Evaluation of oxidation behavior of two potential coating alloys T14 and T19 for superheated steam and supercritical water power plant application

Abstract

In this study, the oxidation behavior of alloy CoCrMoSi (T14) and alloy CoCrNiMoSi (T19) was evaluated in superheated steam (SHS, 0.1 MPa) and supercritical water (SCW, 26 MPa), at temperature of 625 °C for 500 h. After exposure to both conditions, the as-exposed surfaces and cross sections were evaluated using Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS). The identification of phases was carried out based on combined EDS and X-Ray Diffraction (XRD) analyses. The results showed that both T14 and T19 formed very complex oxides on the surface after exposure. And they experienced weight gain under SHS condition, and weight loss under SCW condition. However, T19 had much smaller weight changes after both tests. Weight loss was due to the oxide scale spallation and possibly volatilization of MoO3 and Cr2O3, in addition to preferential attack and subsequent degradation of Laves phase in both alloys. Due to Ni addition acting as FCC stabilizer, the possible SiO2 formation as a subscale, and smaller Laves phase, alloy T19 was found to be superior to T14 as potential coating material for steam power generation system at temperatures up to 625 °C, under SHS and SCW conditions.