Advanced Multilayer Braze foil for Si3N4 Joining

34 Advanced Multilayer Braze Foil for Si3N4 Joining--Eltron Research, Inc., 5660 Airport Boulevard, Boulder, CO 80301-2340; (303) 440-8008 Dr. William J. Donahue, Principal Investigator Ms. Eileen E. Sammells, Business Official DOE Grant No. DE-FG03-97ER82364 Amount: $74,997 Silicon nitride is an important lightweight structural ceramic due to its hardness, wear resistance, high-temperature oxidation resistance, and strength. However, the exploitation of its superior mechanical and chemical properties depends upon reliable joints that can withstand high-temperature corrosive environments. Presently, the use of advanced ceramics in critical applications, such as energy-efficient automotive engines, is limited by a lack of an economical technique for effectively joining these materials. This project will study layered nickel-chromium-based foils for use in silicon nitride brazing applications. Nickel-chromium foils have several attractive characteristics, including good silicon nitride surface wetting, high-temperature strength, and oxidation resistance. Appropriate silicon incorporation into the nickel-chromium alloy will moderate its reactivity while still allowing for strong joining interactions to take place. A surface treatment will prevent the formation of brittle and porous microstructures while ensuring uniform ceramic braze interfaces with good wetting characteristics. The sophisticated chemistry found in this joining issue will be addressed in a prefabricated multilayer braze foil product. The foil will be easily handled and applied to the joint interface. Successful completion of this program will lead to the development of a strong and reliable technique to join silicon nitride to silicon nitride and silicon nitride to metal. This Phase I project will address the fabrication of multilayer foils to determine the relationships between foil layer thicknesses, brazing times, reaction product distributions, microstructure within the joint region, and joint strengths. Commercial Applications and Other Benefits as described by the awardee: This braze material is expected to be useful under oxidizing conditions at high temperature. The anticipated simplicity of brazing using this foil product will greatly reduce the cost of joining components containing silicon nitride. Automotive internal combustion engines, aerospace turbines and leading edges, industrial heat exchangers, and recreational applications all stand to benefit from a reduction in the cost of advanced ceramics.