High-resolution characterization of the fretting corrosion of Alloy 690 in the simulated secondary water of pressurized water reactor

Abstract

The worn scars on Alloy 690 after the fretting corrosion testing in simulated pressurized water reactor (PWR) secondary water have been comprehensively analyzed by scanning transmission electron microscopy (STEM) and transmission Kikuchi diffraction (TKD). The high-quality characterization results experimentally show that the fretting wear accelerates the corrosion of Alloy 690 in two approaches. The first one is to break the integrity of the oxide scale by introducing cavities at the oxide grain boundaries. The second one is to alter the microstructure of the underneath matrix, forming a nano-grained matrix layer. The increased grain boundary density in this layer can accelerate the consumption of Cr in the near-surface matrix. The loss of oxide scale integrity and the accelerated Cr consumption are believed to contribute to the deteriorated corrosion resistance of Alloy 690 during the fretting corrosion process.