Early oxidation behavior of Ni-based Alloy 690 in simulated pressurized water reactor environment with varying surface conditions

Abstract

The composition and morphology of a passive film formed on Ni-based alloy 690 with different surface conditions exposed to high-temperature, high-pressure aerated and deaerated deionized water vapor with different time were characterized by using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) in this study. Shot peened, mechanical polishing and electro polishing were used to obtain different surface conditions. The film thickness remained constant after different exposure treatments, while the film layered structures were different. On specimens exposed to aerated water for 2 min and deaerated water for 1 h, Ni-rich oxide was identified in the outmost oxide films while Cr-rich oxide existed in inner layers. On specimens exposed to aerated water for 1 h, Cr-rich oxide with participating of Ni- and Fe-oxide was identified in all layers, while on specimens exposed to deaerated water for 2 min, Cr-rich oxide in all layers with participating of Ni-oxide was identified. Large oxide particles with a low density were found. The oxide particles were the biggest and least dense for electro polished specimen, whilest smallest and most dense for shot peened specimen. Oxidation for the same time, the surface was oxidized more pronounced in aerated water than in deaeated water.