main-phase crystal grains are miniaturized, as further miniaturization leads to deterioration of magnetization properties and limits the miniaturization of crystal grains.
Innovation Solution
Incorporating a two-grain boundary with a thickness of 5 nm or more and 200 nm or less between adjacent main-phase crystal grains, allowing these grains to be magnetically separated and isolated, thereby reducing the critical size of single magnetic domains and maintaining favorable magnetization properties even with smaller grain sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the main-phase crystal grains are miniaturized to improve coercivity, then coercivity is improved, but magnetization properties deteriorate
Solution Approach 1:
The invention applies local quality by creating a dual-grain boundary structure where the first grain boundary has a specific composition (rich in heavy rare earth elements) different from the second grain boundary (rich in light rare earth elements). This local differentiation allows the fine-grained structure to achieve both high coercivity through the first grain boundary and good magnetization properties through the second grain boundary, resolving the contradiction between grain size miniaturization and magnetization performance.
2Reliability
If the area ratio of crystal grains with grain sizes of 1.8 μm or less is reduced to 5% or less to maintain magnetization properties, then magnetization properties are maintained, but the degree of miniaturization is limited
Solution Approach 1:
The invention segments the grain boundary into two distinct types: first grain boundaries with heavy rare earth element enrichment for coercivity enhancement, and second grain boundaries with light rare earth element enrichment for magnetization property maintenance. This segmentation allows different regions of the microstructure to fulfill different functional requirements, enabling greater miniaturization while maintaining overall performance.
Solution Approach 2:
By creating local compositional differences at grain boundaries (heavy rare earth elements at some boundaries, light rare earth elements at others), the invention enables fine-grained structures to achieve both high coercivity and good magnetization properties, thus increasing the allowable degree of miniaturization beyond conventional limits.
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 enables the attainment of favorable coercivity and magnetization properties by controlling the two-grain boundary thickness, allowing main-phase crystal grains with average sizes between 0.9 μm and 2.8 μm to function as multiple magnetic domain grains, even when they would conventionally be single magnetic domain grains, thus enhancing the magnetic performance of R-T-B based permanent magnets.
Implementation Method 1
a two-grain boundary is contained between the two adjacent main-phase crystal grains... allowing these grains to be magnetically separated and isolated
Data Source
AI summary
An R-T-B based permanent magnet includes R-T-B based compounds as main-phase crystal grains. R is a rare earth element. T is iron group element(s) essentially including Fe or Fe and Co. B is boron. A two-grain boundary is contained between the two adjacent main-phase crystal grains. An average grain size of the main-phase crystal grains is 0.9 μm or more and 2.8 μm or less. A thickness of the two-grain boundary is 5 nm or more and 200 nm or less.