Property Research on Nano-Micro Crystalline Diamond Coated Tools Lapping Sapphire Wafer

Various carbon thin films synthesized by the hot filament chemical vapor deposition (CVD) method with various methane concentrations in hydrogen (1.0-12.5 vol.%) and temperatures of Si substrate (770-1000°C) were characterized by X-ray-absorption near-edge structure (XANES) and Raman spectroscopies as well as by scanning electron microscopy (SEM) and X-ray diffraction. Based on these results, the structural change of carbon thin films is deduced as a function of methane concentration and substrate temperature. Comparison between the Raman and XANES spectra demonstrates the usefulness of XANES spectroscopy for the characterization of carbon thin films and the complementary character between these spectroscopies.

Advantages from various diamond coatings can be fully utilised by constructing a composite structure. However, the composite coating containing microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) is prone to interface delamination, due to the distinct interfaces between layers. In this paper, fine-grained diamond (FGD) is introduced into composite diamond coatings to eliminate obvious interfaces of diamond layers. Various monolayer diamond coatings (MCD, FGD, NCD) and composite diamond coatings (MCD/FGD, MCD/NCD, MCD/FGD/NCD) were prepared on cemented tungsten carbide (WC-Co) substrates adopting hot filament chemical vapour deposition (HFCVD) method. Scanning electron microscopy (SEM) morphologies of differing diamond coatings were observed, revealing no distinct interfaces between the layers of MCD/FGD/NCD coating. Surface roughness of differing coatings was obtained, with MCD/FGD/NCD coating exhibiting lower surface roughness than other composite coatings. X-ray diffraction (XRD) spectra of differing coatings were studied, indicating various composite diamond coatings exhibit high crystal quality. Raman spectra together with residual stress of these samples were analyzed, indicating that FGD layer contributes to a reduction of residual stress. Friction tests were conducted, demonstrating that MCD/FGD/NCD coating shows lower coefficient of friction (COF) than other composite coatings. Milling experiments on high-silicon aluminum alloy were executed for thoroughly evaluating the cutting performance of these coated cutters, revealing that MCD/FGD/NCD coated milling cutter performs outstanding cutting performance because of good interfacial integrity, superior surface smoothness, and low residual stress.

Diamond coated cutting tools are applied for machining difficult-to-machine materials of titanium alloys. However, the temperature field uniformity needs to be further improved for the mass production of diamond coated tools using the hot filament chemical vapor deposition (HFCVD) method. In this paper, the tools temperature distribution is simulated by the finite volume method (FVM) during the deposition of diamond coatings. An optimization method of deposition setting with fine filaments in dense arrangement (FFDA) is proposed, and the temperature distributions of the tools under the coarse filament in sparse arrangement (CFSA) and FFDA are simulated to systematically elucidate the effects of fine filament densification. Subsequently, the different hot filament arrangements are adopted to mass production experiment for deposition of micro/nano composite diamond (MCD/NCD) coatings on WC-6%Co cutting tools. In addition, the cutting experiments on titanium alloys are conducted using diamond coated tools, and the cutting performance of tools at different locations is evaluated. The results indicate that the FFDA method can improve the temperature field uniformity of mass-produced diamond coated cutting tools, and the cutting tools have better consistency in surface morphology, thickness, chemical composition, surface roughness and cutting performance.

Effect of doping level on residual stress, coating-substrate adhesion and wear resistance of boron-doped diamond coated tools

