40 Years Later No Fe16N2 Magnet – Why?
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. Fe16N2 Magnet • 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 NdFeB Segment Magnets [...]
