10000 hours thermal aging behavior and supercritical CO2 corrosion performance of candidate cladding AFA alloys for novel gas - cooled reactors

Abstract

This study investigated the thermal aging (10,000 h at 650 °C) and corrosion performance (3000 h at 650 °C/15 MPa under sCO2) of two AFA alloys (AFA-20 and AFA-14), featuring 20 wt.% and 14 wt.% Cr. The increase in Cr content elevated the thermodynamically stable σ content and promoted its precipitation. The σ precipitation within the matrix significantly decelerated the coarsening kinetics of the Laves phase in AFA-20 over 5000 h aging. The intergranular σ phase facilitated crack formation, potentially increasing elongation, while the intragranular σ phase mitigated stress concentration at grain boundaries, making AFAs more brittle. AFA-20 developed a continuous protective Al2O3 oxide layer, whereas AFA-14, lacking this shielding, experienced increased internal oxidation. M23C6 carbides formed in the internal reaction zone, yet notably enriched in Mo rather than Cr.