Search

For fabricating brazed inserts in machining difficult-to-machine materials, chemical vapor deposition (CVD) diamond thick films are potential candidates for polycrystalline diamond (PCD). In the present study, monolayer microcrystalline diamond (MCD), monolayer nanocrystalline diamond (NCD), and multilayer diamond thick films were respectively deposited on the Si3N4 substrates by the high-power density (HPD) microwave plasma CVD (MPCVD) technique, which were then brazed on WC–Co. Their microstructures, growth rates, and film quality were systematically studied. Within the multilayer film, in order to enhance the secondary nucleation on as-deposited MCD layers and promote the consecutive growth of NCD layers, increasing the nitrogen addition level was much more effective than increasing the methane/hydrogen ratio. The NCD interpositions could guarantee layer thickening, while suppressing the growing up of individual micro diamond grains. As revealed by Raman spectra, the multilayer structure could help restrain the accumulation of the residual stress with increasing the thickness. Besides, the multilayer diamond thick film also presented much enhanced erosive wear resistance, as compared with the monolayer MCD or NCD, because the NCD interlayers could prevent intergranular cracks from further propagating. Finally, cutting performances of various brazed inserts were evaluated, in the case of dry-turning the high-silicon aluminum alloy (40 wt.% Si), demonstrating that the multilayer structure could result in the enhancement of the impact toughness of cutting edges, and improve the machining quality.

Single crystalline diamond (SCD) grits are usually made by a high-pressure and high-temperature (HPHT) method and exhibit cuboctahedral shapes and smooth surfaces. In this paper, we synthesized new kinds of SCD grits and nanocrystalline diamond (NCD) grits by a chemical vapor deposition (CVD) method and explored their grinding performance by single grit grinding of SiC ceramics. Grinding by HPHT grits was also conducted for comparison. The CVD-SCD grits exhibit cuboctahedral shapes, but surfaces are covered by protruded twin crystals of several microns, while the NCD grits are spherical agglomerations of nano-grains. We demonstrated that these morphological features have profound influences on material removal behavior. Results show that the wear of NCD grits is dominated by wear flat and intergranular cracks. The worn NCD grits can exert intense rubbing and ploughing effects on the workpiece. In contrast, the wear of CVD-SCD grits is dominated by fracture of the protruded twin crystals. It is proved that the twins on the grit surface are effective cutting edges to remove the material in a micro scale and thus lead to the formation of fine grinding striations and smaller cracking pits, but this process has little influence on specific grinding energy. Besides, grits with rough twins, especially on the flank face, tend to exhibit lower grinding force ratios and thus better sharpness. Moreover, for grits with smooth rake faces, there exists an explicit critical undeformed chip thickness value around 0.4–0.6 μm, above which the material removal mechanism changes from ductile to brittle rapidly. However, for grits with rough twins on rake faces, this transition process becomes vague.

A method based on the density functional theory calculations is proposed for predicting the influences of dopants on the diamond oxidation, by evaluating the O adsorption energy, chemical bond weakening related to desorption, and probable products. It is proven by verification tests that oxidation resistances of the diamond materials can be indeed selectively controlled (e.g., -36 to 54.3% for diamond films, -36.5 to 45.1% for diamond grits) by adding various doping sources ((CH

Monolayer diamond grinding tools are commonly made by electroplating or brazing. However, electroplated tools involve weak grain/matrix adhesion due to a lack of chemical bonds, and brazed diamonds often suffer thermal damage resulting from the high-temperature brazing process. This paper reports a new method to fabricate monolayer diamond grinding tools by chemical vapor deposition (CVD) technique. First, diamond powders at the range of 7–180 μm are chosen as seeds of the abrasive grains. The seeds are randomly distributed on SiC substrates by spraying the suspension containing the seeds toward the substrates in a spin coater machine, or orderly positioned on the substrates by a patterned mask. Then CVD diamond growth is conducted on both the substrates and the seeds simultaneously. As-grown diamond films on the substrates are regarded as bonding layers of the grinding tools, and the original seeds with irregular and crushed morphologies can grow into blocky cube-octahedral grains with smooth surfaces, which are supposed to have enhanced mechanical strength. Raman spectra demonstrate that as-grown diamonds on both the substrates and the seeds are of high quality and low levels of graphitization. Besides, relatively low residual stresses are detected in the diamond grains, because both the bonding layers and the grains are made of diamond. Grinding tests are conducted using as-fabricated CVD diamond grinding tools and electroplated/brazed diamond grinding tools as comparisons. The results suggest that the CVD diamond grinding tools possess the best wear resistance in terms of the fracture of the diamond grains. This is attributed to the epitaxial grain structure that restrains the crack propagations. In addition, the wear of the CVD diamond grains can generate tiny pyramidal crystalline tips and sharp edges, indicating the unique shelf-sharpness during the grinding.

The frictional resistance and hole quality when drilling CFRP laminates are associated with tribological behaviors of drill materials. In the present study, tribological tests are conducted on various diamond coated WC-Co balls sliding against T800/X850 CFRP laminates with [-45/90/45/0]s lay-up, under specific conditions similar to the drilling process. It is firstly found that the coefficient of friction (COF) varies with the sliding direction. The boron-doped micro-crystalline and nano-crystalline composite diamond (BDMC-NCCD) film synthesized by optimized growth durations (9 h for BDMCD and 2.5 h for NCD) presents relatively low COF and wear rate (0.193 and 0.97 × 10−8 mm3/N m, when the sliding velocity and normal load are respectively 1.5 m/s and 5.0 N), as well as high critical load for the film peeling (35 N), owing to the nano-sized diamond grains and low surface roughness (Ra~125.09 nm measured by the confocal microscopy) of the surface NCD layer, and high hardness and favorable adhesion of the underlying BDMCD layer. Besides, influences of the sliding velocity and normal load are clarified, indicating that the COF increases with the load, but decreases with increasing the velocity, while the wear rate increases with either the load or velocity.

In this work, a comparative study of diamond films consisting of alternate microcrystalline (MCD) and nanocrystalline diamond (NCD) layers is conducted. Diamond films including monolayer, bilayer and multilayer diamond films are coated on cemented tungsten carbide (WC-Co) substrates by adopting a bias-enhanced hot filament chemical vapor deposition (HFCVD) technique. Tribological properties of the diamond films are evaluated by using a reciprocal tribometer without lubrication. Further milling tests are carried out to examine the cutting performances with sintered zirconia ceramics as workpiece comparatively. In friction test against zirconia ceramics, the monolayer NCD film shows the lowest friction coefficient (0.128) because of its smooth surface. Also, the bilayer diamond film with surface coating of NCD layer (MNCD) and both of the multilayer diamond films exhibit good friction property while the monolayer MCD film has the largest friction coefficient (0.292). The milling test demonstrates that the monolayer diamond (MCD and NCD) coated milling tools show poor tool life due to abrasive action of hard workpiece. Working life of all the bilayer and multilayer diamond coated tools is enhanced, but large area shedding of coatings appears after some milling passes except the multilayer diamond film with surface coating of NCD layer (MNMN-CD). The multilayer film (MNMN-CD) presents superior machining performance and its working life increases by 3–7.5 times compared with the monolayer diamond coated ones.

