Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5461492 | Journal of Alloys and Compounds | 2017 | 6 Pages |
â¢The MnAl ε âÂ Ï phase transition studied by in situ synchrotron X-ray diffraction.â¢A cooling rate of 10 °C/min yields pure Ï-phase when cooled from high temperature.â¢No intermediate ε'-phase was observed during the ε-Ï-phase transition process.â¢C doping stabilizes the Ï-phase whereas B doping destabilises the Ï-phase.
The Ï-phase MnAl alloys are promising candidate for rare earth free permanent magnets. In this study, In order to better understand the MnAl εâÏ phase transition mechanism in a continuous cooling process and metastable MnAl Ï-phase high temperature stability, Mn0.54Al0.46, Mn0.55Al0.45C0.02 and Mn0.55Al0.45B0.02 alloys were systematically studied by in situ synchrotron X-ray powder diffraction (SR-XRD). The relationship between Ï-phase formation tendency and different cooling rates of Mn0.55Al0.45C0.02 was investigated. Besides, the high temperature stabilities of undoped Ï-MnAl and carbon/boron doped Ï-MnAl were studied. Differential thermal analysis (DTA) was also employed to study the phase transformation as well. The research results show that a high cooling rate of 600 °C/min leads to a 50/50 wt% mixture of ε- and Ï-phase; almost pure Ï-phase was obtained when cooled at a moderate cooling rate of 10 °C/min; while for a slow cooling rate of 2 °C/min, the Ï-phase partially decomposed into β and γ2 phases. No intermediate ε'-phase was observed during the εâÏ phase transition during the experiments. For the boron and carbon doped Ï-MnAl, the 800 °C high temperature stability experiments reveal that C stabilizes the Ï-MnAl while doped B destabilises the tetragonal structure and it decomposes into β- and γ2-phases.
Graphical abstractThe ferromagnetic Ï-phase is metastable and advanced synthesis protocols are needed to produce the material in high purity. In this study, the ε âÂ Ï phase transition was investigated by in situ synchrotron radiation X-ray powder diffraction (SR-XRD). A continuous cooling process was employed in combination with different cooling rates to gain insight on the ε âÂ Ï phase transition. Furthermore, the effect of doping elements (boron and carbon) on the high temperature stability of the ferromagnetic Ï-phase was systematically studied. The relationship between phase composition and different cooling rates shows the importance of appropriate synthesis protocols in order to obtain the metastable Ï-phase. The results show that a moderate cooling rate of 10 °C/min yields a pure ferromagnetic Ï-phase at the end of the cooling process, and that no intermediate ε'-phase was observed during the experiments.Download full-size image