Micro-grit blasting to enhance adhesion of diamond coating on Ti6Al4V

Diamond coatings are deposited on the end surfaces of mechanical seal rings by the hot filament chemical vapor deposition (HFCVD) method. To improve the homogeneity of batch preparation of HFCVD diamond-coated seal rings, the temperature distributions on the end surfaces of seal rings are simulated and optimized using the finite volume method (FVM). The influence mechanism of various setup parameters on coating deposition is demonstrated systematically with the orthogonal experimental method, including the filament diameter d, the filament temperature [Formula: see text], the separation between two adjacent filaments D and the filament height H. The optimal HFCVD setting parameters for batch preparation of diamond-coated seal rings are proposed based on the simulation results of orthogonal experiments. Afterwards, mass deposition experiments of seal rings are conducted using the optimal setting parameters, and the diamond coatings deposited on the end surfaces of seal rings are characterized. Furthermore, mechanical seal operation bench tests are carried out to evaluate the abrasion resistance of diamond-coated seal rings. The results indicate that the optimized setting parameters can produce a homogeneous temperature field, and diamond coatings with uniform thickness and excellent wear resistance can be obtained in the batch preparation of diamond-coated seal rings.

Fabrication and tribological properties of textured diamond coatings on WC-Co cemented carbide surfaces

PurposeThe purpose of this study is to investigate the mechanical and tribological properties of the synthetic diamond coatings deposited on WC-Co cutting tools for their prospective applications in mechanical industry. In this work, the concept of nanocrystalline diamond, microcrystalline diamond and multilayer-diamond coating systems were proposed and deposited on WC-Co substrates with the top-layer nanocrystallinity, optimum thickness and interfacial adhesion strength for load-bearing tribological and machining applications. Also, the overall mechanical and tribological properties of all synthetic diamond coatings were compared for the purpose of selecting a suitable type of protective layer used on the surfaces of WC-Co cutting tools or mechanical dies.Design/methodology/approachSmooth and adhesive single layered and multilayered synthetic deposited on chemically etched cemented tungsten carbide (WC-Co) substrates using predetermined process parameters in hot filament chemical vapor deposition (HFCVD) method. A comparison has been documented between diamond coatings having different nature and architecture for the purpose of studying their mechanical and tribological characteristics. The friction characteristics were studied experimentally using ball-on-disc type linear reciprocating micro-tribometer under the influence of varying load conditions and within dry sliding conditions. Nanoindentation tests were conducted on each diamond coating using Berkovich nanoindenter for the measurement of their hardness and elastic modulus values. Also, the wear characteristics of all sliding bodies were studied under varying load conditions using cumulative weight loss and density method.FindingsDepositing any type of diamond coating on the cemented carbide tool insert increases its all mechanical and tribological characteristics. When using boron-doping onto the top-layer surface of diamond coatings decrease slightly their mechanical properties but increases the tribological characteristics. Present analysis reveals that friction coefficient of all diamond-coated WC-Co substrates decreases with the increase of normal load. Therefore, maintaining an appropriate level of normal load, sliding time, sliding distance, atmospheric conditions and type of diamond coating, the friction coefficient may be kept to some lower value to improve mechanical processes.Originality/valueAs the single layered synthetic diamond coatings have not given the full requirements of mechanical and tribological properties when deposited on cutting tools. Therefore, the multilayered diamond coatings were proposed and developed to enhance the interfacial integrity of the nanocrystalline and microcrystalline layers (by eliminating the sharp interface) as well as increasing the hardness of tungsten carbide substrate. However, when using boron doping onto the top-layer surface of diamond, coatings decreases slightly their mechanical characteristics but also decreases the value of friction coefficient.

Diamond coatings with three distinct surface textures, namely spherical, pyramidal, and prismatic morphologies, were fabricated using the hot-filament chemical-vapor deposition (HFCVD) method. Scanning electron microscopy (SEM) was employed to analyze the surface morphological characteristics and differences among the coatings. Raman spectroscopic analysis further confirmed that all three diamond films exhibited excellent deposition uniformity and high crystalline quality. A three-dimensional optical microscopy system was used to measure the surface roughness values, which were determined to be Ra 0.423 μm, Ra 0.515 μm, and Ra 0.809 μm, respectively. An HFCVD diamond-coated tool was innovatively employed for the lapping of sapphire wafers, enabling a systematic investigation of the tribological behavior during the lapping process. Based on the experimental results, three morphological material removal models were established. The study demonstrates that the spherical diamond coating achieves a superior surface finish (Ra 0.22 μm) due to its continuous multi-point contact geometry, governed by the agglomerated nanocrystalline structure. Sample 3 had the highest removal rate of 24.3 μm/min. This is related to its surface morphology characteristics and is also due to the two-body contact between the diamond-coated tool and sapphire, offering a high-efficiency alternative for precision machining.

