Characterization of amorphous and nanocrystalline carbon films

Microstructural design of hard coatings

Diamond-like carbon (DLC) films deposited by cathodic vacuum arc evaporation (CVAE) have attracted worldwide interest from research groups and industry since the beginning of the 1990s. Hydrogen-free amorphous carbon (a-C) coatings were first deposited by CVAE about two decades after the first description of hydrogenated a-C coatings (a-C:H) deposited by glow-discharge techniques. This paper highlights the development and broad potential of hard a-C coatings deposited by direct (DCVAE) and filtered (FCVAE) cathodic arc evaporation, including pulsed arc. DLC films offer a wide range of exceptional physical (optical, electrical), chemical (interaction with media), mechanical (hardness, elastic modulus), biomedical and tribological properties. Monolithic tetrahedrally-bonded hydrogen-free coatings (ta-C) provide the highest hardness, while various softer a-C coatings are also useful in some applications. Many film properties such as electrical conductivity and surface energy can be modified by alloying with elements such as H, N, Si, B, F, P and metals. Recent research and industrial solutions for generating DLC coatings by CVAE of carbon-based cathodes are described, and hybrid methods using metal cathodes and gas-phase sources are discussed. Coatings containing additional elements and having complex architectures are also discussed, and selected properties for various coating types are presented. The number of industrial applications of ta-C and a-C coatings continues to increase, mainly for tribological coatings to reduce wear and friction. Various applications of coatings deposited by CVAE are described, including data hard disks, engine parts, razor blades, valve seals, decorative coatings, cutting and forming tools, biomedical products and others.

60 years of DLC coatings: Historical highlights and technical review of cathodic arc processes to synthesize various DLC types, and their evolution for industrial applications

For engineering applications of thin films, appropriate combination of high hardness with other properties (such as high toughness, low residual stress, good adhesion with substrate and oxidation resistance) is of vital importance. Super high hardness alone does not have too much use. For practical application, hardness and toughness are of the same importance. This paper gives a critical review on toughening methodologies for hard nanostructural thin films, these are: ductile phase toughening, nanograin boundary strengthening and sliding, composition and structure grading, multilayer design, carbon nanotube toughening, phase transformation toughening, compressive stress toughening, etc. A summary is given to cap the essence of toughening methodologies in terms of increasing the storage or dissipation of plastic energy.

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Toughening of hard nanostructural thin films: a critical review

Concepts for the design of advanced nanoscale PVD multilayer protective thin films

The objective of nanocomposite coatings combining hard and lubricant phases is the development of advanced multi-functional protective thin films showing abrasion resistance, and simultaneously, low friction. Up to now, no clear relation between constitution, microstructural properties and performance of such nanocomposite coatings based on dry lubricants like carbon or MoS2 has been evaluated. Deposition techniques, constitution, properties and performance of magnetron-sputtered nanocomposite coatings in the TiCC system are presented. The Vickers hardness could be optimized to values of polycrystalline TiC thin films, and at the same time, low friction coefficients against steel, similar to diamond-like amorphous carbon, could be realized. The mechanical properties and the tribological behavior of these thin films are related to the chemical composition and the microstructure of these advanced materials, characterized by electron microprobe analysis, Auger electron spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy.

Microstructure and properties of low friction TiCC nanocomposite coatings deposited by magnetron sputtering

Thin films of silicon nitride (Si3N4) and silicon carbide (SiC) have been deposited by radio frequency (r.f.) magnetron sputtering of stoichiometric targets in non-reactive argon and in the case of Si3N4 additionally in reactive nitrogen–argon atmospheres. The influence of the sputtering atmosphere, the substrate temperature and the substrate bias on the composition and on the mechanical and microstructural properties of the thin films was investigated. FTIR and Raman spectroscopy was used to identify the chemical bonding configuration and to control the chemical composition. Raman investigation showed a change in the bonding configuration from amorphous silicon carbide to a crystalline structure and the incorporation of nitrogen in silicon nitride thin films with increasing substrate bias.

Investigation and characterisation of silicon nitride and silicon carbide thin films

Diamond-like carbon thin films for tribological applications were deposited by d.c.-magnetron sputtering of a graphite target in a pure argon atmosphere or in a reactive hydrogen or methane atmosphere at pressures between 0.1 and 1 Pa in a graded constitution to improve adhesion and reduce residual stress. The temperature of the metallic, carbon- and ceramic-like substrates was below 100°C. The mechanical, thermal, electronic and optical properties of the carbon thin films show a significant dependence on the ion energy. Below 220 eV, strongly adherent black conductive films with hardness values up to 2000 HV0.05 were obtained. Hard and superhard diamond-like carbon thin films were deposited in an energy range between 220 and 370 eV with hardness values up to 4000 HV0.05. They are insulating, optically transparent and show a high degree of hardness combined with high compressive stress in the order of 4 GPa as well as a low adhesion, which means that the critical loads of failure are below 10 N. Above 370 eV, weak black conductive films with a poor adhesion were deposited. A new concept has been realized, which allows the conservation of the positive properties of superhard films, such as high hardness, sp3 content as well as a low friction coefficient (0.08–0.17 against 100Cr6 and Al2O3) with a simultaneously decreasing stress and increasing adhesion. First, a thin TiC interface layer was deposited, and then, the ion energy was gradually increased during the deposition of the carbon layer. Critical loads of failure in a scratch test of up to 50 N were reached when applying this concept. These amorphous carbon films have shown excellent tribological properties, especially low friction coefficients and low wear under dry sliding wear conditions against 100Cr6 and Al2O3. X-ray diffraction and TEM examinations confirmed a fully amorphous structure of hard carbon films. Substrate temperatures above 200°C result in the deposition of nanocrystalline graphite-like carbon films shown by Raman spectroscopy.

H. Holleck

Papers

Concepts for the design of advanced nanoscale PVD multilayer protective thin films

Microstructure and properties of low friction TiCC nanocomposite coatings deposited by magnetron sputtering

Investigation and characterisation of silicon nitride and silicon carbide thin films

Graded layer design for stress-reduced and strongly adherent superhard amorphous carbon films

Constitution and microstructure of magnetron sputtered nanocomposite coatings in the system Ti-Al-N-C