NdFeB Magnet Coating for Grain Boundary Diffusion and Coercivity
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Solution Overview
Problem
Sintered NdFeB permanent magnets face challenges such as insufficient grain shape, surface defects, and difficulty in achieving continuous diffusion of heavy rare earth elements, leading to reduced coercivity and stability issues in the sintering process, which increases costs and complexity.
Innovation Solution
An R-T-B based permanent magnet material is developed, where R is neodymium or praseodymium, T includes iron and other metal elements, and B is boron, with a grain boundary phase enriched with M compounds like M-R and M-T-R, facilitating improved diffusion and coercivity through a uniform coating layer and reduced heavy rare earth metal usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth metal elements (Dy, Tb) are added to increase coercivity, then coercivity is improved, but the amount of scarce heavy metal element needed increases if enrichment in grain boundary phase is not achieved, resulting in high cost
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of heavy rare earth elements through grain boundary diffusion, concentrating these elements specifically at the grain boundaries where they are most effective for improving coercivity, rather than uniformly distributing them throughout the entire magnet material
Solution Approach 2:
The patent uses an M compound coating layer as an intermediary substance that facilitates the diffusion of heavy rare earth elements along grain boundaries. This coating layer acts as a mediator that enables controlled transport of the heavy rare earth elements to their target locations, improving diffusion efficiency and reducing the total amount needed
2Reliability
If Dy or Tb is added to improve coercivity, then coercivity is improved, but defects are easily repaired on grain surface layers or Dy/Tb permeates into main phase grains, causing insufficient Hcj amplification and reverse core-shell structure formation
Solution Approach 1:
The patent applies preliminary action by pre-forming an M compound coating layer on the grain boundaries before introducing heavy rare earth elements. This pre-prepared coating layer creates favorable conditions for controlled diffusion, preventing defects and ensuring proper distribution of heavy rare earth elements before the diffusion process begins
Solution Approach 2:
The M compound coating layer serves as an intermediary that mediates the diffusion process of heavy rare earth elements. It controls the diffusion pathway and rate, preventing uncontrolled permeation into main phase grains and avoiding reverse core-shell structure formation by maintaining proper concentration gradients
3Reliability
If neodymium-rich phases are uniformly and continuously put around hard magnetic main phase to improve coercivity, then grain boundaries become clean and smooth, but the sintering process becomes complicated and costly
Solution Approach 1:
The patent extracts the grain boundary phase formation step from the complex uniform coating process. Instead of uniformly applying neodymium-rich phases throughout, it selectively forms grain boundary phases through diffusion, separating the grain boundary modification from the bulk material processing
Solution Approach 2:
The patent applies parameter changes by controlling temperature and time parameters during a diffusion process to naturally form the desired grain boundary phase distribution. This replaces the need for complex uniform coating procedures with a thermally-driven diffusion process that achieves similar or superior results with simpler process control
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 R-T-B based magnet material enhances coercivity, improves grain boundary distribution, and avoids reverse core-shell structures, allowing for more efficient heavy rare earth element permeation, thus improving the overall magnetic properties and reducing production costs.
Implementation Method 1
the Dy or Tb suffers from relatively large resistance when diffusing to the interior of the magnet along the grain boundaries
Implementation Method 2
a temperature rising rate in the sintering process is controlled so as to be not more than 50° C./min
Data Source
AI summary
An R-T-B based permanent magnet material, a preparation method therefor and use thereof are provided. The M compound is adhered to or coats the R-T-B based alloy powders to form a uniform coating layer on the surface of the neodymium-iron-boron powders, so that the rounding transformation of the R-T-B based alloy powders can be achieved, and further the wettability of the R-T-B based alloy powders is improved under the condition of significantly reducing the amount of heavy rare earth metals in the substrate. In addition, the grain boundary phases of M-R and/or M-T-R are present in the grain boundary of the R-T-B based permanent magnet material, the physicochemical properties of the grain boundary phases can be significantly improved, the distribution of the grain boundary phases is improved, and the grain boundary is strengthened.