Investigation of Oxide Formation During Short-Term Oxidation of Model NiAl Alloys

摘要

Two β-NiAl model materials, one stoichiometric (50 at% Al) and one with low Al (39 at%) content were oxidized at 1050℃ for 1 h. FIB cross sections were analyzed by SEM and TEM. Phase identification was also performed by XRD. Strong influence of metal grain orientation on the diffusion and oxidation was observed. The morphology of the scale surface was similar in both materials and consisted of regions with needle-like oxide and small smoother pits. TEM and SEM analyses showed that the pits correspond to the contact areas between the oxide and the underlying alloy. Moreover TEM investigations revealed that these contact areas consist of α-Al_2O_3, while the detached oxide scale contains mainly transient-Al_2O_3 phases. The measured oxide thickness was similar in both contact and detached areas. The observed voids at the metal side were much more faceted in the Al-poor material. Possible mechanisms responsible for these observations are discussed.