Diamondlike carbon (DLC) has been studied for many years as a wear-resistant material with low friction coefficient. Its tribological behavior is strongly affected by the tribotesting environment and is controlled by tribochemical effects, which may in turn be dependent on the technique used for the deposition of the films. New variations of DLC films, with various dopings, and new deposition methods have been investigated in recent years. The paper presents an updated review of the tribological properties of DLC and related materials, and discusses the mechanisms suggested for the explanation of the wear and friction behavior of these materials.

Tribology of diamondlike carbon and related materials: an updated review

This review highlights the synthesis, processing and properties of non-oxide silicon-based ceramic materials derived from silazanes and polysilazanes. A comprehensive summary of the preparation of precursor compounds containing Si–N–Si units, including commercially available materials, is followed by the discussion of various processing techniques. The fabrication of dense bulk ceramics in the Si/E/C/N systems is reported which involves cross-linking of the polymeric ceramic precursor followed by a polymer-to-ceramic transformation step. The cross-linked precursor can be milled, compacted and pyrolysed to form dense, additive-free, amorphous silicon carbonitride monoliths or polycrystalline composites which withstand oxidation in air at 1600°C. Furthermore, an overview is given on the fabrication of silazane derived powders and coatings involving chemical vapour deposition (CVD) methods utilising volatile precursors. Fibre spinning and fibre properties, as well as other processing techniques like infiltration of preforms, the preparation of porous ceramics and joining are briefly discussed. A state of the art of the mechanical properties of polymer derived amorphous Si/C/N and Si/B/C/N ceramics with respect to hardness as well as high-temperature creep and oxidation resistance is summarised. Finally, some important aspects of industrial applications will be considered. The review is in part based on our own work related to the polysilazane derived ceramics, but will also cover a comprehensive state of the art including the published literature in this field.

Silazane derived ceramics and related materials

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In our recent studies, diamond-like carbon (DLC) films were found to possess low coefficient of friction (f < 0.1) and excellent wear resistance. The reduction in f was found to be consistent with wear-induced graphitization of the DLC structure. The purpose of the present work was to study the effect of load and sliding velocity on the frictional behavior and graphitization process occurring in DLC during wear. Pin-on-disc experiments were conducted on DLC-coated SiC substrates at sliding velocities between 0.06 and 1.6 m s−1 under 1 and 10 N loading levels using ZrO2 balls as the pin material. Analytical transmission electron microscopy was used to characterize the structure and microstructure of the wear debris after testing. The results showed that both sliding velocity and contact load influence the graphitization process. Higher sliding velocities increase the contact frequency and the rate of temperature rise that may facilitate the release of hydrogen atoms from the sp3 structure. Higher loading enhances shear deformation and transformation of the weakened hydrogen-depleted DLC structure into graphite [10]. The present findings are consistent with our earlier proposed wear-induced graphitization mechanism for these films. An equation was developed to describe the transformation kinetics of DLC into graphite as a function of sliding velocity and applied stress.

An investigation of the relationship between graphitization and frictional behavior of DLC coatings

Friction induced phase transformation of pulsed laser deposited diamond-like carbon

Thin films of yttrium‐rich YBa2Cu3O7−x with c‐axis orientation prepared by plasma‐enhanced metalorganic chemical vapor deposition have been examined by high‐resolution transmission electron microscopy. Yttria precipitates smaller than 50 (A) in size have been identified in the matrix. They are uniformly distributed, have a high density as large as 1024 per cubic meter and are oriented with respect to the matrix. The magnetic field dependence of the critical current density of the thin films indicates that the yttria precipitates are effective flux pinning centers.

High density, ultrafine precipitates in YBa2Cu3O7−x thin films prepared by plasma‐enhanced metalorganic chemical vapor deposition

Diamond-like carbon (DLC) films were deposited on (100) silicon wafers and silicon nitride balls by RF plasma-assisted chemical vapor deposition at a pressure of 700 mTorr and a substrate temperature of 360 K. The friction coefficient and the wear rates were measured using a pin-on-disk tribometer in 40% humid and dry air. Friction coefficients are near 0.05 in all cases measured. In dry air, the wear of silicon nitride and steel against DLC is below measurement capability because of a protecting DLC transfer layer, and wear of DLC is 2.5 ± 10−8 mm3/Nm against silicon nitride and 6.5 ± 10−9 mm3/Nm against steel. In humid air, the DLC transfer layer does not adhere to the solids, and wear of both bodies is larger. Unmeasurable wear is obtained when DLC slides against itself in humid air; the wear rate is 5 ± 10−9 mm3/Nm in dry air. These results are interpreted in terms of the properties of a friction-induced transformation of the surface layer of DLC.

Tribology of diamond-like carbon sliding against itself, silicon nitride, and steel

YBa2Cu3O7−x superconducting thin films with a critical current density of 2.3×106 A/cm2 at 77.7 K and 0 T were prepared by a metalorganic chemical vapor deposition process. The films were formed in situ on LaAlO3 at a substrate temperature of 730 °C in 2 Torr partial pressure of N2O. Resistivity and magnetic susceptibility measurements of the as‐deposited films show a sharp superconducting transition temperature of 89 K with a narrow width of less than 1 K. Critical current densities were measured by the dc transport method with a patterned bridge of 120 μm×40 μm. Both x‐ray diffraction and high‐resolution electron microscopy measurements indicate that films grew epitaxially with the c axis perpendicular to the surface of the substrate.

High critical current densities in YBa2Cu3O7−x thin films formed by metalorganic chemical vapor deposition at 730 °C

Highly textured, highly dense, superconducting YBa2Cu3O7−x thin films with mirror‐like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 °C by a remote microwave plasma‐enhanced metalorganic chemical vapor deposition process (PE‐MOCVD). Nitrous oxide was used as the oxidizer gas. The as‐deposited films grown by PE‐MOCVD show attainment of zero resistance at 72 K. PE‐MOCVD was carried out in a commercial scale MOCVD reactor.

Low‐temperature in situ formation of Y‐Ba‐Cu‐O high Tc superconducting thin films by plasma‐enhanced metalorganic chemical vapor deposition

High‐quality BaTiO3 thin films have been epitaxially grown on (001) LaAlO3 and (001) NdGaO3 substrates by plasma‐enhanced metalorganic chemical vapor deposition at a substrate temperature of 680 °C. X‐ray diffraction θ–2θ, ω, and φ scan results all indicate that single‐crystalline BaTiO3 thin films were epitaxially grown on the substrates with 〈100〉 orientation perpendicular to the substrates. The high degree of epitaxial crystallinity is further confirmed by Rutherford backscattering spectrometry which gives a minimum yield of 7.5% and 11% for films deposited on LaAlO3 and NdGaO3, respectively. Cross‐section high‐resolution electron microscopy images also showed that the layer epitaxy of BaTiO3 was characterized by an atomically abrupt film/substrate interface. Scanning electron micrographs showed that these films had very smooth surface morphologies.

Bernard Gallois

Papers

High density, ultrafine precipitates in YBa2Cu3O7−x thin films prepared by plasma‐enhanced metalorganic chemical vapor deposition

Tribology of diamond-like carbon sliding against itself, silicon nitride, and steel

High critical current densities in YBa2Cu3O7−x thin films formed by metalorganic chemical vapor deposition at 730 °C

Low‐temperature in situ formation of Y‐Ba‐Cu‐O high Tc superconducting thin films by plasma‐enhanced metalorganic chemical vapor deposition

Epitaxial growth of BaTiO3 thin films by plasma‐enhanced metalorganic chemical vapor deposition