Polycrystalline Diamond Characterisations for High End Technologies (original) (raw)
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Characterization and tribological evaluation of MW-PACVD diamond coatings deposited on pure titanium
Materials Science and Engineering: A, 2000
ABSTRACT Titanium alloys are widely used in aerospace and biomedical conditions, however, they are notorious for the poor tribological properties. The deposition of a well adherent diamond coating is a promising way to solve this problem. In this study, diamond coatings were deposited on pure titanium using microwave plasma assisted chemical vapour deposition (MW-PACVD). Characterisation of diamond coatings was performed using scanning electron microscopy (SEM), laser profilometry, Raman spectroscopy, grazing incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM). Tribological properties of diamond coatings were evaluated using a ball-on-disk wear tester (sliding with Al2O3 balls) and a scratch tester (sliding with diamond pin). Results showed that the friction and wear properties of polycrystalline diamond coatings as well as the wear of the counterface were dependent significantly on the surface roughness, the morphology and crystalline structure of diamond coatings as well as the counterface materials. For (111)-textured diamond coatings with rough surface and sharp asperities sliding with Al2O3 balls, the coefficient of friction was much higher than that of (100)-textured coatings, and the wear of the counterface material was quite high. After polishing the diamond coating, the surface roughness, coefficient of friction and wear of counterface decreased significantly. If sliding with diamond pins, the coefficient of friction of diamond coating shows a quite low and stable value. To improve the tribological properties, a three-step deposition method was proposed to obtain a smooth and nano-crystalline diamond layer on bulk diamond coatings. The so-formed diamond coating showed the highest load bearing capacity, the lowest coefficient of friction and the lowest wear of the counterface.
High vacuum tribology of polycrystalline diamond coatings
Sadhana, 2009
Polycrystalline diamond coatings have been grown on unpolished side of Si(100) wafers by hot filament chemical vapour deposition process. The morphology of the grown coatings has been varied from cauliflower morphology to faceted morphology by manipulation of the growth temperature from 700 • C to 900 • C and methane gas concentration from 3% to 1·5%. It is found that the coefficient of friction of the coatings under high vacuum of 133·32 × 10 −7 Pa (10 −7 torr) with nanocrystalline grains can be manipulated to 0·35 to enhance tribological behaviour of bare Si substrates.
Synthesis and characterisation of freestanding diamond coatings
Freestanding polycrystalline diamond (PCD) coatings are of immense technological importance. PCD has been grown over silicon substrates by microwave plasma assisted chemical vapor deposition (MWPACVD) process. The coatings are grown by suitable optimisation of the growth parameters of a 915 MHz microwave reactor. Thereafter, 1:1:1 solution of hydrofluoric acid (HF), nitric acid (HNO 3 ) and acetic acid (CH 3 COOH) is used to etch out the silicon wafer from the backside of the coating. Hereby, freshly generated nucleation surface, could be characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and stylus profilometer and could be compared with the growth side. It is found that both the nucleation side and growth side are of very high quality (full width at half maxima, i.e., FWHM < 8 cm -1 ). The growth side is (111) textured, whereas, the nucleation side is very smooth with embedded detonation-nano-diamond (DND) agglomerates. These freestanding coatings are successfully laser cut into different geometrical shapes. They are found to be optically translucent having high refractive index. Cross-sectional microscopy of the laser cut edge reveals novel melting features of the CVD grown diamond columns.
Mechanical and Tribological Behavior of Microcrystalline CVD Diamond Coatings
Journal of Bio- and Tribo-Corrosion, 2018
Smooth and adhesive microcrystalline CVD diamond coatings have been acquired successfully on chemically etched titanium alloy (Ti6Al4V) substrates, using hot filament chemical vapor deposition technique. The mechanical and tribological characteristics of HFCVD microcrystalline diamond coatings on titanium alloy (Ti6Al4V) substrates are investigated in this research. SEM and Raman spectroscopy were used to study the morphology and quality of the coatings. The surface roughness has been determined by 3d profilometer measurements. A ball-on-disk tribometer was used to characterize the friction and wear of the coatings. The frictional behavior of the MCD coating was studied, when sliding against smooth alumina ball with increasing load (1-10 N). A coefficient of friction of ~ 0.3-0.287 was obtained at a sliding speed of 12 m/s. The wear of the diamond coating is negligible. The alumina balls are worn out quickly as compared to the diamond coatings. Nanoindentation tests were carried out using Berkovich nanoindenter, and the average super-hardness of MCD coatings was found to be 55 GPa.
