Deposition Of Diamond Coatings Research Articles

SIMULATION AND EXPERIMENTAL RESEARCH STUDIES ON TEMPERATURE FIELD FOR THE PRODUCTION OF DIAMOND-COATED MILLING TOOLS BY HFCVD DEVICE WITH SEPARATED WORKTABLES

Diamond-coated tools have extremely extraordinary physical and chemical properties and have become ideal tools for machining the emerging materials that are hard to machine. In mass production of diamond-coated milling tools, the homogeneity of diamond coatings has always been sought for and is highly influenced by the uniformity of temperature field near the tool substrate. In order to further improve the uniformity of the temperature field and deposit diamond coatings with uniform thickness, a novel hot filament chemical vapor deposition (HFCVD) device with separated worktables and plates for mass production of diamond-coated milling tools is proposed. First, the simulation models of previous device with integrated worktable versus new device with separated worktables are established using finite volume method. The simulation results shows that the temperature distribution is more uniform in the device with separated worktables. Second, temperature measurement experiments are conducted, which prove the correctness of simulation model. Subsequently, experiments involving the deposition of diamond coatings on milling tools are conducted using two kinds of worktables, utilizing the same parameters as in the simulation. Finally, high-speed milling experiments are conducted to test the diamond-coated milling tools. According to the results of SEM, Raman and high-speed milling experiments, it can be concluded that the homogeneity of coating thickness and cutting performance of the milling tools produced by HFCVD device with separated worktables and plates are better.

Effect of argon on microwave plasma chemical vapor deposition of diamond coatings from an H2+CH4+Ar mixture activated in a microwave discharge

Effect of argon on microwave plasma chemical vapor deposition of diamond coatings from an H2+CH4+Ar mixture activated in a microwave discharge

Comparing the environmental and economic performances of different substrate pre-treatment processes for diamond coating deposition

The deposition of diamond coatings on hard metals substrates is a common strategy to improve mechanical characteristics of parts (e.g. cutting tools), but requires the pre-treatment of substrates. The study aims to investigate the environmental and economic sustainability of two different substrate pre-treatment processes: (i) two-step chemical etching process, and (ii) high-power continuous wave diode laser method. The cradle to gate study considers the superficial treatment of a WC-Co specimen as functional unit. The Life Cycle Assessment results highlight that for most of the ReCiPe impact categories, the environmental impact of laser treatment is greater than that of the chemical process (+38% in case of Climate Change, +45% in case of ReCiPe endpoint Single score), mainly due to the high energy consumption of the laser. The cost estimation, instead, highlights relevant savings for the laser process (about -98%), due to higher cost of chemicals than for electricity.

Hot filament chemical vapor deposition temperature field optimization for diamond films deposited on silicon nitride substrates

The influence of some key parameters of hot filament chemical vapor deposition (HFCVD) on the temperature distribution during the deposition of diamond coatings on silicon nitride (Si3N4) substrates was assessed with the help of the finite element method. Solid heat transfer, fluid heat transfer and surface radiation heat transfer mechanisms were used to calculate the substrate temperature in the steady state during the deposition process. The accuracy of the model was verified by comparing the simulation model with experimental measurements. The comparison shows that the deviation between the model and the actual substrate temperature measurements is within 3%. Furthermore, a Taguchi orthogonal experiment was designed (3 factors, 3 levels, L9). By changing the number of hot filaments, the distance between the filaments and the substrate, and the separation between two adjacent hot filaments, the influence trend of these parameters on the substrate temperature was assessed, leading to an optimal hot filament arrangement. A deposition experiment was carried out using the optimized parameters, and the results showed that the substrate surface temperature obtained by numerical simulation is highly consistent with the temperature measured by the infrared thermometer. The optimized deposition parameters contributed to a more suitable temperature range and more uniform temperature distribution on the Si3N4 ceramic substrate. The deposited diamond film exhibited uniform crystal quality and grain morphology, thus verifying the validity of the simulation results.

Novel conversion annealing pretreatment for improved deposition of diamond coatings onto WC-Co cemented carbide

To maintain the substrate strength and toughness of WC-Co cemented carbide as well as improve its adhesion with a diamond coating deposited by hot filament chemical vapor deposition (HFCVD), a novel conversion annealing pretreatment was studied. The pretreated substrates, as-nucleated, and as-grown diamond coating specimens were characterized using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and Rockwell hardness tests. It was found that conversion treatment could effectively convert the Co in the surface layer into intermetallic (Co3W, Co7W) and/or Co-rich compound (M6C, M12C) phases. The conversion layer underwent a re-carburization process during the nucleation stage of HFCVD. The intermetallic phases returned to the γ-Co (W) phase which will be encapsulated by the freshly formed WC layer. This is beneficial for seeding growth and new diamond nuclei formation. However, those Co-rich carbides consumed much carbon atoms to decompose and react to form a lot of free γ-Co phase during the nucleation stage, which promoted severe graphitization at the growth interface during HFCVD, and caused the film to peel off. A high-quality microscale diamond coating with an adhesion of the HF 2–3 level could be deposited onto the conversion layer with only the WC and Co3W phases.

