Sm-Co Sintered Magnet Composition for High Coercivity
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Solution Overview
Problem
Sm-Co permanent magnets used in hybrid electric vehicles and electric vehicles face challenges in achieving high coercive force and magnetization while maintaining heat resistance, as they tend to have low coercive force and magnetization due to high iron concentration, and replacing cobalt with iron does not consistently improve these properties.
Innovation Solution
A sintered compact permanent magnet with a composition of RFeqCuSCo, where R is a rare earth element like Sm, and a structure comprising a Th2Zn17 crystal phase with a crystal grain boundary, optimized by adjusting the atomic percentages of elements like Zr, Cu, and Co, and controlling the sintering and solution treatment conditions to enhance coercive force and magnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a part of cobalt (Co) is replaced with iron (Fe) to increase magnetization of Sm-Co magnets, then magnetization increases, but coercive force decreases
Solution Approach 1:
The patent optimizes the compositional parameters by precisely controlling the Fe concentration range (20-35 atomic%) and Co concentration range (60-75 atomic%) to achieve the optimal balance between magnetization and coercive force. This parameter optimization resolves the contradiction by finding the specific composition window where both properties are simultaneously improved.
Solution Approach 2:
The patent creates a composite microstructure consisting of multiple phases including Sm2(Co,Fe)17 main phase, Sm(Co,Fe)5L1 phase, and (Sm,Zr)Co3 platelet phase. This composite structure allows different phases to contribute differently: the Sm2(Co,Fe)17 phase provides high magnetization while the Sm(Co,Fe)5L1 and (Sm,Zr)Co3 phases provide high coercive force, thus resolving the contradiction between these two properties.
2Quantity of substance
If Fe concentration is increased to improve magnetization, then magnetization improves, but heat resistance deteriorates
Solution Approach 1:
The patent employs a composite microstructure where the Sm(Co,Fe)5L1 phase and (Sm,Zr)Co3 platelet phase act as heat-resistant components. These phases have higher Curie temperatures and maintain their magnetic properties at elevated temperatures, compensating for the reduced heat resistance caused by high Fe concentration in the Sm2(Co,Fe)17 main phase.
Solution Approach 2:
The patent creates local quality differentiation within the microstructure by forming distinct phases with different thermal stability characteristics. The Sm(Co,Fe)5L1 and (Sm,Zr)Co3 phases are distributed throughout the Sm2(Co,Fe)17 matrix, providing localized heat resistance that compensates for the temperature sensitivity of the high-Fe main phase.
3Temperature
If Dy is used to increase heat resistance of Nd-Fe-B magnets, then heat resistance improves, but cost increases due to Dy being a rare element
Solution Approach 1:
The patent replaces expensive rare-earth elements (Dy in Nd-Fe-B magnets) with more abundant and cheaper elements (Fe and Co in Sm-Co magnets). This substitution maintains or improves heat resistance while significantly reducing material cost, as Fe and Co are much more abundant than Dy.
Solution Approach 2:
The patent changes the compositional parameters by using Sm-Co base system instead of Nd-Fe-B system, and by optimizing Fe and Co concentrations to achieve the desired heat resistance without requiring expensive rare-earth additions. This parameter change fundamentally alters the material system to eliminate dependency on costly Dy.
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 significantly improves the coercive force and magnetization of Sm-Co permanent magnets, achieving high residual magnetization and thermal stability, suitable for high-performance applications in motors and generators.
Implementation Method 1
a variable flux motor, as defined in claim 1, and a variable flux generator, as defined in claim 9
Implementation Method 2
comprising a stationary permanent magnet and a variable permanent magnet
Implementation Method 3
The microstructure forms by nucleation growth of ordered R2:17 cells in the 1:7 matrix, then by nucleation of 1:3 platelets on the twin boundaries in R2:17
Implementation Method 4
The genesis of this microstructure is studied by transmission electron microscopy of heat-treated specimens
Implementation Method 5
The processes are likely limited by diffusion
Implementation Method 6
After isothermal aging, TbCu7 +Th2Zn17 structures transform into Th2Zn17 type structure with precipitation of Cu-rich hexagonal SmCo5 (1:5 H) and Zr-rich platelet phases
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
In one embodiment, a permanent magnet includes a sintered compact having a composition represented by the composition formula: RpFeqMrCusCo100-p-q-r-s (where R is at least one element selected from rare earth elements, M is at least one element selected from Zr, Ti, and Hf, p is 10.5 atomic% or more and 12.5 atomic% or less, q is 24 atomic% or more and 40 atomic% or less, r is 0.88 atomic% or more and 4.5 atomic% or less, and s is 3.5 atomic% or more and 10.7 atomic% or less. The sintered compact has a structure having crystal grains constituted of a main phase including a Th2Zn17 crystal phase, and a crystal grain boundary.