•Two types of amorphous ceramic interlayers (a-SiO2 and s-SiC) are synthesized on WC- 10 wt.% Co substrates by precursor pyrolysis.•Improved adhesion between the diamond coatings and WC- 10 wt.% Co substrates is obtained by employing amorphous ceramic interlayers.•The milling tests against zirconia indicate that the amorphous ceramic interlayers can significantly enhance the cutting performance of diamond coated tools with high cobalt content.In this paper, CVD diamond coatings are deposited on cemented carbides with 10 wt.% Co using amorphous SiO2 and amorphous SiC interlayers. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectrum and X-ray diffraction (XRD) are carried out to characterize the microstructure and composition of as-deposited films. Moreover, the adhesion and cutting performance of as-fabricated diamond coatings are studied. Indentation tests show that the amorphous ceramic interlayers can enhance the adhesion between diamond films and WC–Co substrates. The cutting tests against zirconia indicate that the tools with amorphous ceramic interlayered diamond coatings exhibit improved cutting performance. The amorphous ceramic interlayers can improve the adhesive strength and wear endurance of diamond coatings on WC–10 wt.% Co substrates, which provide a viable way for adherent diamond coatings on cemented carbide tools with high cobalt content.Figure optionsDownload full-size imageDownload as PowerPoint slide

In this study, the temperature and gas velocity distributions in hot filament chemical vapor deposition (HFCVD) diamond film growth on the end surfaces of seals are simulated by the finite volume method. The influence of filament diameter, filament separation and rotational speed of the substrates is considered. Firstly, the simulation model is established by simplifying operating conditions to simulate the temperature and gas velocity distributions. Thereafter, the deposition parameters are optimized as 0.6mm filament diameter, 18mm filament separation and 5 r/min rotational speed to get the uniform temperature distribution. Under the influence of the rotational speed, the difference between temperature gradients along the directions perpendicular to the filament and parallel to the filament becomes narrow, it is consistent with the actual condition, and the maximum temperature difference on the substrates decreases to 7.4 ◦C. Furthermore, the effect of the rotational speed on the gas velocity distribution is studied. Finally, diamond films are deposited on the end surfaces of SiC seals with the optimized deposition parameters. The characterizations by scanning electron microscopy (SEM) and Raman spectroscopy exhibit a layer of homogeneous diamond films with fine-faceted crystals and uniform thickness. The results validate the simulation model.

•Two types of amorphous ceramic interlayers (a-SiO2 and s-SiC) are synthesized on WC- 10 wt.% Co substrates by precursor pyrolysis.•Improved adhesion between the diamond coatings and WC- 10 wt.% Co substrates is obtained by employing amorphous ceramic interlayers.•The milling tests against zirconia indicate that the amorphous ceramic interlayers can significantly enhance the cutting performance of diamond coated tools.In this paper, CVD diamond coatings are deposited on cemented carbides with 10 wt.% Co using amorphous SiO2 and amorphous SiC interlayers. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectrum and X-ray diffraction (XRD) are carried out to characterize the microstructure and composition of as-deposited films. Moreover, the adhesion and cutting performance of as-fabricated diamond coatings are studied. Indentation tests show that the amorphous ceramic interlayers can enhance the adhesion between diamond films and WC–Co substrates. The cutting tests against zirconia indicate that the tools with amorphous ceramic interlayered diamond coatings exhibit improved cutting performance. The amorphous ceramic interlayers can improve the adhesive strength and wear endurance of diamond coatings on WC–10 wt.% Co substrates, which provide a viable way for adherent diamond coatings on cemented carbide tools with high cobalt content.

•MCD films are fabricated using different carbon sources by BE-HFCVD.•Typical carbon sources used include methane, acetone, methanol and ethanol.•The nucleation, growth and basic characteristics are compared.•Methane can guarantee high film quality and low residual stress.•Acetone can provide high growth rate and relatively high film quality.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.

