Microstructure and mechanical properties of metal/oxide and metal/silicide interfaces

Fracture energies of Al₂O₃/Nb interfaces and MoSi₂/Nb interfaces with and without A1₂O₃coating were measured using sandwich-type chevron-notched specimens. The relations between the mechanical properties, microstructures, types of bonds at the interface and processing routes were explored. The fracture energy of the Al₂O₃/Nb interface was determined to be 9 J/m²and changed to 16 J/m²when Nb was pre-oxidized before the formation of the Al₂O₃/Nb interface. The fracture energy of the MoSi₂/Nb interface could not be determined directly because of the formation of the interfacial compounds. However, the fracture energy at the MoSi₂/Nb interfacial region was found to depend on the interfacial bond strength, roughness of interfaces and microstructure of interfacial compounds. The interfacial fracture energies of A1₂O₃with silicides, MoSi₂, Nb₅Si₃, or (Nb, Mo)Si₂were estimated to be about 16 J/m², while the interfacial fracture energies between two suicides or between Nb and a silicide were larger than 34 J/m². The measured fracture energies of the various interfaces are discussed in terms of the interfacial microstructures and types of bonds at the interfaces.