Wetting Transitions in Liquid and Solid Alloys

[9820169 . wynblatt]这项研究包括两个主要的重点。第一个重点是研究液态合金的润湿转变。这是美国国家科学基金会之前对两相液态Ga-Pb合金工作的自然延伸，其中富ga相被富pb相完全润湿。在本研究中使用的方法包括通过固滴技术测量液体合金表面能，以及通过俄歇电子能谱（AES）直接测量液体表面的吸附。此外，还研究了二元Ga-Pb合金中富pb液相表面（较致密）富pb液相层的重力变薄现象。这是通过AES测量铅层厚度作为液滴高度的函数来完成的。研究的第二个重点是固体两相合金的润湿转变。以前没有关于固体二元合金的润湿转变的报道。在Au-Ni体系中，富ni相被富au相润湿的转变很可能发生。通过研究富镍相表面相关的Au吸附（偏析）现象来研究润湿转变。研究了当样品冷却到富金与富镍共存的混相间隙时，Au在单相富镍合金表面的吸附。预计在高于和低于润湿温度的温度下，Au的吸附行为会有很大的不同。尽管在过去几年中进行了大量的研究，以提高对润湿转变的基本理解，但这些工作的大部分集中在液体有机混合物或吸附惰性气体中的润湿转变上。相比之下，很少有研究致力于金属合金中这些现象的性质，其中的相互作用是完全不同的。因此，这项研究有可能导致令人兴奋的新科学。此外，所选择的合金代表了一大类技术上有趣的材料。例如，润湿现象的研究对于更好地理解固相和液相烧结、液态金属连接过程、金属精炼和液态金属脆化显然是很重要的

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.***