AVS 46th International Symposium
    Vacuum Metallurgy Division Tuesday Sessions
       Session VM-TuP

Paper VM-TuP3
Novel Technique for Low Temperature Chemical Vapor Deposition of Titanium Thin Films on Mild-Steel Surfaces for Corrosion Resistance

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: J.H. Hendricks, National Institute of Standards and Technology
Authors: J.H. Hendricks, National Institute of Standards and Technology
M.I. Aquino, National Institute of Standards and Technology
M.R. Zachariah, National Institute of Standards and Technology
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A novel, low temperature technique for growing titanium films on mild-steel substrates has been demonstrated. This method involves the use of a low pressure (600Pa) co-flow diffusion reactor in which sodium vapor and gas-phase titanium tetrachloride react in the presence of a non-reactive gas, Ar. The reaction chemistry is described by the following equation: 4Na(g) +TiCl@sub 4@(g) --@super Ar(g)@-->Ti(s)+ 4NaCl(g). In this reaction, a gas-phase alkali metal (Na) strips multiple halogen atoms (Cl) from a gas-phase metal halide (TiCl@sub 4@). This allows free Ti atoms to attach to a substrate surface placed within the reaction zone, resulting in the growth of a solid metal film. Previously, we have used this technique to grow Ti and TiN thin films on Cu substrates@footnote 1@ at 610°C and TiO@sub 2@ thin films on Si<100> substrates@footnote 2@ at 600°C. This chemistry should be generic for the deposition of a wide class of metallic and ceramic thin films at deposition temperatures which are significantly lower than conventional techniques, and this technique could potentially be used to grow hard and superhard coatings such as CN and BN. Thermodynamics modeling was used to simulate the reactant concentrations and substrate temperatures at which the salt by-product remains in the gas-phase. The modeling predictions were compared to the experimental results and found to be in good agreement. Using the described technique, we have produced Ti thin films on mild-steel substrates with substrate temperatures of 400°C to 800°C. These temperatures are considerably lower than conventional CVD of Ti which involves the thermal decomposition of titanium tetraiodide at 1000°C to 1200°C.@footnote 3@ Lowering the temperature for Ti deposition on mild-steel is of significance since mild-steel undergoes a phase transition at 723°C.@footnote 4@ The corrosion resistance of the titanium coated mild-steel substrates were evaluated to determine the optimum substrate deposition temperature. The quality and composition of the thin films were analyzed by scanning electron microscopy (SEM), energy dispersive x-ray spectrometry (EDS), and x-ray diffraction (XRD). @FootnoteText@ @footnote 1@J. H. Hendricks, M. I. Aquino, J. E. Maslar, and M. R. Zachariah, Chem. Mater. 1998, 10, 2221-2229. @footnote 2@J. H. Hendricks, M. I. Aquino, J. E. Maslar, and M. R. Zachariah, Material Research Society Proceedings, Nov.30-Dec. 4, 1998, Boston, MA. @footnote 3@M. G. Hocking, V. Vasantasree, and P. S. Sidky, Metallic and Ceramic Coatings: Production, High-Temperature Properties and Applications, John Wiley and Sons: New York, 1989, p. 103. @footnote 4@J. M. Camp and C. B. Francis, The Making Shaping and Treating of Steel, United States Steel Company: Pittsburgh, PA, 1951, p. 1203.