Newly Designed Glass Scribing Wheel Made of Chemical Vapor Deposition Diamond Film

The chemical vapor deposition (CVD) diamond and diamond-like carbon (DLC) films are deposited on the cobalt cemented tungsten carbide (WC-Co) cutting tools respectively using the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode. The scanning electron microscope (SEM), optical interferometer profiler and Raman spectroscopy were adopted to characterize the as-deposited diamond and DLC films. The cutting performance of as-fabricated CVD diamond and DLC coated milling tools is evaluated in dry milling SiC particulate reinforced Al-metal matrix composite material (Al/SiC-MMCs), comparing with the uncoated WC-Co milling tool. The milling results demonstrate that the uncoated WC-Co milling tool suffers severest wear in its circumferential cutting edge, while the wear of DLC coated milling tool is slightly lower. Comparatively, the CVD diamond coated milling tool exhibits much stronger wear resistance. The wear on its circumferential cutting edge is less than 0.07 mm at the end of milling test, only a half of that of DLC coated milling tool. This result is attributed to the extremely high hardness and strong adhesive strength of CVD diamond film covered on the WC-Co milling tool.

Owing to their excellent mechanical and tribological properties, like the well-known extreme hardness, low coefficient of friction and high chemical inertness, chemical vapor deposition (CVD) diamond films have found applications as a hard coating for drawing dies. The surface roughness of the diamond films is one of the most important attributes to the drawing dies. In this paper, the effects of different surface roughnesses on the friction properties of diamond films have been experimentally studied. Diamond films were fabricated using hot filament CVD. The WC-Co (Co 6[Formula: see text]wt.%) drawing dies were used as substrates. A gas mixture of acetone and hydrogen gas was used as the feedstock gas. The CVD diamond films were polished using mechanical polishing. Polished diamond films with three different surface roughnesses, as well as the unpolished diamond film, were fabricated in order to study the tribological performance between the CVD diamond films and different metals with oil lubrication. The unpolished and polished CVD diamond films are characterized with scanning electron microscope (SEM), atomic force microscope (AFM), surface profilometer, Raman spectrum and X-ray diffraction (XRD). The friction examinations were carried out by using a ball-on-plate type reciprocating friction tester. Low carbide steel, stainless steel, copper and aluminum materials were used as counterpart balls. Based on this study, the results presented the friction coefficients between the polished CVD films and different metals. The friction tests demonstrate that the smooth surface finish of CVD diamond films is beneficial for reducing their friction coefficients. The diamond films exhibit low friction coefficients when slid against the stainless steel balls and low carbide steel ball, lower than that slid against copper ball and aluminum ball, attributed to the higher ductility of copper and aluminum causing larger amount of wear debris adhering to the sliding interface and higher adhesive strength between the contacting surfaces.

Effects of microstructure of films on CVD diamond X-ray detectors

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.

Chemical vapor deposition (CVD) diamond film has long been investigated as an important coating material for a variety of mechanical components, due to its many excellent mechanical and tribological properties, e.g. extremely high hardness, low friction coefficient and excellent wear resistance. The tribological behaviors of CVD diamond films have been known to show significant dependence on both sliding environment and its surface characteristics. The investigation on the effect of sliding conditions like normal load, sliding velocity, counterpart material and lubricant have been reported extensively hi available literatures. Nevertheless, the suidies on the influence of grain size, surface roughness and homogeneity mainly concentrate on the CVD diamond film self-mated tiibosystem [1, 2]. Inadequate attention has been put on the heterogeneous contact of CVD diamond film with metal or ceramics material, which is a considerable frequently used contact type in its mechanical applications, especially for the CVD diamond coated cutting inserts or drills.

Cutting performance of time-modulated chemical vapour deposited diamond coated tool inserts during machining graphite

Chemical vapor deposition (CVD) diamond is known for its superior characteristics such as hardness, toughness and wear resistance. However, due to these factors, machining CVD diamond is a difficult material removal process. A new technique to polish CVD diamond film efficiently is reported in the present paper. In the CVD deposition process, boron was doped into diamond to fabricate high-quality semi-conductive film, which make it possible to machine diamond film by electro discharged machining (EDM) method. The relationship between EDM parameter and removal processing was investigated in details. The machined surface of boron doped (B-doped) diamond films was studied by Scanning Electron Microscope (SEM) and Raman Scattering Spectroscopy (Raman). The experimental results show that EDM polishing is a highspeed material removal and low cost method for CVD diamond polishing. When the discharge current and pulse-on time increase in a certain range, the cutting-off speed and roughness will increase correspondingly. The roughness of EDM polished CVD diamond film surface is Ra<0.5μm when the discharge current is at 4A and pulse-on time is at 200μs.

