R-T-B Rare Earth Magnet Coercive Force via Zr and Grain Boundary Optimization
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Solution Overview
Problem
Existing R-T-B-based rare earth sintered magnets face challenges in achieving high coercive force without increasing the amount of Dy, which is an eccentrically located and unstable resource.
Innovation Solution
The development of an R-T-B-based rare earth sintered magnet and alloy with specific compositions, including rare earth elements, transition metals, and boron, where the concentration of boron is lower than in conventional alloys, and the inclusion of metallic elements like Al, Ga, and Cu, along with Zr, to enhance coercive force and maintain squareness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the amount of Dy is increased to improve coercive force, then the coercive force increases, but the resource stability and cost increase due to Dy being an eccentrically located and unstable resource
Solution Approach 1:
The patent changes the compositional parameters by reducing the Dy content from conventional levels (typically 5-10 atom%) to 0.01-5 atom%, and compensates by optimizing other elements: increasing rare earth elements (10-20 atom%), adjusting transition metals (70-85 atom%), and controlling boron (2-6 atom%). This parameter transformation achieves high coercive force through a different compositional pathway that relies on stable, abundant resources rather than scarce Dy.
Solution Approach 2:
The patent creates a composite grain boundary phase structure consisting of multiple phases: an R-rich phase (rare earth element rich), a transition metal-rich phase (Fe, Co, Ni rich), and an intermetallic compound phase (R2T17 or R2T29). This multi-phase composite structure in the grain boundary region provides enhanced coercive force through synergistic effects, replacing the need for high Dy content while maintaining resource stability.
2Reliability
If the composition is optimized to reduce Dy content, then resource stability improves, but achieving high coercive force becomes more difficult
Solution Approach 1:
The patent applies local quality by creating a non-uniform grain boundary phase with distinct regions having different compositions and functions. The R-rich phase provides magnetic stability, the transition metal-rich phase enhances coercive force through exchange coupling, and the intermetallic compound phase provides structural stability. This localized functional differentiation compensates for reduced Dy content by concentrating coercive force enhancement in specific grain boundary regions.
Solution Approach 2:
The patent transforms the compositional parameters from Dy-heavy to a balanced multi-element system. Specifically: rare earth elements are optimized at 10-20 atom% (including Nd, Pr, Dy, Tb), transition metals at 70-85 atom% (Fe, Co, Ni), boron at 2-6 atom%, with controlled amounts of Al (0.1-2.0 atom%), Ga (0.1-2.0 atom%), Cu (0.1-2.0 atom%), and Zr (0.01-0.1 atom%). This comprehensive parameter optimization enables high coercive force without relying on high Dy content.
3Quantity of substance
If conventional R-T-B-based alloy composition is used, then the main phase proportion is maximized, but coercive force remains insufficient without high Dy content
Solution Approach 1:
The patent deviates from the conventional R2T14B stoichiometric ratio (which would give approximately 14.3 atom% R, 85.7 atom% T, 0 atom% B) by introducing controlled deviations: reducing B to 2-6 atom% (conventional is typically higher), adding Al (0.1-2.0 atom%), Ga (0.1-2.0 atom%), Cu (0.1-2.0 atom%), and Zr (0.01-0.1 atom%). These compositional parameter changes promote the formation of a transition metal-rich phase in grain boundaries while maintaining adequate main phase proportion, achieving enhanced coercive force through this controlled deviation from conventional composition.
Data Source
AI summary
An R-T-B-based rare earth sintered magnet, comprising a rare earth element R, B, a metallic element M which includes one or more metals selected from Al, Ga and Cu, a transition metal T which includes Fe as a main component, and inevitable impurities, wherein the sintered magnet includes 13 atom % to 15.5 atom % of R, 5.0 atom % to 6.0 atom % of B, 0.1 atom % to 2.4 atom % of M, and T and the inevitable impurities as a balance, and wherein the sintered magnet includes 0.015 atom % to 0.10 atom % of Zr as the transition metal T.