难混溶合金微滴中L_(2)相迁移动力学行为

Dynamic Behaviors of Migrating L_(2)Phase Inside Immiscible Alloy Drops

基于传热模型,计算了直径分别为300、600和900μm的Fe-52%Cu合金微滴在自由凝固条件下的温度场分布,分析了温度梯度的变化及L_(2)相小球动力学特点。结果表明,合金微滴在相分离过程中其中心与表面温差较小(<5 K),而对于给定尺寸的微滴其径向方向上温度梯度却差异较大,但温度梯度值随时间成一次线性减小。通过理论计算,确定了小球在三种微滴内最大可迁移时间,分别是0.0206、0.07和0.141 s。此外,还比较了小球在三种微滴内的迁移距离,发现同尺寸小球在合金微滴内最大迁移距离与微滴半径之比为定值,r/R=0.4849,表明小球在合金微滴内的末态相对位置不依赖于微滴直径。这与目前大部分研究者对合金微滴直径影响核/壳结构形貌的观点有所不同。本研究不仅有助于理解核/壳型粉末的形成过程,同时为新材料设计奠定重要理论基础。

Based on the heat transfer model,the internal temperature fields of Fe-52%Cu alloy drops with diameters of 300μm,600μm and 900μm under free fall condition were calculated.The change of temperature gradient and the movement characteristics of L_(2)phase sphere were fully analyzed.It was found that the temperature difference between center and surface of an alloy drop is very small,which less than 5 K,while the temperature gradient along radial direction is big and its value is almost linearly decreased with time.With the help of calculation,the maximum migration time of L_(2)phase sphere in three drops was determined as 0.0206 s,0.07 s and 0.141 s,respectively.In addition,the maximum migration distances of L 2 phase spheres were compared.It was found that these spheres have same final position,that is,r/R=0.4849,indicating that the final position was independent of the drop diameter.This is such different from the previous understanding on diameter-related ability of core/shell formation.Our study not only helps to understand the process of core/shell formation,but also provides an important theoretical foundation for material design.