Characterization of brazed joints of C-C composite to Cu-clad-Molybdenum
Abstract Carbon–carbon composites with either CVI matrix or resin-derived matrix were joined to copper-clad-molybdenum using two active braze alloys, Cusil-ABA (1.75% Ti) and Ticusil (4.5% Ti). The brazed joints revealed good interfacial bonding, preferential precipitation of Ti at the composite/braze interface, and a tendency toward de-lamination in resin-derived C C composite due to its low inter-laminar shear strength. Extensive braze penetration of the inter-fiber channels in the CVI C C composites was observed. The relatively low brazing temperatures ( C/Cu-clad-Mo joints with relatively low thermal resistance may be promising for thermal management applications.
Integration of Cu-clad-Mo to high conductivity graphite foams
Abstract High conductivity graphite foams with low (125 kg m −3 ), medium (260–270 kg m −3 ), and high (650 and 797 kg m −3 ) densities were integrated with copper-clad-molybdenum using an Ag–Cu–Ti braze alloy (63Ag–35.3Cu-1.75Ti) as powder and foil. The effects of foam density (125–650 kg m −3 ), cladding thickness (0.1–0.3 mm), and Cu–Mo–Cu ratio (in %: 13/74/13 and 20/60/20), on microstructure and composition were evaluated using optical microscopy and scanning electron microscopy coupled with energy dispersive spectroscopy. Low-density foams showed more extensive braze penetration than high-density foams. The carbon/braze interfaces were well-bonded and enriched in Ti. The joint microstructure and penetration depth were independent of clad layer thickness and Cu/Mo/Cu ratio. Differences in elemental distribution were noted between joints made using foil and powders; with foil, the Ti and Cu concentrations were inversely related (high Ti concentrations overlapped areas of low Cu concentrations and vice versa) whereas with powders, high Cu and Ti concentrations coincided. Although a thick Cu-cladding increases the coefficient of thermal expansion (CTE) of the Cu-clad-Mo substrate and the CTE mismatch relative to foam, this effect is offset by better stress accommodation with a thick clad layer. Thermal calculations verified that thermal resistance decreased with increasing thickness of clad layer in joints.
On crack path selection and the interface fracture energy in bimaterial systems
The intent of this article is to apply recent solutions for the mechanics of cracks at and near bimaterial interfaces to rationalize crack trajectories observed by experiment and to provide a basis for interpreting measurements of the interface fracture energy, Γi. It is demonstrated that the choice of test specimen governs the tendency of cracks to either remain at interfaces or deviate away, based on considerations of the phase angle of loading, ψ. It is further revealed that the measured interface fracture energy may be strongly influenced by the crack trajectory, as governed by ψ, through crack shielding and plasticity effects. Consequently, interfaces do not typically have unique fracture energies, but instead Γi depends on ψ which, in turn, is influenced by the test method.