•MCD and NCD films are deposited on balls and microdrills by HFCVD.•The tribological properties between diamond films and aluminum alloy are studied.•The cutting performance of MCD, NCD, DLC, and TiAlN coated microdrills is compared.•NCD coated microdrill exhibits the longest working life in aluminum alloy machining.•The NCD film thickness on microdrill is further optimized to be 4.5 μm.Aluminum alloy 7075 is widely used for producing micro-scale heat sinks, micro-fluidic devices, micro-propellers and so on. This paper deals with optimizing microstructure and thickness of diamond coatings on microdrills used in 7075 aluminum alloy machining. Firstly, the friction tests between microcrystalline diamond (MCD), nanocrystalline diamond (NCD) films and aluminum alloy reveal that the stable coefficient of friction (COF) of MCD–aluminum alloy working pair is 0.240, much higher than that of NCD–aluminum alloy working pair (0.072). The decrease of COF is mainly attributed to the lower roughness of NCD films and the presence of more graphite or the non-diamond phases in NCD coatings. Afterwards, comparative cutting tests involving MCD, NCD, diamond-like coating (DLC) and TiAlN coated microdrills show that after drilling 200 holes, NCD coated microdrills exhibit the best cutting performance. Furthermore, NCD coated microdrills with coating thicknesses of 1 μm, 2 μm, 4.5 μm and 7 μm are fabricated and their cutting performance is studied in aluminum alloy machining. The cutting experiments show that the NCD coated microdrill with coating thickness of 4.5 μm shows the best cutting performance, exhibiting not only lowest flank wear and no tool tipping or chipping on the main cutting edges but also the highest quality of drilled holes because of the outstanding adhesive strength and wear resistance of the NCD coating.

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.

•BDD films of different thicknesses are deposited on SiC substrate.•The erosion performance of as-deposited diamond films is evaluated.•The crack formation, erosion rate and film life in the erosive processes are studied.•Hertz theory is adopted to clarify the erosion mechanism.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.

Boron and silicon doped diamond films are deposited on the cobalt cemented tungsten carbide (WC-Co) substrate by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Acetone, hydrogen gas, trimethyl borate (C3H9BO3) and tetraethoxysilane (C8H20O4Si) are used as source materials. The tribological properties of boron-doped (B-doped), silicon-doped (Si-doped) diamond films are examined by using a ball-on-plate type rotating tribometer with silicon nitride ceramic as the counterpart in ambient air. To evaluate the cutting performance, comparative cutting tests are conducted using as-received WC-Co, undoped and doped diamond coated inserts, with high silicon aluminum alloy materials as the workpiece. Friction tests suggest that the Si-doped diamond films present the lowest friction coefficient and wear rate among all tested diamond films because of its diamond grain refinement effect. The B-doped diamond films exhibit a larger grain size and a rougher surface but a lower friction coefficient than that of undoped ones. The average friction coefficient of Si-doped, B-doped and undoped diamond films in stable regime is 0.143, 0.193 and 0.233, respectively. The cutting results demonstrate that boron doping can improve the wear resistance of diamond films and the adhesive strength of diamond films to the substrates. Si-doped diamond coated inserts show relatively poor cutting performance than undoped ones due to its thinner film thickness. B-doped and Si-doped diamond films may have tremendous potential for mechanical application.Highlights► Mechanical properties of undoped, B-doped and Si-doped diamond films are studied. ► Silicon doping can refine the diamond grain. ► Lowest COF and wear rate for Si-doped diamond films are obtained. ► B-doped diamond films show rougher surface but lower COF than that of undoped ones. ► B-doped diamond films present excellent cutting performance in cutting Al–Si alloy.

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.Highlights► A novel 3-D model is adopted to calculate the substrate temperature distributions. ► Simulation results are tested on the measured data for various HFCVD parameters. ► Deposition parameters are optimized based on the simulations and measurements. ► Diamond films with high quality are obtained with the optimized parameters.

•Deposition parameters on the complicated surfaces are optimized by simulations.•Novel composite diamond films are deposited on the working surfaces of the nozzles.•Composite diamond films exhibit better erosion resistance than SiC and other films.•Coated nozzles present favorable erosion performance and application effects.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.

