Wetting Transitions in Liquid and Solid Alloys

9820169温布拉特这项研究包括两个主要推动力。第一个重点是研究液态合金中的润湿转变。这是之前美国国家科学基金会对两相液态Ga-Pb合金所做工作的自然延伸，在该两相液态合金中，富铅相完全润湿了富镓相。本研究中使用的方法包括用固着液滴技术测量液态合金的表面能，以及用俄歇电子能谱(AES)直接测量液态合金表面的吸附。此外，还研究了二元Ga-Pb合金中(密度较小)富Ga液相表面的(致密)富铅液层的重力减薄作用。这是通过俄歇电子能谱测量铅层厚度作为液滴高度的函数来实现的。研究的第二个重点是固体两相合金中的润湿转变。关于固体二元合金的润湿转变，以前还没有报道。Au-Ni系被认为是富Ni相被富Au相润湿的过渡系统。通过研究Au在富镍相表面的吸附(偏析)现象，研究了润湿转变。研究了Au在单相富镍合金表面上的吸附行为，研究了向富Au相和富Ni相共存的混溶间隙方向冷却时Au在合金表面的吸附行为。在润湿温度以上和以下的温度下，Au的吸附行为预计会有很大的不同。尽管过去几年进行了大量的研究，以提高对润湿转变的基本理解，但这些工作大多集中在液体有机混合物或吸附的稀有气体中的润湿转变。相比之下，很少有人致力于研究金属合金中这些现象的性质，因为金属合金中的相互作用是非常不同的。因此，这项研究有可能导致令人兴奋的新科学。此外，选定的合金代表了一大类技术上感兴趣的材料。例如，对润湿现象的研究显然对更好地了解固相和液态烧结、液态金属连接过程、金属精炼和液态金属脆化具有重要意义。

9820169WynblattThis research consists of two principal thrusts. The first thrust focuses on the study of wetting transitions in liquid alloys. This is a natural extension of work performed under a previous NSF grant on two-phase liquid Ga-Pb alloys in which complete wetting of the Ga-rich phase by the Pb-rich phase was demonstrated. The approaches to be used in this study include measurement of liquid alloy surface energies by means of the sessile drop technique, coupled with direct measurements of adsorption at the liquid surfaces by Auger electron spectroscopy (AES). In addition, the gravitational thinning of the (denser) Pb-rich liquid layer at the surface of the (less dense) Ga-rich liquid phase is investigated in binary Ga-Pb alloys. This is accomplished by AES measurements of the thickness of the Pb layer as a function of liquid drop height. The second thrust of the research addresses wetting transitions in solid two-phase alloys. No previous work on wetting transitions has been reported in solid binary alloys. The Au-Ni system is identified as one in which a transition in wetting of the Ni-rich phase by the Au-rich phase is likely to take place. The wetting transition is investigated by studying the associated Au adsorption (segregation) phenomena at the surface of the Ni-rich phase. The adsorption of Au at the surfaces of single-phase Ni-rich alloys is studied as samples are cooled towards the miscibility gap, where Au-rich and Ni-rich phases coexist. The adsorption behavior of Au is expected to be quite different at temperatures above and below the wetting temperature.%%%Whereas a great deal of research has been performed over the past several years to develop improved fundamental understanding of wetting transitions, most of this work has focused on wetting transitions in liquid organic mixtures, or in adsorbed noble gases. In contrast, little research has been devoted to the nature of these phenomena in metallic alloys, where the interactions are quite different. Thus this research has a potential for leading to exciting new science. In addition, the selected alloys represent a large class of technologically interesting materials. For instance, the study of wetting phenomena is clearly important in developing better fundamental understanding of solid and liquid phase sintering, of liquid metal joining processes, of metal refining, and of liquid metal embrittlement.***