Evaluation of Tribological and Mechanical Properties of Nitride Thin Films Prepared by Cathodic ARC Deposition
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EVALUATION OF TRIBOLOGICAL AND MECHANICAL PROPERTIES OF NITRIDE THIN FILMS PREPARED BY CATHODIC ARC DEPOSITION Pallavi Shukla1,2, A. K. Sikder1, Ashok Kumar1, 2, Robert Durvin3, Mark McDonough3 and M. D. Smith3 1 Nanomaterials and Nanomanufacturing Research Center University of South Florida, Tampa, FL 33620 2 Also with Department of Mechanical Engineering 3 BryCoat Inc., Safety Harbor, Florida 34695-3403. ABSTRACT: Mechanical and tribological properties of thin films draw special attention and differ from those of bulk materials due to the effects of interfaces, microstructure and thick underlying substrates. In this study hard wear resistant nitride coatings (TiN, ZrN, TiAlN, TiCN and CrN) were coated on high speed steel substrates using cathodic arc deposition method. Mechanical properties of the films were evaluated using nanoindentation technique. Continuous stiffness method was employed to evaluate the depth sensing hardness and modulus values. Studies of tribological properties were performed using ball-on-disk friction and wear test. We have also investigated the wear track using optical microscopy. Variation of coefficient of friction with time has been analyzed and coating endpoint was estimated. Nanoindentation evaluation of mechanical properties along with the measurement of tribological properties is very useful in order to use them as wear resistant hard coatings. INTRODUCTION: The interest in thin film technology has grown enormously during the last decades [1]. In the field of metal cutting, 75% of all turning tools and approximately 40% of the milling tools have coatings made either by chemical vapor deposition (CVD) or physical vapor deposition (PVD) [2]. The advantages in the PVD technology over CVD counterpart are the lower deposition temperature, control over deposition rate, the stoichiometry and nitrogen: carbon ratio, and the availability of not-equilibrium coatings such as TiAlN, which cannot be produce by CVD methods [3]. Traditionally the term hard coating refers to the property of high hardness in the mechanical sense with good tribological properties. Coatings are generally classified into two categories, i.e. soft and hard, depending on a hardness value lower or higher than 10 GPa. Nitrides have gained attention due to high hardness, chemical inertness and high wear resistance and coatings is being used on variety of mechanical components such as tools for metal cutting and forming, and machine elements such as rolling or sliding bearing surfaces, seals, piston/cylinder systems, and valves [4-6]. One of the mostly widely used and studied coatings to date is TiN, which has been largely used as a hard protective coating and diffusion barrier in many technological applications die to its high hardness, good wear resistance, low coefficient of friction (COF) and high chemical inertness [7,8]. In recent years, a new generation of coating, titanium carbo-nitride (TiCN) [9], has been gaining focus. In addition to TiCN, other nitrides such as chromium nitride (CrN) [10], zirconium nitr
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