Grain Size Of Diamond Films Research Articles

Fabrication of nanogranular diamond films by MPJCVD system

Nanogranular diamond films have been prepared by microwave plasma jet chemical vapor deposition system (MPJCVD) with argon-rich (Ar/H2:90%) plasma. In this work, the plasma pre-carbonization (P.P.) pre-treatment was employed to obtain uniform and smooth (13.3nm rms) diamond films with high nucleation density. The diamond films were fabricated in various Ar/H2 concentrations from 0% to 100% and fixed at CH4 concentration of 1%. It can be clearly observed that the grain size of diamond films changed from micrometer to nanometer scale and down to 5nm at the concentration of 90% Ar/H2. The reason is due to the rise of C2 dimer in the plasma, which could be proved from the analysis of OES analysis.

Deposition and characterization of nanocrystalline diamond films on Co-cemented tungsten carbide inserts

Nanocrystalline diamond films were deposited on Co-cemented tungsten carbides using bias-enhanced hot filament CVD system with a mixture of acetone, H 2 and Ar as the reactant gas. The effect of Ar concentration on the grain size of diamond films and diamond orientation was investigated. Nanocrystalline diamond films were characterized with field emission scan electron microscopy (FE-SEM), Atomic force microscopy (AFM), Raman spectroscopy and X-ray diffraction spectroscopy (XRD). Rockwell C indentation tests were conducted to evaluate the adhesion between diamond films and the substrates. The results demonstrated that when the Ar concentration was 90%, the diamond films exhibited rounded fine grains with an average grain size of approximately 60–80 nm. The Raman spectra showed broadened carbon peaks at 1350 cm − 1 and 1580 cm − 1 assigned to D and G bands and an intense broad Raman band near 1140 cm − 1 attributed to trans-polyacetylene, which confirmed the presence of the nanocrystalline diamond phase. The full width at half maximum of the <111> diamond peak (0.8°) was far broader than that of conventional diamond film (0.28°–0.3°). The Ra and RMS surface roughness of the nanocrystalline diamond film were measured to be approximately 202 nm and 280 nm with 4 mm scanning length, respectively. The Ar concentration in the reactant gases played an important role in the control of grain size and surface roughness of the diamond films. Nanocrystalline diamond-coated cemented tungsten carbides with very smooth surface have excellent characteristics, which made them a promising material for the development of high performance cutting tools and wear resistance components.

Raman spectroscopy study of the influence of processing conditions on the structure of polycrystalline diamond films

Diamond films are prepared by microwave plasma-enhanced chemical-vapor deposition on Si (100) substrates using the H2–Ar–CH4 gases. Raman scattering data, including the peak position, intensity, area, and width, are analyzed in depth and used to obtain the sp3- and sp2-bonded carbon contents and the nature of internal stresses in the films. Polarization behavior of the Raman peaks is analyzed to assess its role on the quantitative analysis of the diamond films, which suggested that the 1150cm−1 Raman peak in nanocrystalline diamond films could be attributed to sp2-bonded carbon. The role of the H2∕Ar content in the gas mixture and substrate temperature on the characteristics of the diamond film is studied. Thickness and grain size of diamond films are also determined by scanning electron microscopy and related to the deposition conditions and Raman results. Deposition conditions, which led to highest sp3-bonded carbon content and growth rate, are identified.

Adhesion improvement of the diamond film in diamond-coated WC–Co insert prepared with AC substrate bias

The grain size of diamond film deposited on WC–Co insert can be reduced by AC substrate bias during deposition, which enables a smooth surface finish of a workpiece during machining process. However, the adhesion of diamond film deposited on WC–Co insert became poor due to AC bias application, which was attributed to the increased surface Co content. To maintain adhesion strength while achieving grain size refinement by AC-biased growth, a certain thickness of diamond layer grown without bias was introduced as a buffer layer. The AC bias was applied after diamond deposition of 8 and 15 μm in thickness without bias and the total thickness of the diamond film was controlled to be around 20 μm. The adhesion strength of diamond film for the diamond-coated WC–Co insert prepared with AC bias, measured by indentation technique, was greatly improved by the adoption of diamond buffer layer deposited without bias.

The pronounced grain size refinement at the edge position of the diamond-coated WC–Co inserts under microwave plasma with negative bias

The effect of negative direct current (DC) bias on the deposition of diamond on WC–Co insert was investigated. Diamond was deposited by microwave plasma assisted chemical vapor deposition (MW PACVD) on the SPGN type of WC–Co insert at 30 Torr with H 2-2%CH 4 mixed gas. During the deposition process, DC bias was applied to the insert with the range between 0 and −120 V. The grain size of diamond film deposited on WC–Co insert was observed to decrease with the negative bias voltage. Furthermore, its tendency was more pronounced near the edge than at the center of the insert. The ion impact on the growth surface during deposition was considered to induce surface defects, which resulted in the renucleation of diamond crystals and grain size refinement.

