NdFeB Magnet Grain Boundary Diffusion RH Distribution
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Solution Overview
Problem
The grain boundary diffusion method for producing NdFeB system sintered magnets faces challenges in achieving high coercive force and squareness ratio while minimizing the decrease in maximum energy product, due to the blocking effect of a carbon-rich phase on rare-earth element diffusion and uneven distribution of these elements within the magnet.
Innovation Solution
A NdFeB system sintered magnet is produced with a base material where the difference in RH content between the grain boundary at the surface and 3 mm depth is limited to 20 wt%, and the carbon-rich phase volume ratio at grain-boundary triple points is kept below 50%, allowing even RH distribution and minimizing the blocking effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If RH is added to the starting alloy powder (single alloy method), then coercive force is improved, but maximum energy product decreases significantly
Solution Approach 1:
The invention divides the alloy into two separate starting alloy powders: a main phase alloy powder without RH and a grain boundary phase alloy powder containing RH. This segmentation allows RH to be concentrated in the grain boundary phase rather than distributed throughout the main phase grains, thereby improving coercive force while minimizing the negative impact on maximum energy product.
Solution Approach 2:
The invention applies local quality by concentrating RH specifically in the grain boundary phase alloy powder, which then distributes RH preferentially to the grain boundary regions during sintering. This localized distribution of RH enhances coercive force at the grain boundaries without significantly affecting the main phase grain properties, thus preserving maximum energy product.
2Force
If RH is diffused from surface into inner region through grain boundaries, then coercive force is enhanced with minimal decrease in maximum energy product, but diffusion is blocked by carbon-rich phase at grain-boundary triple points
Solution Approach 1:
The invention performs preliminary action by controlling the formation of carbon-rich phase during the sintering process before the RH diffusion treatment. By adjusting sintering temperature and atmosphere, the carbon-rich phase formation is suppressed or controlled to occur after RH has already diffused into the grain boundaries, thereby eliminating the diffusion blocking effect.
Solution Approach 2:
The invention applies dynamics by implementing a two-stage thermal process: first, RH diffusion into grain boundaries at a controlled temperature; second, a subsequent heating stage that promotes carbon oxidation or prevents carbon-rich phase formation. This dynamic, time-dependent approach ensures RH diffusion occurs before carbon-rich phase blocking can occur.
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 with a smaller decrease in maximum energy product, enabling effective diffusion of RH throughout the magnet and maintaining high 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
diffuse RH from the surface of the base material into the inner region through the boundaries 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 that has a high coercive force and squareness ratio with only a small decrease in the maximum energy product. The NdFeB system sintered magnet has 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 Cs-Cd3 between the RH content Cs (wt %) in the grain boundary reaching the surface to which RH is attached and the RH content Cd3 (wt %) in the grain boundary at a depth of 3 mm from the aforementioned attachment surface is equal to or smaller than 20 wt %.