Pinhole Defect Density of CrN x Thin Films Formed by Ion-Beam-Enhanced Deposition on Stainless Steel Substrates

To improve the corrosion protection performance of CrN x films, the relationship between the pinhole defect density of the films and the surface condition of stainless steel substrates was studied. A commercial, heated type 304 stainless steel (ss) and a high purity heated type 316L ss substrate were used. The surface of substrates was finished with wet SiC paper polishing, diamond paste polishing, or electropolishing. CrN x films 41 nm thick were formed by ion-beam-enhanced deposition. The pinhole defect density was evaluated by the critical passivation current density method. The surface roughness was examined by atomic force microscopy. The pinhole defect density of CrN x films on a commercial 304 ss substrate decreased with decreasing surface roughness of the substrate in cases of diamond paste polishing and wet SiC paper polishing. Pits were caused by electropolishing on the surface of 304 ss substrate owing to the dissolution of manganese oxysulfide inclusions, which resulted in an increase in the pinhole defect density of CrN x film. However, no pits were caused by electropolishing on a high purity 316L ss substrate and an extremely low pinhole defect density of 4.1 X 10 -4 area % was obtained for CrN x film on this substrate.