Preparation of α′-Fe(N)/α′-Fe8N by γ′-Fe4N precursor

An approach by using the γ′-Fe4N precursor was proposed to prepare a bulk magnet with high α″-Fe16N2 content, and the feasibility for high N content α′-Fe(N)/α′-Fe8N was demonstrated in ribbon samples. γ′-Fe4N decomposed when it was heated to a high temperature, and then, a supersaturated γ-Fe(N) phase formed because of N atoms diffusing out from the γ′-Fe4N lattice. The short-lived supersaturated γ-Fe(N) had the face-centered cubic lattice, and its nitrogen content is beyond 3.0 wt. %. The supersaturated γ-Fe(N) acts as a precursor of the martensite transformation for a body-centered tetragonal phase. After the cryo-treatment, which was essential to complete the martensite transformation, a mixture of α′-Fe(N) and α′-Fe8N was obtained. The N content of more than 2.5 wt. % in the samples was achieved.