40 Years Later No Fe16N2 Magnet – Why?
• Difficult to synthesize pure Fe16N2 by conventional methods e.g. solubility of N in liquid Fe very low (0.045 versus 5.5 wt % for C).
• Alloy cannot be formed by conventional processing methods e.g. melting and casting.
• Contradictory results over the years probably due to inconsistent sample preparation and measurement techniques.
• Fe16N2 decomposes above 300 C.
• Cannot be formed by powder metallurgical processing.
• Lots of magnetization available but need coercivity for a useful PM compound; theoretical magnetocrystalline anisotropy H is 16 kOe but will need help from other mechanisms e.g. shape, strain.
Bulk Fe16N2 Magnet Reported by UMN Team and Niron Magnetics Formed
• Strained wire method used to enhance magnetic property; strain‐assisted annealing.
Niron Magnetics – Good News
• The company is producing bulk iron nitride magnets today for further research and development.
• First principles calculations demonstrate a theoretical BHmax of 135 MGOe and Hc of 16 KOe.
• Raw materials are cheap and abundant.
• Isotropic bonded magnet BHmax > 30 MGOe feasible.
Niron Magnetics – Bad News
• Iron nitride by itself is inherently heat sensitive.
• It decomposes before it sinters – iron nitride magnets will all be bonded in some fashion.
• Coercivity needs to be improved.
• They will need the same corrosion protection as raw iron.
• Niron hasn’t announced a commercial product yet