Lower surface roughness and sharper cutting edge are beneficial for improving the machining quality of the cutting tool, while coatings often deteriorate them. Focusing on the diamond coated WC-Co milling cutter, the abrasive flow machining (AFM) is selected for reducing the surface roughness and sharpening the cutting edge. Comparative cutting tests are conducted on different types of coated cutters before and after AFM, as well as uncoated WC-Co one, demonstrating that the boron-doped microcrystalline and undoped fine-grained composite diamond coated cutter after the AFM (AFM-BDM-UFGCD) is a good choice for the finish milling of the 6063 Al alloy in the present case, because it shows favorable machining quality close to the uncoated one, but much prolonged tool lifetime. Besides, compared with the micro-sized diamond films, it is much more convenient and efficient to finish the BDM-UFGCD coated cutter covered by nano-sized diamond grains, and resharpen its cutting edge by the AFM, owing to the lower initial surface roughness and hardness. Moreover, the boron incorporation and micro-sized grains in the underlying layer can enhance the film-substrate adhesion, avoid the rapid film removal in the machining process, and thus maximize the tool life (1040 m, four times more than the uncoated one). In general, the AFM is firstly proposed and discussed for post-processing the diamond coated complicated cutting tools, which is proved to be feasible for improving the cutting performance

When drilling the carbon fiber reinforced plastics (CFRP), the tool shape and surface coating both play important roles in the cutting performance, which are complex and comprehensive, and should be systematically studied. In this research, WC-6wt.%Co drills in typical shapes are prepared, on which high-performance composite diamond films are deposited by the hot filament chemical vapor deposition (HFCVD) method. It is firstly proved by drilling tests that the tool shape always acts as a determining factor that significantly influences the drilling force and machining quality, for either the uncoated or diamond coated drills. The shorter chisel edge, smaller actual point angle and the proper double point angles are all factors in their favor. By contrast, as-deposited diamond films can slightly reduce the drilling force, while sometimes it even deteriorates the hole quality, due to the edge roundness caused by the alkali-acid pretreatment and the film growth. However, the diamond films play critical roles in improving the wear resistance, elongating the lifetime and guaranteeing the stability of the machining quality in the long-duration drilling process. In addition, the tool lifetime is also closely associated with the tool shape, attributed to the different thrust forces, consequently the lifetime of the diamond coated standard twist drill is much shorter than those of all other coated ones.

Nano/microcrystalline composite diamond films were deposited on the holes of WC-6%Co drawing dies by a two-step procedure using alternative carbon sources, i.e., methane for the microcrystalline diamond (MCD) layer and acetone for the nanocrystalline diamond (NCD) layer. Moreover, the monolayer methane-MCD and acetone-NCD coated drawing dies were fabricated as comparisons. The adhesion and wear rates of the diamond coated drawing dies were also tested by an inner hole polishing apparatus. Compared with mono-layer diamond coated drawing die, the composite diamond coated one exhibits better comprehensive performance, including higher adhesive strength and better wear resistance than the NCD one, and smoother surface (Ra=65.3 nm) than the MCD one (Ra=95.6 nm) after polishing at the same time. Compared with the NCD coated drawing die, the working lifetime of the composite diamond coated one is increased by nearly 20 times.

Tribological tests are conducted on diamond films under different lubrications, and influences of film type, lubrication, test parameters on coefficient of friction (COF) and film wear (Id) are studied. Diamond films perform better than WC-Co under water-based emulsion lubrication, and the boron doped micro-crystalline and nano-crystalline composite diamond (BDMC-NCCD) film shows the best overall behavior. Considering the performance and economy, the water content in the emulsion is optimized as about 80 vol%. Under this drawing condition, the quality of the production is similar to that drawn by the uncoated dies under the oil lubrication, however, the coated dies present much prolonged lifetime and lower temperature. Most importantly, the use of the water-based lubrication is much more environmentally friendly.

Based on the traditional deposition technique with the filament through the hole (DTFTH), the growth of high-quality diamond films on inner hole surfaces, especially those with small apertures, is rather difficult and laborious. In the present research, the deposition technique with no filament through the hole (DTNFTH) is proposed, and its feasibility and limitations are discussed on the basis of the radiation computation, temperature simulation, analyses on mean free paths of various active radicals, and the experimental verification of the “shading and distance effects”. It is indicated that the ratio of the hole depth to the hole diameter should be smaller than four. Afterwards, the drawing die with an aperture of 2 mm is designed, and a case study focusing on a single die and the mass production of diamond coated dies by the DTNFTH are both accomplished, using optimized deposition parameters. It is demonstrated that the film thicknesses are in the range of 4.8–6 μm (case study) and 3.5–5 μm (mass production), showing acceptable uniformity. Uncoated, DTFTH- and DTNFTH-diamond coated dies are all submitted to field tests, indicating that the lifetime of the DTFTH-diamond coated die is approximately eight times more than that of the uncoated one, while the DTNFTH-diamond film prolongs the lifetime of the uncoated die by a considerable factor of five.

Systematical researches were accomplished on WC–Co with different Co contents (6%, 10% and 12%, mass fraction). Based on the XPS and EDX, from orthogonal pretreatment experiments, it is indicated that the acid concentration, the time of the acid pretreatment and the original Co content have significant influences on the Co-removal depth (D). Moreover, the specimen temperature, original Co content and Co-removal depth dependences of the Co evolution in nucleation, heating (in pure H2 atmosphere) and growth experiments were discussed, and mechanisms of Co evolutions were summarized, providing sufficient theoretical bases for the deposition of high-quality diamond films on WC–Co substrates, especially Co-rich WC–Co substrates. It is proven that the Co-rich substrate often presents rapid Co diffusion. The high substrate temperature can promote the Co diffusion in the pretreated substrate, while acts as a Co-etching process for the untreated substrates. It is finally found that the appropriate Co-removal depth for the WC–12%Co substrate is 8–9 μm.

The drilling performance of four typical types of single-layer diamond coated drills and two-layer boron-doped-microcrystalline/nanocrystalline diamond (BDMC-NCD) composite coated drill is compared, and the growth duration ratio of the NCD layer to the BDMCD layer ( N/B ) is optimized. It is demonstrated that the BDMC-NCD film synthesized using proper N/B shows nice adhesion, moderate diamond quality and a smooth surface mostly composed of nano-sized diamond grains, so it shows the best comprehensive performance, including the thrust force reduction, the improvement of the hole quality, the slowing of the tool wear and coating peeling, and the elongation of the tool lifetime. Taking the time of the coating peeling into consideration, 3/9 is the optimum N/B for the BDMC-NCD coated drill, and such the drill also performs the longest lifetime using delamination factors ( F d ) of 1.2 or 1.3 as the failure criteria. Moreover, the failure mode of the diamond coated drill is the flank wear when using F d = 1.1 or 1.2 as the failure criteria, while the tool failure should be related to the coating peeling when F d = 1.3.

Ultrananocrystalline diamond (UNCD) coating possessing low surface roughness was innovatively deposited on printed circuit board (PCB) end mills in order to improve the surface smoothness and prolong the tool duration while machining 5G PCB material. Six types of diamond coatings, involving microcrystalline diamond (MCD), nanocrystalline diamond (NCD), ultrananocrystalline diamond (UNCD), microcrystalline diamond/nanocrystalline diamond (MCD/NCD), microcrystalline diamond/ultrananocrystalline diamond (MCD/UNCD), microcrystalline diamond/nanocrystalline diamond/ultrananocrystalline diamond (MCD/NCD/UNCD), were synthesized on PCB end mills. The Raman spectrum of diamond coatings were obtained to characterize the phase composition, illustrating that Raman spectra of UNCD, MCD/UNCD and MCD/NCD/UNCD present “M” shape, including dominant D peak and G peak. The adhesion levels were assessed, showing that the bottom MCD layer helps to improve the adhesion of MCD/NCD, MCD/UNCD and MCD/NCD/UNCD on WC-Co substrates and MCD/NCD/UNCD can suppress effectively the crack propagation. Moreover, the tribological properties and wear performances of these diamond coatings were compared. The comparison results of friction coefficients are in good accordance with those of surface roughness. The superior adhesion of bottom MCD, the elegant transition of middle NCD and the low friction coefficient of the top UNCD lead to the outstanding wear performances of MCD/NCD/UNCD coated end mill while machining PCB slots.