Carrier free paths in Chemical Vapour Deposition (CVD) diamond films depend on the presence of traps, which therefore strongly affect the performance of those CVD diamond based devices which rely on the electronic properties of the material, like radiation detectors. For the same reason, these devices can in turn be used as tools to study carrier dynamics. It is well known that some traps may be saturated by pre-irradiation with ionizing radiation (e.g. β-particles), a process called “pumping” or “priming”. Not all traps behave in the same way. Due to the large bandgap of diamond, both shallow (not affected by pumping) and deep traps for electrons and holes may exist. We measured, using 5.5 MeV 241Am α-particles, the response of high quality CVD diamond based detectors after successive annealing steps performed at selected temperatures. The analisys of the decay of the detector efficency with annealing time at several temperatures allows a quantitative evaluation of the activation energy of these defects. Two main trapping centres connected to the pumping process were found, both related to holes, having activation energies of about 1.6 eV and 1.3 eV respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of paramagnetic defects in CVD diamond films (ESR study)

A new technique used for polishing chemical vapor deposition (CVD) diamond films has been investigated, by which rough polishing of the CVD diamond films can be achieved efficiently. A CVD diamond film is coated with a thin layer of electrically conductive material in advance, and then electro-discharge machining (EDM) is used to machine the coated surface. As a result, peaks on the surface of the diamond film are removed rapidly. During machining, graphitization of diamond enables the EDM process to continue. The single pulse discharge shows that the material of the coated layer evidently affects removal behavior of the CVD diamond films. Compared with the machining of ordinary metal materials, the process of EDM CVD diamond films possesses a quite different characteristic. The removal mechanism of the CVD diamond films is discussed.

High-temperature Raman study in CVD diamond

In vivo preliminary evaluation of bone-microcrystalline and bone-nanocrystalline diamond interfaces

Diamond is generally accepted as a material with individual properties such as superlative hardness, low coefficient of friction and very high thermal conductivity. Synthetic diamond can be achieved in the form of thin and thick films using experimental chemical vapor deposition (CVD) methods. Cemented tungsten carbide (WC–Co) is the commonly used tool material with high hardness (~18 GPa) and high elastic modulus (~550 GPa) and, also compatible to the growth of synthetic diamond films. Presently, synthetic diamond coatings have been widely used on carbide cutting tools from long time to prevent the abrasive wear occurred on conventional tools. Based upon the size of the grains, synthetic diamond coatings are basically classified into nanocrystalline diamond (NCD) and microcrystalline diamond (MCD). In the work reported in the present chapter, smooth and adhesive thin NCD and MCD coatings were deposited on chemically treated tungsten carbide substrates using pre-determined process parameters in the hot filament chemical vapor deposition (HFCVD) method. Tungsten carbide with 6% Co is the mostly accepted grade of base material used for the successful growth of synthetic diamond films on its surface and, also to minimize the thermal residual stresses existing during the deposition and cooling down process between the interfaces of coating and substrate. Mostly, these thermal residual stresses are produced due to difference in thermal expansion coefficients between the coating and substrate. During deposition process, the process parameters such as methane concentration (%CH4/H2) and chamber pressure were controlled automatically using pre-programmed recipe for the growth of NCD and MCD films. The structural characteristics and quality of the synthetic diamond films were confirmed using X-ray diffraction and Raman spectroscopy techniques, respectively. The surface morphology was studied using a high resolution scanning electron microscope (HRSEM) and atomic force microscope (AFM). Moreover, the hardness measurement of coatings were done using a Berkovich nanoindenter. After that, a comparative evaluation between these two types of coatings was done.

Aiming at the key problems of the material removal rate and surface integrity of existing tools in the lapping of sapphire hard and brittle crystals, an efficient lapping tool has been developed to explore a new process for HFVCD (hot filament chemical vapor deposition) diamond tools to efficiently lap sapphire wafers. With the premise of ensuring the surface roughness of the wafer is Ra ≤ 0.5 μm, the material removal rate is increased to more than 1 μm/h. To explore a high-efficiency lapping process for sapphire wafers using HFCVD diamond tools. The influence of key preparation parameters on the surface characteristics of CVD (chemical vapor deposition) diamond films was systematically investigated. Three types of CVD diamond coating tools with distinct surface morphologies were fabricated. These tools were subsequently employed to conduct lapping experiments on sapphire wafers in order to evaluate their processing performance. The experimental results demonstrate that the gas pressure, methane concentration, and substrate temperature collectively influenced the surface morphology of the diamond coatings. The fabricated coatings exhibited well-defined grain boundaries and displayed pyramidal, prismatic and spherical features, corresponding to high-quality microcrystalline and nanocrystalline diamond layers. In the lapping experiments, the prismatic CVD diamond coating tool exhibited the highest material removal rate, reaching approximately 1.7 μm/min once stabilized. The spherical diamond coating tool produced the lowest surface roughness on the lapped sapphire wafers, with a value of about 0.35 μm. Surface morphology-controllable diamond tools were used for the lapping processing of the sapphire wafers. This achieved a good surface quality and high removal rate and provided new ideas for the precision machining of brittle hard materials in the plane or even in the curved surface.

Using recent papers on scanning electron microscopy (SEM) of chemical vapor deposition (CVD) diamond films, two analytical applications of the SEM are discussed: the morphologic investigations (secondary electron emission mode) and the recognition of impurities and defects [cathodoluminescence (CL) mode]. Studies of CVD diamond films by SEM demonstrate that the morphologies of these films are affected by synthesis conditions, especially by substrate temperature, methane concentration, and total pressure in the reactor. CL spectra and images are useful tools for clarifying the relationship between emission centers and different types of defects generated during the process of diamond crystal growth. The paper shows that the investigations of the morphology, crystallinity, local CL emission, as well as the surface distribution of CL spectra on CVD diamond films by SEM led to the correlative information for quality estimation of films in comparison with natural diamond.