Computer simulation of sublayer temperature mode during deposition of diamond coatings using gas-plasma method

The research presents a computer simulation of the temperature field on the sublayer surface, performed in a stationary mode during the deposition of diamond coatings using the gas-plasma method with different parameters of the cooling system. The optimization problem of mathematical programming with the search for the extremum of the performance function by varying the controlled parameters within the permissible range is considered.

EFFECT OF SUBSTRATE TEMPERATURE ON TANTALUM CARBIDES INTERLAYERS SYNTHESIZED ONTO WC-Co SUBSTRATES FOR ADHERENT DIAMOND DEPOSITION

Tantalum carbides (TaXC) interlayers have been synthesized by double glow plasma surface alloying (DG-PSA) method at different temperature for subsequent deposition of diamond coatings. The evolution of the microstructures, phase composition and adhesion of the interlayers dependent on substrate temperature has been discussed. The results show that the layers are composed of TaXC (i.e. Ta2C, TaC) with nanocrystalline microstructure and small amounts of CoTa2. The layer produced at 700∘C is formed of specific flower-shaped rings embedded in smooth structures. As the temperature increases to 800∘C, interacted rings are covered the full surface, and the surface roughness is increased. As the temperature increases further, the rings are replaced by irregular-shaped pits, caused a decreasing surface roughness. Besides the special microstructure with interactional rings and relatively high roughness, the layer prepared at 800∘C possesses higher adhesion, better wear performance and higher hardness than those of other layers. The coating obtained on the interlayer pretreated at 800∘C exhibits the best adhesion. Thus, the TaXC interlayers synthesized at 800∘C are demonstrated as a suitable option for adherent diamond coatings deposited onto WC-Co substrates.

Microwave Discharges in Liquids: Fields of Applications

The purpose of this review is to draw attention to the relatively new and poorly studied object of plasma physics, namely to the microwave discharges in liquids. Study of microwave discharges in liquids began only in early 2000-th and now they still remain one of the least studied plasma objects. Nevertheless, they are beginning to find application for solving various applied problems. This brief analytical review describes the results of studies on the use of such discharges in different applied areas: for water decontaminants, for generation of nanoparticles, for deposition of diamond coatings, for etching of photoresists, etc. Discharges can be created at pressure ranged from 0.1 kPa to atmospheric pressure at microwave powers from tens of watts to several kilowatts. Known data on the use of microwave discharges show their high efficiency in comparison with conventional discharges in the gas phase and in comparison with discharges of other types in liquids. Place of microwave discharges in liquids among other types of discharges is analyzed.

TiB2 barrier interlayer approach for HFCVD diamond deposition onto cemented carbide tools

The deposition of diamond coatings is often impaired by poor adhesion on hard metal substrates. To enhance the adhesion of diamond coatings on Co-cemented tungsten carbide (WC-Co), TiB2 thin films (100 nm to 1 μm in thickness) were deposited as interlayers by magnetron sputtering. Diamond coatings were continuously, densely and quickly deposited on the TiB2 interlayers. The adhesion of the diamond coatings evaluated by Rockwell C indentation, was enhanced by utilizing TiB2 interlayer with appropriate thickness compared to that without interlayer. The barrier function of the interlayer versus cobalt is dependent on the thickness of the TiB2 interlayer. As observed by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS), the cobalt diffusion was effectively hindered by utilizing TiB2 interlayers with a thickness greater than 200 nm, whereas the strongest film adhesion was obtained for the TiB2 interlayer with thickness of ca. 200 nm. Furthermore, the thickness of the deposited diamond film was 1.7 times higher than that of the diamond film grown without TiB2 interlayer, indicating an accelerated growth. Raman spectroscopy and X-ray diffraction (XRD) analyses demonstrated the existence of TiB2 and high quality of diamond films. This work indicates that thin TiB2 interlayers are promising candidates for achieving adherent diamond coated cutting tools, such as micro-drills and milling tools.

