Internal Oxidation Depth Penetration in Ni-Based Alloys at High Temperatures

The aim of the paper was to investigate internal oxidation process under steam oxidation conditions and steam oxidation behavior of two solid-solution strengthened alloys, UNS N06230 and UNS N06617, and two gamma-prime (γ′) strengthened alloys, UNS N07263 and UNS N07208. The samples have been tested under 1 bar pressure in 100% water–steam–water system in temperature range 700°C to 800°C for 3,000 hours. The study has showed that Ni-based solid-solution strengthened alloys UNS N06230 and UNS N06617 developed mainly Cr₂O₃ and MnCr₂O₄ phases on their surfaces, whereas gamma-prime (γ′) strengthened alloys UNS N07263 and UNS N07208 presented the formation of Cr₂O₃, and TiO₂ and MnTiO₃ phases, respectively, indicating slightly higher corrosion degradation rate. The oxidized Ni-based alloys showed the formation of an internal oxidation process, with different depths. The observed difference in internal oxidation depth depends mainly on the concentration of Al and Ti in the metal matrix. In the alloys, where Ti and Al concentrations were high, a higher depth of internal oxidation was observed, suggesting a straight correlation between the Ti and Al content and internal oxidation process.