In the present study, at fixed hydrogen flow rate of 400 sccm, we demonstrate the coupling effects of methane/hydrogen ratio ηC (7.5– 15 vol%) and nitrogen flow rate fN (0– 0.9 sccm) on morphologies, mechanical properties and tribology behaviors of the diamond films deposited on cemented carbide (WC-Co) substrates. At lower ηC (7.5 vol%), increasing fN from 0 to 0.9 sccm leads the diamond film to transform from 〈110〉-oriented to 〈110〉- & 〈100〉-oriented. Besides, increasing ηC accelerates the orientation transition, i.e., {110} and {100} crystallographic planes can be formed at even lower nitrogen addition level. Furtherly increasing ηC and fN to 15 vol% and 0.9 sccm, the film morphology transforms to nanocrystalline diamond (NCD). Moderate nitrogen addition acting as a catalyst at the substrate surface increases the growth rate, by the mechanism of promoting the individual grains growth. However, supersaturated nitrogen will suppress the growth of individual grains by generating masses of secondary nucleation on the crystal faces, resulting in a slight reduction of the growth rate. The 〈110〉- & 〈100〉-oriented diamond film deposited at ηC = 7.5 vol% and fN = 0.9 sccm and the NCD film both present low small surface roughness and coefficient of friction (COF) when sliding against the Si3N4 balls, while the former has higher hardness and Young's modulus, along with lower wear rate and better adhesive strength, which has great potential for the application as wear-resistant and anti-friction coating.

Sandblasting combined with acid etching was utilized as pretreatment of Co-cemented tungsten carbide substrates for the deposition of chemical vapor deposition (CVD) diamond films. Diamond films were deposited on the pretreated surface as well as on substrates treated by a two-step alkali-acid pretreatment as a contrast. The field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectroscopy, Rockwell hardness tester and turning test were respectively conducted to characterize the pretreated substrates and deposited diamond films. Surface roughness of the treated surface was controlled by adjusting sandblasting parameters. An enhancement of surface roughness and removal of the binder phase were detected on the treated surface. The porous Co-depleted carbide layer caused by sandblasting and acid-etching pretreatment was obviously thinner compared to the two-step pretreatment. The nucleation stage of CVD process was investigated and the nucleation density was obviously enhanced by the sandblasting pretreatment. Indentation tests exhibited an improvement of adhesive strength compared to the two-step pretreatment. Moreover, the XRD patterns showed that the residual stress of diamond films was decreased. The turning tests showed that the diamond coated tools with sandblasting-acid pretreatment exhibited less area of flank wear and film shedding.

For the chemical vapor deposition (CVD) of diamond films, boron doping with appropriate boron doping levels can enhance the basic mechanical properties of the as-deposited films, especially the film-substrate adhesive strength. However, the boron doping level, which is thought to play a critical role in modifying the properties of the boron-doped diamond (BDD) film, must be further investigated. In the present investigation, the commonly used reaction-bonded silicon carbide (RB-SiC) material is selected as the substrate upon which boron-doped micro-crystalline (BDMCD) films with similar film thickness (24.8–26.3 μm) are synthesized using mixed reactant gas with different B/C atomic ratios, i.e., different boron doping levels. Systematic characterization and solid particle erosion tests are conducted on all specimens to elucidate the influence of the boron doping level on the diamond films' basic mechanical properties and erosion behavior and to elaborate the impact velocity and impact angle dependence of the erosion behavior. The results demonstrate that moderate boron doping levels (5000 and 8000 ppm) are able to maximize the growth rate, reduce the surface roughness, guarantee diamond quality and hardness, minimize the residual stress, and significantly enhance the film-substrate adhesive strength, thereby providing favorable erosion behavior. By contrast, very high boron doping levels (12,000 and 16,000 ppm) deteriorate the erosion behavior of as-deposited BDMCD films, mainly because of the excessive reduction of the film quality and hardness, together with the deterioration of the film-substrate adhesive strength caused by the transformation of the residual stress from compressive to tensile. With increasing either impact velocity or impact angle, the stable erosion rates of all specimens increase, and the film lifetime of the coated specimens become shorter. Moreover, the impact velocity dependence of stable erosion rates for diamond-coated specimens is considerably stronger than that for the uncoated RB-SiC specimen, as indicated by a much higher velocity exponent.

Chemical vapor deposition (CVD) diamond films have been widely applied as protective coatings on varieties of anti-frictional and wear-resistant components, owing to their excellent mechanical and tribological properties close to the natural diamond. In applications of some components, the inner hole surface will serve as the working surface that suffers severe frictional or erosive wear. It is difficult to realize uniform depositions of diamond films on surfaces of inner holes, especially ultra-large inner holes. Adopting a SiC compact die with an aperture of Ф80 mm as an example, a novel filament arrangement with a certain number of filaments evenly distributed on a circle is designed, and specific effects of filament parameters, including the filament number, arrangement direction, filament temperature, filament diameter, circumradius and the downward translation, on the substrate temperature distribution are studied by computational fluid dynamics (CFD) simulations based on the finite volume method (FVM), adopting a modified computational model well consistent with the actual deposition environment. Corresponding temperature measurement experiments are also conducted to verify the rationality of the computational model. From the aspect of depositing uniform boron-doped micro-crystalline, undoped micro-crystalline and undoped fine-grained composite diamond (BDM-UMC-UFGCD) film on such the inner hole surface, filament parameters as mentioned above are accurately optimized and compensated by orthogonal simulations. Moreover, deposition experiments adopting compensated optimized parameters and some typical contrastive parameters are also accomplished for further verifying the rationality of the computational model and the correctness of the compensation coefficient 0.7 defined for the downward translation determined by simulations. More importantly, on the basis of more simulations and verification tests, a general filament arrangement model suitable for Ф50–120 mm circular inner holes is determined, involving all above filament parameters that are functionally dependent on the diameter of the inner hole.

Chemical vapor deposition (CVD) diamond thick film, due to its higher hardness and better wear resistance, is a potential competitor of the poly-crystalline diamond (PCD) when used as the brazed tool tip. Besides, compared with the thin diamond coated tool, the diamond thick film brazed tool does not have the risk of catastrophic coating delamination. However, due to the fragile characteristic of the free-standing diamond thick film, the conventional polishing is complicated and inefficient. In this study, a novel CVD-diamond thick film-Si3N4 brazed WC-Co (i.e. DB) tool is proposed. The diamond thick film was deposited on the Si3N4 substrate by microwave plasma CVD (MPCVD), using the optimized deposition parameters: microwave power = 3.5 kW, reactant pressure = 20 kPa and methane concentration = 10 %. Adopting the sandblasting and nanodiamond seeding pretreatment methods could improve the film surface smoothness and suppress the voids formation on the film-substrate interlayer, which are beneficial for the post polishing process. In addition, Si3N4 as the supportive substrate could help to prevent the diamond film breaking from polishing. The polished CVD diamond thick film-Si3N4 was laser cut to small tips and then brazed on the WC-Co cutter body. The cutting performance of DB tool was tested in dry turning hypereutectic Al-Si alloy, adopting the PCD and thin diamond coated WC-Co (i.e. DC) tools as comparisons. The cutting results suggest that DB tool outperformed the PCD and DC tools in term of service life and surpassed the DC tool in machining quality. Moreover, the novel tool in this study avoided some typical problems for the conventional diamond tools, such as the coating delamination for thin diamond coated tool and preferred wear of the binder for PCD tool. Noteworthy is that the worn DB tool still presents a rather sharp cutting edge, only some micro-columnar diamond crystals chipped from the flank face.

