A NOVEL JOINING METHOD FOR GRAPHITE AND CARBON-CARBON COMPOSITES

IN THE PHASE I PROJECT, THE FEASIBILITY OF DEVELOPING A SUPERIOR JOINING TECHNOLOGY FOR GRAPHITE AND CARBON-CARBON (C-C) COMPOSITES IS BEING INVESTIGATED. A NOVEL TECHNOLOGY,LOW TEMPERATURE ARC VAPOR DEPOSITION (LTAVD), IS BEING USED TO EFFECT THE JOINING OF GRAPHITE AND CARBON-CARBON COMPOSITES TO SIMILAR AND DISSIMILAR MATERIALS. TO OBTAIN STRONG JOINTS THAT ARE RESISTANT TO THERMAL CYCLING, METALLIC NIOBIUM, ZIRCONIUM, AND TANTALUM WERE CHOSEN AS CANDIDATE INTERLAYER MATERIALS BASED ON THEIR THERMOPHYSICALPROPERTIES. THESE PROPERTIES INCLUDE COEFFICIENT OF THERMALEXPANSION (CTE), ELASTIC MODULUS, STRENGTH AND MELTING POINT, AND THERMODYNAMIC COMPATIBILITY WITH CARBON OR GRAPHITE, ALONG WITH LATTICE STRAIN/MISMATCH BETWEEN INTERFACIAL REACTION PRODUCTS (CARBIDES) AND GRAPHITE OR THEMETALS THEMSELVES. THE METALLIC INTERLAYERS ARE INTENDED TOMITIGATE THE STRESSES ARISING FROM CTE MISMATCHES, ESPECIALLY DURING JOINING TO DISSIMILAR MATERIALS. FOLLOWING COATING WITH AN INTERLAYER METAL BY THE LTAVD PROCESS, GRAPHITE OR C-C COMPOSITE WORK PIECES ARE JOINED TOTHEMSELVES OR TO DISSIMILAR MATERIALS (ALSO COATED) USING EITHER SOLID STATE BONDING OR BRAZING. CHARACTERIZATION OF THE INTERFACIAL MICROSTRUCTURE AND RESIDUAL STRESSES WILL ALLOW OPTIMIZATION OF PROCESS PARAMETERS TO ENHANCE THE RESISTANCE OF SUCH JOINTS TO THERMAL CYCLING. MECHANICAL CHARACTRIZATION IN AS-FABRICATED AND THERMALLY CYCLED STATESALLOWS DEMONSTRATION OF THE CONCEPT.