Inconel 600 is applied as the steam generation tubing material in many PWR systems. Pitting attack has been observed in Inconel 600 tubes in the secondary side of some PWR steam generators. TiN films were deposited onto Inconel 600 by plasma assisted chemical vapor deposition (PACVD) using a gaseous mixture of $TiCl_4$, $N_2$, $H_2$, and Ar in order to increase the pitting resistance of Inconel 600.
The deposition rates and properties of the deposited TiN was affected by the deposition temperature as well as the R.F. power density. The deposition rate was decreased with an increase in deposition temperature between 430 and 500℃. The deposited TiN films contain chlorine, and its contents were reduced by increasing the deposition temperature and R.F. power density. The surface morphology of the deposited TiN films was very uniform and smooth.
Pitting resistance of Inconel 600 deposited with TiN films was examined in NaCl solution through usage of potentiodynamic polarization technique. The effect of chloride ion concentration was investigated in the range of 0.001M to 0.1M. Increasing chloride ion concentrations resulted in active shift of the nucleation potential of pit($E_np$).
TiN-coated Inconel 600 showed the superior pitting resistance to Inconel 600 which is not deposited with TiN films as long as TiN films is thicker than 'critical thickness'.
The pitting resistance of TiN-coated Inconel 600 was affected by the quality of TiN films which is the function of deposition conditions. The pitting resistance of TiN films was improved by the increase of deposition temperature as well as R.F. power owing to the decrease of residual chlorine contents. Although the residual chlorine contents decreased and the crystallinity of TiN films was improved at higher R.F. power above 50W, TiN-coated Inconel 600 showed the inferior pitting resistance. This behavior proved to be due to the network type microvoids structure, which was revealed by the transmission electron spectroscopy.
