A Novel Technology for Si3N4-To Superalloy Joints With High Use Temperature Capability

36 A Novel Technology for Si3N4-Superalloy Joints With High Use Temperature Capability--Materials and Electrochemical Research (MER), 7960 South Kolb, Tucson, AZ 85706-9237; (520) 574-1980 Dr. Sumit Guha, Principal Investigator Dr. Raouf Loutfy, Business Official DOE Grant No. DE-FG03-97ER82424 Amount: $75,000 Advanced ceramic heat engines with improved fuel efficiency will require joints between high temperature ceramics silicon nitride, silicon carbide and metal alloys (Inconel 718 or Incoloy 909) to operate in the temperature range of 650-900oC. The joining problem is complicated due to the residual stresses generated within the ceramic; frequently, the ceramic will crack as a result of these stresses. The state-of-the-art approach used to join such ceramics to metals incorporates soft metal interlayers (e.g. copper or nickel). Unfortunately the use of these joints is severely limited due to the low strength of the soft interlayer at operating temperatures. This project will develop a novel joining approach whereby the residual stresses will be lowered to the point that direct bonding occurs between the ceramic and the metal. This will be followed by bonding with metal interlayers that yield at low temperatures but retain their strength at elevated temperatures. Phase I will use a unique stress modeling approach to design the joints. The effect of using a nickel-aluminum interlayer will be investigated. Finally, a brazing technique will be developed to produce ceramic to metal joints, and these will be characterized. Commercial Applications and Other Benefits as described by the awardee: The primary benefit of this joining technology would be in heat engines with improved efficiencies which would reduce the dependence on foreign oil. Such engines would find applications in diesel engines for the trucking industry. Other applications would be within fusion reactors; a successful fusion reactor would provide this Nation with a virtually endless source of energy.