The fracture resistance of metal-ceramic interfaces

The effects of interface structure and microstructure on the fracture energy, Γ_i, of metal-ceramic interfaces are reviewed. Some systems exhibit a ductile fracture mechanism and others fail by brittle mechanisms. In the absence of either interphases or reaction products, Γ_i is dominated by plastic dissipation (for both fracture mechanisms), leading to important effects of metal thickness, h, and yield strength, σ₀. Additionally, Γ_i is larger when fracture occurs by ductile void growth (for the same h and σ₀). A fundamental understanding now exists for the ductile fracture mechanism. However, some basic issues remain to be understood when fracture occurs by brittle bond rupture, particularly with regard to the role of the work of adhesion, W_ad. Interphases and reaction products have been shown to have an important effect on Γ_i. A general trend found by experiment is that Γ_i scales with the fracture energy of the interphase itself, wherein Γ_i tends to increase for the interphase sequence: amorphous oxides > crystalline oxides > intermetallics. However, there also appear to be important effects of the residual stresses in the interface (which influence the fracture mechanism and the layer thickness.