NdFeB Magnet Grain Boundary Diffusion for Coercive Force
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Solution Overview
Problem
In the grain boundary diffusion method for producing NdFeB system sintered magnets, the carbon-rich phase formed at grain-boundary triple points impedes the diffusion of R H, leading to a localized R H content near the surface, resulting in a low maximum energy product and insufficient coercive force and squareness ratio.
Innovation Solution
The method involves controlling the number of grain-boundary triple points with a minimal difference in R H content between triple and two-grain boundary portions, ensuring even R H diffusion throughout the magnet, with a carbon-rich phase volume ratio in the rare-earth rich phase at triple points limited to 50% or less, to prevent R H blocking and enhance deep penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If R H is added to enhance coercive force, then coercive force is improved, but maximum energy product decreases
Solution Approach 1:
The patent applies local quality by concentrating R H elements specifically at grain boundaries rather than uniformly distributing them throughout the magnet. This is achieved through grain boundary diffusion treatment where R H is attached to the surface and diffuses into the inner region through boundaries, creating a localized high concentration at grain boundaries while keeping main-phase grain centers relatively free of R H, thus improving coercive force without significantly reducing maximum energy product
Solution Approach 2:
The patent uses grain boundaries as an intermediary medium to transport R H elements from the surface into the interior of the magnet. The grain boundary diffusion process acts as a mediator that enables controlled delivery of R H to specific locations (grain boundaries) without direct addition to the bulk material, allowing enhanced coercive force while preserving overall magnetic energy product
2Strength
If R H is diffused deeply into the base material, then coercive force is improved, but R H content inside main-phase grains increases, reducing maximum energy product
Solution Approach 1:
The patent achieves local quality by controlling the diffusion process to concentrate R H elements at grain boundaries while preventing their penetration into main-phase grain interiors. The diffusion treatment parameters (temperature, time, surface attachment method) are optimized to create a concentration gradient where R H is present at high levels at grain boundaries but remains minimal in the main-phase grains, thus improving coercive force through boundary effects without the detrimental impact on maximum energy product that would result from bulk incorporation
3Ease of manufacture
If carbon-rich phase is present at grain-boundary triple points, then manufacturing is simplified, but R H diffusion is impeded, reducing coercive force and squareness ratio
Solution Approach 1:
The patent applies the taking out principle by removing or minimizing the carbon-rich phase from grain-boundary triple points. The base material is specifically designed to have a reduced carbon-rich phase content at these critical locations, which would otherwise block the diffusion pathways. This extraction of the harmful carbon-rich phase from triple points enables uninterrupted R H diffusion through grain boundaries, thereby achieving high coercive force and squareness ratio while maintaining manufacturing feasibility
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 results in a higher coercive force and squareness ratio while minimizing the decrease in maximum energy product, ensuring R H is evenly distributed within the magnet, thereby improving magnetic characteristics.
Implementation Method 1
heating the magnet to diffuse R H from the surface of the base material into the inner region through the boundaries inside the base material
Data Source
AI summary
Provided is a NdFeB system sintered magnet which is produced by the grain boundary diffusion method and yet has a high coercive force and squareness ratio with only a small decrease in the maximum energy product. A NdFeB system sintered magnet according to the present invention is a NdFeB system sintered magnet having a base material produced by orienting powder of a NdFeB system alloy and sintering the powder, with Dy and/or Tb (the "Dy and/or Tb" is hereinafter called RH) attached to and diffused from a surface of the base material through the grain boundary inside the base material by a grain boundary diffusion treatment, wherein the number of grain-boundary triple points at which the difference Ct-Cw between the RH content Ct (wt%) at the grain-boundary triple point and the RH content Cw (wt%) at a two-grain boundary portion leading to that grain-boundary triple point is equal to or smaller than 4 wt% is equal to or larger than 60 % of the total number of grain-boundary triple points.