CRACK DIRECTION EFFECTS ALONG COPPER SAPPHIRE INTERFACES

The Rice-Thomson model is used to predict the directional toughness of a copper/sapphire interface, consisting of a {221} face of a copper crystal bonded to a basal sapphire surface. Specimens of this type are subsequently tested, in the form of a layered beam (having two opposing cracking directions) subject to four-point bending and confirm the theoretical predictions. A general observation is that the ductile or brittle response of a crack on a metal/ceramic interface is strongly dependent on the relative orientation of available slip planes to the existing crack plane and growth direction. This conclusion is consistent with earlier results by Wang and Anderson on symmetric tilt grain boundaries in copper and explains, for example, why brittle cracking occurs in the [114BARBAR] direction along the {221} interface of a tensile-loaded copper bicrystal, but along the opposite [114BAR] direction in bending-loaded copper/sapphire specimens with mixed mode conditions at the crack tips.