Fabrication of bulk τ MnAl–C magnets by hot-pressing from ε-phase gas-atomized and milled powder

Isotropic nanocrystalline MnAlC particles with quasi-spherical shape were synthesized by gas-atomization being afterwards milled for a short time of 60 s. Gas-atomized and milled particles were compacted by the hot-pressing method to obtain bulk MnAlC magnets. An adequate combination of the parameters during hot-pressing made it possible to fabricate bulk MnAlC magnets with a simultaneous transformation of ε-phase into the ferromagnetic τ-phase. The study has allowed for correlating the morphology, microstructure and magnetic properties of the bulk magnets obtained from the different powder samples. Hot-pressing experiments performed on milled ε-phase based powders resulted in an increased coercivity as a consequence of a reduced crystallite size (about 25 nm), induced strain (about 0.40%) and the formation of both β-Mn phase and Mn3AlC. This single-step approach has been compared with a two-step process comprising annealing of the gas-atomized ε-phase to develop the τ-phase as a first step followed by compaction via hot-pressing in a second step. Comparable magnetic properties obtained for the bulk magnets resulting from this two-steps route validates the single-step approach followed in this study. This work shows that gas-atomization, flash-milling and hot-pressing of ε-phase MnAlC powder is an efficient path towards the fabrication of bulk τ-MnAlC magnets. •Fabrication of high-density bulk magnets of MnAlC by hot-pressing.•Combination of gas-atomization, flash-milling and hot-pressing.•Novel 1-step process: simultaneous ε-to-τ transformation and powder compaction.•Controlled crystallization and phase transformation are key factors in the process.•Hot-pressed flash-milled powder leads to improved density and magnetic properties.