NdFeB Magnet Grain Boundary Diffusion RH Distribution
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Solution Overview
Problem
In the production of NdFeB system sintered magnets using the grain boundary diffusion method, the carbon-rich phase formed at grain-boundary triple points impedes the diffusion of rare-earth elements, leading to a localized RH content near the surface, resulting in a low maximum energy product and insufficient coercive force and squareness ratio.
Innovation Solution
A NdFeB system sintered magnet is produced with a base material where the difference in RH content between the grain boundary and main-phase grains is maintained at 3 wt % or higher within 3 mm from the surface, reducing the carbon-rich phase's interference and allowing even RH distribution throughout the magnet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If grain boundary diffusion treatment is applied to enhance coercive force, then coercive force is improved, but carbon-rich phase formation at grain-boundary triple points impedes RH diffusion, resulting in localized RH content and reduced maximum energy product
Solution Approach 1:
The patent removes the harmful carbon-rich phase from grain-boundary triple points through optimized sintering conditions and atmospheric control, eliminating the barrier that impedes RH diffusion. This extraction of the harmful element allows uniform RH distribution throughout the magnet while maintaining enhanced coercive force from the grain boundary diffusion treatment.
Solution Approach 2:
The patent creates a non-uniform RH distribution pattern where RH is concentrated at grain boundaries (providing high coercive force) while maintaining low RH content in main-phase grains (preserving maximum energy product). The carbon-rich phase removal ensures this local quality distribution is achieved uniformly throughout the material, including at triple points.
2Force
If RH content is increased at grain boundaries to improve coercive force, then coercive force and squareness ratio are enhanced, but uniform RH distribution is difficult to achieve due to carbon-rich phase barriers
Solution Approach 1:
The patent converts the previously harmful carbon-rich phase at grain-boundary triple points into a beneficial element by removing it through optimized processing. This elimination transforms the triple points from diffusion barriers into effective RH transport pathways, enabling uniform RH distribution and consistent magnetic properties throughout the magnet.
Solution Approach 2:
The patent modifies processing parameters including sintering temperature, holding time, and atmospheric composition to prevent carbon-rich phase formation and promote uniform RH diffusion. These parameter changes ensure consistent RH distribution at grain boundaries while maintaining the desired concentration gradient between boundaries and main-phase grains.
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 enhances the coercive force and squareness ratio while minimizing the decrease in maximum energy product, ensuring a more uniform RH distribution and improved magnetic properties.
Implementation Method 1
heating the magnet to diffuse RH from the surface of the base material into the inner region through the boundaries inside the base material
Implementation Method 2
grain boundary diffusion treatment... diffused from a surface of the base material through the grain boundary inside the base material
Implementation Method 3
the boundaries liquefied by heat in the base material
Implementation Method 4
heating the magnet to diffuse RH from the surface
Data Source
AI summary
A NdFeB system sintered magnet produced by the grain boundary diffusion method and has a high coercive force and squareness ratio with only a small decrease in the maximum energy product. 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 difference Cgx−Cx between the RH content Cgx (wt %) in the grain boundary and the RH content Cx (wt %) in main-phase grains which are grains constituting the base material at the same depth within a range from the surface to which RH is attached to a depth of 3 mm is equal to or larger than 3 wt %.