R-T-B Sintered Magnet Core-Shell Structure
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Solution Overview
Problem
Rare earth sintered magnets with R-T-B composition face challenges in achieving high residual magnetic flux density and coercivity while maintaining corrosion resistance and manufacturing stability.
Innovation Solution
The R-T-B based sintered magnet composition includes specific ranges of Tb, Fe, Cu, Mn, Al, Co, and B, with a higher Tb content at the surface portion and a core-shell structure, optimized through grain boundary diffusion to enhance magnetic properties and thermal demagnetization resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the content of heavy rare earth elements (Tb, Dy) is increased to improve coercivity, then coercivity is improved, but manufacturing cost increases and manufacturing stability deteriorates
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the surface portion has a different composition (higher Tb content) than the core portion. This allows the surface to provide enhanced coercivity and corrosion resistance while the core maintains cost-effective composition, thereby improving manufacturing stability without sacrificing magnetic performance.
Solution Approach 2:
The patent changes the compositional parameter of Tb content from uniform distribution to gradient distribution, with the surface portion containing 0.30-1.50 mass% Tb and the core portion containing 0.05-0.50 mass% Tb. This parameter change enables optimized coercivity at the surface while maintaining manufacturing stability through controlled composition gradients.
2Force
If the content of heavy rare earth elements (Tb, Dy) is increased to improve coercivity, then coercivity is improved, but manufacturing cost increases
Solution Approach 1:
The patent concentrates heavy rare earth elements (Tb) specifically in the surface portion (0.30-1.50 mass%) while keeping the core portion composition more economical (0.05-0.50 mass%). This localized distribution achieves the necessary coercivity enhancement only where needed for magnetic performance, reducing overall heavy rare earth content and manufacturing cost.
Solution Approach 2:
The patent creates a composite structure with two distinct compositional regions: a Tb-enriched surface layer and a cost-optimized core region. This composite approach allows the system to achieve high coercivity through the Tb-rich surface while minimizing the total quantity of expensive heavy rare earth elements used in the overall magnet structure.
3Force
If grain boundary diffusion process is used to increase Tb content at surface, then coercivity is improved, but process complexity increases
Solution Approach 1:
The patent employs grain boundary diffusion as a preliminary action to pre-establish the desired Tb concentration gradient in the surface portion before final magnet assembly. By performing this diffusion treatment during manufacturing, the complex compositional gradient is created in advance, simplifying subsequent processing steps and overall production complexity.
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 configuration improves residual magnetic flux density, coercivity, corrosion resistance, and manufacturing stability, making the magnets suitable for applications like motors and generators.
Implementation Method 1
heating it to conduct the grain boundary diffusion
Data Source
AI summary
An R-T-B based sintered magnet includes “R”, “T”, and “B”. “R” represents a rare earth element including at least Tb. “T” represents a metal element except rare earth elements including at least Fe, Cu, Mn, Al, and Co. “B” represents boron or boron and carbon. With respect to 100 mass % of a total mass of the R-T-B based sintered magnet, a content of “R” is 28.0 to 32.0 mass %, a content of Cu is 0.04 to 0.50 mass %, a content of Mn is 0.02 to 0.10 mass %, a content of Al is 0.15 to 0.30 mass %, a content of Co is 0.50 to 3.0 mass %, and a content of “B” is 0.85 to 1.0 mass %. Tb2/Tb1 is 0.40 to less than 1.0, where Tb1 and Tb2 (mass %) denote a content of Tb at a surface portion and at a core portion, respectively.