Evaluation of pinhole defects in TiN-coated SUS 304 stainless steels by ARE or HCD process

In this study TiN films were formed under various conditions onto SUS 304 stainless steel substrates by a hollow cathode discharge (HCD) type ion plating process and by an activated reactive evaporation (ARE) type ion plating process, and amount of defects on their films was measured by electrochemical measurement and by optical microscope. And then both results were compared. In electrochemical measurement their samples were polarized in 0.5 M-H2SO4 + 0.05 M-KSCN solution and the pinhole ratios (Ri/2) were calculated by the rate of critical passivation current density of a coated and non-coated specimens. In case of ARE process, it is found that Ri/2 decreases by increasing film thickness and bias voltage. In case of HCD process, Ri/2 decreases with the increase of film thickness, but it dose not change by the increase of bias voltage. The pinhole ratio (Rr) was obtained by measuring the size of each pinhole and counting the numbers of pinholes. Ri/2 coincides with Rr comparatively in case of HCD, but this is not the case for ARE. This is because that the pit which do not penetrate through the film to the substrates or the unusual products formed on ARE specimens are also considered defects in the film.