Electrochemical Evaluation of Pinhole Defects in TiN-Coated Stainless Steels

Abstract

Pinhole defects of TiN coated stainless steels were evaluated electrochemically in deaerated 0.5kmol⋅m^-3 H₂SO₄+0.05kmol⋅m^-3 KSCN solution at 298K. The TiN films formed by an activated reactive evapolation method exhibited the columnar structure with ‹111› orientation, which contained more or less pinhole defects. The critical current density for passivation, i_crit, in the TiN-coated stainless steels decreased with an increasing film thickness, and the resulting corrosion resistance was improved remarkably by TiN-coating. The area fraction of pinhole defects was evaluated by the ratio of i_crit of a coated and a non-coated specimen. Thus, the result coincided well with the ‘true’ area fraction based on the optical micrographs before or after polarized anodically. Consequently, such electrochemical measurement is superior as an evaluation method for the pinhole defects of corrosion-resistible coating.