Behaviors of diamond coated Ti-related parts are significantly affected by carbonized interlayers, so it is essential to determine or predict the carbonization depth during diamond growth. Following the Fick’s law of diffusion with carbon concentration-dependent diffusion coefficients, it is roughly predicted that carbonization depths in Ti and Ti–6Al–4V substrates hardly reach 30 μm within a long duration of 16 h. After trying some characterization methods (XPS, EDS, metallographic analysis and ToF-SIMS), the EDS line scanning is selected as the practical one with sufficient accuracy and convenience. Influences of some critical factors, including growth duration, substrate temperature, reactant pressure and acetone (carbon source) concentration, are studied and discussed. Considering all of the factors, especially those related to the diamond coverage that can suppress carbon diffusion, the modified diffusion models for describing the carbon diffusion, are constructed, defining carbon concentration and diamond coverage (duration, pressure, carbon concentration)-dependent diffusion coefficients. Such the models can be used for well predicting the carbonization depths under most conditions, which are valuable for controlling the carbonized layers during fabrications of diamond coated Ti-related components facing to various applications.

5G printed circuit boards (PCBs), composed of glass fiber, epoxy resin and ceramic, are a kind of difficult-to-machine material. The manufacture of massive high-quality micro holes on 5G PCBs raise high requirements on the tool life and machining precision of PCB micro drills. Chemical vapor deposition (CVD) diamond coatings can be used as effective protective films on PCB micro drills. The surface smoothness and coating-substrate adhesion of diamond coated micro drills are two important factors affecting the drilling performances. Different from previously reported microcrystalline diamond (MCD) or nanocrystalline diamond (NCD) coating types on cutting tools, undoped (UD-) and boron doped (BD-) ultrananocrystalline diamond (UNCD) coatings with higher surface smoothness are firstly applied on PCB micro drills to reduce the friction and cutting resistance and improve the cutting performances while machining PCBs. Moreover, different from the usual argon-rich gas atmosphere for UNCD synthesis, the synthesis mechanisms of UD-UNCD and BD-UNCD with hydrogen-rich atmosphere adopting HFCVD method are clarified. Sufficiently high renucleation rate of diamond crystallites, long mean free path of reactive precursor species and high removal rate of non-diamond carbon phases lead to the successful synthesis of UNCD films. UDMCD, UD-UNCD, UD-MCD/UD-UNCD, BD-MCD, BD-UNCD, and BD-MCD/BD-UNCD, were synthesized on PCB micro drills using HFCVD. The tribological performances and wear mechanisms of these different diamond coatings were studied systematically. The dominant wear mechanism causing tool wear and fracture of diamond coated micro drills in high-speed machining PCBs is abrasive wear. The degree of abrasive wear while machining PCBs are mainly determined by the surface smoothness, surface roughness and coefficient of friction of diamond coatings. The top layer UNCD with tiny grain size leads to the improvement of surface smoothness and tribological properties, which enhance the chip evacuation capacity and reduce the tool wear. Besides, both boron doping and middle layer MCD can contribute to the strong coating-substrate adhesion. Therefore, BD-MCD/BD-UNCD coated micro drill exhibits the best cutting performances while machining PCBs.

H-, O-, OH- and F-terminated N-doped diamond surfaces are calculated by the density functional theory in the present study. Combined effects of terminating species and substitutional N dopants in the 1st or 2nd carbon layers on several critical features (i.e., bond length, total electron density, bond population, atomic charge, Fukui function, and density-of-states) are systematically studied and discussed. The N dopant presents clear, but local, effects for all the terminating species and dopant positions. The adsorption of any individual species to the N dopant in the 1st carbon layer results in the reduction of adsorption energy (less negative), most probably owing to the full shell structure of this N dopant. The H, OH and F each provides one unpaired electron to occupy the antibonding states within the N–H, N–OH and N–F bonds, making the bonds elongated, reducing the corresponding electron densities and bond populations. On the contrary, the N dopant in the 2nd carbon layer induces slight increment of the adsorption energy for O, OH and F, attributed to the positive atomic charges of neighboring topmost C atoms. Amongst the four adsorbates, the O shows the highest reactivity to either an electrophilic or a nucleophilic attack. Besides, N dopants have slight influences on the reactivity of the adjacent adsorbates. The present results can help to understand some related chemical processes (such as the oxidation and electrochemical analysis) on N-doped diamond films.

The study concentrates on systematic investigations on the effects of extremely high or low carbon concentration (2%–14%) and gas pressure (800 Pa–3200 Pa) on crystal structures, grain sizes, phase compositions, surface and cross-sectional morphologies, growth rates, surface roughness, mechanical and tribological performances of various polycrystalline diamond films synthesized on cemented carbide (WC-Co) substrates with hydrogen-rich/argon-lean gas mixture adopting hot filament chemical vapor deposition (HFCVD) method. The crystal structure, grain size and phase composition of various diamond films synthesized with different carbon concentration and gas pressure were analyzed, indicating that as-deposited diamond films cover microcrystalline diamond (MCD), submicrocrystalline diamond (SMCD), nanocrystalline diamond (NCD) and ultrananocrystalline diamond (UNCD). The surface and cross-sectional morphologies of these various polycrystalline diamond films were observed, and the growth rates of various diamond films were calculated. The three-dimensional morphologies and surface roughness were obtained. With increasing the carbon concentration and decreasing the gas pressure during the synthesis, the crystal size decreases so that diamond film with high smoothness, low surface roughness can be obtained. Subsequently, the synthesis mechanisms of MCD, SMCD, NCD and UNCD films with different carbon concentration and gas pressure under hydrogen-rich gas mixture adopting HFCVD were discussed in detail. The elastic modulus and nanohardness of different diamond films were measured quantitatively, and the film-substrate adhesion were evaluated qualitatively. Moreover, the tribological performances of various diamond films synthesized with different carbon concentration and gas pressure were studied by sliding against silicon nitride (Si3N4) ceramic balls. Results indicate that obtaining the dynamic equilibrium between sufficiently renucleation rate of diamond nuclei and effectively removal rate of non-diamond carbon phase by adjusting carbon and gas pressure under the hydrogen-rich gas chemistry can contribute to the synthesis of high-quality UNCD film.

Printed Circuit Board (PCB) filled with a large amount of Alumina ceramics has broad application prospects in the fifth-generation industry but is hard to drill. This work focuses on high-performance diamond films to improve the working life of drilling tools and holes quality of products. By utilizing hot filament chemical vapor deposition (HFCVD) methods, the monolayer microcrystalline diamond (MCD), bilayer micro-nanocrystalline diamond (MNCD), and four-layer diamond (MNMNCD) are coated on commercial PCB drills (WC-6% Co). Solid particle erosion tests are conducted to study erosive wear mechanism of diamond films impacted by ceramic powders/particles. Besides, cutting performances of diamond coated drilling tools are evaluated by performing high-speed drilling tests with PCB as workpieces. In Erosion tests, the monolayer MCD film presents intergranular fracture and shows the lowest erosive resistance. The MNCD and MNMNCD films have similar fracture forms, where curved boundaries and steps between layers indicate their discontinuous fracture, and minor deep cone holes on the surfaces demonstrate their high resistance to crack growth. Moreover, only one minor deep cone hole is observed on the four-layer film which indicates it has the best resistance to particle impinging. In drilling tests, the number of holes drilled by the diamond coated tools before failure is regarded as criteria of working life. Then surface and sectional morphologies of holes are also observed to evaluate the quality of products. The results indicate the number of holes machined by the four-layer MNMNCD coated drills reaches 10,000, while that of the monolayer and the bilayer MNCD ones are 3000– 4000 and 6000 respectively. More importantly, different from the other two types of diamond coated tools, almost no burrs with a height of over 20 μm are observed on the hole entrance using the four-layer diamond coated tools. Therefore, considering both the working life and holes quality, the MNMNCD films excel in the cutting performance of the new type of PCB drilling.

