Corrosion of stellite‐6 in lithiated and borated high‐temperature water

Corrosion of the cobalt‐based alloy Stellite‐6 in lithiated and borated water at 300°C with a hydrogen overpressure has been investigated. These conditions simulate a well‐defined chemistry regime in the primary circuit of an operating pressurized water reactor. The resulting oxide films were characterized using a combination of surface analytical and electron microscopy techniques. X‐ray photoelectron spectroscopy (XPS) was employed to evaluate the chemical composition of the oxide films. The morphology of the corroded surfaces was revealed by transmission and scanning electron microscopy. Scanning Auger microscopy (SAM) was used to map the distribution of elements within the oxide and underlying alloy layers. Composition depth profiles were determined by sequential ion‐sputter etching in conjunction with either XPS or SAM surface analysis. Although some differences exist, the oxide films are qualitatively similar to those described for exposure of Stellite‐6 to lithiated high‐temperature water in the absence of boron. In both cases, preferential dissolution of cobalt leads to strongly enhanced chromium concentrations within the oxide films.