Corrosion of titanium nitride deposits on AISI 630 stainless steel used in radioactive water with and without chloride at pH 11

The electrochemical behavior of samples was studied using potentiodynamic techniques at low scan rates, cyclic voltammetry at high scan rates and electrochemical impedance spectroscopy. The surfaces were examined by scanning electron microscopy and the Scanning Reference Electrode Technique. The results from these different methods are discussed. They show that the AISI 630 stainless steel is partially protected by the TiN deposit, in presence or absence of chloride. Without chloride, the Warburg straight line indicates that there is ionic diffusion in steel passive oxide and TiN deposit; the ohmic resistance associated with the pores of TiN is determined and indicates localized corrosion by these. The use of high scan rates shows the transient kinetics of the oxide layer during the pitting incubation period. With chloride, the pitting currents are lower with TiN; however, the SEM photographs show that the deposit is detached leading to possibility of crevice formation under this. The SRET examinations show the formation of anodic and cathodic micro-cells due to localized pitting corrosion in presence of TiN. (author)