Hot filament chemical vapor deposition (HFCVD) diamond-coated small aperture wire-drawing dies from [Formula: see text] to [Formula: see text][Formula: see text]mm are in high demand. A new deposition technique without filaments through the inner hole of wire-drawing dies is proposed, accompanied with the specially designed fixtures. Temperature distribution on the deposition surfaces is studied by computational fluid dynamics (CFD) simulation based on the finite volume method (FVM); both case study and mass production simulations are accomplished. Excellent performance and uniform multilayer MCD/NCD/MCD/NCD films are successfully deposited on the inner-hole surfaces of total 16 cemented carbide (WC-6wt.%Co) wire-drawing dies with an aperture of [Formula: see text][Formula: see text]mm in one batch. Drawing results of gas shield welding wires show that the lifespan of the multilayer diamond coated wire-drawing dies is about 20 times of the uncoated cemented carbide dies and 2 times of the monolayer MCD coated dies.

Based on a well-designed growth procedure, a tri-material, namely, a three-layer boron-doped micro-crystalline, undoped micro-crystalline and undoped nano-crystalline composite diamond film, is deposited on the pretreated WC–6 wt% Co substrate, the basic characters of which are systematically studied and compared with some other commonly used diamond films. Besides, the growth times for three respective layers are accordingly determined. It is further clarified that the underlying boron-doped micro-crystalline diamond layer can well adhere to the WC–Co substrate due to either the reduction in the residual stress or the formation of B–Co compounds. There is no doubt that the surface undoped nano-crystalline diamond layer with relatively lower hardness and initial surface roughness is more convenient to be polished to the required surface roughness. Moreover, when the growth times for the middle undoped micro-crystalline diamond layer and the surface undoped nano-crystalline diamond layer are both appropriate, the undoped micro-crystalline diamond layer with extremely high diamond quality and hardness can effectively reinforce the surface hardness of the whole composite film. Based on the discussions on the influences of the growth times for the different layers on the performance of the composite diamond film, the growth times for the boron-doped micro-crystalline diamond, undoped micro-crystalline diamond and undoped nano-crystalline diamond layers are, respectively, determined as 4, 4 and 2 h. Under such conditions, the reinforcement effect of the middle layer on the surface hardness can be guaranteed, and the undoped nano-crystalline diamond grains have totally covered the undoped micro-crystalline diamond layer.

Micro-crystalline diamond (MCD) films are deposited on reactive sintering SiC substrates by the bias enhanced hot filament chemical vapor deposition (BE-HFCVD) method, respectively using the methane, acetone, methanol and ethanol as the carbon source. Two sets of standard tribotests are conducted, adopting Si 3 N 4 balls as the counterpart balls, respectively with the purpose of clarifying differences among tribological properties of different MCD films, and studying detailed effects of the carbon source C , normal load F n and sliding velocity v based on orthogonal analyses. It is clarified that the methane-MCD film presents the lowest growth rate, the highest film quality, the highest hardness and the best adhesion, in consequence, it also performs the best tribological properties, including the lowest coefficient of friction ( COF ) and wear rate I d , while the opposite is the methanol-MCD film. Under a normal load F n of 7 N and at a sliding velocity v of 0.4183 m/s, for the methane-MCD film, the maximum COF ( MCOF ) is 0.524, the average COF during the relatively steady-state regime ( ACOF ) is 0.144, and the I d is about 1.016 × 10 −7 mm 3 /N m; and for the methanol-MCD film, the MCOF is 0.667, the ACOF is 0.151, and the I d is 1.448 × 10 −7 mm 3 /N m. Moreover, the MCOF , ACOF , I d and the wear rate of the Si 3 N 4 ball I b will all increase with the F n , while the v only has significant effect on the ACOF , which shows a monotone increasing trend with the v .

In the present study, high-quality chemical vapor deposition (CVD) micro-crystalline diamond (MCD) film was successfully deposited on the surface of the Φ0.5 mm×120 mm tungsten wire using a special designed graphitic jig for supporting the substrate and a two-step deposition procedure for guaranteeing the uniformity of as-deposited diamond film. It is proved that as-deposited film indeed presented much more uniform thickness than that obtained using a conventional jig described in the previous literature, and a very thick WC interlayer spontaneously formed between the substrate and the diamond film, which together with as-deposited MCD film have significant effects on mechanical properties of the wire. Generally speaking, the coated wire remains extremely high surface hardness of the MCD film and considerable toughness of the substrate, along with favorable film-substrate adhesion. It is recognized that these the coated tungsten wires have broad application prospects, but the technologies for depositing diamond films that are thick enough on even longer and thinner wires still need further investigation.

Mechanical properties and solid particle erosion of chemical vapor deposition (CVD) diamond films are strongly influenced by the adopted carbon source in the deposition process. In the present study, methane, acetone, methanol and ethanol are respectively used as the carbon source to deposit micro-crystalline diamond (MCD) films on SiC substrates by the bias-enhanced hot filament CVD (BE-HFCVD) method. A standard air–sand erosion rig is employed to conduct erosion tests, using angular SiC sands of 320 meshes as impact abrasives. The impact velocity v e and impact angle α e are fixed as 100 m/s and 90°, respectively. The steady-state erosion rate e s , film life t r and a unit film life t ru are defined to assess the erosion behaviors of as-deposited films, which have close relationships with the mechanical properties, as measured by the Rockwell hardness tester and the nanoindentation test. It's found that under the condition of the same film thickness, the methane-MCD film shows the lowest e s and the longest t r , owing to the highest surface hardness and the most favorable film-substrate adhesion which is equivalent to the highest fracture strength, but the opposite is true for the methanol-MCD film. Moreover, due to the relatively higher growth rate, the acetone- and ethanol-MCD films both perform even longer t ru than the methane-one, indicating better “average” erosion behavior. Consequently, the optimal efficiency and economy can be achieved when adopting either the acetone or the ethanol to deposit MCD films of sufficient thickness on working surfaces of erosion resistant components suffering severe erosive wear, especially in the case of mass production.