Chemical vapor deposition (CVD) diamond coated drills are fabricated by depositing diamond films on Co-cemented tungsten carbide (WC-Co) drills. The characteristics of as-deposited diamond coatings are investigated by scanning electron microscope (SEM) and Raman spectra. To evaluate the cutting performance of diamond coated drills, comparative drilling tests are conducted using diamond coated and uncoated WC-Co drills, with carbon fiber reinforced plastics (CFRPs) as the workpiece on a high-speed computer numerical control (CNC) machine. Thrust force and tool wear are measured during the drilling process. The results show that diamond coated drill exhibits better cutting performance, compared with the uncoated drill. The value of flank wear is about 70 μm after machining 90 holes, about a half of that of theWC-Co drill with 145μm after drilling only 30 holes. The wear rate of WC-Co drill is higher than that of diamond coated drill before diamond films peeling off. The diamond coated drill achieves more predictable hole quality. The improved cutting performance of the diamond coated drill is due to the high hardness, wear resistance and low coefficient of friction.

Tribological properties of chemical vapor deposition (CVD) diamond films greatly affect its application in the mechanical field. In this paper, a novel multilayer structure is proposed, with which multilayer diamond films are deposited on silicon carbide by hot filament CVD (HFCVD) method. The different micrometric diamond grains are produced by adjusting deposition parameters. The as-deposited multilayer diamond films are characterized by scanning electron microscope (SEM) and white-light interferometry. The friction tests performed on a reciprocating ball-on-plate tribometer suggest that silicon carbide presents the friction coefficient of 0.400 for dry sliding against silicon nitride (Si3N4) ceramic counterface. With the water lubrication, the corresponding friction coefficients of silicon carbide and as-deposited multilayer diamond films further reduce to 0.193 and 0.051, respectively. The worn surfaces indicate that multilayer diamond films exhibit considerably high wear resistance.

The micro-crystalline diamond (MCD) and fine-grained diamond (FGD) films are deposited on commercial silicon nitride inserts by the hot-filament chemical vapor deposition (HFCVD) method. The friction and cutting properties of as-deposited MCD and FGD films coated silicon nitride (Si3N4) inserts are comparatively investigated in this study. The scanning electron microscopy (SEM) and Raman spectroscopy are adopted to study the characterization of the deposited diamond films. The friction tests are conducted on a ball-on-plate type reciprocating friction tester in ambient air using Co-cemented tungsten carbide (WC-Co), Si3N4 and ball-bearing steel (BBS) balls as the mating materials of the diamond films. For sliding against WC-Co, Si3N4 and BBS, the FGD film presents lower friction coefficients than the MCD film. However, after sliding against Si3N4, the FGD film is subject to more severe wear than the MCD film. The cutting performance of as-deposited MCD and FGD coated Si3N4 inserts is examined in dry turning glass fiber reinforced plastics (GFRP) composite materials, comparing with the uncoated Si3N4 insert. The results indicate that the lifetime of Si3N4 inserts can be prolonged by depositing the MCD or FGD film on them and the FGD coated insert shows longer cutting lifetime than the MCD coated one.

•Sandblasting combined with acid etching was utilized as pretreatment of Co-cemented tungsten carbide substrates.•The porous Co-depleted carbide layer caused by sandblasting and acid-etching pretreatment was thinner.•The residual stress of diamond films was decreased.•Diamond coated tools with sandblasting-acid pretreatment exhibited less area of flank wear and film shedding in turning test.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.

•Microcrystalline diamonds are grown on the scratched substrates by HFCVD.•The pressure has the strongest influence on the nucleation of microcrystals.•The morphology of nuclei plays a decisive role on that of final crystals.•As-grown diamonds directly meet size requirements of commercial powders.In the present work, microcrystalline diamond powders are deposited by using a bias-enhanced hot filament chemical vapor deposition (HFCVD) apparatus. Mirror-polished silicon wafers are served as substrates, pretreated by the scratching process for 10–15 s. A systematic investigation is under taken into the combined effects of deposition parameters on nucleation and growth characteristics of microcrystalline diamonds, based on the orthogonal collocation method. The results show that the morphology of final microcrystals depend mainly on that of nuclei rather than the deposition parameters, while the quality and grain size of crystals largely depend upon the deposition parameters. A high reactor pressure (3–4.5 kPa) in the nucleation process is a necessary condition for depositing the ideal nuclei with the single-crystal structure and euhedral diamond faces. Then under a set of optimized growth parameters, the final single crystals exhibit the regular-shaped morphology and smooth surfaces. The CVD microcrystals with various grain sizes in the range of 0.3–2 μm can be obtained by regulating the deposition time; moreover, they have a dramatically narrow particle size distribution, meeting the requirements on certain types of commercial powders without the process of sieving grain.