中文摘要：

本文采用自由落体实验技术和格子玻尔兹曼计算方法研究了低重力条件下液态Fe-Sn-Si/Ge合金的相分离过程.实验发现,二种合金液滴在自由下落过程中均发生显著的液相分离,形成了壳核和弥散组织.当Fe-Sn-Si合金中的Si元素被等量的Ge元素替换后,壳核组织中富Fe区和富Sn区的分布次序会发生反转.计算表明,在液相分离过程中冷却速率、Marangoni对流和表面偏析对壳核构型的选择和弥散组织的形成起决定性作用.

英文摘要：

The liquid phase separation of small Fe-Sn-Si/Ge alloy droplets under reduced-gravity condition is investigated experimentally by free fall technique and theoretically by lattice Boltzmann method.In the drop tube experiments,the Fe-Sn-Si/Ge monotectic alloys are heated by induction heating in an ultrahigh vacuum chamber and further overheated to 200 K above their liquid temperatures for a few seconds.Finally,the molten alloy melt is ejected out from the small orifice of a quartz tube by high pressure jetting gas of He and dispersed into numerous tiny droplets,which are rapidly solidified during free fall in a protecting He gas environment.These droplets benefit from the combined advantages of high undercooling,containerless state and rapid cooling,which can provide an efficient way to study the liquid phase separation of high-temperature alloys in microgravity.In order to efficiently reproduce the dynamic process of phase separation inside drop tube equipment,the effects of surface segregation and Marangoni convection are introduced into the interaction potential of different liquids within lattice Boltzmann theory.Based on this modified model,the dynamic mechanism of phase separation can be sufficiently analyzed and the phase separation patterns can be realistically simulated.Experimental results demonstrate that conspicuous liquid phase separations have taken place for both Fe-Sn-Si and Fe-Sn-Ge alloy droplets and the corresponding morphologies are mainly characterized by core-shell and dispersed structures.The phase separation process can be modulated by the third-element addition.As the Si element of Fe-Sn-Si alloy is replaced by the Ge element with the same fraction,the distribution order of Fe-rich and Sn-rich zones is reversed within core-shell structure.A core-shell structure composed of a Fe-rich core and a Sn-rich shell is frequently observed in Fe-Sn-Si alloy droplets whereas the Fe-Sn-Ge alloy droplets tend to form a core-shell structure consisting of a Sn-rich core and a Fe-rich shell.Theoretical cal