Interface fracture toughness evaluation for MA956 oxide film

Microelectronics, optoelectronics, and thermal barrier coating technologies are dependent on a thin or thick film of one material deposited onto a substrate of a different material. Fabrication of such a structure inevitably gives rise to stress in the film due to lattice mismatch, differing coefficients of thermal expansion, chemical reactions, and/or other physical effects. Therefore, the weakest link in this composite system often resides at the interface between the film and substrate. In order to assume the long-term reliability of the interface, the fracture behavior of the material interfaces must be known. A new approach of using a spiral notch torsion fracture toughness test system for evaluating interface fracture toughness is described. This innovative technology was demonstrated for oxide scales formed on high-temperature alloys of MA956. The estimated energy release rate (in terms of J-integral) at the interface of the alumina scale and MA956 substrate is 3.7 N-m/m², and the estimated equivalent Mode I fracture toughness is 1.1 MPa √m.