Unraveling the Scc Behavior and Enhanced Creep Strength Mechanism of Afa Alloy in Supercritical Co2

Abstract

The oxide scale of 20Cr25Ni2.5Al AFA alloy formed under the coupling of stress and supercritical carbon dioxide (sCO2, 650 °C / 15 MPa) consisted of Fe3O4, Cr2O3, intergranular IOZs, but lacked a thin Al2O3 protective layer. The poor oxidation resistance resulted in significant CO2 penetration into the matrix and subsequent formation of Cr2O3, thereby hindering the initiation of Cr - rich σ phase beneath the oxide scale. This competition between internal oxidation and precipitation effectively reduced crack initiation and delayed the connection between SCC and creep cracks, thus significantly prolonging the creep lifetime in sCO2 compared to that in air.

Keywords: Supercritical CO2, AFA alloy, Creep strength, SCC, σ phase, Internal oxidation