AVS 51st International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoM

Paper SE-MoM7
Oxide Nanolaminate Coatings for Protection Against Perforated Pitting Corrosion in Stainless Steel

Monday, November 15, 2004, 10:20 am, Room 303D

Session: Nanolayered and Gradient Coatings for Surface Engineering
Presenter: W.F. Gaertner, University of Wisconsin-Milwaukee
Authors: W.F. Gaertner, University of Wisconsin-Milwaukee
C.R. Aita, University of Wisconsin-Milwaukee
Correspondent: Click to Email
Perforated pitting corrosion is disastrous in stainless steel (SS) medical implants where even a low released cation concentration causes rejection by the surrounding tissue. Protection by oxide nanolaminates on 316L SS in saline is reported here. The behavior of constituent oxide single-layer films is also reported. We previously found [1] that a tetragonal ZrO@sub 2@/A1@sub 2@O@sub 3@ smart nanolaminate protects a rough 316L SS substrate (15 µm finish) against pitting. We constructed a model for corrosion prevention after a pit has initiated. This model involves mesoscopic film fracture accompanied by passivation of the underlying exposed SS. Here, we apply this model to (a) films on highly polished (1 micron finish) substrates where adhesion can be a problem, and (b) to a TiO@sub 2@/A1@sub 2@O@sub 3@ nanolaminate (which is not a smart coating) on both rough and substrates. 200 to 250 nm thick films were grown at room temperature by sequential sputtering of metal targets in Ar with 20% O@sub 2@ rf discharge. Cyclic polarization was used to determine the corrosion current, i@sub o@, as a function of applied potential after a steady state open circuit potential (OCP) was established. Samples were examined by scanning electron microscopy and energy dispersive spectroscopy. The results show that: (1) Corrosion current in all samples was low, on the order of 1 to 100 nA/cm@super 2@. (2) Single layer ZrO@sub 2@ and TiO@sub 2@ films did not protect against perforated pitting in polarized samples of either surface finish. (3) Single layer A1@sub 2@O@sub 3@ did prevent pitting but catastrophically failed after a single polarization cycle.(4) Nanolaminates protected by the synergic effect of a tough (ZrO@sub 2@, TiO@sub 2@) nanolayer combined with a brittle (A1@sub 2@O@sub 3@) became important in 316L SS with a rough finish. @FootnoteText@ NSF-CMS Grant No. 9988892 is acknowledged. [1]W.F.Gaertner,et al.,JVST A 22, 272 (2004).