Ti-containing Diamond-like Carbon Research Articles

Investigation of the microstructure, mechanical properties and tribological behaviors of Ti-containing diamond-like carbon films fabricated by a hybrid ion beam method

Diamond-like carbon (DLC) films with various titanium contents were investigated using a hybrid ion beam system comprising an anode-layer linear ion beam source and a DC magnetron sputtering unit. The film composition and microstructure were characterized carefully by X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy, revealing that the doped Ti atoms had high solubility in the DLC films. The maximum solubility was found to lie between about 7 and 13at.%. When the Ti content was lower than this solubility, the doped Ti atoms dissolved in the DLC matrix and the films exhibited the typical features of the amorphous DLC structure and displayed low compressive stresses, friction coefficients and wear rates. However, as the doped content exceeded the solubility, Ti atoms bonded with C atoms, resulting in the formation of carbide nano-particles embedded in the DLC matrix. Although the emergence of the carbide nano-particles promoted graphitizing due to a catalysis effect, the film hardness was enhanced to a great extent. On the other hand, the hard carbides particles caused abrasive wear behavior, inducing a high friction coefficient and wear rate.

Magnetron reactively sputtered Ti-DLC coatings on HNBR rubber: The influence of substrate bias

In this study, Ti-containing diamond-like carbon (Ti-DLC) coatings have been deposited on HNBR (hydrogenated nitrile butadiene) rubber and also on Si wafer as reference via unbalanced magnetron reactive sputtering from a Ti target in C 2H 2/Ar plasma. The deposition rates of coatings on rubber and Si wafer were about the same. Columnar structures resulting from a rough interface were often observed in the coatings deposited on rubbers. Only at a high bias voltage of − 300 V the coating on HNBR rubber became column-free whereas a bias voltage of − 100 V could already restrain the columnar structure and thus produced dense and smooth coatings on Si wafer. A segmented morphology of the coatings on HNBR rubber is formed as a result of the large difference in thermal expansion between the coating and HNBR rubber. The crack network that separates the patches plays an important role in maintaining the coating flexibility. The size of the patches reduces with increasing bias voltage and thus the variation of deposition temperature. A high bias voltage enhances the hardness of Ti-coating and the rubber-coating adhesion, and guarantees a good tribological performance. When sliding against ø6 mm 100Cr6 steel ball counterpart, very low coefficients of friction were achieved (< 0.25 for the coated rubber versus > 1.3 for the uncoated). The Ti-DLC coating can be considered as a promising material for the enhancement of tribological performance of rubbers.

Deposition of Ti-containing diamond-like carbon (DLC) films by PECVD technique

Diamond-like carbon (DLC) films have been largely studied for their excellent mechanical properties and their high potential in many industrial applications. Although DLC films have poorer physical properties than diamond films, their lower thermal stability and high internal residual stress can be avoided with the incorporation of other elements, such as silicon, nitrogen and some metals.Nanostructured DLC coatings are usually deposited by a combined plasma assisted PVD/CVD technique and sputtering system. We have prepared Ti-containing DLC films deposited by plasma decomposition of CH4/H2/Ar gas mixture with titanium isopropoxide (Ti[OCH2CH3]4), as a metal precursor. The deposited films were found to be composed of amorphous titanium oxide and nanocrystalline titanium carbide, embedded in an amorphous hydrogenated (a-C:H) matrix (DLC). The TiC/TiO2 ratio in the DLC matrix was dependent on the process parameters. The films' composition was monitored as a function of gaseous fluxes. The structural and chemical–physical characterization has been performed by means of XRD and XPS techniques.

A cathodic arc enhanced middle-frequency magnetron sputter system for deposition of hard protective coatings

A new cathode arc enhanced magnetron sputter system for deposition of hard protective coatings is reported in this article. This system consists of eight targets: four outer targets are mounted on the wall of the chamber and four inner targets are placed around the center of the chamber. The outer and inner targets form four pair targets and are powered by four middle frequency power supplies. One of the outer targets can run either in the cathode arc mode or in the magnetron sputter mode. The Ti-containing diamond-like carbon nanocomposite coatings were deposited by using this system. The prepared coating exhibits high hardness (∼20 GPa), good adhesion (critical load is 50 N), very low friction coefficient (∼0.07), and excellent tribological performance with a wear rate of 1.4 × 10 −16 m 3-·N −1·m −1.

An analysis of the nanotribological behaviour of Ti-containing hard carbon film

Diamondlike carbon (DLC) coatings are well known for their self-lubricating properties. Metal-containing DLC films exhibit reduced internal stress, improved adhesion and reduced sensitivity to humidity. Furthermore, Ti-containing DLC coatings are compatible with biological environments. In view of this, the primary aim of the present work was to evaluate and analyse the friction force behaviour of Ti-containing hard carbon films. This work is primarily intended for application to microelectromechanical systems. In order to achieve the above mentioned objective, a hard carbon layer containing 6 at.-%Ti was deposited using an unbalanced magnetron sputter system on a silicon substrate. The deposition rate of the film was monitored by a quartz microbalance. Using a stylus profilometer, the thickness of the film was found to be 1·67 μm. The hardness and the elastic modulus of the film were determined using a nanoindenter. The hardness and the elastic modulus were determined to be 1·7 GPa and 17·7 GPa, respectively. The pull-off force, topography and friction force surface of the film were characterised with the use of an atomic force microscope. The pull-off force and the friction force were found to be 165·9 nN and 1·7 nN, respectively. The surface roughness Ra was found to be 2·65 nm. The friction coefficient was evaluated as a ratio of the friction force and the summation of the pull-off force and the normal force. Using the topography, and lateral force image, the topography induced friction force surface and the adhesion induced friction force surface were evaluated. The influences of applied loads and scan speeds on friction coefficient and various friction force surfaces are described in detail.

