| A solid state wetting technique has been used to investigate metal/SiC and metal/graphite interfaces. Compared with the conventional sessile drop method, this technique uses smaller (&sim10 micron) drops and is performed in ultrahigh vacuum under conditions where surface and interfacial composition can be monitored. The objective of this thesis was to demonstrate that the energy of the interfaces selected for study could be controlled by alloying the metallic phase with interfacially active elements, so as to modify interfacial composition by taking advantage of interfacial segregation effects, without leading to the formation of brittle interfacial reaction products.Cu (with Si as an alloying element) and Au (with Sn, Ge, Si as alloying elements) were deposited onto the (0001) surface of 6H-SiC single crystal substrates. The Cu/SiC interface was found to be reactive at the temperatures of interest, with the reaction product adopting the form of hexagonal plates. The Au/SiC interface, on the other hand, was quite stable at 1123K and showed a contact angle of 133°. Additions of Ge and Si. to Au were found to segregate to the metal SiC interface, thereby lowering the contact angle by more than 20°, and doubling the work of adhesion of Au on SiC. Additions of Sn to Au, however, led to segregation of Sn to both the Au surface and the Au/SiC interface, with the overall effect of lowering the contact angle of pure Au on SiC by 16° at a concentration of 4.0at%Sn. The segregation of alloying elements at the interface was established independently by Auger electron spectroscopy analysis.The study of pure Au on SiC also provided an opportunity to redetermine the equilibrium crystal shape of pure Au, under conditions where the surface was free of any contaminants. This produced improved measurements of the surface energy anisotropy of pure Au.Simple monolayer and multilayer segregation models were applied to the Au-alloy/SiC interfaces. It was shown that with slight modification, models developed for surface segregation can also be usefully applied to relatively complex metal/ceramic interfaces.A first order wetting transition was observed for the Pb-Ni/graphite system in the solid state. The transition manifested itself by a sudden drop in contact angle for Pb-Ni alloys on graphite with increasing Ni concentration, somewhere between 0.15--0.20wt% Ni. Several possible explanations are provided to account for the observed transition. |
