Research Areas

Current Research Interests

Understanding high temperature ceramic-metal reactions is important to ceramic joining, to metallizing and brazing, to ceramic-metal composites and for making reliable electrical contacts to electronic ceramics. Fabrication of complex ceramic components can be difficult and expensive because of the increased likelihood of catastrophic defects with increasing part size, and the high cost of machining to produce the final shape. Availability of reliable joining techniques would allow components to be assembled from simpler parts that have been pretested for flaws, thus increasing reliability and lowering overall costs. Likewise, most ceramics used in structural applications must be connected to metals at some point, so practical ceramic-metal joining techniques also are needed.

Development of ceramic joining methods, as well as techniques for electroding and fabricating multi-layer electronic ceramics all require a fundamental understanding of ceramic interfaces and reactions. Typically we wish to know the relation between interfacial reactions and adhesion. Thus, we study the composition and structure of the interface, the nature of any reaction products that are produced, the mechanical properties of the interface and the influence of process variables such as time, temperature, atmosphere. Experimental techniques include scanning and transmission electron microscopy, electron microprobe, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. We also study the thermodynamics of wetting by measuring the contact angles of liquid reactant phases as a function of heating time, temperature and atmosphere.

For some applications we develop novel glass-ceramics that make strong seals to metals that cannot be joined with conventional ceramics. For example, we synthesized glass-ceramics with thermal expansion coefficients of 200 x 10-7 ^o/C that can be joined to 304 stainless steel. We determined the crystallization mechanism of the glass-ceramic, which gives us the knowledge for better process control. In other studies we have made experimental braze alloys that contain reactive elements such as Zr or Nb and then investigated their reaction mechanisms with a variety of oxide and nitride ceramics. We also have devoted considerable effort to understanding mechanisms for metal bonding to nitrides such as Si₃N₄ and AlN.

The mechanical properties of promising systems are measured in collaborative studies with other Sandia researchers. The mechanical and thermal behavior of experimental systems that are selected for use in developmental components are modeled for different device configurations using sophisticated finite-element techniques.