Chemical Vapor Deposition Diamond Coating Research Articles

Enhanced Growth Rate of Chemical Vapor Deposition Diamond Coating Motivated by Graphene Oxide

To improve the growth rate of chemical vapor deposition (CVD) diamond coating, increasing the chemical reaction rate is essential. A novel method of dispersing graphene oxide (GO) particles as adsorbent on the substrate prior to deposition was proposed, with which the diamond coating with large grain size and high thickness was deposited on the silicon nitride under the normal CVD environment. The as-deposited diamond coating was characterized by scanning electron microscopy (SEM), surface profilometer, atomic force microscope (AFM), Raman spectrum, and indentation. The surface morphologies showed that the GO particles were covered by a layer of diamond coating. The diamond coating without and with GO particles had growth rates of 1.10–1.38 and 1.50–2.94 μm h−1, respectively. No differences in the Raman spectra of the microcrystalline diamond (MCD) coatings without and with GO particles were found. Indentation tests suggested that GO particles could enhance the adhesive strength and the crack resistance of diamond coating, which may result from the large thickness and the strong adsorbed capacity of destructive energy. Hence, dispersing particles on the substrate can be regarded as a potential and alternative technique by accelerating the CVD chemical reaction to obtain desired diamond coating.

Impact of Peak Material Volume of Polycrystalline CVD Diamond Coatings on Dry Friction Against Aluminum

For economic and environmental reasons, dry forming is of increasing interest due to the shortening of process chains, cost savings and reduction of environmental pollution. The aim of these investigations is to examine to what extent chemical vapor deposited (CVD) diamond coatings are suitable for dry forming of aluminum and to identify the surface topology requirements for a low friction coefficient and low wear. Nine different surface topologies of CVD diamond coatings were tested in an oscillating ball-on-plate tribometer test against aluminum balls with a Hertzian contact stress of 759 MPa and 99,900 cycles. It could be concluded that the peak material volume (Vmp) of the diamond coating is the most important factor for achieving a low abrasion of aluminum as well as a low friction coefficient against aluminum. The Vmp should be smaller than 0.04 ml/m2. Microcrystalline CVD diamond with a post-treated surface has great potential for dry forming of aluminum.

Surface Microstructuring of Steel Components for CVD Diamond Coating by Ultrasonic Vibration Superimposed Face Milling using Tailored Tools

Diamond coatings applied by chemical vapor deposition (CVD) provide extraordinary properties concerning hardness and wear resistance, which enables an increase of the performance or lifetime of highly stressed components. In particular, the combination of steel substrates and diamond coatings allows for numerous applications in several sectors of industry. However, there are significant challenges considering the coating adhesion strength. For example, the mismatch concerning the thermal expansion of steel and diamond commonly leads to a delamination of the coating. Thus, a suitable pre-treatment of the substrate surface is compulsory.With the aim of improving CVD diamond coating adhesion, ultrasonic vibration superimposed machining (UVSM) is applied when doing face milling on steel X46Cr13 specimens. The vibration direction is parallel to the tool axis and perpendicular to the feed direction. The tool wear and the surface microstructure are determined by 3D laser scanning microscopy.The investigations show, that predefined microstructuring of the substrate surface by UVSM contributes to an enhancement of the CVD diamond coating adhesion, especially regarding coatings with a thickness up to 10 µm. This can be referred to a better distribution or a reduction of thermally induced residual stresses in the diamond layer. However, a reliable generation of deterministic microstructures by UVSM significantly depends on the wear behavior of the tool. Uncoated cemented carbide grades exhibit considerable deficits reflecting in rapid tool wear. Therefore, adapted tool coatings are experimentally investigated, which result in an increase of the tool life and a reduction of the geometrical deviations of the microstructures. With an appropriate system of surface microstructure and coating, for example for tribological applications substantial improvements in terms of wear resistance and coefficient of friction are expected.

Design of Deterministic Microstructures as Substrate Pre-Treatment for CVD Diamond Coating

The coating of highly stressed components with chemical vapor deposition (CVD) diamond can extend their lifetime. In particular, the combination of steel substrates with diamond layers would find many applications in industrial production. However, there are some challenges, for example, the high mismatch in the thermal expansion between steel and diamond, which commonly leads to the delamination of the coating. Thus, a pre-treatment of the substrate surface is needed. Particle blasting has been established in some studies as a suitable process. However, apart from particle residues in the surface of the substrate, these surfaces have a stochastic character, which limits their reproducibility and modification options. This paper presents some instructions for the recording and derivation of defined properties of those surfaces. The conversion of characteristic surface features into quantitative process parameters could serve as the foundation for the manufacturing of deterministic microstructures, especially those produced by ultrasonic vibration superimposed machining. This should increase the reproducibility and the possibilities of the modification with regard to the structural shaping of the functional surface. The design was developed using both a kinematic surface simulation tool as well as a finite elements analysis for the cooling process of the coating–substrate–composite. A high accordance with real finished surfaces was achieved.

