R-T-B Sintered Magnet Grain Boundary Phase Design
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Solution Overview
Problem
Current R-T-B based sintered magnets suffer from insufficient magnetic coupling cutoff at high temperatures due to thin two-grain boundary parts, limiting their coercivity and demagnetization resistance.
Innovation Solution
The formation of two-grain boundary parts by R—Co—Cu-M-Fe phases with a thickness of 5–500 nm, where M is at least one of Ga, Si, Sn, Ge, or Bi, effectively cuts off magnetic coupling between R2T14B crystal grains, enhancing coercivity and suppressing demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earth elements such as Dy or Tb are used to replace part of Nd in the main phase, then coercivity at room temperature is improved, but residual magnetic flux density decreases due to antiferromagnetic coupling
Solution Approach 1:
The patent applies local quality by concentrating heavy rare earth elements specifically in the two-grain boundary parts rather than uniformly distributing them throughout the magnet. This localized approach allows the heavy rare earth elements to enhance coercivity at the critical grain boundary regions where magnetic coupling occurs, while minimizing their negative impact on the overall residual magnetic flux density of the bulk material.
Solution Approach 2:
The patent introduces Cu and Al as intermediary elements that form specific phases (Cu-Al-Fe-Si intermetallic compounds) at the grain boundaries. These intermediary phases mediate the magnetic coupling between grains, providing a mechanism to control and reduce unwanted magnetic interactions without requiring heavy rare earth element substitution in the main phase, thereby preserving residual magnetic flux density while still improving coercivity.
2Productivity
If the two-grain boundary parts are made thinner to increase the volume fraction of main phase, then productivity is improved, but magnetic coupling cutoff effectiveness decreases leading to reduced coercivity
Solution Approach 1:
The patent changes the compositional parameters of the two-grain boundary parts by introducing specific elements (Cu, Al, Si, Fe) in controlled amounts. This compositional modification allows the grain boundaries to achieve optimal thickness (balancing productivity and performance) while the altered chemistry provides enhanced magnetic coupling cutoff effectiveness through the formation of specific intermetallic phases that suppress magnetic interactions between grains.
Solution Approach 2:
The patent creates a composite structure at the grain boundary level, where multiple elements (Cu, Al, Fe, Si) form a complex intermetallic phase rather than a simple eutectic structure. This composite grain boundary material provides superior magnetic coupling cutoff properties compared to conventional single-phase boundaries, enabling effective coercivity enhancement even with optimized (thinner) grain boundary dimensions that maximize the volume fraction of 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
This approach significantly improves the coercivity and reduces demagnetization at high temperatures, ensuring reliable motor performance even under harsh conditions.
Implementation Method 1
the two-grain boundary parts formed by R—Co—Cu-M-Fe phases (M is at least one selected from the group consisting of Ga, Si, Sn, Ge, and Bi) exist
Data Source
AI summary
The present invention provides an R-T-B based sintered magnet that inhibits the demagnetization rate at high temperature even when less or no heavy rare earth elements such as Dy, Tb and the like are used. The R-T-B based sintered magnet includes R2T14B crystal grains and two-grain boundary parts between the R2T14B crystal grains. Two-grain boundary parts formed by R—Co—Cu-M-Fe phase exist, and M is at least one selected from the group consisting of Ga, Si, Sn, Ge and Bi.