CVD diamond coating on WC-Co substrate with Al-based interlayer

Diamond coating with sufficient adhesion on WC-Co cutting tools is expected to significantly increase their cutting performance. In order to enhance the coating-substrate interfacial adhesion, Al2O3 and Ta mono-interlayer, Al-Al2O3, Al-AlN and Al-Ta duplex interlayer systems have been developed in this study. These interlayer materials were prepared using a magnetron sputtering method, and diamond coating were deposited on them using microwave plasma enhanced chemical vapor deposition. Grazing incident X-ray diffraction was carried out to determine the phase components in the Al-Al2O3 and Al-AlN interlayers. Raman spectroscopy and scanning electron microscopy were used to evaluate the quality, morphology and microstructure of the deposited diamond coatings. Rockwell C indentation testing was performed to evaluate the adhesion of the coatings. To elucidate the coating failure mechanism, the compositions around the delaminated spots of diamond coatings after indentation were identified by Energy-dispersive X-ray spectroscopy. The results show that continuous diamond coatings were achieved on Al2O3, Al-Al2O3, Al-AlN and Al-Ta interlayered substrates, whereas a graphite layer was still formed with the Ta monolayer accompanied by an easy spallation of diamond coatings. The Al interlayer has played an important role in obtaining high purity diamond by in-situ forming an alumina barrier layer. Especially, the diamond coating deposited with an Al-AlN interlayer demonstrates superior interfacial adhesion in comparison with all the other interlayers.

Nano- and microcrystalline diamond deposition on pretreated WC–Co substrates: structural properties and adhesion

Many developments have been made to improve the quality and adherence of CVD diamond films onto WC–Co hard metal tools by the removing the cobalt from the substrate surface through substrate pretreatments. Here we compare the efficiency of three chemical pretreatments of WC–Co substrates for this purpose. First, the work was focused on a detailed study of the composition and structure of as-polished and pretreated substrate surfaces to characterize the effects of the substrate preparation. Considering this objective, a set of WC–9% Co substrates, before and after pretreatment, was analyzed by FEG-SEM, EDS and x-ray diffraction (XRD). The second stage of the work was devoted to the evaluation of the influence of seeding process, using 4 nm diamond nanoparticles, on the morphology and roughness of the pretreated substrates. The last and most important stage was to deposit diamond coatings with different crystallite sizes (nano and micro) by hot-filament CVD to understand fully the mechanism of growth and adhesion of CVD diamond films on pretreated WC–Co substrates. The transition from nano to microcrystalline diamond was achieved by controlling the CH4/H2 gas ratio. The nano and microcrystalline samples were grown under same time at different substrate temperatures 600 °C and 800 °C, respectively. The different substrate temperatures allowed the analysis of the cobalt diffusion from the bulk to the substrate surface during CVD film growth. Furthermore, it was possible to evaluate how the coating adhesion is affected by the diffusion. The diamond coatings were characterized by Raman spectroscopy, XRD, EDS, FEG-SEM, atomic force microscope and 1500 N Rockwell indentation to evaluate the adhesion.

Deposition of diamond coatings on Fe-based substrates with Al and Al/AlN interlayers

Abstract Because of the carbon diffusion into the substrate and the formation of graphite at the interface, direct deposition of adherent diamond coatings on Fe-based materials is difficult. To address the issue, Al-based interlayers including Al and Al/AlN interlayers were introduced on Fe based substrates (SS316, FeNiCo) to enhance diamond deposition, which was carried out in a microwave plasma chemical vapor deposition (MPCVD) reactor using a CH4–H2 mixture. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, synchrotron-based X-ray absorption spectroscopy (XAS), and indentation testing. The results show that single Al layer can effectively suppress the formation of graphite and the inward diffusion of carbon into the substrate, and thus enhance diamond nucleation and growth. The dual layers of Al/AlN can further enhance the adhesion of diamond coatings comparing to the single Al interlayer.

Plasma enhanced chemical vapor deposition of diamond coatings on Cu–W and Cu–WC composites

In this study, two Cu–W (Cu30–W, Cu40–W) and one Cu50–WC composites (all in wt.%) were synthesized by powder metallurgy and used as substrates for diamond coating in a microwave plasma enhanced chemical vapor deposition reactor. Optical microscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, indentation test and synchrotron-based high resolution X-ray near edge absorption spectroscopy were used to investigate the morphology, composition, microstructures and adhesion of diamond films. The results show that the adhesion of diamond coatings formed on these Cu–W alloy substrates is much higher than on pure Cu substrate. The adhesion improvement is primarily attributed to the reduced mismatch in the thermal expansion coefficients, and the formation of WC phase on the sub-surface of the substrate that strengthens the coating-substrate interfacial bonding.

Preparation of Diamond Coatings on Alumina by Hot Filament Chemical Vapor Deposition

Diamond coatings were prepared on alumina by hot filament chemical vapor deposition, which constituted an insulator used in a laser pump. The composition and morphologies of the diamond coatings were characterized by Raman spectra and scanning electron microscope. The effects of the pressure of the deposition chamber and the distance from the filament to the base on the composition and structure of the deposited diamond coatings were studied.

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.