Engineered CVD Diamond Coatings for Machining and Tribological Applications

Diamond is an allotropes of carbon and is unique because of its extreme hardness (~100 GPa), low friction coefficient (<0.05), high thermal conductivity (~2000 Wm−1 K−1), and high chemical inertness. Diamond is being synthesized artificially in bulk form as well as in the form of surface coatings for various engineering applications. The mechanical characteristics of chemical vapor deposited (CVD) diamond coatings such as hardness, adhesion, friction coefficient, and fracture toughness can be tuned by controlling the grain size of the coatings from a few microns to a few nanometers. In this review, characteristics and performance of the CVD diamond coatings deposited on cemented tungsten carbide (WC-Co) substrates were discussed with an emphasis on WC-Co grade selection, substrate pretreatment, nanocrystallinity and microcrystallinity of the coating, mechanical and tribological characteristics, coating architecture, and interfacial adhesion integrity. Engineered coating substrate architecture is essential for CVD diamond coatings to perform well under harsh and highly abrasive machining and tribological conditions.

A Novel Method for Specimen Preparation and Analysis of CVD Diamond Coated Tools Using Focussed Ion Beams (FIB) and Scanning Electron Microscopy (SEM)

Investigations of the microscopic properties of chemical vapor deposited diamond coatings on tungsten carbide tools are important to understand the coating–substrate interface (Uhlmann et al. in Prod Eng Res Dev 11(2):83–86, 2004; Surf Coat Technol 131, 395–399, 2000), the coating morphology, and the properties of cracks. Commonly the microscopic properties are analyzed in the transmission electron microscope (TEM). This paper presents a novel investigation method that includes a faster specimen preparation and that offers new analyzing possibilities. It applies a well-established device combining a scanning focused ion beam (FIB) column for the preparation of the specimens and a scanning electron microscope (SEM) for the analysis of the specimen. The aim of the paper is to verify preparation parameters for which the microscopic properties of the diamond coating are preserved during the FIB preparation and to show that the SEM analysis provides the same results of microstructure and element distribution compared to the TEM analysis. Furthermore, the feasibility of new analysis methods is studied. The FIB/SEM method traces and images defects in the nanometer range like cracks, crack propagation directions, delaminations, and layer inhomogeneities directly. The bulk FIB-prepared specimens are suitable for a precise standard-based element quantification and distribution analysis using energy or wavelength (WDX) dispersive X-ray spectroscopy. Moreover, the WDX analysis distinguishes between graphite-like carbon and diamond.

Acid Pretreatment of WC-Co for Surface Roughening and Cobalt Removal Prior to CVD Diamond Coating

Chemical vapor deposition (CVD) diamond coatings are being developed to be applied on carbide cutting tools to enhance wear resistance and increase tool life. As a prerequisite, for ensuring adhesion of CVD diamond on tungsten carbide substrate, it is necessary to prepare high surface roughness and to remove the cobalt on tungsten carbide surface during the pretreatment. In this study, a two step acid pretreatment was examined for those purposes. Etching using modified Murakamis reagent was initially performed to roughen the surface. Subsequently, the carbide was immersed in nitric acid to remove cobalt. Concentration of the acid solutions and reaction time were varied. Results showed that the initial step by modified Murakamis reagent etching resulted in a surface roughness of Ry = 6.95 µm, which is a 15% increase from the average initial surface roughness. The second step by nitric acid immersion on modified Murakamis reagent etched carbide samples resulted in carbide surfaces with zero cobalt content, confirming the effectiveness of the pretreatment.

Acid Pretreatment of WC-Co Prior to CVD Diamond Coating

Pretreatment on tungsten carbide (WC-Co) surface is critical for obtaining perfectly adherent diamond coatings by chemical vapor deposition (CVD). The carbide surface should have high roughness to facilitate diamond nucleation and adhesion. The presence of cobalt—common binder for tungsten carbide—on the surface to be coated should be made minimum since it has negative influence on the diamond deposition process. In this study, surface pretreatment on tungsten carbide using sulfuric acid was evaluated in terms of the resulted cobalt removal and the surface roughening. The variables included were acid concentration, reaction temperature, and reaction time. The resulted surface roughness was 29% higher than initial, averaged at 1.07 µm. The acid pretreatment was also found effective in eliminating surface cobalt.

Growth and adhesion of hot filament chemical vapor deposited diamond coatings on surface modified high speed steel

Diamond coatings were deposited by hot filament chemical vapor deposition on high speed steel substrates. Iron boride diffusion barrier and WC–Co layers were used as interlayers. At high deposition pressure, the quality of the diamond deposits is poor due to the extensive formation of graphitic deposits. At low pressure, diamond films of better quality were obtained, but their adhesion to the substrate was insufficient. A two-step deposition process at low pressure was developed. In a first deposition step performed at high methane percentage, a high nucleation density was achieved. In a second deposition step, the methane percentage was reduced to achieve continuous, dense, and adherent diamond layers on borided or WC–Co coated high speed steel substrates. Adhesion of these diamond layers on the surface modified high speed steel substrates was tested based on reciprocating sliding tests.

