Solid-State wetting of graphite by Pb and Pb-Ni alloys
- PDF / 1,285,373 Bytes
- 9 Pages / 598.28 x 778.28 pts Page_size
- 14 Downloads / 146 Views
I.
INTRODUCTION
INTERFACES in solids play an important role in many phenomena of scientific and technological significance. As a result, there have been numerous studies on solid-solid interfaces, such as those between metalmetal, metal-ceramic, and other metal-nonmetal systems. While these studies have addressed many issues, such as interfacial structure, mechanisms of bonding, and interfacial reactions, there has been limited study devoted to the equilibrium composition of those interfaces, i.e., segregation phenomena, and the effects of interfacial composition on interfacial energy. The lack of information on these important aspects of interfaces constitutes the primary motivation for this work. One area involving interfaces between metals and nonmetals, which has evoked considerable interest in recent years, is that of metal-matrix composites. These composites combine the high fracture resistance of the metals with the high strength of the nonmetallic fibers. In this class of composites, the weak link in the chain of factors that determine the mechanical properties is the metal-fiber interfacial strength, as this property controls the effectiveness of the load transfer from the metal to the fiber. Interfaces in composites are often characterized by the "work of adhesion," or the "wettability" of the fiber by the surrounding metal. In general, the lower the interfacial energy, the higher the wettability and, consequently, the higher the interfacial strength. The objective of the present study is to investigate a model metal-nonmetal system with the aim of developing better fundamental insights into the role that alloying additions to the metal phase may play in altering the metal-nonmetal interfacial energy. It is hypothesized that suitably chosen alloying elements will segregate to the interface, thereby lowering the interfacial energy and improving wettability. It should be stated that significant work has been reported in recent years on the study of alloying additions to metal-nonmetal systems. However, the bulk of that work was aimed at effecting improved adhesion through chemical reactions at the interface. UTPAL GANGOPADHYAY, Graduate Student, and PAUL WYNBLATT, Professor and Head of Department, are with the Materials Science and Engineering Department, Carnegie Mellon University, Pittsburgh, PA 15213. Manuscript submitted June 16, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
The present study takes another approach, namely, that of lowering interfacial energy through the formation of a nonreacting adsorbed layer at the interface. This approach could provide a means of improving metal-fiber adhesion without the formation of often brittle bulkreaction products at the interface. The experimental approach used here is to perform contact-angle measurements of small metal crystallites (with and without alloying addition), equilibrated on a graphite substrate, under ultrahigh vacuum (UHV) conditions. The term "crystallite" is used to describe small metal single crystals. Wetting studies of this type have
Data Loading...
