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Session Chairperson: TBA
THE USE OF ION BEAM SURFACE MODIFICATION TECHNIQUES FOR CORROSION PROTECTION: P.M. Natishan, E. McCafferty, G.K. Hubler, B.D. Sartwell. Naval Research Laboratory, Washington, DC 20375
Ion beam alloying techniques overcome many of the problems associated with conventional alloying and provide a means to produce new and unique corrosion resistant alloys. These techniques can be used to tailor metal surfaces to enhance the corrosion resistance of the surface without affecting the bulk properties of the metal. In addition, novel metastable phases unattainable by conventional alloying can be produced, and scarce or critical materials can be conserved since only the surface of the metal is alloyed. This paper will discuss advances in and issues related to various ion beam alloying techniques including ion implantation, ion beam mixing and ion beam assisted deposition as related to their application to corrosion protection.
CORROSION RESISTANT ALLOYS AND COATINGS PRODUCED BY PHYSICAL VAPOR DEPOSITION: Barbara Shaw, Elzbieta Sikora, Tim Miller, Department of Engineering Science and Mechanics, Penn State University, University Park, PA 16802
Evaporation techniques, such as PVD and CVD are increasing in popularity as methods for tailoring surface properties for specific engineering applications. One of the attributes of PVD is the ease with which graded, layered and nonequilibrium coatings and alloys can be produced. Not surprisingly, defects, coating morphology and deposit composition strongly influence deposit properties such as strength and corrosion resistance. As an example of how passivity enhancing species influence corrosion resistance, the addition of 8 at% Mo to Al (via electron beam PVD) was found to increase the pitting potential 600mV over that of pure Al. Similar enhancements have been observed with Al-Ta alloys. In addition to the constant composition deposits, graded and layered coatings can also be used to improve corrosion resistance and mechanical properties. In this presentation, the results of an ongoing investigation of nonequilibrium Al and Mg deposits ( both constant and graded composition deposits) produced via electron beam PVD will be presented and discussed.
THE ELECTROCHEMICAL BEHAVIOR OF METAL SURFACES SUBJECTED TO PULSED ION BEAM SURFACE TREATMENT: N.R. Sorensen1, R.G. Buchheit1, K.S. Grabowski2, T.R. Renk1, M.O.Thompson3 ; 1Sandia National Laboratories, P.O. Box 5800 Albuquerque, NM 87185; 2Naval Research laboratory, Code 6670, Washington, DC 20375; 3Department of Materials Sciences, Cornell University, Ithaca, NY 14853
Pulsed high energy ion beams have been used to thermally treat metal surfaces to alter their electrochemical response. Two general processing regimens have been explored: 1) rapid melt and resolidification (RMR) and 2) ion beam mixing (IBM). RMR uses the pulsed ion beam to melt and in some cases ablate the top most several microns of the surface. Subsequent solidification is sufficiently fast (>106K/s) for nonequilibrium structures and compositions to be attained. IBM uses the ion beam to mix a previously applied metallic layer into the substrate to produce a compositionally and structurally distinct surface alloy. The surface that results from these treatments often displays interesting characteristics. For example, a Grade-2 Ti sample, which pits at a potential of 1.7V, is immune to pitting up to 2V following ion beam treatment. This talk will discuss the changes in electrochemical behavior of several alloys following ion beam treatment.