Grain size refinement of the diamond film deposited on the WC–Co cutting inserts using direct current biasing

The effect of negative direct current (DC) bias has been investigated in the deposited diamond on WC–Co insert. SPGN type of WC–Co was used as a substrate where diamond was deposited by hot filament chemical vapor deposition at 60 Torr with H2–3%CH4 gas. DC bias was applied to the insert with the range between 0 and −120 V. The grain size of diamond film deposited on WC–Co insert decreased with the increase in negative bias voltage. The grain size was more refined near the edge than the center of the insert. Compared to other processing parameters such as pressure, temperature and carbon concentration, the biasing is a very effective way to reduce the grain size of diamond film, especially at the edge region where workpiece contacts during machining process.

Ultraviolet and visible Raman spectroscopy characterization of chemical vapor deposition diamond films

Polycrystalline diamond films with different grain sizes (10 nm, 100 nm and 5 μm) were prepared by hot-filament chemical vapor deposition (HFCVD). The diamond films have been studied using ultraviolet (UV, 244 nm), visible (Vis, 514 nm) and (Vis, 633 nm), near-infrared, micro-Raman scattering. The fluorescence in the excited diamond film is found to change considerably with the incident photon energy. The scattering intensity of amorphous sp 2-bonded carbon compared to the strength of the 1331 cm −1 Raman line from sp 3-bonded diamond is found to vary considerably as functions of the grain size of diamond film and the incident photon energy. Possible models for the structures of amorphous sp 2-bonded carbon and sp 3-bonded diamond phases are discussed on the basis of the present Raman data. It is shown that UV Raman spectroscopy has provided significantly greater information than visible Raman spectroscopy in characterizing diamond phases.

Diamond, diamond-like and titanium nitride biocompatible coatings for human body parts

A new approach is proposed for fabricating human body parts that last longer and are more biocompatible than those presently available. In this approach, bulk material is chosen that has desirable mechanical properties (low modulus, high strength, high ductility and high fatigue strength) and then this material is coated with highly corrosion- and erosion-resistant and totally biocompatible layers. As an example, we have investigated diamond, TiN, diamond/diamond-like, and diamond/TiN coatings on Ti−6wt.%Al−4wt.%V alloy used for hip prosthesis. This alloy has desirable mechanical properties but the toxicity of vanadium and the neurological disorders associated with aluminum have raised some concerns. To overcome this problem, we have developed a laser physical vapor deposition method to form TiN and diamond-like coatings, and a hot-filament-assisted chemical vapor desposition method to form diamond layers. Cementless diamond-coated hip prostheses of titanium alloys are expected to last approximately ten times longer or more compared with the polymethylmethacrylate-cement-coated CoCr prostheses used at present. The microstructure of diamond films can be controlled by substrate and deposition variables. The microstructures of these films have been investigated using optical and scanning electron microscopy, chemical composition by Auger electron spectroscopy, structure by X-ray diffraction, and atomic arrangements (lattice vibration) characteristics by Raman spectroscopy. The average grain size of diamond films varied from 0.5 to 2.0 μm, and the diamond-like films were amorphous. The average grain size of TiN films was found to vary from 10 to 20 nm. The diamond films showed characteristics Raman peak at 1332 cm −1 (sp 3 bonding), and diamond-like films contained 1350 and 1580 cm −1 Raman peaks (a mixture of sp 2 and sp 3 bonding). The mechanical properties and adhesion characteristics of these films together with biocompatibility issues are discussed for titanium alloy hip prosthesis.

Microstructural control of boundary region between CVD diamond film and cemented carbide substrate

Effects of the composition, texture and pretreatment of cemented carbide substrates on the microstructure of the boundary region between CVD diamond film and the substrate were investigated using a microwave plasma CVD in the CO-H2 system. Optimum CVD conditions for a uniform coating on to the edge part of cutting insert were: microwave power, 550 W; total pressure, 30 Torr; total flow rate, 200 ml/min; CO concentration, 5–20 vol%; treatment time, 3–5 h. An adherent and tough diamond coating was prepared by initial coating at lower CO concentrations and by subsequent coating at higher CO concentrations. A cemented carbide substrate in the binary WC-Co system which comprised fine-grained tungsten carbide and low content of cobalt was suited for preparation of adherent diamond coating. De-cobaltization pretreatment of the substrate surface in acid solution followed by an ultrasonic microflawing treatment enhanced the nucleation density and adherence of diamond film to the substrate. The rotation of substrate was found to be effective for increasing the uniformity and decreasing the grain size of diamond film.