Synergistic Oxidative and Tellurium-Induced Corrosion of 15–15Ti Austenitic Stainless Steel Under High Oxygen Potentials

The synergistic oxidative and tellurium-induced (Te-induced) corrosion of the fast-reactor candidate 15–15Ti austenitic stainless steel under high oxygen potentials was investigated in this study. Specimens were exposed at 900 K in both Te-free and Te-containing environments, with the oxygen potentials controlled using Mo/MoO 2 and Ni/NiO redox buffers. Under Te-free conditions, a duplex oxide scale formed on 15–15Ti, comprising an Fe-rich outer oxide layer and a Cr-enriched inner oxide layer. In contrast, in the presence of Te, a markedly thicker multilayer reaction scale developed, consisting of four distinct layers arranged from the surface inward: (i) a Mn–O outer oxide layer; (ii) an Fe–Ni–Te metallic telluride layer; (iii) a Cr-enriched outer telluride reaction layer with Cr 3 Te 4 as the dominant phase; and (iv) an inner Te/Cr-enriched reaction layer, in which a phase consistent with Cr 2 Te 4 O 11 was identified. These findings indicate that, under high oxygen potentials, corrosion of 15–15Ti is governed by the coupled action of Te and oxidation. The introduction of Te more strongly promotes outward diffusion of metal cations (especially Fe) and suppresses the formation of a protective Cr-rich oxide layer, thereby markedly accelerating scale thickening and stabilizing the multilayer architecture.