Influence of Cu 2 O and CuAlO 2 Interphases on Crack Propagation at Cu/α‐Al 2 O 3 Interfaces

In‐situ crack‐propagation experiments, in conjunction with thermochemical experiments, have been used to examine the role of discontinuous interphases on the fracture behavior of solid‐state diffusion‐bonded Cu/α‐Al 2 O 3 couples. Clean, interphase‐free interfaces exhibit crack extension by brittle decohesion at the crack tip at an initiation fracture energy of 125 J/m 2 . Crack propagation is characterized by an increase in the fracture energy with increases in the crack length ( R ‐curve behavior). When interfacial chemical reaction products are present, the crack growth is altered, depending on the characteristics of the interphase. The presence of Cu 2 O needles results in preferential debonding along the Cu 2 O/Al 2 O 3 interface. On the other hand, finer CuAlo 2 needles visibly impede crack propagation and result in a higher interface initiation fracture energy (}190 J/m 2 ) than that of the interphase‐free interface. The effects of the Cu 2 O and CuAlo 2 phases on the fracture energy are discussed.