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In this study, the residual stress of boron-doped diamond (BDD) films is investigated as a function of boron doping level using X-ray diffraction (XRD) analysis. Boron doping level is controlled from 1000ppm to 9000ppm by dissolving trimethyl borate into acetone. BDD films are deposited on silicon wafers using a bias-enhanced hot filament chemical vapor deposition (BE-HFCVD) system. Residual stress calculated by method varies linearly from 2.4GPa to 1.1GPa with increasing boron doping level. On the BDD film of 1.75GPa, free standing BDD cantilevers are fabricated by photolithography and ICP-RIE processes, then tested by laser Doppler vibrometer (LDV). A cantilever with resonant frequency of 183KHz and factor of 261 in the air is fabricated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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 100–140m/s and 90° nominal impact angle. The erodents are silica sands with an average diameter of 180μm. 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 12μm 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. [Copyright &y& Elsevier]

Abstract: 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 <15°C) and gas density fields are obtained. Thereafter, boron-doped diamond (BDD) films are fabricated and characterized, showing that high-quality films with uniform thickness (24–25μm) have been deposited on the whole interior-hole surface. Compared with the undoped diamond film, the BDD one presents much better adhesion and long-tested wear resistance. Moreover, the BDD film is also much easier to be polished to the appropriate surface smoothness due to the grain refinement and hardness reduction. Particularly, by comparison to the WC–Co drawing die, the working lifetime of the BDD coated one increases by a factor of above eight and in the course of processing, copper rectangular wires with higher surface quality and better dimensional precision are obtained. [Copyright &y& Elsevier]

Abstract: 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 (C3H9O3B) and tetraethyl orthosilicate (C8H20O4Si) 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. [Copyright &y& Elsevier]

• HFCVD is used to synthesize UD-MCD, UD-UNCD, UD-MCD/UD-UNCD, BD-MCD, BD-UNCD, BD-MCD/BD-UNCD films on WC-Co substrates. • Growth mechanism of UNCD with high carbon concentration and low gas pressure in hydrogen-rich chemistry are illustrated. • Undoped and boron doped UNCD coatings are firstly applied on WC-Co micro drills to improve the surface smoothness. • Both boron doping and middle layer MCD contribute to the strong adhesive level of UD-MCD/UD-UNCD and BD-MCD/BD-UNCD. • The UD-MCD/UD-UNCD, BD-UNCD and BD-MCD/BD-UNCD coated PCB micro drills show superior cutting performances. 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. [ABSTRACT FROM AUTHOR]