Preparations and tribological properties of soft-metal/DLC composite coatings by RF magnetron sputter using composite ta
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Preparations and tribological properties of soft-metal/DLC composite coatings by RF magnetron sputter using composite targets Minoru Goto
Received: 29 October 2016 / Accepted: 31 May 2017 Ó Springer Science+Business Media B.V. 2017
Abstract This work reports the characteristics and tribological properties of both Ag/DLC nanocomposite coatings (RF-Ag-DLC) and Cu/DLC nanocomposite coatings (RF-Cu-DLC) with hydrogen-free DLC matrix deposited by RF magnetron sputtering using a concentric composite target (CCT). The CCT consisted of a C base target and metal tablet, and the tablet was located on the center of the base target concentrically where the etching rate by Ar ions is extremely low. By changing the diameter of Ag or Cu tablets in CCT, RF-Ag-DLC with an Ag concentration ranging from 6 to 65 at.% and RF-Cu-DLC with Cu concentration ranging from 7 to 75 at.% can be prepared. These coatings show a granular structure having Ag or Cu nano-crystals with a diameter ranging from 5 to 10 nm dispersed homogeneously in the hydrogen-free DLC matrix. The friction coefficient of DLC varied depending on the species and content of metal. The transition of the friction coefficient became stable when metal-rich tribofilms formed on the counterfaces. Keywords Soft metal DLC Nanocomposite RF magnetron sputter Tribology
M. Goto (&) Department of Mechanical Engineering, National Institute of Technology, Ube College, Ube, Japan e-mail: [email protected]
1 Introduction Diamond-like carbon (DLC) is a carbon material exhibiting various attractive characteristics, and has been drawing considerable attention among researchers in the field of material science, biology as well as tribology. The characteristics of DLC coatings vary not only by changing the structure of the carbon network but also by adding other elements as dopants or additives (Robertson 2002; Morrison et al. 2006; Donnet and Erdemir 2008; Fontaine 2008). Adding metals to DLC coatings (Me-DLC) is thus considered an effective method to improve electrical and/or biological properties as well as tribological properties. Copper and silver are good candidates as additives because of their low electrical resistivity, good tribological properties and unique biological properties. Cu has been a well-known metal component of tribo-material in industrial applications such as journal bearings for internal combustion engines, and electric contact points for electric switches because of its good running-in property and embed ability against abrasive particles as well as good electric conductivity (Schouwenaars et al. 2007; Kubo and Kato 1998). On the other hand, Ag is a well-known material not only showing low electric conductivity but also for applying solid lubricant in a vacuum (The Japan Institute of Metals and Materials 1974; Scharf and Prasad 2013). My previous work revealed that pure Ag film with an average thickness of 5 nm on Si (111) clean surface showed an extremely low coefficient of friction lower
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M. Goto Fig. 1 Schematic images of target layout a convent
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