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

• Ternary Fe-Mo-Si eutectic and peritectic alloys were rapidly solidified under containerless and microgravity condition.
• The microstructures are composed of intermetallic phases, and change obviously with the alloy droplet diameter.
• The rapid solidification mechanisms of ternary eutectic and peritectic transformations are discussed.

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.

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