Deposition and microstructure of Ti-containing diamond-like carbon nanocomposite films

Ti-containing diamond-like carbon (DLC) films were deposited by plasma decomposition of CH 4/Ar gas mixtures with an introduction of tetrakis(dimethylamino)titanium (TDMAT, Ti[(CH 3) 2N] 4), which was used as a precursor of titanium. The films deposited were found to be nanocomposite coatings consisting of TiN nanocrystalline clusters and amorphous hydrocarbon (a-C:H), indicating that the nanocrystalline clusters were embedded in the DLC matrix. The crystallinity of TiN clusters, as well as the Ti atomic concentrations in the films, increased with an increase of substrate temperature. The substrate temperature applied to form a crystalline phase in the DLC matrix induced a graphitization of amorphous hydrocarbon matrix. The increase of volume fraction of TiN nanocrystalline clusters in the DLC matrix enhanced the mechanical properties of nanostructured coatings, although the graphite-like structural transition of DLC matrix happened due to the applied heating.

Friction and wear characteristics of a Ti-containing diamond-like carbon coating with an SRV tester at high contact load and elevated temperature

The friction and wear characteristics of a Ti-containing diamond-like carbon (Ti-DLC) coating have been evaluated with a Schwingungs Reibung und Verschleiss (SRV) tester when reciprocating sliding against a steel ball and a CrN-coated pin at high contact load and elevated temperature under a boundary-lubricated condition. The Ti-DLC coatings exhibit a friction coefficient of 0.06–0.12 and a wear rate of 1.99×10 −10 to 9.5×10 −7 mm 3/N m, depending on the counterfaces, load and temperature. The Ti-DLC/CrN-coated pin pair shows a low friction coefficient than the Ti-DLC/steel ball pair under the identical wear conditions. Increasing the test temperature reduces the coefficient of friction and, however, clearly increases the wear rate of the Ti-DLC coatings at 20 N. At 50 N and 150 °C, the Ti-DLC coating was removed completely and the wear was applied to the substrate. At below 100 °C, the wear mechanism of the Ti-DLC coatings is dominated by surface polishing effects. At 150 °C, brittle fracture, delamination, partial graphitization, and tribo-chemical reactions are found in the tribo-contact areas. The formation of iron oxides on worn surfaces of the Ti-DLC coatings at 150 °C is attributed to the dissolved oxygen in the oil lubricant and the tribo-chemical reactions. Furthermore, these friction and wear data have been compared quantitatively with pure DLC coatings and multilayered VTiN coatings under the identical wear conditions.

Improvement of boundary lubrication properties of diamond-like carbon (DLC) films due to metal addition

The effects of added materials such as metals like titanium (Ti), molybdenum (Mo) and iron (Fe) diamond-like carbon (DLC) films on boundary lubrication and microtribological properties were investigated. The nanoindentation hardness and microwear resistance can be improved by adding the proper metal to DLC films, as evaluated by atomic force microscopy (AFM). Boundary lubrication properties of DLC films with metals are improved as comparing with DLC films without metal under lubricant with both MoDTC and ZDDP additives. Moreover, lower friction coefficient of μ=0.03 than carburized steel is exhibited with the appropriate quantity of Ti added. The tribochemical reactant was formed on the sliding surface of the Ti-containing DLC film like as carburized steel. Higher mechanical damping materials containing elements, such as Mo, Zn, P and S, formed tribochemical reactors as observed by X-ray photoemission spectroscopy (XPS) and AFM force modulation methods.

Structural and mechanical properties of Ti-containing diamond-like carbon films deposited by filtered cathodic vacuum arc

Titanium-containing diamond-like carbon films were deposited on silicon wafer substrates at room temperature by the filtered cathodic vacuum arc technique. A wide range of negative bias voltage from 0 to 500 V was applied to the substrates during film deposition. The structural and mechanical properties of the films were analysed by Rutherford backscattering spectroscopy, Raman spectroscopy, surface profilometry, the scratch test, and nanoindentation. For comparison, a set of pure diamond-like carbon films were also deposited and analysed. Raman spectra showed that all the samples had the lowest intensity ratio of the D peak to G peak ( I D/ I G) at a bias voltage of approximately 80 V, which normally represents the highest sp 3-bonded carbon components in the films. Correspondingly, the highest internal stress (σ), hardness ( H) and Young's modulus ( Y), and the lowest scratch critical load ( L c) were observed at the bias voltage of approximately 80 V. With the increase of titanium content in the films, I D/ I G increased, while σ, H, and Y reduced, and L c increased. The results demonstrate that the addition of titanium into the diamond-like carbon films could significantly reduce the internal stress and, as a consequence, effectively improve the adhesion properties of these films.

Plasma-assisted deposition and characterization of Ti-containing diamondlike carbon coatings

We report on the synthesis of Ti-containing diamondlike hydrocarbon (Ti-DLC) coatings by plasma-assisted physical vapor deposition and the characterization of coating microstructure and mechanical properties. We find that Ti-DLC coatings with Ti compositions higher than 5.5 at. % are composites consisting of nanocrystalline TiC in an amorphous hydrocarbon matrix. The hardness and elastic modulus of Ti-DLC coatings are found to increase monotonically with increasing Ti composition, while the ratio of the hardness to the modulus remains approximately constant.