R-T-B Sintered Magnet Grain Boundary Composition
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Solution Overview
Problem
R-T-B based sintered magnets suffer from low corrosion resistance due to oxidation of rare earth elements, leading to hydrogen storage in grain boundaries, which accelerates corrosion and deteriorates magnetic properties, while conventional methods to improve corrosion resistance increase production costs and reduce magnetic properties.
Innovation Solution
Incorporating an R—Co—Cu—N concentrated part with higher concentrations of R, Co, and N in the grain boundaries, and optionally an R—O—C or R—O—C—N concentrated part, to prevent hydrogen storage and enhance corrosion resistance without compromising magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbon content in the magnet alloy is reduced to 0.04 mass % or less to improve corrosion resistance, then corrosion resistance is improved, but residual magnetic flux density Br decreases due to reduced degree of orientation of magnetic powder
Solution Approach 1:
The patent applies local quality by creating a specific compositional structure where the grain boundary phase has different composition (higher C and lubricant content) compared to the main phase. This allows the grain boundary to provide corrosion protection while the main phase maintains its magnetic properties. The localized concentration of carbon and lubricant in the grain boundary region enables simultaneous achievement of corrosion resistance and magnetic performance.
Solution Approach 2:
The patent creates a composite structure consisting of the main phase (R2T14B) and the grain boundary phase with specific composition ratios. This composite material approach allows combining the advantages of both phases: the main phase provides magnetic properties while the grain boundary phase provides corrosion resistance. The controlled composition ratio between these phases enables optimization of both corrosion resistance and magnetic properties.
2Reliability
If Co concentration in the R-rich phase is increased to improve corrosion resistance, then corrosion resistance is improved, but production cost rises and magnetic properties deteriorate due to substitution of Co for Fe in the main phase
Solution Approach 1:
The patent applies local quality by concentrating Co specifically in the grain boundary phase rather than distributing it throughout the main phase. This localized placement ensures that Co provides corrosion protection at the grain boundaries without substituting Fe in the main phase, thereby avoiding deterioration of magnetic properties and unnecessary increase in production cost.
Solution Approach 2:
The grain boundary phase acts as an intermediary that contains the Co additive, preventing direct substitution of Fe in the main phase. This intermediary structure allows Co to fulfill its corrosion-resistant function without interfering with the magnetic properties of the main phase, solving the contradiction between corrosion resistance and magnetic performance.
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 corrosion resistance and maintains good magnetic properties, reducing the risk of corrosion progression and production costs associated with excessive Co usage.
Implementation Method 1
The hydrogen is stored in an R-rich phase present in a grain boundary in the R-T-B based sintered magnet, which accelerates change of an R-rich phase to hydroxide.
Implementation Method 2
water such as water vapor under a use environment oxidizes 'R' in the R-T-B based sintered magnet and generates hydrogen
Data Source
AI summary
An R-T-B based sintered magnet having R2T14B crystal grains and a grain boundary formed by two or more adjacent R2T14B crystal grains. An R—Co—Cu—N concentrated part whose concentrations of R, Co, Cu and N are respectively higher than those in the R2T14B crystal grains may be in the grain boundary. An R—O—C concentrated part or an R—O—C—N concentrated part may be further provided in the grain boundary.