Investigation of the mechanical properties of oxide scales on nickel and TiAl

In this paper, a modified four-point bending test is described, which allow s a quantitative determination of the mechanical properties of oxide scales on metallic substrates at temperatures from ambient to 900 degreesC. Scale failure is detected by acoustic emission. By combining deformation data,wi th the physical defect-structure values for the scales, fracture toughnesse s have been evaluated for the cases of through-scale cracking and delaminat ion/spalling. The test was applied to NiO scales on pure nickel and to the oxide scales on an intermetallic TiAl alloy at room temperature and 900 deg reesC, respectively. The fracture-toughness values determined in these inve stigations correspond to the order of magnitude expected from the rare lite rature data. The test itself can also be applied to a variety of brittle co atings on more-or-less ductile substrates.