Stabilization of τ-phase in carbon-doped MnAl magnetic alloys

In this work, the effect of carbon addition on the L10 τ-phase stability in (Mn0.54Al0.46)100-xCx (x = 0-5) magnetic alloys are investigated. By microstructural analysis, single-phase and dual-phase microstructure are confirmed in 0 ≤ x ≤ 3 and x > 3 alloys, respectively. The solubility limit of carbon atoms in τ-phase of about 3 at.% is also determined by the characterization of the intrinsic magnetic properties and the crystal structure. The solid solution of carbon can significantly stabilize the thermodynamically metastable τ-phase, reflecting by the reversible τ→ε transformation path, and suppressing of the τ-phase decomposition effectively at high temperatures. The stabilized τ-phase by carbon doping exhibits higher magnetization in the as-milling state, with the highest magnetization for x = 3. After annealing at high temperature, the carbon-doped τ-phase is also more stable, resulting in the obvious improvement in magnetization. The magnetization of 86.7 emu/g under 30 kOe and the coercivity of 3.26 kOe are approached in the as-annealed x = 3 powders. These results clarify the effect of doping carbon on τ-phase stability in MnAl alloys and highlight the guidance and routine for high performance MnAl permanent magnets.