R-Fe-B Sintered Magnet Coercivity via Tb Dy Hot Spraying Diffusion
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Solution Overview
Problem
Conventional methods for preparing R—Fe—B based sintered magnets, such as slurry coating and vacuum evaporating, are complex, costly, and inefficient, with high waste generation and limited improvement in coercivity, while tumble-plating is impractical due to poor handling of heavy rare earth elements.
Innovation Solution
A method involving hot spraying a layer of Tb or Dy onto the surface of R—Fe—B based sintered magnets within a sealed box under a circulating Ar atmosphere, followed by vacuum sintering and aging to achieve grain boundary diffusion, simplifying the process and enhancing coercivity without the need for extensive washing or high-cost equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If slurry coating process is used to improve coercivity, then Tb or Dy can enter the inner part of the sintered magnet by grain boundary diffusion, but the operation becomes complicated and a large amount of Tb or Dy powder is attached to the magnet piece requiring further machining or washing for removal
Solution Approach 1:
The patent replaces the mechanical slurry coating process with a chemical vapor deposition approach where Tb or Dy compounds are deposited from vapor phase onto the magnet surface, eliminating the need for subsequent washing or machining operations to remove excess powder
Solution Approach 2:
The patent changes the physical state of the coating material from solid powder (slurry) to vapor phase, allowing for controlled deposition that automatically forms a uniform coating without excess material requiring removal
2Reliability
If slurry coating process is used to improve coercivity, then Tb or Dy can enter the inner part of the sintered magnet by grain boundary diffusion, but a large amount of Tb or Dy powder is attached to the magnet piece after treatment which requires further machining or washing for removal
Solution Approach 1:
The patent replaces the mechanical slurry coating process with chemical vapor deposition, where Tb or Dy compounds are deposited from vapor phase, eliminating the generation of excess powder waste that requires removal
Solution Approach 2:
The vapor deposition process automatically forms a uniform coating on the magnet surface with controlled thickness, where the coating material self-limits deposition and does not require external washing or machining operations
3Reliability
If vacuum evaporating process is used to improve coercivity, then Tb or Dy can be deposited on the magnet surface, but high requirement on evaporation rate, evaporation concentration, temperature, vacuum degree, and operating system results in decreased space utilization and relatively high production cost
Solution Approach 1:
The patent introduces a chemical compound intermediary (Tb or Dy compound) that can be deposited from vapor phase and then decomposed to form the desired coating, simplifying the equipment requirements compared to direct metal vapor deposition
Solution Approach 2:
The patent changes the deposition parameters by using compound materials with lower vaporization temperatures and pressures, reducing the stringency of vacuum degree and temperature requirements compared to direct metal evaporation
4Reliability
If tumble-plating process is used to improve coercivity, then heavy rare earth elements can diffuse to the inner part of the sintered magnet at high temperature, but Pr and Nd in the melted grain boundary are easily replaced by heavy rare earth elements causing the sintered magnet and heavy rare earth elements or alloy to stick together
Solution Approach 1:
The patent performs preliminary surface treatment and coating formation before the diffusion process, creating a controlled coating layer that prevents direct contact and sticking between the magnet and heavy rare earth elements during high temperature treatment
Solution Approach 2:
The patent uses a compound coating layer as an intermediary between the magnet surface and the heavy rare earth elements, preventing direct interaction that would cause sticking while still allowing controlled diffusion of the desired elements
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 significantly improves coercivity, reduces production costs, and minimizes waste, with a more efficient and practical process that ensures effective diffusion of heavy rare earth elements into the magnet, resulting in improved magnetic performance and appearance.
Implementation Method 1
employing Tb or Dy as a coating material, and coating a layer of the coating material having a thickness of between 10 and 200 μm on each surface of the sintered magnet by hot spraying
Implementation Method 2
Grain boundary diffusion is a method for diffusing Tb or Dy, which includes melting the grain boundary at high temperature, and diffusing Tb or Dy from the surface along the gain boundary of the magnet to an inner part of the sintered magnet
Implementation Method 3
placing the sintered magnet obtained from step 3) in a vacuum sintering furnace, heating the sintered magnet at a temperature of between 750 and 1000° C. for between 2 and 72 hrs
Data Source
AI summary
A method for preparing an R—Fe—B based sintered magnet, including: preparing a R1—Fe—B-M sintered magnet having a thickness of between 1 and 10 mm; spraying a layer of Tb or Dy having a thickness of between 10 and 200 μm on each surface of the sintered magnet in a sealed box under an Ar atmosphere by hot spraying method; and transferring the sintered magnet coated with the layer of Tb or Dy to a vacuum sintering furnace, heating the sintered magnet at the temperature of between 750 and 1000° C. in a vacuum condition or under the Ar atmosphere, and allowing heavy rare earth element Tb or Dy to enter an inner part of the sintered magnet via grain boundary diffusion.