Rare-Earth Permanent Magnet Grain Boundary Concentration
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Solution Overview
Problem
The challenge is to enhance the coercive force of Nd-Fe-B permanent magnets while minimizing the use of expensive Tb or Dy, as substituting these elements for Nd increases coercive force but reduces remanence, and existing methods struggle to achieve this effectively in larger magnet bodies.
Innovation Solution
A method involving the repeated application of a powder containing an oxide, fluoride, or oxyfluoride of rare earth elements on the magnet surface, heated below the sintering temperature, to concentrate Dy or Tb only at grain boundaries, enhancing the anisotropic magnetic field and coercive force without compromising remanence, even in larger magnet sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If Dy or Tb is substituted for part of Nd in the Nd2Fe14B compound to increase coercive force, then the anisotropic magnetic field and coercive force are increased, but the saturation magnetic polarization and remanence are reduced
Solution Approach 1:
The invention applies local quality by concentrating Dy or Tb elements specifically at the grain boundaries rather than uniformly distributing them throughout the magnet. This localized substitution at grain boundaries enhances the anisotropic magnetic field and coercive force without significantly reducing the overall saturation magnetic polarization and remanence, as the bulk grain interior maintains its magnetic properties.
2Volume of stationary object
If the magnet body size is increased, then the application range is expanded, but the effectiveness of Dy or Tb addition for increasing coercive force is reduced
Solution Approach 1:
By localizing the Dy or Tb elements at the grain boundaries through the repeated powder application and heating process, the invention ensures that the coercive force enhancement mechanism operates effectively at the critical grain boundary regions regardless of the overall magnet size. This local concentration approach maintains effectiveness in larger magnet bodies where uniform distribution would be less efficient.
Solution Approach 2:
The invention employs periodic action through repeated cycles of powder application and heating treatment. This multi-step process ensures thorough and uniform concentration of Dy or Tb elements at all grain boundaries throughout the magnet body, including in larger-sized magnets, by performing the treatment in multiple passes rather than a single application.
3Quantity of substance
If Tb or Dy usage is minimized to reduce cost, then the expense is reduced, but the coercive force enhancement is insufficient
Solution Approach 1:
The invention achieves cost reduction by minimizing the overall usage amount of expensive Tb or Dy elements while maintaining sufficient coercive force enhancement. This is accomplished by concentrating these elements locally at the grain boundaries where they have the maximum effect on coercivity, rather than using large amounts throughout the entire magnet body.
Solution Approach 2:
The repeated powder application and heating process enables self-service by allowing the Dy or Tb elements to naturally diffuse and concentrate at the grain boundaries through thermal activation, reducing the need for precise control and minimizing material waste.
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
This approach effectively increases coercive force while maintaining high remanence, particularly in larger magnet bodies, by concentrating rare earth elements at grain boundaries through repeated absorption treatments, resulting in high-performance rare earth permanent magnets with minimized Tb or Dy usage.
Implementation Method 1
R contained in the powder is absorbed in the magnet body so that Dy or Tb is concentrated only in proximity to grain boundaries
Implementation Method 2
heated at a temperature below the sintering temperature
Data Source
AI summary
A method for preparing a rare earth permanent magnet material comprises the steps of disposing a powder on a surface of a sintered magnet body of R1aTbAcMd composition wherein R1 is a rare earth element inclusive of Sc and Y, T is Fe and/or Co, A is boron (B) and/or carbon (C), M is Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta, or W, said powder comprising an oxide of R2, a fluoride of R3 or an oxyfluoride of R4 wherein R2, R3, and R4 are rare earth elements inclusive of Sc and Y and having an average particle size equal to or less than 100 µm, heat treating the magnet body and the powder at a temperature equal to or below the sintering temperature of the magnet body for absorption treatment for causing R2, R3, and R4 in the powder to be absorbed in the magnet body, and repeating the absorption treatment at least two times. According to the invention, a rare earth permanent magnet material can be prepared as an R-Fe-B sintered magnet with high performance and a minimized amount of Tb or Dy used.