Tribological testing of self-mated nanocrystalline diamond coatings on Si3N4 ceramics
Surface and Coatings Technology, 2006
Due to their much lower surface roughness compared to that of microcrystalline diamond, nanocrystalline diamond (NCD) films are promising candidates for tribological applications, in particular when deposited on hard ceramic materials such as silicon nitride (Si 3 N 4 ). In the present work, microwave plasma-assisted chemical vapour deposition of NCD is achieved using Ar/H 2 /CH 4 gas mixtures on plates and ball-shaped Si 3 N 4 specimens either by a conventional continuous mode or by a recently developed pulsed regime. The microstructure, morphology, topography and purity of the deposited films show typical NCD features for the two kinds of substrate shapes. Besides, tribological characterization of the NCD/ Si 3 N 4 samples is carried out using self-mated pairs without lubrication in order to assess their friction and wear response. Worn surfaces were studied by SEM and AFM topography measurements in order to identify the prevalent wear mechanisms. Friction values reached a steady-state minimum of approximately 0.02 following a short running-in period where the main feature is a sharp peak which attained a maximum around 0.44. Up to the critical load of 35 N, corresponding to film delamination, the equilibrium friction values are similar, irrespective of the applied load. The calculated wear coefficient values denoted a very mild regime (K ∼ 1 × 10 − 8 mm 3 N − 1 m − 1 ) for the self-mated NCD coatings. The predominant wear mechanism was identified as self-polishing by micro-abrasion.
Property mapping of polycrystalline diamond coatings over large area
Journal of Advanced Ceramics, 2014
Large-area polycrystalline diamond (PCD) coatings are important for fields such as thermal management, optical windows, tribological moving mechanical assemblies, harsh chemical environments, biological sensors, etc. Microwave plasma chemical vapor deposition (MPCVD) is a standard technique to grow high-quality PCD films over large area due to the absence of contact between the reactive species and the filament or the chamber wall. However, the existence of temperature gradients during growth may compromise the desired uniformity of the final diamond coatings. In the present work, a thick PCD coating was deposited on a 100-mm silicon substrate inside a 915-MHz reactor; the temperature gradient resulted in a non-uniform diamond coating. An attempt was made to relate the local temperature variation during deposition and the different properties of the final coating. It was found that there was large instability inside the system, in terms of substrate temperature (as high as ΔT = 212 ℃), that resulted in a large dispersion of the diamond coating's final properties: residual stress (15.8 GPa to +6.2 GPa), surface morphology (octahedral pyramids with (111) planes to cubo-octahedrals with (100) flat top surfaces), thickness (190 µm to 245 µm), columnar growth of diamond (with appearance of variety of nanostructures), nucleation side hardness (17 GPa to 48 GPa), quality (Raman peak FWHM varying from 5.1 cm 1 to 12.4 cm 1 with occasional splitting). This random variation in properties over large-area PCD coating may hamper reproducible diamond growth for any meaningful technological application.
Surface & Coatings Technology, 1997
In this study, we explored and compared the friction and wear performance of smooth (30 nm, root mean square) and nanocrystalline diamond films (average grain size = 15 nm) grown i3 an Ar-C6,, microwaveplastna with the friction a_nd wear performance of laserpolished microcrystalline diamond films (grain size = 20-50 pm) grown in a conventional CH4-H2 microwave plasma. Tribological tests were run under 2-N load in open air (30-50% relative humidity) and in dry Nz. The-frjctional performances of both the as-grown smooth and laser polished diamond films were comparable. They both afforded very low friction coefficients (0.06-0.15) and low wear rates (2-6 x IO-' mm3/N.m) to counterface Si3N4 balls. We used Raman spectroscopy, electron microscopy, and atomic force microscopy to ascertain the structural, chemical, and surface topographical characteristics of the films and cpflelated the-results with the friction and wear mechanisms of diamond films in open air and dry N2. 0 1997 Elsevier Science S.A.
Effect of the substrate material on diamond CVD coating properties
Materials Chemistry and Physics, 2003
Diamond coatings were deposited onto different substrates (Cu, Si, WC-Co, Mo) by hot-filament chemical vapor deposition (CVD). Characterization of the obtained coatings was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared reflection (FTIR) spectroscopy. The results and observed differences are discussed from the aspect of the chemical nature of the substrate and its reactivity with a gaseous medium.
Tribological properties of smooth polycrystalline diamond films
Diamond and Related Materials, 1995
We have used a pin-on-disk txibometer with either a monocrystalline ruby or a lOOCr6 steel ball to evaluate the tribological properties of a series of polycrystalline chemical vapour deposition diamond films. Different polishing treatments of the as-grown films resulted in marked differences of their tribological behaviour.
Processing and Application of Ceramics, 2014
Polycrystalline diamond (PCD) coatings ranging from few microns to several hundred microns thickness have been grown by 915 MHz microwave plasma reactor with 9000 W power. The coatings were deposited on 100 mm diameter silicon (Si) substrate from few hours to several days of continuous runs. PCD coatings were made freestanding by wet chemical etching technique. The deposited PCDs were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) for physical characterization and compared with authors' earlier work. Refractive index of 2.41 was obtained at 633 nm wavelength and a maximum of 6.6 W·cm -1 K -1 value for thermal conductivity could be achieved with the grown coatings. The values are well above the existing non-diamond heat spreading substrates, which makes the grown PCDs as candidates for heat spreaders in different technological applications. High refractive index along with translucent nature of the white freestanding PCDs, make them potential candidate for optical windows.