Nd-Fe-B Magnet Coercivity via Mn-Bi Grain Alignment
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Solution Overview
Problem
Neodymium-iron-boron (Nd—Fe—B) alloy magnets experience a decrease in coercivity with increasing temperature, which is a challenge for high-temperature applications like electric and hybrid vehicles, and the addition of heavy rare earth elements to stabilize them increases production costs.
Innovation Solution
A method involving mixing Nd—Fe—B alloy powder with Mn—Bi alloy, aligning particles within a magnetic field, and annealing to form elongated Mn—Bi grains that are aligned with the magnetic moment, enhancing coercivity without using rare earth elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth elements are added to stabilize coercivity at high temperatures, then thermal stability is improved, but production cost increases
Solution Approach 1:
The patent creates a composite permanent magnet material combining Nd-Fe-B anisotropic particles with Mn-Bi alloy matrix. This composite structure allows the Mn-Bi phase to form elongated grains during annealing that align with the magnetic moment, providing thermal stability enhancement without requiring heavy rare earth elements. The composite material approach resolves the contradiction by achieving the reliability improvement through material composition rather than costly additives.
2Temperature
If temperature increases for high-temperature operation, then application range is expanded, but coercivity decreases
Solution Approach 1:
The patent changes the microstructural parameters of the magnet by forming elongated Mn-Bi grains with specific orientation during annealing. The grain morphology and alignment parameters are controlled to enhance coercivity at elevated temperatures. This parameter change approach allows the magnet to maintain reliability across a wider temperature range without sacrificing operating temperature capability.
Solution Approach 2:
The dual-phase composite structure with Nd-Fe-B particles embedded in an elongated Mn-Bi grain matrix provides synergistic effects. The Mn-Bi phase contributes to thermal stability while the aligned structure maintains coercivity, enabling the magnet to operate reliably at higher temperatures than conventional single-phase Nd-Fe-B magnets.
3Reliability
If Mn-Bi alloy is mixed with Nd-Fe-B powder and annealed to form elongated grains, then coercivity at high temperature increases, but manufacturing process complexity increases
Solution Approach 1:
The patent performs preliminary mixing of Nd-Fe-B powder with Mn-Bi alloy in specific compositions before pressing and annealing. The preliminary preparation of the alloy mixture with controlled composition facilitates the subsequent formation of elongated grains during annealing. This preliminary action simplifies the overall process by pre-establishing the conditions needed for grain alignment and reducing the need for complex post-processing steps.
Solution Approach 2:
The manufacturing process utilizes phase transitions during annealing to form elongated Mn-Bi grains from the mixed alloy. The controlled thermal treatment induces specific phase transformations that naturally lead to grain elongation and alignment along the magnetic field direction. This phase transition mechanism simplifies the process by leveraging material physics rather than requiring complex mechanical or chemical interventions.
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 significantly increases coercivity at higher temperatures, improving thermal stability of the magnets for high-temperature applications without the need for expensive rare earth elements, thus reducing production costs.
Implementation Method 1
annealing the magnet within a second magnetic field to form elongated Mn—Bi grains and align the elongated Mn—Bi grains with the moment
Implementation Method 2
annealing the magnet within a second magnetic field to form elongated Mn—Bi grains
Implementation Method 3
pressing the mixture within a first magnetic field to form a magnet having Nd—Fe—B anisotropic particles aligned with a magnetic moment of the magnet
Implementation Method 4
Coercivity is the ability of a magnet to withstand an external magnetic field without becoming demagnetized
Data Source
AI summary
A method includes mixing first and second alloys to form a mixture, pressing the mixture within a first magnetic field to form a magnet having anisotropic particles of the first alloy aligned with a magnetic moment of the magnet, and heat treating the magnet within a second magnetic field to form elongated grains from the second alloy and align the elongated grains with the moment.