Carbon fiber reinforced plastics (CFRP), which are widely used in the aerospace and some other new-tech industries, are considered very difficult to machine due to the material anisotropic and inhomogeneous features. Chemical vapor deposition (CVD) diamond films are suitable as protective coatings on cutting tools for machining advanced composite materials, owing to their extremely high hardness, favorable wear resistance, low friction coefficient and high thermal conductivity. Among different types of diamond films, the fine grained diamond (FGD) film can provide much more favorable environment for machining CFRP due to the small grain size, low surface roughness and the retentivity for the sharpness of the cutting edge. In the present study, aiming at drilling CFRP, FGD films of different thicknesses are deposited on Φ3 mm drills by controlling the growth time, adopting the common-used hot filament CVD (HFCVD) technology. It can be directly proved by deposition experiments that overlong growth time can induce spontaneous film delamination and removal before the cooling stage, probably as a result of the excessive residual stress concentrated on the complicated surfaces. As demonstrated by the cutting tests, with increasing the growth time, the main failure mode of the FGD coated drill changes from film delamination to flank wear/tipping to film delamination, and the maximum tool life exists when the growth time is moderate, because the flimsy film cannot provide sufficient protective effects on the film-substrate interface and even hasn’t totally cover the substrate, while there’s relatively higher residual stress in the film that is too thick, and such the residual stress can significantly deteriorate the film-substrate adhesion. Moreover, during the life cycle of each FGD film, relatively shorter growth time often means the slightly better hole quality, attributed to the retentivity of the initial shape of the uncoated drill that is optimal designed for machining CFRP, especially the weaker passivation of the cutting edge.

Based on the density functional theory calculations, more reasonable model and calculation method were proposed for evaluating the local adsorption energy of certain terminating species on Si-doped diamond surfaces. Influences of substitutional Si dopant in the 1st or 2nd C layer on local adsorption energy of the H, O, OH or F terminating species were studied for the first time. The combined influences of the terminating species and Si dopant on various parameters, such as bond length, total electron density, bond population, atomic charge, Fukui function and density-of-states (DOS), were further discussed. The Si dopant, either within the 1st or the 2nd layer, showed clear, but local, effects for all the species. It was found that onto the clean surface (without any adsorbate in the initial state), the Si1 dopant contributed to the increase of local adsorption energy values for the O, OH and F adsorbates binding to it, as well as the decrease of that for H, because it had smaller electronegativity than C and positive atomic charge. The adsorption energy for one OH attracted by the adjacent C1 binding to the Si2 was smaller than that by other C1, owing to the negative atomic charge. However, those for O and F atoms were larger instead, owing to the 3d unoccupied orbital around Si2 that was probably occupied by the lone electron pairs around O and F. The primary structural change induced by Si incorporation was the elongation of the Si C and Si A (adsorbates) bonds, accompanied by the decrease of electron density, compared with corresponding C C and C A bonds, attributed to the larger radius of the Si. Among the four terminating species, the O atom performed the highest reactivity to the electrophilic or nucleophilic attack. This is the first time the adsorption on the Si-doped diamond films is calculated, and above results can help to understand related chemical processes on the Si-doped diamond films.

To improve the precision and homogeneity for mass-production of HFCVD diamond coated milling tools, the simulation of substrate temperature field generated by the HFCVD setup was conducted, adopting a 3D simulation model well in accordance with the actual equipment. Firstly, the deviation of the simulation model is assessed by comparing the simulated temperature and measured temperature based on a validation test. The comprehensive influences of various critical setup parameters on the fabrication of diamond coatings are illustrated systematically according to the Taguchi simulation scheme (L16, five factors and four levels), including the filament diameter d, the filament temperature Tf, the separation between two adjacent filaments D, the filament height H, and the material of sample holder M, in order to obtain an optimal HFCVD setup. The results indicate that filament diameter d and the separation between two adjacent filaments D can effectively contribute to adjusting the average temperature; the distance between filaments and tool tips H, and the material of sample holder M exhibit remarkable effects on the temperature uniformity; the filament temperature Tf shows obvious influences on both the average temperature and the temperature uniformity. Furthermore, the optimal HFCVD setup has been proposed, based on which a more uniform temperature field around all the tool tips can be acquired, contributing to the mass-production of high-quality and high-precision diamond coated milling tools. Afterwards, the mass-production experiments of depositing MCD and NCD diamond coatings on WC-6% Co milling tools were conducted in the actual HFCVD reactor, and tool-tip temperature were measured, revealing that the optimal setup can produce an extremely uniform temperature field. Moreover, the characterizations and cutting performances of MCD and NCD diamond coatings deposited on milling tools were evaluated, indicating that high-quality and high-precision diamond coatings with quite satisfactory homogeneity of thickness, surface and cross-sectional morphologies, chemical compositions and phases can be acquired during mass-production of diamond coated milling tools on the base of the optimal HFCVD setup.

It is environmentally friendly to use water-based emulsion instead of the oil when cold drawing Al alloy production. In this research, adopting specially prepared water-based emulsion, contact angles and tribological properties of as-selected multilayer diamond films are clarified. The contact angle on diamond film is much smaller than that on WC-Co with the same surface roughness, and tribological behaviors of the diamond film are much better. The effects of surface roughness Ra of the film, lubrication, and water content in the emulsion W are studied, indicating that the contact angle increases with W or Ra. For the diamond film, lower Ra is beneficial for reducing the coefficient of friction (COF), Al alloy ball wear and oxidation, while lower W contributes to the reduction of the COF, ball oxidation, and coated disk wear. Finally, high-speed drawing of high-quality 6021 Al alloy wires (AWs) is accomplished, proving that using coated drawing dies, the water-based emulsion (W

The differences between the nucleation, growth and basic characteristics of bias-enhanced hot filament chemical vapor deposition (BE-HFCVD) microcrystalline diamond (MCD) films fabricated under the different carbon source (methane, acetone, methanol and ethanol) environments are studied in this article, adopting SiC chips as substrates. With the same commonly-used nucleation parameters, acetone and ethanol can provide either higher nucleation density (ND) or larger nuclei size (NS). Besides, under the same commonly-used growth conditions, relatively higher growth rate (R) of the MCD film is obtained adopting methanol than methane, and both acetone and ethanol can further increase it. Moreover, as characterized by the X-ray Diffraction (XRD) and Raman spectroscopy, the MCD film fabricated using methane shows much lower total residual stress (σ), better film quality and lower (220)/(111) ratio compared with those fabricated using all the other carbon sources. The above results can be attributed to the presence of oxygen elements, the different dissociation energies of chemical bonds in the carbon sources, the different quantities of CH3 radicals generated from the carbon sources or the different amounts of defects in as-deposited diamond films. Based on the present study, it is suggested that the carbon source should be reasonably chosen in order to, respectively, improve the film quality or obtain high ND, NS and R.

Deposition parameters that have great influences on hot filament chemical vapor deposition (HFCVD) diamond films growth on inner hole surfaces of WC–Co substrates mainly include the substrate temperature ( t ), carbon content ( ϕ ), total pressure ( p ) and total mass flow ( F ). Taguchi method was used for the experimental design in order to study the combined effects of the four parameters on the properties of as-deposited diamond films. A new figure-of-merit (FOM) was defined to assess their comprehensive performance. It is clarified that t, ϕ and p all have significant and complicated effects on the performance of the diamond film and the FOM, which also present some differences as compared with the previous studies on CVD diamond films growth on plane or external surfaces. Aiming to deposit HFCVD diamond films with the best comprehensive performance, the key deposition parameters were finally optimized as: t =830 °C, ϕ =4.5%, p =4000 Pa, F =800 mL/min.

