Effects of NiB, PbO, and TiO2 on SCC of sensitized inconel alloy 600 in RT-tetrathionate solution

Abstract

The effects of NiB, PbO, and TiO2 additives (impurities) on stress corrosion cracking (SCC) of sensitized alloy 600 were investigated in 0.1 M Na2S4O6 solution using potentiodynamic polarization experiment, electrochemical impedance spectroscopy, and electrochemical noise measurement. From the analysis of the electrochemical noises based upon the shot-noise theory, the induction time for stress corrosion (SC) crack initiation was quantitatively determined. Furthermore, SC crack propagation was satisfactorily distinguished from uniform corrosion in terms of the frequency of events in an engineering sense by employing the stochastic theory based upon the Weibull distribution function. The results revealed that electrochemical noises contain valuable information on SC crack propagation as well as SC crack initiation; SC crack propagation rate increased with increasing conditional event generation rate. The effects of NiB, PbO, and TiO2 additives have been discussed in terms of induction time for SC crack initiation and the conditional event generation rate. The susceptibility to SCC decreased in the following order: PbO > absence of additives approximate to NiB > TiO2. (C) 2007 The Electrochemical Society.