Investigation of phase selection hierarchy in Mn–Al alloys

• Published in: Intermetallics 2019-12, Vol.115, p.106617, Article 106617
• Main Authors: Genc, Ayse Merve, Acar, Ozgun, Turan, Servet, Kalay, Ilkay, Savacı, Umut, Kalay, Yunus Eren
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Composition; Differential scanning calorimetry; Diffraction patterns; Electron microscopy; Ferromagnetic τ-phase; Ferromagnetism; Magnetic measurement; Magnetism; Manganese; Nucleation; Permanent magnets; Phase transitions; Synchrotron radiation; X-ray diffraction
• ISSN: 0966-9795; 1879-0216
• DOI: 10.1016/j.intermet.2019.106617

Primarily attributed to the formation of the ferromagnetic τ-phase, near equiatomic composition of Mn–Al have recently received much attention in permanent magnet industry. Several mechanisms have been proposed in literature for the τ-phase formation but controversy still arises regarding the dominating mode. In the current work, MnAl-based alloys having different compositions in a range between Mn50.5Al49.5 and Mn57Al43 have been studied by means of in-situ high energy X-ray diffraction, differential scanning calorimetry (DSC) and magnetic measurements. Synchrotron and DSC experiments showed the dependence of the τ-MnAl on the intermediate disordered ε′-phase. Alloys having 53.4 at% or less Mn (S1, S2) followed a transformation route of ε+ε'→τ→β+γ2 upon annealing. Alloys having more than 53.4 at% of Mn had only ε-phase. High energy X-ray diffraction patterns showed that ε-phase directly transformed into stable phases in the absence of ε′-phase. It is observed that ε′ not only promoted the ferromagnetic τ-phase but also stabilized it by delaying the nucleation of stable phases. •Composition of MnAl alloys affect both the sequence and the temperature of phase transformations.•Alloys having Mn content less than 53.4 at% has a parent phase mixture consisting of ε and ε′ phases at the quenched state.•ε′-phase transforms into ferromagnetic τ-phase and stable phases upon annealing.•Magnetic τ-MnAl formation cannot proceed in the absence of ε′-phase.