R-T-B Permanent Magnet Grain Boundary Phase Design
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Solution Overview
Problem
The existing R-T-B based permanent magnets require a large magnetizing field to switch magnetization, leading to inefficiencies and uncontrollable magnetization changes, especially in low magnetizing fields, which limits their application in variable magnetic flux motors.
Innovation Solution
An R-T-B based permanent magnet with a tetragonal structure and a grain boundary phase containing an R-T-B-C compound, where the R concentration is higher than in the main phase, and the T concentration is lower, with specific atomic ratios of R, B, and C, to achieve low coercive force and high residual magnetic flux density, and improved minor curve flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional R-T-B based permanent magnets are used, then high residual magnetic flux density is achieved, but large magnetizing field is required to switch magnetization
Solution Approach 1:
The patent changes the chemical composition parameters of the permanent magnet by incorporating specific rare earth elements (R = Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and transition metals (T = Fe, Co, Ni, Cu, Zn, Ga, Ge, In, Sn, Sb, Te, I) in controlled amounts. This compositional parameter adjustment reduces the coercive force while maintaining high residual magnetic flux density, enabling magnetization switching at lower magnetizing fields
Solution Approach 2:
The patent creates a composite permanent magnet material system combining multiple rare earth elements, transition metals, and boron in specific proportions. This composite structure leverages the complementary magnetic properties of different elements to achieve both high residual flux density and reduced magnetizing field requirements through synergistic effects
2Stability of the object's composition
If high coercive force permanent magnets are used, then magnetic stability is improved, but magnetization control becomes difficult in low magnetizing fields
Solution Approach 1:
The patent adjusts the coercive force parameter by controlling the ratios of rare earth elements and transition metals. Specifically, the presence of certain elements like Ga, Ge, In, Sn, Sb, Te, or I in small amounts (0.01-5 at%) modifies the magnetic anisotropy and domain wall pinning, reducing coercive force to enable controllable magnetization switching while preserving adequate magnetic stability through the dominant R2T14B phase structure
3Adaptability or versatility
If Sm-Co based permanent magnets are used, then variable magnetic flux capability is achieved, but cost increases due to high Co price
Solution Approach 1:
The patent replaces expensive cobalt with more abundant and cheaper transition metals such as Fe, Ni, Cu, Zn, Ga, Ge, In, Sn, Sb, Te, or I. The use of Fe-rich compositions (T including Fe) provides comparable or superior magnetic properties at significantly lower material cost, making the permanent magnet economically viable for variable magnetic flux motor applications
Solution Approach 2:
The patent modifies the base composition from Sm-Co to R-T-B system with T including Fe and optional Co (0-10 at%). This parameter change in the alloying strategy allows achieving variable magnetic flux capability through compositional control rather than relying on expensive Sm-Co, reducing manufacturing cost while maintaining functional performance
4Ease of operation
If R-T-B based permanent magnet with low coercive force is used, then magnetization switching becomes easier, but residual magnetic flux density decreases
Solution Approach 1:
The patent optimizes the composition parameters within the R2T14B phase structure, maintaining high R content (10-30 at%) and Fe content (60-80 at%) while controlling Co content (0-10 at%). This parameter optimization ensures that the main phase retains strong magnetic properties for high residual flux density, while the grain boundary phase and overall composition provide low coercive force for easy magnetization switching
Solution Approach 2:
The patent employs a composite microstructure with R2T14B main phase crystal grains embedded in a grain boundary phase containing rare earth rich compounds. This composite structure separates the functions: the main phase provides high residual magnetic flux density through its tetragonal structure and composition, while the grain boundary phase contributes to low coercive force by reducing domain wall pinning, achieving both contradictory requirements simultaneously
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 solution provides a low coercive force and low magnetizing field requirements, along with high residual magnetic flux density and minor curve flatness, enabling efficient and controllable magnetization changes even in low magnetizing fields, suitable for variable magnetic flux motors.
Implementation Method 1
the external magnetic field required to set the residual magnetic flux density Br to zero is 1.10 HcJ or less
Implementation Method 2
R-T-B based permanent magnet comprising crystal grains including a rare earth element R, a transition metal element T, and boron B
Data Source
AI summary
An object of the present invention is to provide an R-T-B based permanent magnet having a low coercive force and a low magnetizing field, and having a high residual magnetic flux density and a high minor curve flatness even in the low magnetizing field. Provided is an R-T-B based permanent magnet including a main phase including a compound having an R2T14B type tetragonal structure and a grain boundary phase existing between the main phases, in which R is at least one rare earth element including scandium and yttrium, T is at least one transition metal element including iron, or at least two transition metal elements including iron and cobalt, the grain boundary includes an R-T-B—C based compound having a higher R concentration, B concentration and C concentration than that of the main phase and having a lower T concentration than that of the main phase.