MEASUREMENT OF THE INTERFACIAL MECHANICAL-PROPERTIES OF A THIN CERAMIC COATING ON DUCTILE SUBSTRATES

The interfacial mechanical properties of two systems, SiOx/Au and SiOx /Cu, were measured by a modified periodic cracking method. The state o f stress in the SiOx-coated metal wires with cylindrical symmetry were analyzed using a classic model of continuum elasticity. Experimentall y, the measurement was carried out by a uniaxial tensile test. Specime ns for the tensile test were prepared by depositing a thin layer of Si Ox on the metal wires by a plasma enhanced chemical vapor deposition ( PECVD) technique. After tensile loading, it was found that the fractur e morphology of the SiOx coating depended upon the bonding strength of the interfaces. For a weak interface such as SiOx/Au with a measured bonding strength of 0.230 MPa, debonding at the interface prevailed an d most of the cracks in the SiOx coating were inclined to the tensile axis by 45 degrees. In contrast, cracks in the coating of a strong int erface such as SiOx/Cu showed periodicity and were perpendicular to th e tensile axis. The bonding strength of the interface was estimated to be, at least, 0.885 MPa, while the ultimate shear strength was measur ed to be 49.5 MPa. (C) 1997 Elsevier Science S.A.