R-T-B Magnet Composition for Stable High-Coercivity Performance
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Solution Overview
Problem
Existing NdFeB magnets face challenges in maintaining high coercivity at elevated temperatures due to the limited and costly Dy and Tb resources, and exhibit coercivity fluctuations with variations in boron content, necessitating a new composition and process for R-T-B magnets with high remanence and coercivity.
Innovation Solution
An R-T-B magnet with a specific elemental composition and microstructure, including a main phase and grain boundary phase with a delt-like R-T-M-Ti phase, is developed, where the synergistic addition of Ti, B, and Ga suppresses the R2T17 phase, enhancing coercivity and remanence while minimizing Dy and Tb content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Dy or Tb is used to substitute Nd in the main phase to improve coercivity, then coercivity is improved, but resource availability deteriorates due to limited and unstable prices
Solution Approach 1:
The patent replaces expensive heavy rare earth elements (Dy, Tb) with cheaper light rare earth elements (Pr, Nd) combined with Ga and Ti additions. This substitution uses more abundant, cost-effective materials to achieve the same coercivity enhancement, directly addressing the resource availability and cost issues while maintaining magnetic performance.
Solution Approach 2:
The patent creates a composite grain boundary phase consisting of R-T-Ga and R-T-M-Ti phases through the synergistic combination of Ga and Ti elements. This composite structure provides coercivity enhancement comparable to or exceeding that of Dy/Tb-substituted magnets, while using abundant light rare earth elements instead of scarce heavy rare earths.
2Ease of manufacture
If B content is reduced to improve other properties, then manufacturing flexibility is improved, but coercivity stability deteriorates due to fluctuations in HcJ
Solution Approach 1:
The patent introduces Ga and Ti as intermediary elements that mediate the relationship between B content and coercivity. These elements form specific intermetallic phases (R-T-Ga and R-T-M-Ti) at the grain boundaries that stabilize the coercivity mechanism, making HcJ less sensitive to variations in B content and enabling broader manufacturing flexibility.
Solution Approach 2:
The patent changes the compositional parameters by adding Ga (0.05-0.5 mass%) and Ti (0.15-0.29 mass%) to the R-T-B system. This parameter modification creates new phase formation mechanisms that decouple coercivity stability from B content, allowing B content to be adjusted for manufacturing ease without compromising HcJ stability.
3Strength
If Ga content is increased to form R-T-Ga phase and suppress R2T17 phase, then coercivity is improved, but manufacturing precision deteriorates due to narrow composition window
Solution Approach 1:
The patent merges the functions of multiple elements (Ga, Ti, B) to work synergistically in forming the desired grain boundary phases. The combination of Ga and Ti creates a more robust phase formation mechanism that is less sensitive to individual element variations, broadening the acceptable composition window and reducing the need for extreme manufacturing precision while maintaining high coercivity.
4Stability of the object's composition
If Ti content is increased to stabilize HcJ, then coercivity stability is improved, but harmful factors increase due to potential R2T17 phase formation
Solution Approach 1:
The patent uses Ga as an intermediary element that mediates the effect of Ti on phase formation. Ga preferentially forms R-T-Ga phases that suppress R2T17 phase formation, while Ti forms beneficial R-T-M-Ti phases. This intermediary作用 of Ga allows Ti to be used for HcJ stabilization without triggering harmful R2T17 phase formation, resolving the contradiction between coercivity stability and harmful phase suppression.
Data Source
AI summary
A magnet with an elemental composition of R1xR2yT1-x-y-z-u-a-b-cBzTiuCuaGabAc. R1 is a light rare earth element, and the light rare earth element includes at least one of Pr or Nd, R2 is a heavy rare earth element including at least one of Dy or Tb, T includes Fe and Co, A includes at least one of Al, Nb, Zr, Sn, or Mn, and x, y, z, u, a, b, and c are mass percentages and satisfy: 28%≤x+y≤30.5%, 0.88%≤z≤0.92%, 0.12%≤u≤0.15%, 0≤a≤0.15%, 0.15%≤b≤0.25%, and 0≤c≤2%.