ICMCTF2004 Session B3: CVD Coatings and Technologies

Wednesday, April 21, 2004 3:10 PM in Room Golden West

Wednesday Afternoon

Start	Invited?	Item
3:10 PM	Invited	B3-6 CVD and CVI of Pyrocarbon from Various Precursors G.L. Vignoles, F. Langlais (CNRS, France); C. Descamps, A. Mouchon, H. Le Poche (LCTS, France); N. Reuge (ENSIACET, France); N. Bertrand (University Bordeaux, France) The control of pyrocarbon Chemical Vapor Infiltration (CVI) is a key issue in the processing of high-performance C/C composites with applications in aerospace parts and braking technology. For years, the precise investigation of deposition kinetics and pyrocarbon nanotexture (i.e. anisotropy at nanometer scale) has been rehearsed in various process configurations, such as hot-wall or cold-wall reactors, and several variants of CVI with wide pore size ranges, and using various hydrocarbons as source precursors, like propane, propylene, and methane. Recent experimental data and modelling efforts have brought new insights into the respective roles of various gas-phase hydrocarbon intermediate species particularly in the heterogeneous mechanisms occurring from propane precursor decomposition ; a coherent modelling frame, also suitable for methane - which has a neatly lower reactivity - has been set up and tested. The relation between nanotexture and processing conditions are then explained.
3:50 PM		B3-8 Progress of CVD-Diamond Coated Cutting Tools R. Cremer, D. Breidt, M. Frank, M. Krings (CemeCon AG, Germany) CVD-Diamond tools are well established in machining graphite, green compacts and aluminum alloys. These achievements were possible not only by improving the technology but also by tailoring the CVD-diamond films to the specific applications. New challenges arise form new machining techniques, like high speed and dry cutting, as well as from novel high-tech materials, like fiber reinforced materials, that cannot be machined with conventional cutting tools. Extreme differences in thermal expansion coefficients and elastic constants of diamond and tool material lead to high stresses in the interface. This is disadvantageous esp. in interrupted cutting. On the other side, dry cutting gives increased adhesion of workpiece material and increased chemical wear, mainly oxidation, to the diamond itself. New features for CVD-diamond are introduced, that will overcome these difficulties: New adapted tool materials, improved surfaces and cutting edges, diamond multilayers with increased fracture toughness, pre-treatments for strengthening the interface, oxidation resistant coatings are elements to improve the system 'diamond coated tool' and will extent the applicability significantly. These new features can be used solely, combined with each other or together with the conventional CVD-diamond in respect to the specific applications. This will be illustrated by presenting cutting test results for different applications.
4:10 PM		B3-9 High-rate Thermal Plasma Chemical Vapor Deposition of Silicon Carbide F. Liao, S. Park (University of Minnesota); M.R. Zachariah (University of Maryland); S.L. Girshick (University of Minnesota) The use of thermal plasmas for chemical vapor deposition has been little explored except for diamond. Thermal plasma CVD offers the possibility of atmospheric or near-atmospheric operation, and deposition of high quality (if not epitaxial) films at high rates. An RF thermal plasma consisting of argon and hydrogen with injected SiCl₄ vapor and methane was used to deposit polycrystalline β-SiC films at rates up to about 1000 µm/h, with uniform thickness over 19-mm-diameter molybdenum substrates. Experiments were conducted with chamber pressures ranging from 150 to 400 Torr, substrate temperatures ranging from 500 to 1300 C, and a range of reactant flow rates. Films were characterized by scanning electron microscopy, X-ray diffraction, Rutherford backscattering spectroscopy and nanoindentation. Chemical composition of gas sampled through a small orifice in the substrate was measured by molecular beam mass spectrometry. We here report the effects of deposition parameters on film properties, growth rates and chemical composition.
