EFFECTS OF NEAR INTERFACIAL MICROSTRUCTURE ON TOUGHNESS AND SUBSCRITICAL CRACK GROWTH IN CERAMIC/METAL SYSTEMS

Methods to toughen ceramicmetal interfaces that employ prescribed arrays of non-coplanar microcrack-like-voids and inclined interface steps are assessed. These features, developed in glasscopper samples made using photolithographic, metal deposition and diffusion bonding processes, promote crack-tip shielding principally from crack bridging by ligaments generated by plastic void growth within the copper. The ensuing plastic stretching, and sometimes tearing, of the Cu film ligaments yield the major energy dissipation. Crack deflection can also provide a smaller toughening contribution. Resistance-curve (R-curve) behavior obtains from the bridging, with fracture energies rising to an asymptote that varies from 9 to 160 Jm/sup 2/, compared with inherent toughness values of /approximately/2 Jm/sup 2/ for the specific glassCu interfaces used. The arrays retard subcritical crack-growth rates, which are higher in moist atmospheres, by orders of magnitude compared to rates for plain interfaces. The behavior is contrasted with that gained by using better interface chemistry to increase the inherent fracture toughness of glassCu bonds. 38 refs., 10 figs.