Abstract
Pinhole defects of TiN-coated stainless steels were evaluated potentiodynamically in a deaerated 0.5kmol/m3 H2SO4+0.05kmol/m3 KSCN solution at 298K. The TiN films prepared by radio frequency (r.f.) reactive sputtering exhibited the columnar structure with the preferential ‹220› or ‹111› orientation, and they contained more or less pinhole defects. The critical passivation current density icrit in the TiN-coated specimens decreased considerably with increasing film thickness. Above 1.5μm in thickness, however, there was an increasing tendency in icrit with cracking and/or peeling. The area ratio of pinhole defects was evaluated by the ratio of icrit a coated and a non-coated specimen. The result coincided comparatively well with the true defect area ratio based on the optical micrographs before and after anodically polarized. Such electrochemical method was concluded to be a reliable evaluation technique for the pinhole defects of corrosion-resistive coating.
