Influence of Segregation Effects on the Energies of Lead/Graphite and Gold/Graphite Interfaces
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graphite from 131 to 1230. These contact angle changes are used to compute the interfacial energy at both Pb/graphite and Au/graphite interfaces. Direct evidence of Ni segregation at those interfaces is also obtained by crater edge profiling measurements. It is found that the enrichment factor of Ni is much larger in the Pb- than in the Au-based system. Also, for similar changes in interfacial energy, the effects of Ni segregation on contact angle are larger in the Pb- than in the Au-based system. These effects are discussed in terms of the relative surface and interfacial energies in the two systems. INTRODUCTION Interfaces between metals and non-metallic solids play an important role in determining the properties of many systems, such as microelectronic components, metal-matrix composites, and metal-ceramic joints. In the context of mechanical behavior, interfacial strength is considered to scale with the so-Called work of adhesion, which represents the difference between the sum of the energies of the two surfaces which would be produced if the interface were to be parted, and the energy of the interface. Thus, a lowering of interfacial energy generally leads to mechanically stronger interfaces. Control of interfacial energy in such systems is therefore of considerable practical interest. One way the interfacial energy can be controlled in metal-nonmetal systems is through judicious alloying of the metallic constituent with interface active elements, as the segregation of alloying elements to the interface results in a lowering of interfacial energy. There have been many studies of the effects of alloying on interfacial energy in metal-ceramic and metal-carbon systems. Most of these studies have evaluated the effects of alloying on interfacial energy by means of wetting measurements of liquid metals and alloys on a variety of substrates [1-5]. Major improvements in wetting due to alloying were generally attributed to the formation of reaction products at the interface. The previous use of wetting studies suffer from several shortcomings. First, previous experimental studies were generally performed under conditions where freedom from contamination of the surfaces and interfaces could neither be ensured nor even monitored. Since impurity adsorption can influence both surface and interface energetics, the reliability of those studies is in question. Second, the energetics of liquid-solid interfaces are expected to differ from those of solid-solid interfaces. Third, the lowering of interfacial energy by alloying with elements which result in interfacial reactions can lead to the formation of brittle interfacial reaction products which can in turn lead to mechanically weaker rather than stronger interfaces. Thus, the motivation of this work was to develop an approach which could address these issues. We summarize here, and provide comparisons of the results of experiments performed on two solid metal-graphite systems [6,7] performed under conditions of ultrahigh vacuum (UHV), so as to control surface and interface c
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