The activation energies for diamond growth were determined by an advanced hot filament chemical vapor deposition (AHF-CVD) method, which accurately controls the substrate temperature independently against other CVD parameters. The activation energies, as determined from an Arrhenius plot, were 22–24 kcal/mol in the range of 740–930 °C. These values are the lowest level reported in the literature. Reported growth mechanisms were evaluated in view of the obtained activation energies.

Pre-treatment for diamond coatings on free-shape WC–Co tools

abstractBoronizing treatment was done to form a boride surface layer well bonded with cemented carbide substrate. Multilayer microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) coatings were prepared on the boronizing cemented carbide substrate by hot filament chemical vapor deposition (HFCVD) method. The surface and the cross section micrograph, coating component, hardness and adhesion of the as-deposited diamond coatings were observed with a SEM, Raman spectroscopy, nano-indenter and a Rockwell hardness tester accordingly. The results show that the MCD coating consists of well-faceted grains and the hardness of the MCD coating is about 85GPa. The NCD coating has morphological features with grain sizes of several tens of nanometer. The hardness of the NCD coating is about 52GPa. The boron doping of cemented carbide substrate can improve the fracture strength of the diamond film to some extent, and the adhesion of multilayer NCD/MCD coating is better than that of monolayer MCD and monolayer NCD coating.

In this study, diamond coatings were deposited through the hot filament chemical vapor deposition method on cemented carbide under different methane concentrations, ranging from 1% to 5%, to analyze the performance of the diamond coatings under different loads and lubrication conditions . Friction and wear tests were carried out using ball-disk friction and wear tester under different loads and lubrication conditions. Scanning electron microscopy, high-resolution Raman spectrometry, optical microscopy, and a surface profiler were used to observe the surface morphology and quality of the coatings after the wear test. The results revealed that the coating prepared under 3% methane concentration was more stable during the friction test than that prepared under other methane concentrations. In addition, the coating prepared under 5% methane concentration had poor adhesion and experienced failure under excessive load. Furthermore, lubricating the friction surface with water effectively reduced the formation of abrasive wear and the friction coefficient, and thus the sample reached the stable stage faster. In addition, the wear rate of the coating under wet condition was approximately 4–5 times less than that under dry friction conditions.

Spherical diamond particles have great potential as additive materials for improving lubricity of lubricants, and yet the complicated preparation process is difficult to meet the current industrial demand. Therefore, a novel method was proposed to deposit mass spherical diamond on the discontinuous silicon nitride (Si3N4) powder substrate by the hot filament chemical vapor deposition method. The results revealed that the substrate was covered by the spherical diamond grains with a diameter of about 20 μm. Thereafter, they were used as lubricant additives to examine the tribological and grinding properties. Therein, the Si3N4 surface had a remarkable reduction in surface roughness by a factor of 124.62% as compared to that without spherical diamond powder, while GCr15 alloy had a 31.17% increase under the same condition. Hence, our method provides a promising way to deposit the mass spherical diamond powder that might become a great abrasive material for machining the ceramic.

A great deal of attention has been paid to friction and wear caused by current-carrying friction. In this study, diamond coatings were deposited on the cemented carbides (WC-Co) substrate by hot filament chemical vapor deposition method. Although the diamond coating possessed a higher roughness than the WC-Co substrate, it was effective at reducing the friction coefficient and improving the effectiveness of WC-Co in the current-carrying friction process. In the presence of 1 A, the diamond coating exhibited a lower friction coefficient than the WC-Co matrix, and the diamond transformed into graphite as a result. The results show that diamond-coated surfaces have a better wear condition than WC-Co.