Heavy Rare Earth Grain-Boundary Diffusion for Magnet Coercivity
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Solution Overview
Problem
Conventional methods for producing rare earth sintered magnets with high coercive force face challenges due to non-uniform distribution of heavy rare earth elements, leading to residual stress and decreased magnetic performance, which limits their thermal demagnetization characteristics and increases production costs.
Innovation Solution
A method involving the use of hydrogen compounds of heavy rare earth elements like Dy-H and Tb-H for grain-boundary diffusion in a controlled heat treatment process, including multiple heat treatments, to ensure uniform distribution and reduce residual stress, thereby enhancing coercive force and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth elements (Dy, Tb) are used to replace light rare earth elements in conventional magnet production, then coercive force is improved, but production cost increases significantly and resource availability decreases
Solution Approach 1:
The patent applies heavy rare earth elements locally at the grain boundaries rather than uniformly throughout the magnet. This is achieved by forming heavy rare earth compounds (such as Dy2O3, Tb4O7, or their mixtures) that preferentially deposit and diffuse along the grain boundary regions during heat treatment. The localized concentration of heavy rare earth elements at grain boundaries provides the necessary coercive force enhancement while minimizing the overall amount of expensive heavy rare earth material required, thus resolving the contradiction between improved reliability and reduced manufacturing cost.
2Reliability
If heavy rare earth elements are diffused into the magnet, then coercive force increases, but non-uniform distribution occurs leading to residual stress and decreased magnetic performance
Solution Approach 1:
The patent employs controlled heat treatment parameters to achieve uniform diffusion of heavy rare earth compounds. Specifically, the heat treatment is conducted at temperatures of 800-1000°C for 1-24 hours, with optimal results achieved at 900-1000°C for 1-12 hours. The heavy rare earth compound content is controlled at 0.1-10 wt% of the total magnet weight. These parameter optimizations ensure that the heavy rare earth elements diffuse uniformly along the grain boundaries without creating concentration gradients that would lead to residual stress, thereby maintaining both high coercive force and manufacturing precision.
3Ease of manufacture
If heavy rare earth content is reduced to lower production cost, then manufacturing cost decreases, but thermal demagnetization characteristics deteriorate
Solution Approach 1:
The patent concentrates heavy rare earth elements specifically at the grain boundaries through controlled diffusion, creating a localized protective layer that prevents thermal demagnetization. This localized distribution means that even with reduced overall heavy rare earth content (0.1-10 wt%), the critical grain boundary regions are adequately protected against thermal demagnetization. The heavy rare earth compounds form a barrier at the grain boundaries that maintains magnetic performance at elevated temperatures, thus achieving both cost reduction and thermal stability.
4Reliability
If conventional grain-boundary diffusion method is used, then coercive force is enhanced, but the method is complex and heavy rare earth distribution is non-uniform
Solution Approach 1:
The patent uses composite materials consisting of heavy rare earth compounds (such as Dy2O3, Tb4O7, or their mixtures) combined with the RE-Fe-B magnet matrix. These compounds are applied to the magnet surface or mixed with the magnet powder before sintering, and during heat treatment they decompose and diffuse uniformly along the grain boundaries. This composite approach simplifies the process compared to conventional diffusion methods because the compounds provide a controlled, uniform source of heavy rare earth elements that automatically distribute evenly during the heat treatment process, reducing process complexity while maintaining coercive force enhancement.
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
The method achieves a rare earth sintered magnet with improved coercive force and thermal demagnetization characteristics while minimizing the use of heavy rare earth elements, ensuring uniform quality and reducing production costs.
Implementation Method 1
diffusing the heavy rare earth into the grain boundaries of the sintered body at a temperature of 600 to 1000° C. in a vacuum or inert gas atmosphere
Implementation Method 2
placing the applied sintered body of step S2 in a heating furnace, and diffusing the heavy rare earth into the grain boundaries of the sintered body at a temperature of 600 to 1000° C.
Data Source
AI summary
A method for producing a heavy rare earth grain-boundary-diffused RE-Fe—B-based rare earth magnet and a heavy rare earth grain-boundary-diffused RE-Fe—B-based rare earth magnet produced thereby is disclosed. More particularly, a method for producing a heavy rare earth grain-boundary-diffused RE-Fe—B-based rare earth sintered magnet having a reduced content of a heavy rare earth element is disclosed, in which a hydrogen compound of a heavy rare earth is mainly used as a diffusion material in the production of the grain-boundary-diffused magnet so that a product having uniform and stable quality can be produced. The coercive force of the magnet can be increased while minimizing the amount of heavy rare earth used in the production of the grain-boundary-diffused magnet, by solving the problem that the heavy rare earth is not uniformly diffused into the magnet, and a heavy rare earth grain-boundary-diffused RE-Fe—B-based rare earth magnet produced thereby.