CORROSION INHIBITION MECHANISMS IN EPOXY COATED ALUMINUM: R.D. Granata, R.C. MacQueen, R.R. Miron, M.M. Madani Zettlemoyer, Center for Surface Studies, Lehigh University, 7 Asa Drive, Bethlehem, PA 18015
Corrosion inhibition mechanisms in model systems were evaluated for use in barrier-type protective polymeric coatings systems. Emphasis was on complaint, low VOC coatings applications technologies such as powder coatings, UV-cured and electrocoating systems on aluminum substrates. Candidate inhibitor systems wee studied using low VOC epoxy polymer and porous polymer films on conversion coated, aluminum alloy 2024. Inhibition in these systems was observed in short exposure times. The model defect systems were studied using electrochemical impedance and positron annihilation lifetime spectroscopies. The positron lifetime measurements determined free volume cavity sizes and concentrations through which corrosion-active species diffuse. Electrochemically active and inactive (positron accessible) regions within the polymer matrix were monitored versus water saturation. Corrosion inhibitors modified the polymer matrix barrier properties in regions adjacent to the filler particles. Inhibition processes will be discussed relative to known mechanisms.
3:20 pm BREAK
CYCLIC OXIDATION BEHAVIOR OF AN ALUMINIDE COATING FORMED ON DESULFURIZED Ni-BASED SUPERALLOYS BY CHEMICAL VAPOR DEPOSITION: Y. Zhang1, W.Y. Lee2, K.M. Cooley2, I.G. Wright2, P.K. Liaw1; 1Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996; 2Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831
The cyclic oxidation behavior of Ni-based superalloys can be significantly improved by lowering the level of sulfur impurities in the alloys to below ~1 ppm. This presentation addresses the feasibility of preparing a low-sulfur bond coat, which would be compatible with desulfurized single-crystal superalloys and therefore could be attractive for possible use in advanced thermal barrier coating applications. Rene N5 substrates containing ~3 ppm and ~0.4 ppm sulfur were aluminized using a chemical vapor deposition technique. The level of sulfur incorporated into the aluminide coating was measured as a function of coating thickness by glow discharge mass spectroscopy. The effects of the sulfur content on the cyclic oxidation behavior of the aluminized substrates and the morphological stability at the scale-coating interface were studied and compared.
AN XPS STUDY OF THE ROLE OF NITROGEN IN OXYANION FORMATION DURING AQUEOUS CORROSION OF MOLYBDENUM AND CHROMIUM NITRIDE COATINGS: G. Halada, C. Clayton, Department of Materials Science and Engineering, State University of New York at Stony Brook, NY 11794-2275; J. Beatty, J. D. Demaree, U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5069
A dual electrode electrochemical approach, in combination with variable angle X-ray Photoelectron Spectroscopy, was used to determine the role of nitrogen in the generation of oxyanionic species, MoO42- and CrO42-, from MoN and CrN coatings. During simultaneous anodic polarization of a coupling of Fe and either pure Mo and Cr or their respective nitrides in deaerated 0.1M HCl, the presence of nitrogen was found to enhance the formation of molybdate and chromate oxyanions. These oxyanions deposited back onto the nitride surfaces as insoluble salts formed with cations released from the iron electrode. The increased formation of oxyanions is postulated to be the result of deprotonation of electrolyte in contact with the nitride coating and a subsequent shift in pH to higher values. In addition to acting as a kinetic barrier, the oxyanionic species act as an electrostatic barrier to the ingress of the Cl- anions which cause pitting.
A STUDY OF THE PASSIVATION MECHANISM IN HIGHLY CORROSION RESISTANT "STAINLESS STEEL" ALLOY COATINGS FORMED USING THE JVDTM PROCESS: Clive R. Clayton, M.E. Monserrat, G.P. Halada, Dept. of Materials Science and Engineering, SUNY at Stony Brook, NY 11794; Jamie Di, Takashi Tamagawa, Arun R. Srivatsa, Bret L. Halpern, Jet Process Corporation, 24 Science Park, New Haven, CT 06511
Recently we reported the formation of highly corrosion resistant "stainless steel" based alloy coatings formed using the JVD process. In this paper, a detailed study aimed at obtaining a fundamental understanding of the passivation mechanisms operating in these alloy coatings is reported. Passivation behavior of the coatings was determined by electrochemical polarization in 4.0M and 0.1M solutions respectively. The surface chemistry of the coatings was studied using XPS and correlated to the observed passivation behavior.
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