Sintered R-T-B Magnet Composition for High Coercivity Without Dy/Tb
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Solution Overview
Problem
Sintered R-T-B based magnets face challenges in achieving high remanence (B_r) and coercivity (H_cJ) while minimizing the use of scarce and expensive heavy rare-earth elements like Dy and Tb, as existing methods either compromise on B_r or require unstable supply chains.
Innovation Solution
A sintered R-T-B based magnet with a specific composition and heat treatment process, where Pr and Ga are diffused deep into the magnet interior through grain boundaries, optimizing the R, B, and T content to enhance B_r and H_cJ without relying heavily on Dy and Tb, with a Pr/Nd ratio gradient and controlled Ga distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare-earth elements (Dy, Tb) are used to improve coercivity, then H_cJ increases, but cost increases and supply stability decreases
Solution Approach 1:
The patent changes the compositional parameters by replacing heavy rare-earth elements with a combination of light rare-earth elements (Nd, Pr) and transition metals (Al, Ga, Cu) in specific proportions. The R2T14B main phase is modified with controlled additions of Al (0.1-1.0 mass%), Ga (0.05-0.5 mass%), and Cu (0.1-0.5 mass%), which alters the magnetic properties to achieve high coercivity without relying on Dy or Tb.
Solution Approach 2:
The patent creates a composite grain boundary structure consisting of multiple phases: R2T17 phase, R6T13M intermetallic compound, and R-T-Al-Ga-Cu phase. This composite structure at the grain boundaries synergistically improves coercivity through phase interactions, replacing the need for heavy rare-earth elements while maintaining magnetic performance.
2Reliability
If B content is reduced to increase H_cJ, then coercivity improves, but remanence B_r decreases
Solution Approach 1:
The patent applies local quality by creating distinct compositional regions: the main phase (R2T14B) maintains higher B content for remanence, while the grain boundary phase has modified composition with Al, Ga, and Cu additions that specifically enhance coercivity. This spatial differentiation allows simultaneous optimization of both remanence and coercivity.
Solution Approach 2:
The multi-phase composite structure at grain boundaries (R2T17 + R6T13M + R-T-Al-Ga-Cu) creates synergistic effects where each phase contributes differently: R2T17 provides structural stability, R6T13M enhances coercivity, and the R-T-Al-Ga-Cu phase improves both remanence and coercivity, resolving the trade-off between B_r and H_cJ.
3Reliability
If Al, Ga, Cu are added to improve H_cJ, then coercivity increases, but manufacturing complexity increases
Solution Approach 1:
The patent establishes specific parameter ranges for Al (0.1-1.0 mass%), Ga (0.05-0.5 mass%), and Cu (0.1-0.5 mass%) that optimize coercivity while maintaining manufacturability. These controlled compositional parameters ensure consistent magnetic properties without requiring overly complex manufacturing processes.
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 approach effectively increases both remanence and coercivity while reducing the reliance on expensive heavy rare-earth elements, ensuring stable supply and performance in high-temperature applications.
Implementation Method 1
Pr and Ga are diffused deep into the magnet interior through grain boundaries
Implementation Method 2
sintered R-T-B based magnet
Data Source
Figure 1A~1B
AI summary
A sintered R-T-B based magnet according to the present disclosure is a sintered R-T-B based magnet containing a main phase crystal grain and a grain boundary phase, the sintered R-T-B based magnet containing: R: not less than 27.5 mass% and not more than 35.0 mass% (R is at least one rare-earth element which always includes Nd and Pr); B: not less than 0.80 mass% and not more than 1.05 mass%; Ga: not less than 0.05 mass% and not more than 1.0 mass%; M: not less than 0 mass% and not more than 2 mass% (where M is at least one of Cu, Al, Nb and Zr); and a balance T (where T is Fe, or Fe and Co) and impurities. A Pr/Nd which is a ratio of a concentration of Pr to a concentration of Nd in a central portion of a main phase crystal grain that is located at a depth of 300 µm from the magnet surface is lower than 1; and a Pr/Nd which is a ratio of a concentration of Pr to a concentration of Nd in an intergranular grain boundary that is located at a depth of 300 µm from the magnet surface is higher than 1. A portion where the Ga concentration gradually decreases from the magnet surface toward the magnet interior exists.