Cr-diamondlike carbon nanocomposite films: Synthesis, characterization and properties V. Singh a,b , J.C. Jiang a , E.I. Meletis c, * a Mechanical Engineering Department, Louisiana State University, Baton Rouge, LA 70803, U.S.A. b Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70803, U.S.A. c Materials Science and Engineering, The University of Texas at Arlington, Arlington, TX 76019, U.S.A. Received 15 June 2004; received in revised form 17 January 2005; accepted 29 April 2005 Available online 13 June 2005 Abstract Diamondlike carbon (DLC) films, known for exhibiting attractive combination of properties, have been extensively studied in the recent past. The inherent, internal compressive stresses affecting their adhesion and their relatively low thermal stability above 400 -C are two major drawbacks preventing wide usage of these films. Carbide formers incorporated into the carbon network have the potential to stabilize the film structure, relax internal stresses and improve their performance. The present work focuses on the synthesis, structure and mechanical and tribological property characterization of Cr-containing nanocomposite DLC films. The films were synthesized using a plasma-enhanced hybrid chemical vapor and physical vapor deposition process in a discharge composed of a mixture of CH 4 and Ar gases. The Cr content in the films varied up to 18 at.%. The film morphology and composition were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and nuclear reaction analysis. The mechanical and tribological behavior of the films was studied as a function of Cr concentration by conducting nanoindentation and pin-on-disc experiments, respectively. The results showed that the films can be either amorphous with dispersed metallic-like Cr (at low Cr content) or nanocomposite consisting of face-centered cubic metastable CrC nanoparticles dispersed in the DLC matrix. Films with low Cr content (<5 at.%) were found to possess similar tribological characteristics with those of pure DLC films. Incorporation of more Cr (> 12 at.%) results in larger chromium carbide particles that have an adverse effect on wear resistance. The films with the low Cr content offer the opportunity to combine the excellent tribological behavior with other desirable properties deriving from the presence of the second phase. D 2005 Elsevier B.V. All rights reserved. Keywords: Tribology; Plasma processing and deposition; Diamondlike carbon; Chromium 1. Introduction Diamondlike carbon (DLC) films have been extensively studied for more than a decade, due to their unique combination of chemical inertness, mechanical, tribological and optical properties. The inherent compressive stresses that develop during synthesis from their diamondlike content (sp 3 carbon bonding) that affects adhesion and their thermal stability are two major drawbacks with DLC films. It is well known that DLC films are thermally unstable beyond 350 -C [1,2]. Above 400 -C the changes are more profound and graphitization of the film occurs by conversion of C bonds from sp 3 to sp 2 . Such temperatures can very well be reached at hot spots during wear, as has been shown by Liu and Meletis [3]. The graphitization process and its kinetics are the controlling parameters of the tribological behavior of these films as has been proposed by the latter authors in their wear- induced graphitization mechanism [3]. Thereby, for more than a decade, most of the scientific studies in the area of DLC films have been concentrated in the area of metal-containing DLC (Me-DLC) films in an effort to improve wear resistance, adhesion, thermal stability and toughness. A number of studies on synthesis and characterization of Me-DLC films have been con- ducted [4–20]. Among these the main emphasis had been 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.04.104 * Corresponding author. Tel.: +1 817 272 2559; fax: +1 817 272 2538. E-mail address: meletis@mae.uta.edu (E.I. Meletis). Thin Solid Films 489 (2005) 150 – 158 www.elsevier.com/locate/tsf