R-T-B Magnet Composition for Grain Growth Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
R-T-B based permanent magnets face challenges in achieving high residual magnetic flux density, coercive force, and squareness ratio while maintaining a wide sintering temperature range without abnormal grain growth, which is difficult to achieve with existing techniques that often require high rare earth element content or narrow sintering temperature ranges.
Innovation Solution
The R-T-B based permanent magnet composition includes specific elements such as Ga, Zr, and C, with controlled mass percentages of R, B, and Zr, forming phases like Zr-B, Zr-C, and R6T13Ga, which suppress abnormal grain growth and enhance magnetic properties, including a high Zr-B phase with a long side length of 300-500 nm, and the absence of R2T17 phase, to achieve high Br, Hcj, and Hk/Hcj ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If B content is reduced to achieve high coercive force, then Hcj is improved, but the squareness ratio (Hk/Hcj) deteriorates and abnormal grain growth occurs more easily
Solution Approach 1:
Zr-B compounds act as intermediary substances that pin grain boundaries and suppress abnormal grain growth. This allows the use of low B content (0.6-1.0 mass%) to achieve high coercive force while maintaining squareness ratio above 90%, as the Zr-B compounds prevent the detrimental effects of low B content
Solution Approach 2:
The patent creates a composite structure with main phase (R2T14B), grain boundary phase containing Zr-B compounds, and R-rich phase. This composite approach enables simultaneous achievement of high coercive force (through low B content and Zr-B compounds) and high squareness ratio (through controlled grain growth suppression)
2Force
If sintering temperature is increased to improve squareness ratio, then Hk/Hcj is improved, but abnormal grain growth occurs reducing production stability
Solution Approach 1:
Zr-B compounds are introduced into the alloy composition before sintering to pre-establish grain boundary pinning sites. This preliminary action suppresses abnormal grain growth during sintering, allowing a wider sintering temperature range (1050-1150°C) to achieve high squareness ratio without production stability issues
Solution Approach 2:
The patent changes the chemical composition parameters by adding Zr (0.1-2.0 mass%) and controlling B content (0.6-1.0 mass%) to form Zr-B compounds. This compositional parameter change enables thermodynamic control of grain growth behavior, widening the optimal sintering temperature range and improving production stability
3Force
If heavy rare earth element content is increased to improve coercive force, then Hcj is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive heavy rare earth elements (Dy, Tb) with cheaper light rare earth elements (Nd, Pr) combined with Zr-B compounds. The Zr-B compounds provide the necessary grain boundary pinning and coercive force enhancement at lower cost, making the magnet economically viable while maintaining high performance
Solution Approach 2:
The patent changes the rare earth element composition parameters by reducing heavy RE content to 1.0 mass% or less and using specific ratios of light rare earth elements. Combined with Zr-B compound formation, this parameter change achieves high coercive force (Hcj≥1432 kA/m) without relying on expensive heavy rare earth elements
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 composition results in magnets with high magnetic properties, a wide sintering temperature range, and improved production stability, achieving Br of 1305 mT or more, Hcj of 1432 kA/m or more, and Hk/Hcj of 95% or more, while minimizing the need for heavy rare earth elements and avoiding abnormal grain growth.
Implementation Method 1
precipitating at least two selected from an M-B based compound, an M-B—Cu based compound, and an M-C based compound (M is at least one selected from Ti, Zr, and Hf) and also precipitating oxides of R in a magnet composition
Implementation Method 2
a main phase mainly including R2Fe14B
Implementation Method 3
the R-T-B based sintered magnet can have the maximum coercive force at a specific B concentration
Data Source
AI summary
An R-T-B based permanent magnet in which R is a rare earth element, T is Fe or a combination of Fe and Co, B is boron, and further includes M. The R-T-B based permanent magnet includes main phase grains consisting of R2T14B phase. M at least includes Ga and Zr. The R-T-B based permanent magnet further includes C and O. R content is 29.0 mass % to 33.0 mass %, B content is 0.85 mass % to 1.05 mass %, Ga content is 0.30 mass % to 1.20 mass %, 0 content is 0.03 mass % to 0.20 mass %, and C content is 0.03 mass % to 0.30 mass %. Further, the R-T-B based permanent magnet satisfies 3.48m(B)−2.67≤m(Zr)≤3.48m(B)−1.87 in which m(B) (mass %) is B content and m(Zr) (mass %) is Zr content.