Core-Shell R-T-B Sintered Magnet Reducing Heavy Rare Earth Cost
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Solution Overview
Problem
R-T-B based sintered magnets face challenges with high costs due to the expensive and rapidly increasing prices of heavy rare earth elements, necessitating a reduction in their usage while maintaining high magnetic properties.
Innovation Solution
The development of an R-T-B based sintered magnet with a core-shell structure in its main phase grains, where the core portion has a higher concentration of light rare earth elements and a lower concentration of heavy rare earth elements, and the shell portion has a higher concentration of heavy rare earth elements, along with specific compositions and processing methods to optimize magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earth elements (Dy, Tb, Ho) are added to R-T-B based sintered magnets to elevate coercivity at room temperature, then coercivity is improved, but manufacturing cost increases due to the expensive and rapidly rising prices of heavy rare earth elements
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the shell portion contains a high concentration of heavy rare earth elements (x=0.05 to 0.50) specifically at the grain boundaries and outer regions, while the core portion contains a low concentration (x=0.00 to 0.05). This localized distribution ensures that heavy rare earth elements are concentrated only where they are most effective for coercivity enhancement, rather than being uniformly distributed throughout the entire magnet, thereby reducing overall heavy rare earth content while maintaining high coercivity.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the concentration parameter x of heavy rare earth elements in different regions of the main phase crystal grains. By setting x to 0.05-0.50 in the shell and 0.00-0.05 in the core, the patent optimizes the balance between coercivity enhancement and cost reduction. Additionally, the patent controls the thickness of the shell portion to be 10-100 nm, which is a critical parameter change that ensures effective coercivity improvement with minimal heavy rare earth usage.
2Reliability
If heavy rare earth elements are added to maintain high coercivity, then magnetic properties are maintained, but the usage amount of heavy rare earth elements increases leading to higher costs
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the shell portion contains a high concentration of heavy rare earth elements (x=0.05 to 0.50) specifically at the grain boundaries and outer regions, while the core portion contains a low concentration (x=0.00 to 0.05). This localized distribution ensures that heavy rare earth elements are concentrated only where they are most effective for coercivity enhancement, rather than being uniformly distributed throughout the entire magnet, thereby reducing overall heavy rare earth content while maintaining high coercivity.
Solution Approach 2:
The patent applies partial action by concentrating heavy rare earth elements only in the shell portion (10-100 nm thickness) at the grain boundaries and outer regions, rather than distributing them throughout the entire crystal grain. This partial distribution is sufficient to maintain high coercivity and magnetic properties, as the heavy rare earth elements are placed precisely where they provide the greatest benefit, without the need for excessive amounts throughout the entire material.
Data Source
AI summary
An R-T-B based sintered magnet maintains high magnetic properties and decreases usage of heavy rare earth elements. The magnet includes main phase grains and grain boundary phases, the main phase grain containing a core portion and a shell portion. X in the main phase LR(2-x)HRxT14B of the core portion ranges from 0.00 to 0.07; x in the main phase LR(2-x)HRxT14B of the shell portion ranges from 0.02 to 0.40; and the maximum thickness of the shell portion ranges from 7 nm to 100 nm. LR contains Nd and one or more light rare earth elements consisting of Y, La, Ce, Pr and Sm; HR contains Dy or/and Tb and one or more heavy rare earth elements consisting of Gd, Ho, Er, Tm, Yb and Lu; T contains Fe or/and Co and one or two kinds of Mn and Ni; and B represents boron partly replaced by C (carbon).