Hydrogenation-Disproportionation NdFeB Magnet Production
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Solution Overview
Problem
The production of rare earth magnets, particularly NdFeB magnets, faces challenges such as brittleness, difficulty in shaping, and material wastage during slicing, as well as the need for air-sensitive handling and expensive dysprosium additives, which limit their application in high-performance applications like high-speed motors.
Innovation Solution
A process involving hydrogenation and disproportionation of rare earth alloys at elevated temperatures, followed by mechanical processing and degassing, to produce a more ductile and easily shapeable material, allowing for the creation of thin sheets and reducing the need for air-sensitive powder handling and dysprosium usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional hydrogen decrepitation process is used to produce NdFeB powder, then the powder can be obtained for magnet production, but the material becomes air-sensitive requiring inert atmosphere handling and the structure becomes brittle
Solution Approach 1:
The invention changes the chemical composition parameters by adding boron (0.1-5 wt%) and controlling rare earth content (5-20 wt%), which fundamentally alters the material's reactivity with hydrogen. This parameter change enables the material to undergo disproportionation instead of simple decrepitation, producing a less air-sensitive and more ductile powder that doesn't require inert atmosphere handling
Solution Approach 2:
The invention utilizes the phase transition mechanism of disproportionation where the intermetallic compound Nd2Fe14B transforms into a mixture of phases (Nd-rich phase, Fe-rich phase, and boride phase) upon hydrogen exposure. This phase transition creates a microstructure that is both less air-sensitive and more ductile compared to the original intermetallic structure
2Reliability
If sintered NdFeB magnets are produced to achieve high density and magnetic properties, then the magnets have superior performance, but the material becomes extremely brittle and difficult to shape
Solution Approach 1:
The invention performs preliminary shaping of the magnet material in the form of thin sheets or complex geometries before the final sintering process. The green compacts are formed with the desired shape while the material is still in a more ductile state, and then sintered to achieve high density. This preliminary action eliminates the need for post-sintering machining and slicing
Solution Approach 2:
The invention segments the manufacturing process into distinct stages: powder preparation with controlled composition, green compact formation with desired geometry, and controlled sintering. This segmentation allows each stage to be optimized independently, achieving both shapeability and high magnetic performance
3Strength
If dysprosium additives are used to increase coercivity in NdFeB magnets, then the magnetic performance is improved, but the production cost increases due to the expensive and limited supply of dysprosium
Solution Approach 1:
The invention replaces expensive dysprosium additives with cheaper alternative compositions, specifically using controlled amounts of boron (0.1-5 wt%) and optimized rare earth content (5-20 wt%). These alternative compositional elements provide the necessary magnetic properties at a fraction of the cost of dysprosium, making the magnet production economically viable
Solution Approach 2:
The invention changes the compositional parameters by optimizing the rare earth content (5-20 wt%) and adding boron (0.1-5 wt%), which fundamentally alters the magnetic properties of the material. This parameter optimization achieves high coercivity and magnetic performance through compositional design rather than expensive additive elements
4Reliability
If thin sheet magnets are produced by slicing from solid sintered blocks to reduce eddy-current losses, then the magnetic performance is improved, but the process is time-consuming and results in significant material wastage
Solution Approach 1:
The invention performs preliminary shaping of the magnet material into thin sheets or complex geometries before the final sintering process. The green compacts are formed with the desired thin-sheet geometry, and then sintered to achieve high density. This preliminary action eliminates the need for post-sintering slicing and prevents material wastage
Solution Approach 2:
The invention replaces the mechanical slicing process with a powder metallurgy approach where thin sheets are formed directly during compacting. Instead of mechanically cutting solid blocks (which causes material loss), the material is consolidated into the desired thin-sheet shape from powder form, achieving both high magnetic performance and manufacturing efficiency
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 process enhances the ductility of NdFeB alloys, enabling the production of fully dense and aligned rare earth magnets with improved magnetic properties and reduced material wastage, while minimizing the use of expensive additives and simplifying the manufacturing process.
Implementation Method 1
exposing a rare earth alloy to hydrogen gas at an elevated temperature so as to effect hydrogenation and disproportionation of the alloy
Implementation Method 2
heating NdFeB powder in H2 to high temperatures (generally around 750-900° C.), and then, whilst still at high temperatures, desorbing the H2 under carefully controlled conditions. During the hydrogenation and disproportionation stages, initially the Nd-rich grain boundary material reacts with the H2 to form a hydride, and subsequently the matrix grains of Nd2Fe14B disproportionate to form an intimate mixture of NdH2, Fe2B and α-Fe
Implementation Method 3
mechanically processing the disproportionated alloy
Implementation Method 4
degassing the processed alloy so as to effect hydrogen desorption and recombination of the alloy
Implementation Method 5
when the pressure is subsequently reduced (e.g. by vacuum application) the hydrogen desorbs from the disproportionated material and the three constituents recombine to give grains of Nd2Fe14B but with a much reduced grain size
Implementation Method 6
a magnetic field is applied to align the grains of the powdered material and thus achieve anisotropy
Implementation Method 7
The material is then pressed and sintered at around 1000° C. to produce a magnet
Data Source
AI summary
A process is provided for the production of rare earth magnets comprising the steps of exposing a rare earth alloy to hydrogen gas at an elevated temperature so as to effect hydrogenation and disproportionation of the alloy, mechanically processing the disproportionated alloy, and degassing the processed alloy so as to effect hydrogen desorption and recombination of the alloy. The process of the invention finds use in the production and shaping of rare earth magnets, and may be particularly applicable to the production of thin magnetic sheets.