Thermal Plasma Chemical Vapor Deposition of Superhard Nanostructured Si-C-N Coatings
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Thermal Plasma Chemical Vapor Deposition of Superhard Nanostructured Si-C-N Coatings Nicole J. Wagner1, Megan J. Cordill2, Lenka Zajickova1, William W. Gerberich2 and Joachim V. R. Heberlein1 1 Mechanical Engineering, University of Minnesota Minneapolis, MN 55455, USA 2 Chemical Engineering and Materials Science, University of Minnesota Minneapolis, MN 55455, USA ABSTRACT A triple torch plasma reactor was used to synthesize Si–C–N composite films via the thermal plasma chemical vapor deposition process. The argon-nitrogen plasma provided atomic nitrogen to carbon- and silicon-based reactants, which were injected through a central injection probe and ring configuration. Films were deposited with variations of the total nitrogen flow through the torches (1.5-4.5slm), reactant mixture (silicon tetrachloride and acetylene or hexamethyldisilazane) and substrate material (silicon and molybdenum). Micro X-ray diffraction was used to determine that both α-Si3N4 and β-Si3N4 were dominant in most of the depositions. Composites of silicon nitride and silicon carbide were synthesized on molybdenum. The bonding of amorphous phases was investigated using Fourier transform infrared spectroscopy, which indicated the presence of N–H, CHx and C 1LQYDULRXVILOPV,QGHQWDWLRQ tests on the polished film cross-sections determined that large variations in hardness and elastic modulus existed for minor changes in film composition. Correlations between indentation results and scanning electron and optical microscope images showed that the mechanical properties greatly depend on the film morphology; the denser, smoother, and more crystalline films tended to display enhanced mechanical properties. INTRODUCTION Materials that protect against erosion, wear, and other harmful degradation are of great interest for various industries to coat, for example, automotive engine parts and machining tools. Nanostructured composite coatings offer enhanced mechanical properties that would reduce and possibly eliminate the necessity of costly and hazardous coolants for such applications. Nanostructured composite films consisting of silicon nitride and silicon carbide have attracted great interest for their enhanced mechanical properties [1]. It is believed that the composite displays enhanced mechanical properties over its individual components [2]. The ideal design of this composite material is composed of nano-crystals dispersed in an amorphous nitride matrix [3]. Various methods are utilized for the preparation of the silicon nitride-silicon carbide nanocomposite, including polymer pyrolysis [4], powder mixing [5], and high-pressure nitridation and sintering [6]. In this study, a thermal plasma chemical vapor deposition (TPCVD) process was used to grow the Si-C-N composite on a silicon or molybdenum substrate. This process allows the possibility of using versatile multiphase reactants and producing a controllable film structure at high growth rates.
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EXPERIMENTAL Film Deposition Nanostructured Si-C-N films were de
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