Tribological characteristics of DLC films and duplex plasma nitriding/DLC coating treatments

• Published in: Surface & coatings technology 1995-07, Vol.73 (1), p.39-45
• Main Authors: Meletis, E.I., Erdemir, A., Fenske, G.R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Diamond-like carbon; Duplex plasma treatments; Exact sciences and technology; Friction, lubrication, and wear; Materials science; Metals. Metallurgy; Physics; Plasma nitriding; Treatment of materials and its effects on microstructure and properties; Tribology
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/0257-8972(94)02375-1

An innovative approach to improving tribological behavior of surfaces and meeting long-term durability requirements of engineering devices is to design and develop novel systems incorporating multilayers and/or duplex diffusion/plasma coating treatments. In the present work, the wear and friction characteristics of diamond-like carbon (DLC) films and composite surface layers were studied by conducting pin-on-disc experiments. M 50 steel and Ti-6A1-4V alloy were used as substrate materials. The composite layers consisted of a N-diffusion zone obtained by ion nitriding, followed by a 500 Å vapor-deposited Si bond layer and a 0.4 µm DLC film. The purpose of the bond layer was to enhance adhesion between the substrate and the DLC films. An ion-beam method was used for the deposition of the DLC films. The pin-on-disc results showed that for both materials the DLC coating produced a reduction in the coefficient of friction of about one order of magnitude. The reduction in the coefficient of friction was found to be consistent with the formation of a carbon-rich transfer film on the contact surfaces. Wear scar profiling and weight loss calculations showed that the wear resistance of the DLC-coated materials was dramatically improved. Comparisons between duplex N-diffusion layer/DLC coating and single DLC coating on Ti-6A1-4V alloy substrates showed that the duplex treatments possessed a significantly higher wear resistance. Nitriding was found to cause substrate hardening that reduces subsurface deformation, thus improving coating support and extending considerably DLC film lifetime.