Comparison of oxidation-growth stresses in NiO film measured by deflection and calculated using creep analysis or finite-element modeling

An attempt was made to determine the strain and the stresses generated by the growth of an oxide film using several approaches: an experimental one by means of deflection tests and modeling using either a recently developed creep analysis or a finite-element simulation. A new deflection apparatus was developed and NiO growth studied during the early stages of oxidation of a Ni80Cr20 alloy at 900degreesC, since many microstructural, kinetics and mechanical data are available for this system. The comparison of experiments and modeling indicate that the oxide layers are mostly subjected to compressive stresses when NiO is growing and the stress level and evolution clearly show that viscoplastic strain occurs in both the substrate and the oxide during oxidation. The comparison between the two modeling approaches with experiment leads to good agreement and suggests that the compressive-growth stresses derive from the lateral expansion of the fraction of new oxide that is formed within the oxide layer.