ABSTRACT
Mechanical properties of interfaces between dissimilar or similar materials (e.g. grain boundaries) have become the focal point of research in several fields, including composite materials (metal, ceramic and intermetallic matrix composites), tribology and in the solid state device area. This is not surprising because the interfaces between dissimilar materials are sites for mechanical stress concentrations and often become the nucleus of the overall failure process. Interfaces of interest in composite materials exist between fibers and their diffusion barrier coatings or between the matrix and
continuous, discontinuous or particulate reinforcements. In the field of tribology, interfaces exist between various types of functional (magnetic, conducting, optical and electrical), protective (thermal barrier, corrosion, wear resistant) or decorative coatings and their underlying substrates, and finally, metal/ceramic interfaces are of interest in multilayer devices and in magnetic discs and head technology. In all of the above applications, mechanical properties of the interface (tensile and shear strength, toughness, etc.) often control the overall functionality of the coated part. Therefore, improving the mechanical properties of the interface for prolonged life of the coated part is of fundamental interest. However, in ceramic and metal matrix composites, where the fiber/matrix interface is used to deflect impinging cracks from the matrix [1-5], it is often desirable to impair the strength of the interface. To accomplish either of the above goals, the first step is to measure reliably the fundamental mechanical properties of the interface (free from artifacts generated by the experimental setup). Among the various mechanical interface properties, the tensile strength tends to dominate the behavior and thereby determines the mode of interface failure and the resulting toughness or ductility, according to Varias et al. [6]. Accordingly, the measurement and control of interface strength through control of interface chemistry and structure is important.
