The strength of ceramics bonded with metals

Joining of alumina via copper/niobium/copper interlayers

“…Testing was done with a displacement rate of 50 µm/min. Strengths were calculated from the load at failure using standard relationships derived for monolithic elastic materials, i.e., no correction for stress concentrations arising from modulus misfit [78,79] was attempted. Prior work had determined that under identical testing conditions, the average four-point bend strength of (unbonded and unannealed) alumina beams prepared from the same source material using similar cutting and polishing procedures is ≈280 MPa [18].…”

Transient-liquid-phase and liquid-film-assisted joining of ceramics

“…The temperatures required for joining are often a high fraction of the melting temperature of the least refractory component due to the need to activate solid-state diffusion [1- 9,11,[13][14][15]. Component deformation and microstructural changes such as grain growth or precipitate coarsening within the components can degrade properties.…”

Effects of processing conditions and ambient environment on the microstructure and fracture strength of copper/niobium/copper interlayer joints for alumina

“…The development of residual stresses during cooling can result from the metal and ceramic having different thermal expansion coefficients (termed thermal mismatch or misfit). Additionally, metals and ceramics will generally have different elastic moduli (modulus misfit) causing a complex stress state to develop when a joined assembly is loaded [6,50] . Stresses resulting from thermal misfit and modulus misfit are concentrated in regions near the interface and are further concentrated near beam edges, a frequent initiation site for failure [6,51] .…”

“…Such joints often exhibit increased fracture toughness in comparison to the bulk ceramic, since the metal layer will exhibit some plasticity [5][6][7][8] . Structures which undergo some plastic deformation instead of catastrophic failure would be preferred, and joining smaller ceramic parts is beneficial in comparison to fabricating larger parts for this reason also.…”