Enhanced diamond deposition on Kovar alloy substrate with Al interlayer

During chemical vapour deposition of diamond coatings on transition metal (Fe, Co, Ni) substrates, porous graphitic carbon preferentially forms on the substrate surfaces and it induces a spontaneous spallation of the diamond films. In this study, an Al surface barrier film of 80nm thick has been used on a Kovar alloy substrate to enhance the interfacial adhesion of diamond films. Characterisation of the top deposit, interlayer and the underlying substrate was performed by Raman spectroscopy, energy dispersive X-ray analysis, scanning electron microscopy, synchrotron NEXAFS, and X-ray diffraction. The Al interlayer has effectively inhibited the formation of intermediate graphitic carbon and markedly enhanced the adhesion of diamond films. Continuous and adherent diamond films were achieved on the alloy substrate. This investigation also indicates the importance of the continuity of the Al interlayer in maintaining an integrity of the adherent diamond films.

Competitive graphitization and diamond growth on hot-dip aluminized carbon steel substrate

Abstract When carbon steel is directly exposed in 99%H 2 –1%CH 4 gas mixture for plasma enhanced CVD deposition of diamond coatings, an intermediate graphite layer is preferentially formed on the substrate surface, and the substrate is subjected to a severe internal carburization attack. The diamond coatings formed easily delaminate from the steel substrate. Hot dip aluminizing treatment of the carbon steel has markedly promoted diamond nucleation, growth and interfacial adhesion. The formation of graphite intermediate phase on the substrate surface is effectively inhibited and the substrate carburization is also suppressed. The possible mechanism of this transition is discussed based on a series of analytical techniques.

Chemical Vapor Deposition of Highly Adherent Diamond Coatings onto Co-Cemented Tungsten Carbides Irradiated by High Power Diode Laser

The present investigation deals with the definition of a new eco-friendly alternative to pretreat Co-cemented tungsten carbide (WC-Co) substrates before diamond deposition by hot filament chemical vapor deposition (HFCVD). In particular, WC-5.8 wt %Co substrates were submitted to a thermal treatment by a continuous wave-high power diode laser to reduce surface Co concentration and promote the reconstruction of the WC grains. Laser pretreatments were performed both in N(2) and Ar atmosphere to prevent substrate oxidation. Diamond coatings were deposited onto the laser pretreated substrates by HFCVD. For comparative purpose, diamond coatings were also deposited on WC-5.8 wt %Co substrates chemically etched by the well-known two-step pretreatment employing Murakami's reagent and Caro's acid. Surface morphology, microstructure, and chemical composition of the WC-5.8 wt %Co substrates after the different pretreatments and the deposition of diamond coatings were assessed by surface profiler, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses. Wear performance of the diamond coatings was checked by dry sliding linear reciprocating tribological tests. The worn volume of the diamond coatings deposited on the laser pretreated substrates was always found lower than the one measured on the chemically etched substrates, with the N(2) atmosphere being particularly promising.

Recent Advances in the Deposition of Diamond Coatings on Co-Cemented Tungsten Carbides

Co-cemented tungsten carbides, namely, hard metals are largely used to manufacture high wear resistant components in several manufacturing segments. Coating hard metals with superhard materials like diamond is of utmost interest as it can further extend their useful lifespan. The deposition of diamond coatings onto WC-Co can be extremely complicated as a result of poor adhesion. This can be essentially ascribed to (i) the mismatch in thermal expansion coefficients between diamond and WC-Co, at the typical high temperatures inside the chemical vapour deposition (CVD) chamber, generates large residual stresses at the interface; (ii) the role of surface Co inside the WC-Co matrix during diamond CVD, which promotes carbon dissolution and diffusion. The present investigation reviews the techniques by which Co-cemented tungsten carbides can be treated to make them prone to receive diamond coatings by CVD. Further, it proposes interesting ecofriendly and sustainable alternatives to further improve the diamond deposition process as well as the overall performance of the coated hard metals.

Study on Milling Testing of WC-Co Cemented Carbides Diamond Coated PCB Milling Cutters

Because of the complicated shape of the structural characteristics of the tool and the use of performance requirements, the tool substrate pretreatment, deposition equipment and deposition process, diamond film after film substrate adhesion test and tool evaluation has its own peculiarities. Currently, study on the complex shape of diamond coated tools At home and abroad is still in its infancy, and the further study complicated shape for the deposition of diamond coatings on cutting tools and milling properties of adhesion is even more lacking towards to complex shapes for the structural characteristics of diamond coated tool and use requirements. In this paper, it will use the WC-Co (YG6) PCB carbide cutter (STARBIDE455060, diameter 6.35mm) as the matrix material and use the milling testing of glass fiber reinforced composite to assess the adhesion of diamond coated tools and milling performance.