Thermally grown Al2O3 on a H2-annealed Fe3Al alloy: Stress evolution and film adhesion

Stress evolution in Al2O3 films grown on a Fe3Al-based alloy, with or without a prior H2-anneal heat treatment, was followed in situ with a synchrotron X-ray source at 1000 and 1100 °C and during cooling. These results are complimented by studies of oxidation kinetics, the scale/alloy interfacial chemistry, and the oxide, alloy and interface microstructures. The H2-anneal reduced the sample sulfur impurity to less than 1 ppm, significantly improved scale adhesion, maintained a planar scale/alloy interface, but did not demonstrably affect the oxidation rate or the growth stress development. On the untreated alloy, interface wrinkling was a major stress relief mechanism, but for the H2-annealed samples it was oxide creep with contribution from alloy grain boundary sliding. The interface strength and the extent of oxide spallation were closely related to the amount of sulfur segregated at the interface.