R-T-B Sintered Magnet Core-Shell Grain Design
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Solution Overview
Problem
R-T-B system sintered magnets face challenges in achieving both high residual magnetic flux density and coercive force, with existing techniques either prioritizing one over the other or failing to maintain coercive force at elevated temperatures.
Innovation Solution
The R-T-B system sintered magnet features a core-shell structure with a heavy rare earth element concentration gradient, where the inner shell has a lower concentration than the outer shell, and a specific composition of R2T14B compounds, along with a proportion of grains with this structure exceeding 20% of the total, to optimize both magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If heavy rare earth elements (Dy, Tb, Ho) are added to enhance coercive force, then coercive force is improved, but residual magnetic flux density decreases
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the heavy rare earth element concentration varies spatially within the grain. The outer shell has high heavy rare earth element concentration to provide high coercive force, while the inner core has low or zero heavy rare earth element concentration to maintain high residual magnetic flux density. This spatial differentiation of composition allows simultaneous optimization of both magnetic properties that are normally mutually exclusive.
Solution Approach 2:
The patent segments the grain into distinct regions (core and shell) with different compositional characteristics. By dividing the grain structure and assigning different heavy rare earth element concentrations to different segments, the patent resolves the contradiction between coercive force (requiring heavy rare earth elements) and residual magnetic flux density (benefiting from light rare earth elements).
2Stability of the object's composition
If heavy rare earth elements are added to maintain coercive force at elevated temperatures, then thermal stability is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the concentration parameter of heavy rare earth elements from a uniform distribution to a gradient distribution. By controlling the concentration parameter to be high at the grain boundary region and low or zero at the grain center, the patent achieves thermal stability through the heavy rare earth elements at the boundary while minimizing the overall amount of expensive heavy rare earth materials used in the magnet.
Data Source
AI summary
An R-T-B system sintered magnet is provided which achieves both a high residual magnetic flux density and a high coercive force. The R-T-B system sintered magnet comprises main-phase grains 1 each having a core-shell structure comprising an inner shell part 2 and an outer shell part 3 surrounding the inner shell part 2, wherein the concentration of the heavy rare earth element in the inner shell part 2 is lower by 10% or more than the concentration of the heavy rare earth element in the periphery of the outer shell part 3, and (L/r)ave falls within a range from 0.03 to 0.40 in the main-phase grains 1 each comprising the inner shell part 2 and the outer shell part 3, wherein L represents the shortest distance from the periphery of the main phase grain 1 to the inner shell part 2, r represents the equivalent diameter of the main phase grain 1, and (L/r)ave represents the average value of L/r for the main-phase grains 1 present in the sintered body and having the core-shell structure.