Fundamental Aspects of Meta1-to-Ceramic Brazing.

Research has continued to develop fundamental understanding of wetting and spreading of reactive metals on alumina and to model the metal to ceramic bonding process. A study was completed on the modeling of spreading kinetics of reactive brazing alloys on ceramic substrates. Based on nucleation and growth of islands of reaction product at the ceramic- metal interface, in particular, the Avrami type surface nucleation and growth kinetics, Dr. Alan Meyer developed a non-empirical theoretical spreading model for reactive metals. Dr. Paulo Camargo focused on the effect of minor contamination in the metal to ceramic bonding system. Residual oxygen in the system plays a fundamental role in the wetting and bonding process. Too low an oxygen content will result in non-spreading of the liquid filler metal. Too high an oxygen content will result in excess growth of the interfacial product layer which jeopardizes the mechanical integrity of the joint. These two research programs are complementary since they both expanded the understanding and modeling of the bonding mechanism. The concept of joining ceramic to metal using ductile, multilayer reactive metal coatings is also being developed. Mr. Don Bucholz, a Ph.D. student, is carrying out a program to explore the technological barriers of using multilayer coatings of ductile and reactive metals in brazing. Both diffusion bonding solid state and diffusion brazing transient liquid phase bonding are being examined. Satisfactory bonds have been obtained using the diffusion bonding process and detailed chemical and structural analysis of the bond region are in progress.