R-T-B Magnet Grain Boundary Phase Design
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Solution Overview
Problem
Existing R-T-B rare earth sintered magnets do not achieve sufficiently high coercivity without increasing the amount of Dy, which is unstable and costly, and existing methods to enhance coercivity through metal elements like Al, Si, Ga, and Cu are ineffective.
Innovation Solution
An R-T-B magnet with a main phase of R2Fe14B and a grain boundary phase having a higher R concentration, including both R-rich and transition metal-rich phases with specific atomic concentrations, and crystal grains with elliptical or oval shapes aligned along the c-axis direction, manufactured using a strip cast method with controlled cooling and sintering processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Dy concentration is increased to improve coercivity, then coercivity is improved, but supply stability deteriorates and cost increases
Solution Approach 1:
The patent applies local quality by creating a dual-phase grain boundary structure where R-rich phases and transition metal-rich phases are distributed at grain boundaries. The transition metal-rich phases (containing Fe, Co, Ni) provide localized magnetic strengthening at critical grain boundary regions, while R-rich phases maintain structural integrity. This localized functional differentiation achieves high coercivity without requiring uniform increase of Dy throughout the entire alloy, thus resolving the contradiction between coercivity improvement and supply stability.
Solution Approach 2:
The patent employs composite materials by combining multiple phases within the grain boundary region: R-rich phases (containing rare earth elements) and transition metal-rich phases (containing Fe, Co, Ni). This composite grain boundary structure synergistically combines the magnetic properties of transition metals with the structural stability of rare earth phases, achieving high coercivity through compositional complexity rather than relying solely on increased Dy concentration, thereby resolving the supply stability issue.
2Ease of manufacture
If R 2 T 17 phase is present in R-T-B alloy, then alloy formation is facilitated, but coercivity and squareness are reduced
Solution Approach 1:
The patent applies the taking out principle by extracting and isolating the R 2 T 17 phase into distinct transition metal-rich phases located at grain boundaries, separated from the main R 2 T 14 B matrix phase. By confining these phases to specific grain boundary regions rather than allowing them to form throughout the bulk alloy, the patent eliminates their harmful effect on coercivity while maintaining their role in facilitating alloy formation and grain boundary stability, thus resolving the contradiction between ease of manufacture and coercivity.
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 achieves high coercivity without increasing Dy content, ensuring stable and efficient magnetic properties for applications in motors by optimizing the composition and structure of the magnet.
Implementation Method 1
a casting step of producing a cast alloy using a strip cast method including supplying a molten alloy to a cooling roll and solidifying the molten alloy
Implementation Method 2
R-T-B magnets are obtained by molding an R-T-B alloy powder containing Nd, Fe, and B as main components and by sintering the resulting molded product
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3
AI summary
An R-T-B rare earth sintered magnet contains R which represents a rare earth element; T which represents a transition metal essentially containing Fe; a metal element M which represents Al and/or Ga; B; Cu; and inevitable impurities the R-T-B rare earth sintered magnet including 13.4 to 17 at% of R, 4.5 to 5.5 at% of B, and 0.1 to 2.0 at% of M, and T as the balance; in which the R-T-B rare earth sintered magnet is formed of a sintered body which includes a main phase composed of R2Fe14B and a grain boundary phase including a larger amount of R than the main phase; in which the magnetization direction of the main phase is a c-axis direction, in which crystal grains of the main phase have one of an elliptical shape and an oval shape extended in such a direction so as to cross the c-axis direction; and in which the grain boundary phase includes an R-rich phase in which the total atomic concentration of the rare earth elements is 70 at% or greater and a transition metal-rich phase in which the total atomic concentration of the rare earth elements is 25 to 35 at%.