Bonding, Structure and Properties of Metal/Ceramic Interfaces
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BONDING, STRUCTURE AND PROPERTIES OF METAL/CERAMIC INTERFACES
JAMES M. HOWE Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
ABSTRACT This paper reviews the effects of chemical bonding, reaction, interfacial structure, fabrication, specimen geometry and testing conditions on the strength and fracture behavior of metal/ceramic interfaces. It is shown that a number of important properties of metal/ceramic interfaces such as the wetting behavior and work of adhesion can be qualitatively predicted from simple bonding models based on the elements in the metal and ceramic. In addition, the interfacial structure can often be predicted from principles of equilibrium thermodynamics and minimization of interfacial energy for relatively thick metal/ceramic layers. More quantitative description of interfacial structure employing atomistic calculations has been performed for simple interfaces and this area is progressing. The fracture behavior of metal/ceramic interfaces is a complicated process which depends on many factors such as the specimen geometry and loading conditions, strength of the interfacial bond, thermal, elastic and fracture properties of the metal and ceramic, thickness of the metal layer and testing environment. Advances in this area include the development of favorable specimen geometries for measuring interface properties and an understanding of the relationship among the phase angle of loading, crack trajectory and interface fracture energy for these geometries. Conversely, little is known about the stress corrosion and fatigue behavior of metal/ceramic interfaces although data on these time dependent failure modes are beginning to appear in the literature. Much progress has been made but considerably more work is needed to understand the properties of metal/ceramic interfaces. INTRODUCTION Understanding the relationship among the processing, structure and properties of metal/ceramic interfaces is becoming increasingly important as performance requirements demand a combination of these materials in applications ranging from electronic packaging to high-temperature aircraft structures [1]. The purpose of this review is to assess the current understanding of the relationship among the processing, structure and properties of metal/ceramic interfaces, emphasizing work on planar metal/ceramic interfaces produced by diffusion bonding. This particular area was chosen in order to focus the review and because considerable work has been performed on this type of interface. However, it is importent to note that many of the topics that are discussed in this review apply to other types of metal/ceramic interfaces. Table I lists some of the main factors that are involved in fabricating, testing and understanding the behavior of metal/ceramic interfaces. There are sixteen subheadings in this list, and it is not all inclusive, which serves to illustrate the complexity of the problem. The topics in Table I were divided into three categories for convenience and this review
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