Chemical vapor deposition (CVD) diamond films have attracted more attentions due to their excellent mechanical properties. Whereas as-fabricated traditional diamond films in the previous studies don’t have enough adhesion or surface smoothness, which seriously impact their friction and wear performance, and thus limit their applications under extremely harsh conditions. A boron doped, undoped microcrystalline and fine grained composite diamond (BD-UM-FGCD) film is fabricated by a three-step method adopting hot filament CVD (HFCVD) method in the present study, presenting outstanding comprehensive performance, including the good adhesion between the substrate and the underlying boron doped diamond (BDD) layer, the extremely high hardness of the middle undoped microcrystalline diamond (UMCD) layer, as well as the low surface roughness and favorable polished convenience of the surface fine grained diamond (FGD) layer. The friction and wear behavior of this composite film sliding against low-carbon steel and silicon nitride balls are studied on a ball-on-plate rotational friction tester. Besides, its wear rate is further evaluated under a severer condition using an inner-hole polishing apparatus, with low-carbon steel wire as the counterpart. The test results show that the BD-UM-FGCD film performs very small friction coefficient and great friction behavior owing to its high surface smoothness, and meanwhile it also has excellent wear resistance because of the relatively high hardness of the surface FGD film and the extremely high hardness of the middle UMCD film. Moreover, under the industrial conditions for producing low-carbon steel wires, this composite film can sufficiently prolong the working lifetime of the drawing dies and improve their application effects. This research develops a novel composite diamond films owning great comprehensive properties, which have great potentials as protecting coatings on working surfaces of the wear-resistant and anti-frictional components.

The characteristics of hot filament chemical vapor deposition (HFCVD) diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentration. Orthogonal experiments were introduced to study the comprehensive effects of such three parameters on diamond films deposited on WC-Co substrates. Field emission scanning electron microscopy, atomic force microscopy and Raman spectrum were employed to analyze the morphology, growth rate and composition of as-deposited diamond films. The morphology varies from pyramidal to cluster features with temperature decreasing. It is found that the low total pressure is suitable for nano-crystalline diamond films growth. Moreover, the substrate temperature and total pressure have combined influence on the growth rate of the diamond films.

Chemical vapor deposition (CVD) diamond film has been considered as a good candidate protective coating under hostile and abrasive conditions due to its outstanding erosion behavior. In the present study, the conventional micro-crystalline diamond (MCD) film, nano-crystalline diamond (NCD) film and the boron-doped diamond (BDD) film are respectively fabricated by the hot filament CVD (HFCVD) method. Solid particle erosion tests are conducted on diamond films in an air–sand erosion rig under different impact velocities (v) and angles (α) with angular SiC sands as the erodents, and WC–Co and SiC materials are adopted as comparisons. The field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Raman spectroscopy, Rockwell hardness tester and surface profilometer are respectively used to characterize diamond films before and after tests, exhibiting that compared with MCD and NCD films, the BDD film performs relatively higher fracture strength and better adhesion. Typical solid impact erosion stages of the different diamond films are observed. The solid particle erosion behavior of diamond films has close relationships to their fracture strength and adhesion. As a result, when the impact angle α ≤ 30°, the steady-state erosion rate of the BDD film is lower than those of MCD and NCD ones. More importantly, under all the impact angles and velocities, much quicker film delamination and removal can be noticed on the MCD and NCD films, especially the NCD one. By contrast with WC–Co and SiC materials, diamond films present much better erosion resistance and higher velocity exponents, which should be attributed to different impact mechanisms caused by the different hardness of eroded samples.

Chemical vapor deposition (CVD) diamond film has extensively applied as the protective coating under hostile and abrasive conditions, the erosion mechanism of which is significantly influenced by the composition and thickness of the film. This paper describes an erosion study, which examines the effects of the film thickness on the erosive wear behavior of the boron-doped diamond (BDD) films deposited on the SiC substrates by the hot filament CVD (HFCVD) method, with the undoped ones as comparisons. A laboratory designed air–sand erosion rig is used to conduct the erosion tests, with the velocities in the range of 100–140 m/s and 90° nominal impact angle. The erodents are silica sands with an average diameter of 180 μm. The diamond films are examined both pre- and post-test by the field emission scanning electron microscopy (FESEM) in order to determine the erosion mechanisms of the diamond films. Firstly, it is observed that the higher residual compressive stress and critical tensile strength can slow down the formation of the ring cracks. Moreover, the 12 μm diamond film has the highest steady-state erosion rate because the depth of the maximum shear stress is much close to the film–substrate interface. Furthermore, the complicated effects of the film thickness on the film lives of both the BDD and undoped diamond films are also further studied, as well as the velocity exponents of the different diamond films. The research results in the present study are conductive to the widespread applications of BDD films on the erosion resistant components.

The non- and O-terminated diamond (1 1 1)-1 × 1 surfaces, with the substitutional B (or N) dopants in different atomic layers, have been modelled in the present study. The influences of the O adsorbates, dopant and dopant position on the adsorption energy, have been studied by performing the density functional theory (DFT) calculations. Various parameters were additionally calculated in order to analyze the obtained results: bond lengths, total electron densities, bond populations, atomic charges, Fukui functions (FFs) and density-of-states. Dangling bonds on non-terminated surfaces, O adsorbates, as well as dopants within various atomic layers were all found to induce local effects. In fact, the degree of influences of the dopant on the adsorption energy of the O adsorbates, as well as on parameters like the near-surface bond lengths, total electron density, bond populations and atomic charges, were all found to be dependent on the dopant position. More generally, the deeper the dopant position, the less influence it had on the surface structures and properties. The influences by the dopant in the 1st or 2nd C atomic layer were observed to be significant, but those in the 3rd to 5th C layers were almost negligible. It was also found that the B dopant would decrease the adsorption energy of the adjacent O adsorbates, while the N dopant in the 2nd layer would increase it. Furthermore, the combination of the O adsorbates, together with the dopants within the 1st or 2nd C layer, could induce significant elongation of the bonds between neighboring atoms within the 1st and 2nd layers (i.e. C-C, C-B or C-N bonds). Moreover, all the terminating O atoms could react strongly with either the electrophilic or the nucleophilic species.

The boron-doped (B-doped) and silicon-doped (Si-doped) diamond films are deposited on Co-cemented tungsten carbide (WC–Co) drills by the hot filament chemical vapor deposition (HFCVD) method, adopting trimethyl borate (C 3 H 9 O 3 B) and tetraethyl orthosilicate (C 8 H 20 O 4 Si) as the dopant sources, respectively. The characterization of as-deposited diamond films are investigated by scanning electron microscopy (SEM) and Raman spectroscopy. The adhesive strength between the diamond films and the WC–Co substrates is assessed by Rockwell indention tests. The drilling tests for evaluating the performance of the diamond coated drills are conducted with carbon fiber reinforced plastics (CFRP) as the workpiece. For the sake of comparison, conventional diamond coated and bare WC–Co drills are also used in the drilling tests. The wear performance of the tools is compared and discussed in terms of the diamond coating microstructure. According to the results, the diamond coated drills exhibit a better wear resistant with respect to the uncoated one. Besides, the Si-doped diamond coated drill displays the best cutting performance for the smooth surface and favorable adhesive strength.

Recently, shaped drawing dies with complicated hole shapes have attracted intensive interests to produce shaped wires. In order to produce high-quality wires, the surface smoothness of the drawing dies is a major requirement and as important as the wear resistance. In the present investigation, the deposition parameters in diamond films growth on the interior-hole surfaces of the WC–Co rectangular-hole shaped drawing dies are optimized by orthogonal simulations, for which homogeneous substrate temperature ( dT

Diamond films have been considered as good candidate protective coatings on varieties of substrates in order to improve their erosive wear performance. In the present study, boron-doped diamond films with thicknesses of about 6–7 µm are first deposited on five different substrates using the hot filament chemical vapor deposition method, including SiC, WC-Co, Ta, Ti, and Si substrates. The residual stress and adhesive strength of the five boron-doped diamond films are estimated, respectively, by means of material properties of substrates and the diamond, Raman spectra, and static indentation results. Erosion tests are conducted on all the boron-doped diamond coated samples in an air–sand erosion rig with angular SiC sands as erodents. The results exhibit that the formation of ring cracks on the boron-doped diamond film in the erosion process has a strong link to the total residual stress. The higher residual compressive stress in the Ti-based boron-doped diamond film can slow down the formation of ring cracks to some extent. Nevertheless, the erosive wear performance, which is mainly evaluated based on the erosion rate and film removal, is much related to the film–substrate adhesion. As a result, the Ti-based boron-doped diamond film is quickly worn and removed because of the poorest adhesion. On the contrary, both the SiC- and Si-based boron-doped diamond films with favorable adhesion perform much better erosion resistance. Moreover, comparative erosion tests on thicker SiC- and WC-Co-based boron-doped diamond films (21–23 µm) and their applications on nozzles can both further manifest the same kind of relationship, the SiC-based boron-doped diamond film presenting longer steady erosive stage and slower film removal than the WC-Co-based one.

