ABSTRACT
Interfaces between metals and ceramic materials have been the subject of extensive research in recent years because they control, to a great extent, the properties of metalceramic composites, protective coatings, thin metal/ceramic films in electronic devices, etc. For instance, low hardness and poor wear resistance are the principal limitations on the potential applications of aluminum alloys. Hardfacing on aluminum alloys, for example, by electrodeposition and anodizing, may significantly improve hardness and wear resistance. However, there are still major drawbacks in these conventional methods. The bonding between these coatings and aluminum alloys is usually weak and may cause failure during application. The amorphous anodizing layer is brittle and with a relatively low hardness (HV0.1 250-500), neither of which is useful in resisting abrasive wear. For these reasons, it would be of great practical importance to have a basic fundamental understanding of the bonding between dissimilar materials such as metals and protective ceramic layers. Their obvious technological importance notwithstanding, our basic understanding of interfaces, even relatively simple interfaces as grain-boundaries, is still rudimentary, particularly in relation to materials properties. The importance of interfaces is primarily determined by their inherent inhomogeneity, that is, the fact that physical and chemical properties may dramatically change at or near the interface itself. An important property of a heterophase interface is its free energy per unit area, and the closely related work of adhesion. Thermodynamic and mechanical properties of the interface have been found to depend on these parameters. Experimental determination of the interface energy is an important step toward understanding heterophase interfaces. In principle, there are several ways in which information on the interface energy can be extracted from experiments, for example, either by measurement of wetting angles or by study of interface fracture behavior by four-point bending tests.
