Interfacial fracture toughness of alumina/niobium systems

In this paper, the interfacial fracture toughness of an aluminum/niobium composite is measured as a function of phase angle. The interface was formed by solid-state bonding bulk Coor's AD-999 fine-grain alumina with a commercial purity niobium at 1600 degrees C for 0.5 hr under a pressure of 10.5 MPa. The alumina/niobium system has a number of features which makes it ideal for an investigation of interfacial fracture toughness. From HREM data we estimate that the width of the interface is no more than 10 atomic planes. Furthermore the thermal expansion coefficients of the two materials differ by less than 5% so residual stresses due to the bonding process are small. Using symmetric and asymmetric four point bend specimens the authors have measured the fracture toughness of homogeneous alumina and that of the alumina/niobium bimaterial in combinations of in-plan shear and tension