Ternary eutectic and peritectic solidification of undercooled liquid Fe-Mo-Si alloys

Liquid ternary Fe-6.5%Mo-18.5%Si eutectic and Fe-4%Mo-19%Si peritectic alloys were highly undercooled and rapidly solidified under containerless and microgravity condition inside the drop tube. In this situation, the cooling rate and undercooling of the alloy droplets increased obviously when their diameters decreased, and the alloy droplets exhibited maximum undercoolings up to 184 K and 468 K respectively. For the Fe-6.5%Mo-18.5%Si eutectic alloy, the ternary eutectic is composed of Fe₃Si, Fe₂Si and Fe₅MoSi₄ intermetallic phases. With the decrease of the droplet diameter, the volume fraction of the ternary (Fe₃Si + Fe₂Si + Fe₅MoSi₄) eutectic increases and the morphology of the ternary eutectic vary from lamellar structure to granular structure. In the Fe-4%Mo-19%Si peritectic alloy, the primary phase is Fe₂Si intermetallic phase, and the peritectic structure consists of Fe₃Si and FeSi intermetallic phases. With the increase of the undercooling, the primary phase vanishes, the peritectic transformation nearly accomplishes, and the growth of (Fe₃Si + FeSi) peritectic phases transform from faceted blocks into non-faceted granules.