OXIDE INVESTIGATION FORMED ON ALLOY 600 IN LEADED AQUEOUS SOLUTIONS

摘要

The properties of the surface passive films formed in a near neutral aqueous solution at 315 °C were analyzed as a function of PbO as an SCC accelerator and NiB as an SCC inhibitor by using the Auger electron spectroscopy, the x-ray photoelectron spectroscopy and the transmission electron microscopy, equipped with the energy dispersive x-ray spectroscopy. An electrochemical impedance spectroscopy technique was also used to characterize the electrochemical behavior of the surface films. Stress corrosion cracking behavior of Alloy 600 was studied by using the slow strain rate tensile tests in a caustic aqueous solution at 315qC. Lead was incorporated into the surface oxide in a metallic state and as an oxide state of PbO, which causes a degradation of the passivity leading to a PbSCC susceptibility. The NiB inhibitor reduced the lead incorporation level into the oxide layer, thus substantially improving the oxide passivity, and decreasing its susceptibility to a PbSCC.