The substrate temperature distribution in hot filament chemical vapor deposition (HFCVD) diamond films growth on drill tools in large quantities are simulated by the finite volume method (FVM), adopting a detailed 3-D computational model corresponding with the actual reactor. Firstly, the correctness of the simulation model is verified by comparing the temperature data obtained from the simulation with that measured in an actual depositing process, and the results show that the error between them is less than 3%. Thereafter, the influences of several parameters are studied, including the filament separation (D), the length of the filament (L) and the filament-substrate distance (H). The simulation results show the three parameters have different effects on the distribution of temperature field. The influence of D is the greatest, L is followed and then H. The simulation has important theoretical guidance on both the development of HFCVD deposition equipment using for the diamond coating on tools with complex shapes in large quantities and the research of related production process.

In the present investigation, both micro-crystalline and nanocrystalline diamond (MCD and NCD) films are fabricated, which are characterized by FESEM (Field Emission Scanning Electron Microscopy), surface profilemeter, Raman spectroscopy and Rockwell hardness tester. Moreover, under the dry environment, the frictional behavior of both the films sliding against commonly-used materials in the metal drawing industry is studied on a ball-on-plate rotational frictional tester, including the stainless steel, low-carbon steel, high-carbon steel and copper, demonstrating that the frictional coefficients between NCD films and all these materials are relatively smaller. Furthermore, the wear rates of both the films, which are hardly measured in the ball-on-plate friction tests, are evaluated using a home-made inner-hole line drawing apparatus, with both the diamond films deposited on the inner-hole surfaces and the low-carbon steel wires as the counterparts. Inversely, the NCD films present higher wear rates than the MCD ones, which can be attributed to the deteriorative film purity and adhesion.

LiNbO3 films were grown on nanocrystalline diamond (NCD)/Si substrates with amorphous SiO2 buffer layer by pulsed laser deposition technique at various oxygen pressures ranging from 10 Pa to 80 Pa. The stoichiometric LiNbO3 ceramic target was used. Significant effects of oxygen pressure on c-axis orientation, stoichiometry, crystallinity and surface morphology of LiNbO3 films were investigated. It was found that the above properties are strongly dependent on the oxygen pressure. Completely c-axis oriented LiNbO3 films with the average surface roughness of 9.0 nm could be achieved under an optimum oxygen pressure of 40 Pa. Surface acoustic wave devices were fabricated and characterized utilizing the structure of LiNbO3/SiO2/NCD/Si.

In the present study, adopting the optimized deposition parameters determined by orthogonal simulations, high-quality boron-doped and undoped composite diamond (BD–UCD) films with uniform thickness are deposited on both the inner hole and conical surfaces of the SiC nozzles used in the spray drying equipment. The erosion behavior of the novel diamond film is firstly evaluated in an air–sand erosion rig, with single-layer boron-doped diamond (BDD) and undoped diamond films as comparisons. Thereafter, the erosive wear performance of the BD–UCD coated nozzles is further studied under the industrial condition. The results show that the BD–UCD film exhibits an apparent increase in the erosion resistance over the other two types of diamond films. The mechanism responsible is found to be that the surface undoped diamond layer in the BD–UCD film has outstanding hardness, and boron doping can improve the adhesion between the underlying BDD layer and the substrate. Moreover, under the industrial condition, the ethylene catalytic cracking catalyzers produced with the BD–UCD coated nozzles have much more stable quality than those produced with the uncoated nozzles owing to the aperture stability of the inner hole, further proving the high erosion resistance of the BD–UCD protecting coatings.

The micron well-faceted diamond powders have attracted an increasing attention in the polishing filed, owing to improve the surface finish of components using the powders. In the present work, the hot filament chemical vapor deposition (HFCVD) technique is employed for synthesizing such diamond powders. A great many of micron diamonds are grown simultaneously but independently onto a large-area substrate. First, a novel seeding method, spraying the diamond seeds suspension toward the substrate using a spin coater machine, is proposed, with which the seeds with a controlled density are distributed evenly onto the substrate. Also, the method is more suitable for the fabrication of the micron isolated diamonds, compared with other nucleation initiation methods, such as the scratching pre-treatment and electrical biasing on substrates. Afterwards, a systematic investigation is under taken into the effects of deposition parameters on the basic growth characteristics of CVD micron diamonds, and on the inhibition of films growth. Furthermore, the reactive pressure, substrate temperature, carbon concentration, and growth duration are determined to be 4500 Pa, 850 °C, 1.3–1.4%, 60–90 min, respectively. Eventually, under the preferred deposition conditions, approximately 15 million cube-octahedral crystals with the mean size of 2–3 μm are deposited simultaneously on the 1000 mm 2 substrate.

The substrate temperature distribution in HFCVD diamond film growth on the inner hole surface is simulated by the finite volume method in the present study, adopting a detailed 3-D computational model agreeing with the actual reactor. Firstly, the influences of several key deposition parameters are studied by the control variable method, including the cooling condition C, the filament temperature Tf, the filament diameter d and the substrate aperture D. Afterwards, the substrate temperatures in the actual reactor are measured. Deviations between the simulated and measured temperature values are all less than 5%, and the substrate temperature distribution trends in the measurement results are well coincident with those in the simulation results. Furthermore, corresponding deposition experiments are also conducted, the results of which can further validate the correctness of the simulations. Finally, the optimized deposition parameters are used to deposit diamond films on the inner hole surfaces of the WC–Co substrates with apertures of either 6 mm or 8 mm. The characterizations show that homogeneous diamond films with fine-faceted diamond crystals are obtained, indicating that this deposition parameter optimization method is feasible for fabricating high-quality diamond films on the inner hole surfaces.

In the present investigation, titanium (Ti), silicon carbide (SiC), silicon (Si) and tantalum (Ta) samples with the same geometry are selected as substrates to deposite HFCVD boron-doped diamond films with the same deposition parameters, using trimethyl borate as the dopant. FESEM, EDS, Raman spectroscopy and Rockwell hardness tester are used to characterize as-deposited boron-doped diamond (BDD) films. The FESEM micrographs exhibit that the film deposited on Si substrate presents the best uniformity and that on Ti substrate has smallest grain size and film thickness, with titanium element detected in the EDS spectra. Moreover, it’s speculated by indentation test that the adhesive strength between the BDD films and different substrates can be order as SiC>Ta>Ti for the different thermal expansion coefficient gaps between the substrate and diamond, and the hardness of the BDD coated samples measured using Rockwell hardness tester can also be order as SiC>Ta>Ti due to the different hardness of substrate materials. Finally, similar and representative characterization for BDD films is obtained from the Raman spectra for all the BDD films on different substrates.