NdFeB Magnet Diffusion Coating for Coercivity and Resistivity
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Solution Overview
Problem
Existing methods for enhancing the temperature resistance of NdFeB permanent magnets either reduce remanence and increase costs or fail to improve resistivity, leading to inefficiencies in magnetic steel performance.
Innovation Solution
A method involving a three-stage heat treatment process for flaky NdFeB magnet blanks, where a slurry containing heavy rare earth powder, carbide or oxide powder, and organic solvent is applied to the surface, allowing heavy rare earth elements to penetrate and form a high-coercivity phase while the interlayer increases resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth (Dy or Tb) is added to improve coercivity, then coercivity increases, but remanence is reduced and material costs increase significantly
Solution Approach 1:
The patent applies local quality by concentrating heavy rare earth elements at the grain boundaries through diffusion treatment rather than uniform distribution throughout the bulk material. This localized approach enhances coercivity at critical interfaces while preserving the bulk magnetic properties including remanence, thereby resolving the contradiction between improving coercivity and maintaining remanence.
Solution Approach 2:
The patent utilizes parameter changes by controlling the diffusion process parameters (temperature, time, composition) to achieve optimal concentration gradients of heavy rare earth elements at grain boundaries. By adjusting these parameters, the invention achieves enhanced coercivity without the need for high bulk concentrations that would reduce remanence and increase costs.
2Reliability
If heavy rare earth fluorides are applied to the surface and subjected to thermal diffusion treatment, then coercivity increases, but resistivity cannot be increased
Solution Approach 1:
The patent employs composite materials by combining heavy rare earth fluorides with specific oxide powders (such as Al2O3, SiO2, MgO) in the slurry coating. This composite approach allows the heavy rare earth components to enhance coercivity through diffusion while the oxide components simultaneously increase resistivity, thereby resolving the contradiction between improving coercivity and enhancing resistivity.
Solution Approach 2:
The patent achieves multi-functionality by designing a slurry coating that performs multiple functions simultaneously: heavy rare earth fluorides provide coercivity enhancement through diffusion, while oxide powders provide resistivity enhancement. This single coating process accomplishes both objectives that previously required separate treatments, resolving the contradiction between improving coercivity and increasing resistivity.
3Object-affected harmful factors
If oxide powder or fluoride powder is added to reduce eddy, then eddy loss is reduced, but the performance of the magnet is reduced
Solution Approach 1:
The patent applies local quality by placing oxide or fluoride powders specifically at the grain boundaries through the slurry coating and diffusion process, rather than uniformly distributing them throughout the bulk material. This localized positioning allows the powders to effectively reduce eddy currents at interfaces while minimizing their detrimental impact on the bulk magnetic performance, thereby resolving the contradiction between reducing eddy loss and maintaining magnet performance.
4Object-affected harmful factors
If magnetic steel is cut into small pieces and bonded together to increase resistance, then resistivity increases and eddy loss is reduced, but the process has a long technological flow and high processing cost
Solution Approach 1:
The patent extracts the essential function of increasing resistivity from the complex mechanical segmentation and bonding process, and achieves it through a chemical diffusion process. By applying a slurry coating containing oxides or fluorides and performing thermal diffusion, the invention creates high-resistivity grain boundary phases directly during heat treatment, eliminating the need for separate cutting and bonding operations, thereby resolving the contradiction between increasing resistivity and reducing process complexity.
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 method effectively increases both the coercivity and resistivity of NdFeB permanent magnets, reducing eddy losses and improving temperature resistance without significant increases in material costs or complexity.
Implementation Method 1
after the magnet is subjected to thermal diffusion treatment, heavy rare earth can enter the interior of the magnet, and forms a (Nd, Dy) 2Fe14B phase with a high magnetocrystalline anisotropy field on the surface of the crystalline grain
Implementation Method 2
performing three-stage heat treatment on the stack of NdFeB magnet blanks to obtain the NdFeB permanent magnet with high coercivity and high resistivity
Implementation Method 3
it is impossible to increase resistivity of the magnet. For the magnetic steel in a motor, temperature rise from eddy cannot be effectively reduced
Data Source
AI summary
The invention discloses an NdFeB permanent magnet with high coercivity and high resistivity and a method for preparing the same. The method comprises the steps of: spraying powdery slurry containing heavy rare earth compounds, oxides and/or carbides on a flaky NdFeB permanent magnets blank after it is subjected to surface cleaning process; then stacking magnets on top of each other, and performing three-stage heat treatment on the stacked magnets to obtain the NdFeB permanent magnet with high coercivity and high resistivity. Heavy rare earth penetrates into interior of the flaky magnets at a high temperature, so that coercivity of the flaky magnets is improved. However, part of the heavy rare earth elements or alloy elements and carbide powder or oxide powder, which are not penetrated into the flaky magnets, form an interlayer bonding two of flaky magnets together.