R-T-B Sintered Magnet Grain Boundary R-O-C Concentration
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Solution Overview
Problem
R-T-B based sintered magnets suffer from low corrosion resistance due to oxidation by water vapor, leading to hydrogen generation and subsequent corrosion of the R-rich phase, which deteriorates magnetic properties and increases production costs.
Innovation Solution
Forming an R—O—C concentrated part or R—O—C—N concentrated part in the grain boundary with higher concentrations of rare earth elements, oxygen, carbon, and nitrogen, and a specific O/R ratio to prevent hydrogen storage and corrosion, while maintaining good magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon content is reduced to improve corrosion resistance, then corrosion resistance is improved, but magnetic field orientation decreases and residual magnetic flux density decreases
Solution Approach 1:
The invention applies local quality by creating an R-O-C concentrated part specifically in the grain boundary region, rather than uniformly distributing carbon throughout the magnet. This localized carbon enrichment at the grain boundary provides corrosion protection where it is most needed (at the vulnerable interface) while maintaining low overall carbon content in the bulk material, thus preserving magnetic field orientation in the main phase.
Solution Approach 2:
The invention segments the magnet structure into distinct regions with different compositions: the main phase (R2T14B) with low carbon content for good magnetic properties, and the grain boundary region with concentrated R-O-C for corrosion resistance. This segmentation allows each region to be optimized for its specific function without compromising the other.
2Reliability
If Co concentration in R-rich phase is increased to improve corrosion resistance, then corrosion resistance is improved, but production cost increases and magnetic properties decrease
Solution Approach 1:
The invention changes the compositional parameters by forming an R-O-C concentrated part with specific concentration ratios (C/R = 0.01 to 0.1 and O/R = 0.1 to 1.0) in the grain boundary. This parameter optimization provides effective corrosion protection through controlled carbon and oxygen enrichment rather than relying on expensive cobalt addition, thus reducing production cost while maintaining corrosion resistance.
3Reliability
If Co substitutes Fe in main phase to increase Co concentration in R-rich phase, then Co concentration in R-rich phase increases, but magnetic properties decrease
Solution Approach 1:
The invention applies local quality by concentrating carbon and oxygen specifically in the grain boundary region to form the R-O-C concentrated part, while keeping the main phase composition relatively pure (R2T14B) to maintain excellent magnetic properties. This localized approach provides corrosion protection without the need for cobalt substitution in the main phase.
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
Significantly improves corrosion resistance and maintains excellent magnetic properties by preventing hydrogen storage and corrosion within the R-T-B based sintered magnet, reducing production costs and enhancing reliability.
Implementation Method 1
water such as water vapor in a used environment oxidizes 'R' in the R-T-B based sintered magnet and generates hydrogen
Implementation Method 2
an R-rich phase in grain boundary absorbs said hydrogen which progresses corrosion of the R-rich phase
Data Source
AI summary
The present invention provides an R-T-B based sintered magnet including R2T14B crystal grains wherein; a grain boundary is formed by two or more adjacent R2T14B crystal grains, an R—O—C concentrated part, in which concentrations of R, O and C are higher than those in the R2T14B crystal grains respectively, is in the grain boundary, and a ratio (O/R) of O atom to R atom in the R—O—C concentrated part satisfies the following formula (1):0.4<(O/R)<0.7.