Formation of a metastable ferromagnetic tgr; phase during containerless melt processing and rapid quenching in Mnhyphen;Alhyphen;C alloys

摘要

Solidification of selected Mnhyphen;Alhyphen;C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable tgr; (L10) phase formed directly from the melt. Complete solidification to tgr; phase was interrupted by the competitive evolution of an equilibrium egr; phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic tgr; phase in a Mn0.55Al0.433C0.017alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at.thinsp;percnt; (i.e., Mn0.55Al0.416Co0.034alloy), a transition in structure development occurred so that the samples exhibited ggr;2phase formation as well as tgr; and egr; phases. Both microstructural observations and xhyphen;ray diffraction examination were used to guide the interpretation and the analysis of solidification pathways. The attainment of the high liquid undercooling required to nucleate the metastable tgr; phase from the melt may be facilitated by containerless processing.