A comparative study of the mechanical strength of chemical vapor-deposited diamond and physical vapor-deposited hard coatings

Four mechanical parameters of physical vapor-deposited (PVD) hard coatings were obtained, which were the residual strain, Young's modulus, film toughness, and interface toughness, concerning titanium aluminum nitride (TiAlN) and titanium nitride (TiN) coatings deposited on WC–Co substrates. The results were quantitatively compared with the author's previous trials for the case of chemical vapor-deposited (CVD) diamond coatings. Due to the significant difference in the mechanical properties between PVD hard coatings and CVD diamond coatings, it was necessary to develop new experimental techniques, which could properly evaluate those parameters for the case of PVD hard coatings. As a conclusion, film toughness of PVD hard coatings was surprisingly brittle. It was an order of magnitude smaller than that of CVD diamond coatings. In contrast, no significant difference was found in interface toughness between these different kinds of coatings. Concerning the residual strain, TiN had far larger level than the other two. These differences in mechanical properties were further discussed in relation to the difference in their wear behavior.

Mechanical Characterization of a CVD Diamond Coating by Nanoindentation Test

A FEM analysis was carried out to study the mechanical behavior of a hard coating subjected to a nanoindentation test performed with a Berkovich indenter. The nanoindentation test was simulated by FEM code MSC Marc. The case study is a coating of CVD (Chemical Vapor Deposition) diamond. By the simulation it is possible to obtain the load-displacement curve by which Young modulus and hardness may be evaluated. The paper also analyzes the residual stresses developed at the end of the unloading phase and the influence of the strengthening law to determine the hardness and the elastic modulus of the CVD diamond. The analysis has demonstrated, by the comparison with the experimental results, that the numerical model well describes the behavior of the coating of CVD diamond in the nanoindentation test; in addition it was pointed out that the choice of the hardening law is a crucial aspect in the simulation.

CVD Diamond Coating for Erosion Protection at Elevated Temperatures

Small solid particles entrained in a gas-fluid turbomachinery flow can cause degradation of the component surfaces containing the flow by erosion and corrosion processes. As diamond is the hardest known material, much work has been done to use polycrystalline diamond (PCD) as a protective coating on parts operating in a hostile and abrasive environment. Little attention is given in the literature to the high-temperature erosion behavior of chemical vapor deposition (CVD) diamond on different substrates. The objectives of this research were to develop CVD diamond erosion barriers for surface protection of cemented tungsten carbide at high temperatures and to study the erosion behavior of the coatings. Microwave plasma chemical vapor deposition (MPCVD) was used to apply diamond films on WC-6%Co. The erosion behavior of the coated specimens was investigated experimentally by exposing them to abrasive particle-laden flow in a high-temperature wind tunnel. The obtained results show the effects of impingement angle, temperature, and particle dose on the erosion rate. The data demonstrate that uncoated substrates suffer 6–7 times higher wear compared to diamond-coated samples at elevated temperatures up to 538 °C when exposed to alumina particle flow. This study indicates that polycrystalline diamond is emerging as a promising erosion protective coating for high-temperature applications.

Tribological performance of mechanically lapped chemical vapor deposited diamond coatings

Polycrystalline diamond layers were deposited onto the titanium alloy Ti–6Al–4V via microwave plasma chemical vapor deposition (CVD). It is shown that the diamond film reduces wear and friction immensely compared with uncoated titanium/titanium tribo systems. An additional polishing process of the CVD-diamond layer improves the wear behavior even further. An influence of air humidity is found.In addition, different ceramic materials (Al2O3, SiC, Si3N4, ZrO2) were tested against as-deposited and polished CVD-diamond layers. Al2O3 and Si3N4 exhibit very good wear behavior accompanied by very low friction against as-deposited CVD-diamond. SiC and ZrO2, however, show somewhat inferior wear and friction behavior. Suggestions are made to explain the different performance. Again, a wear increase is found with increasing humidity. Polishing of CVD-diamond layers improves the tribological performance further.

Friction and wear properties of diamonds and diamond coatings

Abstract The recent development of chemical vapor deposition techniques for diamond growth enables bearings to be designed which exploit diamond's low friction and extreme resistance to wear. However, currently produced diamond coatings differ from natural diamond surfaces in that they are polycrystalline and faceted, and often contain appreciable amounts of non-diamond material ( i.e. graphitic or amorphous carbon). Roughness, in particular, influences the friction and wear properties; rough coatings severely abrade softer materials, and can even wear natural diamond sliders. Nevertheless, the best available coatings exhibit friction coefficients as low as those of natural diamond and are highly resistant to wear. This paper reviews the tribological properties of natural diamond, and compares them with those of chemical vapor deposited diamond coatings. Emphasis is placed on the roles played by roughness and material transfer in controlling frictional behavior.