ICMCTF2003 Session H4: Novel Approaches to Nonchromate Corrosion Protection
Wednesday, April 30, 2003 8:30 AM in San Diego
H4-1 The Structure, Chemistry and Properties of Vanadate Conversion Coatings for High Performance Aluminum Alloys
R.G. Buchheit, H. Guan (Ohio State University)
A process has been developed to form inorganic conversion coatings 300 to 600 nm thick on aluminum alloy substrates by immersion in aqueous vanadate solutions. Such coatings, termed "vanadate conversion coatings" form spontaneously at ambient temperatures in 1 to 3 minutes without application of external voltage or current. In electrochemical and exposure testing, vanadate coatings provide levels of corrosion protection comparable to chromate conversion coatings when applied to Al alloy 2024-T3 (Al-4.4Cu-1.5Mg-0.6Mn). Experimental results suggest that coating formation occurs by polymerization of vanadates at the Al alloy surface. The resulting coating is conformal and continuous with a small amount of shrinkage cracking due to dehydration. Surface analysis is and x-ray absorption indicate that vanadium is present in several oxidation states. Some of the vanadium can be leached from the coating, migrate to defects elsewhere on the surface, and stifle incipient corrosion. In this sense, these coatings possess a self-healing character similar to that observed in chromate conversion coatings.
H4-4 Application of Inclusion Complexes of Cyclodextrin with Organic Corrosion Inhibitors for Corrosion Protection of Aluminum Alloys
A.N. Khramov, V.N. Balbyshev (Universal Technology Corporation); N.N. Voevodin (UDRI); M.S. Donley (Air Force Research Laboratory)
Cyclodextrins are cyclic oligosacharides that have known capability to form inclusion complexes with various organic molecules by including the guest molecule into a hydrophobic cavity. The host/guest inclusion complexes of cyclodextrins with organic corrosion inhibitors are attractive systems for slow-release of corrosion inhibitor during the lifetime of corrosion protection coating. @paragraph@ In order to improve corrosion resistance properties of previously developed sol-gel derived chromate-free conversion coatings, we have incorporated inclusion complexes of various organic corrosion inhibitors with two cyclodextrins -beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin. Structural characteristics of the films contributing to coating properties were evaluated by FT-IR and FT-Raman spectroscopy. Barrier properties of the coatings were examined by Scanning Vibrating Electrode Technique, Electrochemical Impedance Spectroscopy, and Potentiodynamic Scan method. @paragraph@ Corrosion protection performance of sol-gel derived coatings doped with inclusion complexes of cyclodextrins with organic corrosion inhibitors has been disscused with the emphasis on the effectiveness of the coating performance for long-term protection of aluminum alloys against atmospheric corrosion.
H4-5 Investigation of Quaternary Al-based Quasicrystal Thin Films for Corrosion Protection
V.N. Balbyshev, A.N. Khramov (Universal Technology Corporation); L.S. Kasten (University of Dayton Research Institute); D.E. Palaith (Technology Assessment & Transfer, Inc.); M.S. Donley (Air Force Research Laboratory)
Recent work has shown that thin film quasicrystal coatings have unique properties such as very high electrical and thermal resistivities and very low surface energy. Aluminum alloy based quasicrystals are insulator alloys composed of about 70% of aluminum. @paragraph@The corrosion related properties of aluminum alloy based quasicrystal thin film coatings have been studied on quasicrystal-coated AA-2024 substrates. The thin film deposition parameters are discussed. The effects of post-deposition heat treatment have been studied. Results of the microstructural, surface chemistry, and surface energy analysis of the quasicrystal films are presented. The corrosion protection properties of the films have been studied by potentiodynamic scan and electrochemical impedance spectroscopy. Analysis of the electrochemical data indicates that nanostructured quasicrystal films significantly inhibit corrosion of AA2024-T3 substrates in constant immersion environment. Morphology studies and electrochemical analysis of quasicrystal films have shown that quaternary Al-based quasicrystal thin films possess unique corrosion control properties. Superior resistance to electrolyte attack makes these coatings strong candidates for corrosion protection surface treatment of Al alloys. These films can be utilized as conversion coatings for Al substrates or incorporated into a full coating system containing an organic primer and a topcoat.
H4-6 Electrochemical Processing of High Temperature Conducting Polyimide Nanocomposite Coatings
J.O. Iroh (Air Force Research Laboratory); K. Shah, Y. Zhu (University of Cincinnati); M.S. Donley (Air Force Research Laboratory); V.N. Balbyshev (Universal Technology Corporation)
Bi-layer conducting polymer/polyimide composite coatings have been successfully applied onto aluminum alloy, AA 2024-T3 by a two-step deposition process. A PPy/PANi conversion coating was deposited onto the substrate by an electrochemical method. Subsequently, a clay-filled polyimide primer coating was cast onto the modified substrate from an NMP solution of the polymer. @paragraph@ The bi-layer composite coating showed exceptional corrosion resistance. The coatings were characterized by advanced analytical techniques such as reflection absorption infrared spectroscopy, RAIR, scanning electron microscopy, SEM, DC polarization studies and electrochemical impedance spectroscopy, EIS.
H4-8 Correlation Between Structure Non-uniformity and Internal Stress in Cr Thin Films Deposited by Magnetron Sputtering
H.M. Lee (SungKyunKwan University, South Korea); L.R. Shaginyan (National Academy of Sciences of Unkraine, Ukraine); H.S. Myung, J.G. Han (SungKyunKwan University, South Korea)
The microstructure and lattice parameters at different positions of Cr films deposited by magnetron sputtering at various deposition conditions were studied by using high resolution transmission electron microscopy, selected area diffraction and XRD methods. It was revealed that the microstructure and lattice parameter of the films deposited onto cooled or non-heated substrates are non-uniform along the film thickness. Lattice parameter a has maximal value in the part of the film adjacent to the substrate which gradually decreases towards the regular a meaning in the middle and upper film parts. It was found that as internal stress decreases, the crystalline size increases in the direct-ion from the lower to upper parts of the film. Increasing the substrate temperature results in development of uniformity of the film microstructure and stress distribution throughout the film thickness. At a certain combination of the substrate temperature and bias voltage unstressed films with large crystallites uniformly distributed along the film thickness can be deposited. The model proposed for explanation of obtained resu-lts is based on the supposition of dynamic elevation of the condensation surface tempe-rature during the growth of the film, which promotes the development of stress and structure non-uniformity throughout the film