Characterization of Alloy 600 joints exposed to a high-temperature supercritical-carbon dioxide environment

Abstract

Two types of Alloy 600 joints, such as diffusion-bonded joint and Alloy 182 fusion-weld, were exposed to supercritical-CO2 environment at 550 and 650 degrees C (20 MPa) for 1000 h. The diffusion-bond region showed similar oxidation characteristics as parent Alloy 600, but the migration of diffusion bond line below oxide layer was observed due to the Cr-depletion induced recrystallization. For Alloy 182 fusion-weld, outer Mn-rich oxides (Mn3O4 and MnCr2O4) and a small amount of inner SiO2 mixed with chromia were formed due to high Mn and Si contents. The presence of SiO2 in chromia suppressed carburization at the oxide/matrix interface, which resulted in the formation of an amorphous C layer between the outer Mn-rich oxide and inner Cr-rich oxide. For Alloy 182 fusion-weld, tensile property changes after exposure to supercritical-CO2 environment were negligible.