ステンレス鋼上に成膜された酸化物皮膜の欠陥評価 電気化学的手法と光学的手法の比較

Abstract

PVD and CVD ceramic coatings have been developed to improve the corrosion resistance of stainless steel. In films coated by processes such as rf sputtering, piercing defects such as pinholes inevitably exists and these defects play a significant role in corrosion. In this study, various oxide films were coated on stainless steel by rf sputtering and pinhole defects in the coating films were evaluted using an electrochemical and an optical technique. The electrochemical technique was to evaluate the total defect area of the film using the value of the critical passivation current density in the course of anodic polarization in an 0.5kmol/m3H2SO4+0.01kmol/m3 KSCN solution, which restricts the passivation of the substrate steel. The optical technique was to evaluate film defects by observing the dynamic scattering of liquid crystal molecules induced by current flow through the film defects (a liquid crystal was inserted between the oxide film and a tranparent electrode). The defect probabilities of the films obtained through the two techniques showed good agreement. The optical techniques can observe the defects in films non-destructively, though it is limited to use with insulating films on conductive substrates.