BONDING, STRUCTURE, AND PROPERTIES OF METAL-CERAMIC INTERFACES .1. CHEMICAL BONDING, CHEMICAL-REACTION, AND INTERFACIAL STRUCTURE

Chemical bonding, chemical reaction, and the interfacial structure of metal/ceramic interfaces are reviewed with particular emphasis placed on Al and Ti alloys bonded to Al2O3 and SiC ceramics. It is shown that a number of important properties of metal/ceramic interfaces such as the wetting behaviour and work of adhesion can be predicted qualitatively from simple bonding models based on the elements in the metal and ceramic. A variety of chemical reactions can occur at metal/ceramic interfaces and equilibrium thermodynamics is useful in predicting possible reactions. The kinetics of reaction at metal/ceramic interfaces generally follow a parabolic rate law and reaction layers thicker than about 1 mum usually have a deleterious effect on interface strength. Interfacial energy minimisation dominates the atomic structure of metal/ceramic interfaces with the result that close packed planes and directions in the metal, ceramic, and reaction product when present, are often parallel across the interface. Important processing variables such as the temperature, time, and pressure and alloying additions to the metal can have a large effect on the properties of metal/ceramic interfaces and these are discussed.