THE EFFECT OF REACTION-PRODUCTS ON THE FRACTURE-RESISTANCE OF A METAL CERAMIC INTERFACE

Solid state diffusion bonds between a Ta(Ti) alloy and Al2O3 have been used to study the effect of reaction products on the fracture resistance of a metal/ceramic interface. The reaction layer consists of brittle intermetallics, consistent with the Ti-Ta-Al ternary phase diagram. The interface fracture energy GAMMA(i) was found to be dominated by periodic tunnel cracking of the reaction products, and was relatively insensitive to layer thickness, because of the self-similar nature of the periodic cracking. The contribution to GAMMA(i) from plastic dissipation within the alloy was minimal because the intervening reaction layer inhibited yielding. A sequence of cracking observations was used to bound the unknown values of the fracture energy of the reaction products, the residual stress within the layer and the fracture energy of the reaction product/sapphire interface.