Abstract

In this paper, a modified four-point bending test is described, which allows a quantitative determination of the mechanical properties of oxide scales on metallic substrates at temperatures from ambient to 900°C. Scale failure is detected by acoustic emission. By combining deformation data with the physical defect-structure values for the scales, fracture toughnesses have been evaluated for the cases of through-scale cracking and delamination/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°C, respectively. The fracture-toughness values determined in these investigations correspond to the order of magnitude expected from the rare literature data. The test itself can also be applied to a variety of brittle coatings on more-or-less ductile substrates.

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