Tribological behavior of CrN coating on aluminum alloys deposited by arc ion plating
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Chang-Min Suh and Seock-Sam Kim School of Mechanical Engineering, Kyungpook National University, Daegu, 702-701, Republic of Korea
Ri-ichi Murakami Department of Mechanical Engineering, Tokushima University, Tokushima 770-8506, Japan (Received 9 July 2002; accepted 6 September 2002)
Dry sliding wear and friction tests of CrN coating on two types of aluminum alloy substrates, 6061 Al and 7075 Al, deposited by arc ion plating were performed with a ball-on-disk tribometer. The effects of normal load and the mechanical properties of the substrate on the friction coefficient and wear resistance of CrN coating were investigated. The worn surfaces were observed by scanning electron microscopy. The results show that surface microhardness of CrN-coated 7075 Al is higher than that of CrN-coated 6061 Al. With an increase in normal load, wear volume increases, while the friction coefficient decreases. The friction coefficient of CrN-coated 6061 Al is higher than that of CrN-coated 7075 Al, while the wear resistance of CrN-coated 6061 Al is lower than that of the CrN-coated 7075 Al. This indicates that the substrate mechanical properties have strong influence on the friction coefficient and wear of CrN coating. The main wear mechanism was fragments of CrN coating, caused by apparent plastic deformation of substrate during wear tests. I. INTRODUCTION
Aluminum alloys have many excellent properties such as high strength-to-weight ratio, good ductility, light density, and low cost. Thus, they are often used in the automotive and aerospace industries.1 However, when they are applied as tribological machine parts, they show poor wear resistance. This causes the service life of components to decrease.2 Therefore, it is imperative to enhance their wear resistance to increase their service life. Ceramic coatings are well known to be the most efficient method for improving the wear resistance of machine parts.3–7 Previous research works for CrN and TiN coated on steel8–13 and 2024 Al14 indicated that the physical and chemical properties of CrN coating were superior to those of TiN coating.8–13 The excellent wear resistance of CrN coating is related to its good oxidation resistance and adhesion to the substrate during wear test.13,14 However, research work related to the wear properties of CrN coating deposited on aluminum alloy is still limited. In this study, CrN coating was deposited on two types of aluminum alloy substrates, 6061 Al and 7075 Al, by using an arc ion plating (AIP) method. The tribological behavior of the CrN coating on two different aluminum alloys was investigated at various loads on a ball-on-disk J. Mater. Res., Vol. 17, No. 12, Dec 2002
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wear tester in dry air. The effect of the substrate mechanical properties on the wear behavior of CrN coating was studied.
II. EXPERIMENTAL A. Substrate materials
Two types of extruded aluminum alloys, 6061 Al and 7075 Al, were used as the substrates. Two types of aluminum alloy bars were machined to six small-size tensile s
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