4:30 PM		B3-10 Vanadium Oxides Prepared by Liquid Injection MOCVD using Vanadyl Acetylacetonate D. Vernardou, M.E Pemble, D.W. Sheel (University of Salford, United Kingdom) Among the many compounds present within the V-O system¹, VO₂ and V₂O₅ are undoubtedly the most studied because of their electrical, optical and catalytic properties. The main uses of V₂O₅, when deposited as thin films, can be found in electrochromic devices, oxidation catalysts and optical switches². On the other hand VO₂ experiences a thermally induced semiconductor-to-metal structural phase transition at a transition temperature of 68oC, where substantial changes in electrical conductivity and optical properties can be found. This characteristic finds some applications in thermal relays, electrical switching elements and optical storage media³. While many film deposition techniques including sputtering@super 1,4@, evaporation@super 3,5@, pulsed laser deposition⁶, and chemical methods⁷ have been used to prepare these materials, in the present paper liquid injection MOCVD is used to deposit vanadium oxide films. This is an attractive method to produce thin films with good step coverage ability, high control of stoichiometry, crystallinity and uniformity. The deposition was carried out on SiO₂-coated glass and Si(100) substrates using vanadyl acetylacetonate as precursor at different deposition temperatures and oxygen partial pressures. The influence of substrate, deposition temperature and oxygen pressure on the degree of crystallinity, microstructure and morphology of the films was studied in detail. ¹C. H. Griffiths and H. K. Eastwood, J. Appl. Phys., 45, 2201 (1974) ²H.-K.Park, W.H. Smyrl, and M.D. Ward, J. Electrochem. Soc., 142, 1068 (1995) ³M.-H.Lee and M.-G.Kim, Thin Solid Films, 286, 219 (1996) ⁴J. F. De Natale, P.J. Hood and A. B. Harker, J. Appl. Phys., 66, 5844 (1989) ⁵F. C. Case, J. Vac. Sci. Technol, A., 1984, 2, 1509 super 6@Z. P. Wu, A. Miyashita, I. Nashiyama and H. Naramoto, Philos. Mag. Lett., 79, 813 (1999) ⁷H. L. M. Chang, Y. Gao, J. Guo, C.M.Foster, H. You, T. J.Zhang and D. J. Lam, J. Phys. IV, 1, C2-953 (1991).
4:50 PM		B3-11 Atmospheric Pressure MOCVD of TiO₂ Thin Films using Various Reactive Gas Mixtures F.D. Duminica, F. Maury, F. Senocq (CIRIMAT, France) TiO₂ thin films were deposited under atmospheric pressure by MOCVD in the temperature range 350-700°C on Si(100) and stainless steel substrates. Titanium tetraisoproxide (TTIP) was used as metal source. The influence on the growth process of oxidant co-reactives (O₂ and H₂O) has been investigated. The growth rate, the microstructure and the composition of the coatings were determined and correlated to the process parameters. TTIP mole fraction and the substrate temperature are the major parameters to control the growth rate and the microstructure of the films. Addition of oxygen in the input gas phase does not change significantly the main features of the oxide layers. By contrast, TTIP/H₂O gas mixture exhibits a higher reactivity leading to the deposition of TiO₂ at lower temperature and with a higher growth rate. For instance the deposition rate at 450°C is approximately 440 and 90 nm/min with and without H₂O addition during the growth, respectively. Typical conditions to optimize the growth rate of these functional oxide thin films are given. Single-phased (anatase or rutile) and bi-phased coatings with a controlled composition can be deposited depending on the temperature and the TTIP mole fraction. These results are discussed in relation with literature data where related molecular precursors were used.
5:10 PM		B3-12 Performance and Evaluation of Chemical Vapour Deposited (CVD) Diamond Coated Cutting Tools for Biomedical Applications W Ahmed, H. Sein (Manchester Metropolitan University, United Kingdom); M. Sarwar (Northumbria University, United Kingdom); M.J. Jackson, L.J. Hyde (Tennessee Technological University); R.P. Flaxman (University of Cambridge, United Kingdom) CVD diamond coatings are highly attractive for use in cutting tool applications due to their high hardness, low friction co-efficient, excellent wear resistence and chemical inertness. In recent years the application of diamond coatings onto tungsten carbide (WC-Co) cutting tools has been the subject of much attention in order to improve the cutting performance and tools life. WC-Co burs containing 6% Co and 94% WC substrates have been used in this study. In order to improve adhesion between the diamond film and the WC-Co substrate it is necessary to etch away the surface cobalt and prepare the surface for subsequent diamond growth using a modified vertical hot filament arrangement CVD reactor. Scanning electron microscopy (SEM) and Raman spectroscopy have been used to characterise diamond film quality and purity. The performance of diamond coated WC-Co burs, uncoated WC-Co and sintered diamond have been compared by drilling holes into various materials such as human teeth, borosilicate glass and acrylic teeth. Flank wear has been used to assess the wear rates of burs when machining biomedical materials such as those mentioned above.