R-T-B Rare Earth Magnet Grain Boundary Optimization
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Solution Overview
Problem
R-T-B based rare earth permanent magnets exhibit low coercive force, squareness ratio, and minor curve flatness when magnetized in a low magnetic field, limiting their efficiency in variable magnetic force motors, which require high torque generation across a wide rotational speed range.
Innovation Solution
The composition (R11-x(Y1-y-zCeyLaz)x)TbBcMd is optimized, with R1 being a rare earth element excluding Y and Ce, T including Fe or Fe and Co, and M comprising Ga or Ga and Sn, Bi, Si, within specific atomic ratios, to achieve a low coercive force while enhancing squareness ratio and minor curve flatness by stabilizing a single domain structure and reducing nucleation field dispersion through controlled grain size and grain boundary phase coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If R-T-B based rare earth permanent magnet is magnetized in a low magnetic field, then the motor can operate in a wide speed range with field-weakening control, but the coercive force, squareness ratio, and minor curve flatness become low, reducing motor efficiency
Solution Approach 1:
The invention changes the magnetic field parameters by optimizing the composition to enable magnetization in low magnetic fields (≤8 kOe) while maintaining high coercive force (≥7 kOe) and squareness ratio (≥0.90). This allows the motor to operate efficiently across a wide speed range without the energy losses associated with conventional field-weakening control
Solution Approach 2:
The invention uses a composite material system with specific composition (R11-x(Y1-y-zCeyLaz)x)TbBcMd where R1 is Nd, Pr, Dy, Ho, or Tb, and M is Ga, Sn, Bi, or Si. This composite structure provides both low magnetizing field requirement and high coercive force, resolving the contradiction between adaptability and energy efficiency
2Loss of energy
If Sm-Co based permanent magnet is used to achieve variable magnetic force with low coercive force, then motor efficiency is improved in medium and high speed ranges, but the cost increases significantly
Solution Approach 1:
The invention replaces expensive Sm-Co based permanent magnets with a cost-effective R-T-B based magnet system. By optimizing the composition to achieve the required magnetic properties using abundant rare earth elements and small amounts of Ga, Sn, Bi, or Si, the invention provides an economical alternative that maintains high motor efficiency
Solution Approach 2:
The invention changes the material parameters by developing an R-T-B based magnet with controlled grain size (D50≤4.00 μm) and specific composition that achieves low coercive force and high squareness ratio, enabling variable magnetic force operation at a fraction of the cost of Sm-Co magnets
3Strength
If the composition is optimized for high coercive force to maintain magnetic strength, then the squareness ratio and minor curve flatness improve, but the magnetization field strength increases, requiring higher external fields for operation
Solution Approach 1:
The invention simultaneously optimizes multiple parameters: composition (adding Ga, Sn, Bi, or Si), grain size (D50≤4.00 μm), and grain boundary phase (70% or more coating rate). This multi-parameter optimization achieves the remarkable result of high coercive force (≥7 kOe) with low magnetization field (≤8 kOe), resolving the contradiction between strength and force requirements
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 enables R-T-B based rare earth permanent magnets to maintain high efficiency across a wide rotational speed range with low coercive force and high squareness ratio and minor curve flatness, suitable for variable magnetic force motors, by stabilizing a single domain structure and reducing nucleation field dispersion.
Implementation Method 1
a grain boundary phase, and main phase crystal grains, wherein an average crystal grain diameter of the main phase crystal grains satisfies the following formula: D50≤4.00 μm, and a grain size distribution satisfies the following formula: (D90−D10)/D50≤1.60
Data Source
AI summary
An R-T-B based rare earth permanent magnet is expressed by a compositional formula: (R11−x(Y1−y−z Cey Laz)x)aTbBcMd in which R1 is one or more kinds of rare earth element not including Y, Ce and La, “T” is one or more kinds of transition metal, and includes Fe or Fe and Co as an essential component, “M” is an element having Ga or Ga and one or more kinds selected from Sn, Bi and Si, and 0.4≤x≤0.7, 0.00≤y+z≤0.20, 0.16≤a/b≤0.28, 0.050≤c/b≤0.075 and 0.005≤d/b≤0.028. The magnet includes a main phase, including a compound having a R2T14B type tetragonal structure, and a grain boundary phase. D10, D50, D90 of crystal grain diameter according to the main phase crystal grains satisfies the following formula: D50≤4.00 μm and (D90−D10)/D50≤1.60. A coating rate of the grain boundary is 70.0% or more.