Melting Kinetics of Faceted and Non-Faceted Crystals

融化是人类已知的最常见的物理现象之一，但也是最难理解的。这项拨款的目的是为了更好地了解金属和合金的熔化行为。该研究将提供固液界面动力学的准确数据，作为界面过热、熔化速率和成分的函数。界面过热将由两固液界面产生的塞贝克电位差直接测量；一个静止，另一个以给定的速度融化。测量技术的一个重要特点是它允许对界面温度进行精确、非侵入性和连续监测。为研究选择的材料将包括纯Sn（非面形金属）和Bi（面形成型金属）的单晶，以及含有高达4 % Bi的Sn-Bi单晶。本研究的主要目的是获得界面动力学作为单晶熔化速度函数的定量信息，以及熔化过程中溶质重新分布的定量信息。这项研究的科学意义源于这样一个事实，即熔融动力学提供了界面性质的信息，因为它对偏离局部平衡的反应。这些信息将描述熔化界面是扩散的，还是与凝固过程中的行为相似。除了理论意义外，熔炼动力学规律对铸件等轴结构的形成等一系列技术问题也具有重要意义。这种结构的形成在很大程度上取决于孕育剂的熔化和溶解动力学、固有固体颗粒以及局部凝固条件。该项目将使研究生接触到材料科学与工程的基础研究和测量技术。

Melting is among the most common physical phenomena known to mankind, yet it has been the most difficult to understand. This grant is aimed at a greater understanding of melting behavior of metals and alloys. The research will provide accurate data on the solid-liquid interface kinetics as a function of the interface superheating, melting rate, and composition. The interface superheating will be measured directly from the Seebeck potential difference generated across two solid-liquid interfaces; one stationary and the other melting at a given velocity. An important feature of the measurement technique is that it allows for a precise, non-intrusive and continuous monitoring of the interface temperature. The materials selected for the study will consist of single crystals of pure Sn (a non-facet forming metal) and Bi (a facet former), and Sn-Bi single crystals containing up to 4 at % Bi. The primary objective of the research is to obtain quantitative information on the interfacial kinetics as a function of melting velocity for single crystals, and on the solute redistribution during melting.The scientific significance of the investigation stems from the fact that melting kinetics provide information on the nature of the interface as it responds to deviations from local equilibrium. Such information will delineate whether the melting interface is diffuse, or whether it behaves similar to that during solidification. In addition to its theoretical significance, the melting kinetics laws are of interest for a series of technical problems such as in the formation of equiaxed structures in castings. Formation of such structures strongly depends on the melting and dissolution kinetics of inoculants, intrinsic solid particles, as well as on the local solidification conditions. The project will expose graduate students to fundamental research and measurement techniques in materials science and engineering.