Characterization of diamond-like carbon films deposited on commercially pure Ti and Ti–6Al–4V Dong-Hwan Kim a , Hyoun-Ee Kim a , Kwang-Ryeol Lee b , Chung-Nam Whang c , In-Seop Lee c, * a School of Material Science and Engineering, Seoul National University, San 56-1, Shillim-dong, Kwanak-gu, Seoul 151-742, South Korea b Division of Ceramics, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650 South Korea c Atomic-scale Surface Science Research Center, Yonsei University, 134 Shinchon-dong, Sudaemoon-ku, Seoul 120-749, South Korea Received 1 November 2001; received in revised form 25 February 2002; accepted 22 May 2002 Abstract The diamond-like carbon (DLC) films deposited on the articulating surface of medical-grade Ti and Ti– 6Al–4V were characterized. The DLC films were synthesized by r.f. plasma assisted chemical vapor deposition (PACVD) using C 6 H 6 at 10 mTorr. For wear tests, the ball-on- disk type wear tester was employed by wearing a 5-mm diameter ruby ball against a rotating metal disk. The DLC coating dramatically improved the wear performance of Ti and Ti –6Al– 4V, and protected the substrates from corrosion. The wear behavior of DLC films on the Ti-alloy was that of normal abrasive wear. However, the softer Ti substrate deformed plastically and the films were prefractured. The lifetime of the DLC coating in saline solution was reduced due to the delamination of the coating. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Diamond-like carbon (DLC); Wear; Ti; Ti–6Al–4V; r.f. PACVD; Delamination 1. Introduction Wear was not a major issue in orthopedics until about 1980 when the widespread use of Ti–6Al–4V alloy instead of the, then standard, cast Co–Cr–Mo alloys was consid- ered. The principal advantages of the alloy were thought to be its very high biocompatibility and low modulus of elasticity. In articulating Ti–6Al–4V against ultra-high molecular weight polyethylene (UHMWPE) wear, although quite significant, is not as severe as for the alloy. This is apparently so because oxide wear debris became embedded in the polymer and continued to wear the alloy during subsequent rotations. The wear process is thought to be autocatalytic because the passivating oxide is only weakly adherent to the metal surface. Once an oxide particle is removed and becomes embedded in the UHMWPE, an associated wear band is formed, for which the sample is deeply grooved. Consequently, a large amount of new wear debris is generated. This process can be suppressed by hardening of the passive film on the surface; one method of which is ion implantation [1–4]. Implantation of nitrogen or carbon into the Ti-alloy has been commercialized. How- ever, due to its nature of shallow penetration by implanta- tion process, the hardened titanium oxide surface layer is thin and not durable. DLC films have distinct tribological properties, such as low friction and high wear resistance with a very smooth surface [5–11]. Such excellent tribological properties make them good candidates as wear-resistant layers, and many studies have reported DLC as a protective coating for the articulating surface of implants [12–17]. Firkins et al. [16] showed that the wear rate of UHMWPE was much lower on DLC-coated 316L stainless steel than on the bare metal itself. DLC films have also been reported to have good biocompatibility, such as the absence of inflammatory responses in vitro when assessed by mouse peritoneal macrophages [18], and the absence of histopathological changes in vivo when implanted in animal bone [17]. However, the tribological behavior of DLC films is strongly dependent on the substrate and the test conditions. For example, the very low friction coefficient, often below 0.05, when a steel slider slides over a DLC surface in dry air gradually increases with increasing humidity and reaches values in the range of 0.15–0.3 at 100% relative humidity [19,20]. 0928-4931/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0928-4931(02)00106-6 * Corresponding author. Fax: +82-2-312-7090. E-mail address: inseop@yonsei.ac.kr (I.-S. Lee). www.elsevier.com/locate/msec Materials Science and Engineering C 22 (2002) 9 – 14