Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl

Area of Science:

• Materials Science
• Condensed Matter Physics
• Magnetism

Background:

• The τ-phase of Manganese-Aluminum (MnAl) is a promising rare earth-free material for permanent magnets, offering a lower-cost alternative to Neodymium-Iron-Boron (Nd2Fe14B) magnets.
• However, the metastable nature of the τ-phase and the difficulty in producing fine powders with high purity and controlled microstructure hinder its widespread application.
• Achieving the required fine particle size and high τ-phase purity is crucial for effective alignment in permanent magnet manufacturing.

Purpose of the Study:

• To present a novel method for synthesizing high-purity τ-phase MnAl fine powders suitable for permanent magnet applications.
• To investigate the effects of cryo milling and flash heating on the phase purity, microstructure, and magnetic properties of MnAl.
• To demonstrate the potential of this new method to overcome the limitations of current τ-phase MnAl powder production.

Main Methods:

• Synthesis of a high-purity τ-phase Mn0.55Al0.45C0.02 alloy using the drop synthesis method.
• Cryo milling of the synthesized alloy for 2 and 4 hours, followed by a flash heating process.
• Characterization using X-ray in situ powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy, electron backscatter diffraction, magnetometry, and neutron powder diffraction.

Main Results:

• The developed method successfully produced high-purity τ-phase MnAl powders.
• Cryo milling (2 and 4 hours) followed by flash heating resulted in micron-sized, round particles with high τ-phase purity.
• The flash-heated samples exhibited enhanced magnetic properties, including high saturation magnetization and increased coercivity.

Conclusions:

• The combination of drop synthesis, cryo milling, and flash heating is an effective route for producing high-purity τ-phase MnAl fine powders.
• These powders possess favorable microstructural and magnetic characteristics for use in rare earth-free permanent magnets.
• This advancement offers a viable pathway to partially replace traditional rare earth magnets with a more sustainable and cost-effective alternative.