Computational Modeling and Design of Adaptive Thin-Film Composite Coatings
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Computational Modeling and Design of Adaptive Thin-Film Composite Coatings James Deon Pearson, Mohammed A. Zikry, and Omid Rezvanian Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, 27695-7910
ABSTRACT The tailoring of thin film coatings comprised of high strength constituents, such as diamond like carbon and partially stabilized zirconia and ductile constituents, such as gold and molybdenum is investigated by new microstructurally-based finite-element techniques for applications related to the wear, durability, and performance of these coatings over a broad range of temperatures and loading conditions. The effects of contact transfer films, grain-shape sizes and distributions, grain-boundary structure and sliding, texture, and strength are used to determine the optimal thin film coating compositions. Comparisons are made with experimental measurements and observations, and guidelines for optimal thin film composite coatings are proposed. INTRODUCTION Thin-film coatings for lubrication are commonly used in applications related to severe changes in loading conditions and environments. A single optimized coating which adapts to changes in loading as well as maintains both a low and stable wear rate and coefficient of friction would be highly desirable [1]. Recent materials processing techniques, including magnetron sputtering and pulsed laser deposition (PLD), allow potentially the processing of any combination of constituent elements. Recent experiments [2] have identified four coating constituents, Au, YSZ (yttria stabilized zirconia, ZrO2-Y2O3), MoS2 (molybdenum disulfide) and diamond-like carbon (DLC) whose chemistry result in superior behavior pertaining to low wear, environmental stability and low friction coefficient in dry, humid and high temperature operating conditions when processed as a nanocomposite coating [2-4]. This combination is referred to as the ‘chameleon’ coating because of its adaptive behavior due to environmental changes. This adaptive coating with its combination of crystalline and amorphous materials provides toughness plus strengthening. However, what has not been understood is how failure evolves due to wear, and what the optimal combination of materials should be for desired wear response due to different loading and environmental changes. Hence, the objectives of the present study are to determine, using a predictive finiteelement computational methodology, optimal material coating constituents and composition due to wear mechanisms related to indentation, sliding, and wear transfer film effects and film adhesion. This computational methodology accounts for the interrelated effects of different material distributions, microstructural effects such as grain shapes and spacing of material constituents, stress and strain evolution, and thermal effects.
COMPUTATIONAL FINITE ELEMENT MODELS The finite element mesh was developed to account for nine different materials that account for the four coating constituents, the interlayer
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