Nd-Fe-B Magnet Coercivity via Heavy Rare Earth Diffusion
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Solution Overview
Problem
Existing methods for improving the coercivity of Nd—Fe—B magnets often reduce remanence and are costly, with issues related to the use of heavy rare earth elements and adverse effects on mechanical properties and corrosion resistance.
Innovation Solution
A method involving the formation of solidified films of pure heavy rare earth elements on the surface of Nd—Fe—B magnets, followed by diffusion and aging treatments in a vacuum or inert atmosphere, which increases coercivity without reducing remanence and improves the utilization rate of heavy rare earth metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If Dy or Tb or an alloy of Tb and Dy is introduced into the sintered Nd—Fe—B magnets to improve coercivity, then the coercivity increases, but the remanence decreases
Solution Approach 1:
The patent applies segmentation by dividing the magnet structure into two distinct regions: a core region containing the Nd2Fe14B main phase, and a shell region comprising a gradient structure with an inner shell (Nd, Dy)2Fe14B phase and an outer shell phase. This segmentation allows the heavy rare earth elements to be concentrated in the shell region rather than uniformly distributed throughout the main phase, thereby improving coercivity at the boundaries while preserving the high remanence properties of the pure Nd2Fe14B core region.
2Force
If Dy or Tb or an alloy of Tb and Dy is introduced through diffusion and aging treatments to increase coercivity, then the magnetic anisotropy and coercivity improve, but the process consumes a large amount of rare earth elements
Solution Approach 1:
The patent implements local quality by creating a spatially varying composition profile where heavy rare earth elements (Dy, Tb) are selectively concentrated in the outer shell region and grain boundary areas, while the core region maintains a Nd-rich composition. This localized distribution ensures that the expensive heavy rare earth elements are used only where they are most effective for enhancing coercivity, rather than being uniformly distributed throughout the entire magnet volume, thereby reducing overall rare earth element consumption.
3Force
If oxides, flurides, or oxiflurides of Dy and Tb are disposed on the surface and subjected to diffusion treatment, then coercivity increases, but fluorine and oxygen diffuse into the magnet adversely affecting mechanical properties and corrosion resistance
Solution Approach 1:
The patent applies the taking out principle by removing harmful elements (fluorine and oxygen) from the composition scheme entirely. Instead of using oxides, fluorides, or oxiflurides as the source of heavy rare earth elements, the invention employs pure metallic Dy and/or Tb powders. This extraction of harmful substances eliminates the risk of F and O diffusion into the magnet bulk during thermal processing, thereby preserving mechanical properties and corrosion resistance while still achieving the desired coercivity enhancement through pure heavy rare earth element diffusion.
4Force
If vacuum evaporation, ion plating, or sputtering processes are used to deposit heavy rare earth element layers, then coercivity improves, but the high temperatures affect the Nd—Fe—B magnets and the cost increases due to low utilization of heavy metals
Solution Approach 1:
The patent employs a simple, low-cost deposition method using pure metallic powders that are disposed of after use, rather than expensive and complex vacuum deposition equipment. The process involves placing pure Dy and/or Tb metal powders directly onto the magnet surface and performing diffusion treatment in a conventional furnace atmosphere. This approach replaces costly vacuum evaporation, ion plating, or sputtering systems with a simple powder deposition method, significantly reducing equipment investment and operational costs while maintaining effective heavy rare earth element diffusion into the magnet.
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 enhances the coercivity of Nd—Fe—B magnets with minimal impact on remanence and mechanical properties, while being cost-efficient and suitable for mass production.
Implementation Method 1
the Nd—Fe—B magnet including the first solidified film is subjected a diffusion treatment in a vacuum or an inert atmosphere
Implementation Method 2
Following the Nd—Fe—B magnet including the first solidified film is subjected to an aging treatment in the vacuum or the inert atmosphere
Data Source
AI summary
A method of improving coercivity of an Nd—Fe—B magnet includes a first step of providing an Nd—Fe—B magnet having a first surface and a second surface. Next, a first solidified film of at least one pure heavy rare earth element is formed and attached to the first surface of the Nd—Fe—B magnet to prevent a reduction in corrosion resistance caused by oxygen and fluorine and hydrogen. After forming the first solidified film, the Nd—Fe—B magnet is subjected a diffusion treatment in a vacuum or an inert atmosphere. After the diffusion treatment, the Nd—Fe—B magnet is subjected to an aging treatment in the vacuum or the inert atmosphere.