Adhesion Of Diamond-like Carbon Films Research Articles

Investigating the fracture resistance and adhesion of DLC films with micro-impact testing

Micro-impact testing, a new repetitive contact testing technique has been developed to simulate the fatigue conditions which coatings experience in service more closely than existing testing methods. Diamond-like carbon (DLC) films deposited on silicon under different RF powers have been investigated with the new technique. The technique provides a new approach to the investigation of the fracture properties of thin films. Single-point impact data for brittle materials, such as DLC films, show an initial period of damage generation followed by catastrophic failure. The time-to-failure and the overall change in probe depth during a test are measures of the resistance of the coating to fracture. Differences in impact resistance between the DLC films are explained in terms of variations in film toughness and adhesion strength, which, in turn, are a function of the DLC deposition conditions.

Design of W buffer layer for adhesion improvement of DLC films on tool steels

Diamond-like carbon (DLC) has been a candidate for various applications due to its excellent tribological and mechanical properties. However, poor adhesion on tool steels limits its applications over a wide range. In the present work, we investigated the effect of W and W–C intermediate layers on the adhesion of DLC films to AISI D2 tool steels. The intermediate layers were deposited by dc magnetron sputtering and the DLC films were deposited on the various intermediate layers by rf-PACVD. Adhesion of the DLC film was significantly improved by introducing W and W–C intermediate layers. The adhesion was strongly dependent on the thickness of W layer and the CH 4 fraction in the sputtering gas during the intermediate layer deposition. TEM cross section revealed that, in addition to the chemical compatibility between carbon and the intermediate layer materials, the microstructure of the intermediate layer is also important to improve the adhesion. Columnar grains of the intermediate layers and structural continuity between the W and W–C mixed layers were the significant factors affecting the adhesion of DLC films.

A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2×10−4 Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl), N) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (≥20 μm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1–3 μm) were investigated using a ‘Fischerscope’, and Young's module of thin films (20–70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS), X-ray excited Auger electron spectroscopy (XAES), and X-ray photoelectron spectroscopy (XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coefficient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43–3.65 g/cm3. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.

Enhanced adhesion of diamond-like carbon films with a composition-graded intermediate layer

Adherent diamond-like carbon films were deposited on silicon substrates by the pulsed laser deposition method under a magnetic field. A composition-graded intermediate layer with a composition gradient from the substrate to the film was used to enhance the adhesion. It was found that adhesion was dependent on the thickness and composition gradient of the intermediate layer. For diamond-like carbon films deposited at room temperature, intrinsic stress in the interlayer played a key role. When an intermediate layer with a thickness of about 103 nm was used, the intrinsic stress was maximum and adhesion was poor. For films deposited at 60 °C and 100 °C, thermal stress and intrinsic stress should be considered together. Very thin intermediate layers ( 34 nm) were not suitable for good adhesion due to the presence of thermal stress. Adhesion was poor when the thickness of the intermediate layer was about 178 nm owing to imposition of the intrinsic stress. A composition profile with an exponent greater than 1 (silicon-riched) was beneficial to good adhesion.

Micro- And Nano-Mechanical Behavior of Diamondlike Carbon Containing Foreign Atoms Prepared by Pulsed Laser Deposition

AbstractWe have prepared diamondlike carbon (DLC) films using KrF excimer pulsed laser (248 nm). The DLC films were deposited on Si (100) substrates and Cu and Ti were incorporated into the films through adopting a new target design. Visible Raman spectroscopy analysis of G-peak was correlated to internal stress changes in the DLC films due to incorporation of foreign atoms. Reduction of internal stresses in the presence of foreign atoms was established. This is consistent with adhesion studies that showed significant improvement in adhesion of DLC films containing dopants. Nanohardness and Young's modulus of DLC films containing Ti and Cu showed some decrease as compared to pure DLC. The experimental results are discussed in terms of the effect of dopants on the short range environment of the continuous random network (CRN) of DLC.

Micro-Hardness and Adhesion of Diamond-Like Carbon Films

Diamond-like carbon films have been synthesized by the pulsed laser deposition under a magnetic field. The hardness of the films was increased considerably. However, due to the large compressive stress in the films, adhesion of the films became a serious problem. Two methods, i.e. laser irradiation of the silicon substrate surface and growing a composition-graded intermediate layer, were used to increase the adhesion. With the variations of the interface conditions, the change of the stress type from compressive stress to tensile stress was observed. By careful choosing the composition change of the intermediate layer, adherent diamond-like carbon films with a thickness of 1145 nm were successfully grown on silicon substrates at 80°C.

The effect of biological fluids on the adhesion of diamond-like carbon films to metallic substrates

Abstract Diamond-like carbon (DLC) films deposited by standard r.f. glow discharge CVD were exposed to various fluids (distilled water, phosphate-buffered saline (PBS) solution and 40% serum in PBS) to study the effect of this exposure on the stability of DLC coatings on metallic substrates. A substrate plastic straining technique was used to study the strength and adhesion of the coatings before and after exposure to various fluids. Distilled water had no apparent effect, whereas PBS caused localized debonding and cracking of the film. The serum-PBS solution had an intermediate effect. X-Ray photoelectron spectroscopy (XPS) measurements indicated that PBS tends to penetrate through surface perforations and attack the thin transition layer of graded Si C composition between the Si-rich layer on the substrate and the DLC coating. An increase in exposure temperature increased the population of defects in samples exposed to PBS. Coatings on Ti were found to be more resistant to damage.

Adhesion assessment of DLC films on PET using a simple tensile tester: Comparison of different theories

The adhesion of Diamond-Like Carbon (DLC) films on Poly(ethyleneterephthalate) (PET) sheet has been characterised by tensile testing, using simple equipment. Three theoretical analyses of the tensile test are described, and their validity has been studied by calculating in three different ways the adhesion of the same samples (DLC on PET). The theoretically predicted adhesion from the longitudinal strain required for coating debonding did not appear to be an appropriate indicator for coatings on polymers. An approach consisting of measuring either the minimum or the maximum crack spacing led to results which were more consistent with the literature. The adhesion of DLC films on PET has been increased by a factor of 1.8 when a 5 min argon plasma treatment is applied prior to deposition. Although quantitative results have to be considered with caution, this method is a simple and quick means of obtaining semi-quantitative results.

Adhesion of diamond-like carbon films on polymers: an assessment of the validity of the scratch test technique applied to flexible substrates

The validity of the scratch test as a method of assessing the adhesion of diamond-like carbon (DLC) on polymers has been studied. Sheets of 12 μm thick polyethylene terephthalate (PET) and 100 μm t...

Use of ion implantation for improving the adhesion of diamond-like carbon films deposited by means of other techniques

Nanoindentation and friction tests have been used to establish the beneficial effect of pre-implantation of low C fluences upon the adhesion of diamond-like coatings synthesized by a laser plasma or by plasma enhanced chemical vapour deposition. The improvement is attributed to an interfacial layer of carbide.