ICMCTF1999 Session B3: Structure and Properties of Hard Coatings

Monday, April 12, 1999 1:30 PM in Room Golden West

Monday Afternoon

Start	Invited?	Item
1:30 PM	Invited	B3-1 Nanoscaled Multilayer and Compound Films Consisting of a Hard Matrix Phase and a Soft Lubricious Phase E. Pflüger, A. Savan (Centre Suisse D'Electronique et de Microtechnique S.A., Switzerland); R. Goller, W. Gissler (Joint Research Centre of the European Commission, Italy) Efforts to produce nanocomposite films of soft particles in a hard matrix are reviewed. Films consisting of a hard matrix phase in combination with a soft, lubricious phase grown as either multilayers or composite films show promise as hard, lubricating, wear-resistant coatings. Here we will report on films of TiN or CrN with MoS₂ nanoclusters grown by two deposition techniques: cathodic arc evaporation and magnetron sputter deposition. The effects of changing the deposition parameters on mechanical properties such as hardness, adhesion and wear behavior have been investigated by nano-indentation, scratch and indent adhesion characterization, pin-on-disk tribometry at both ambient and elevated temperatures, and micro-abrasive wear testing. These results are correlated with changes in film chemistry (XPS and RBS) and film microstructure (X-ray diffraction).
2:30 PM		B3-4 The Effects of Substrate Bias Voltage and Thermal Treatment on the Microstructure of Arc- Evaporated CrN Coatings M. Odén (Linköping University, Sweden); G. Hakansson (Tixon Brukens Sverige AB, Sweden); J.D. Almer (Linköping University, Sweden) Cr-N coatings were grown by arc-evaporation onto high-speed steel substrates. The coatings were each grown using a different negative substrate bias voltage,V_S, ranging between 20 and 400 V. X-ray diffraction indicates that the coatings were fiber textured and consisted primarily of the CrN phase, although the presence of Cr and Cr₂N was also observed, especially at high V_S. AES and TEM showed a sub-stoichiometric composition and dense columnar microstructure for all coatings. The column width decreased as V_S was increased, except for the sample grown at V_S = 400 V which showed a slight increase. Also, at V_S = 400 V, equiaxed grains and microcracks parallel the substrate-coating interface were observed. The residual stress in the coatings was always compressive and increased from approximately 3 to 9 GPa as V_S was increased from 20 to 100 V. At higher bias voltages, a decrease of the compressive residual stress was seen. The thermal stability of these coatings was examined by tempering samples grown at V_S = 50 and 300V, which had the same level of initial residual stress (about 4 GPa). These samples showed large differences in stress relaxation behavior, with the 50 V sample displaying a more rapid stress decrease than the 300 V sample. After being tempered for 4.5 h at 550 °C both samples relaxed to the same stress (about 1 GPa). Both the dramatic stress relaxation and difference between the two sets of samples were correlated to changes observed in the coating microstructure. When tempered, the microstructure changed from a columnar structure with diffuse grain boundaries to equiaxed grains with distinct grain boundaries. At the same time, a larger fraction of Cr₂N was formed and the lattice defect density was decreased. These microstructural changes occurred at lower temperature in the 50 V sample than in the 300 V sample. This suggests differences in defect stability as a function of bias voltage, which are considered responsible for the observed residual stress relaxation.
2:50 PM		B3-5 Characterization of Sputter Deposited Chromium Oxide Thin Films P. Hones (EPFL-Institut de physique appliquée, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland); M. Diserens, F. Lévy (EPFL-Institut de physique appliquée, Ecole Polytechnique Fédérale de Lausanne, Switzerland) Cr₂O₃ thin films exhibit high hardness values and low coefficients of friction. These properties make chromium oxide a serious candidate to replace transition metal nitrides or Al₂O₃ in special applications. The CrO_x films were deposited on silicon, glass and HSS substrates by rf reactive magnetron sputtering. The phase and the texture were determined by X-ray diffraction (XRD) analysis. The morphology was examined by cross sectional scanning electron microscopy and atomic force microscopy. The chemical composition was measured by electron probe microanalysis. Films with a pure Cr₂O₃ phase were obtained in the range between 15% and 30% oxygen in the sputtering gas. The grain size varied significantly with the oxygen content and the substrate temperature. The real and imaginary parts of the pseudo-dielectric function were determined by spectroscopic ellipsometry in the photon energy range of 1.5 to 5.0 eV. Hardness values up to 32 GPa were obtained by nanoindentation. Compressive residual stress levels below 1 GPa were measured by XRD using the sin²Ψ method. The hardness and the coefficient of friction are compared to those of CrN and Cr(N,O) thin films.
3:10 PM		B3-6 On the H Uptake in PVD-Alumina Thin Films J.M. Schneider (Linköping University, Sweden); B. Hjörvarsson (Royal Institute of Technology, Sweden); K. Macák, U. Helmersson (Linköping University, Sweden) Alumina thin films have been grown using cathodic arc deposition, pulsed laser ablation, and magnetron sputtering. The effect of the film stoichiometry and the growth temperature on the H uptake in alumina thin films has been studied. Chemical analysis of the films was performed by Rutherford backscattering spectroscopy and nuclear reaction analysis. Structure and properties have been evaluated by x-ray diffraction and nanoindentaion, respectively. Significant H uptake was found if films were grown in high vacuum environment. Stoichiometric alumina thin films grown by cathodic arc at 350 °C substrate temperature contained approximately 8 % H and sub-stoichiometric films contained approximately 4 % H. The uptake was found to be reduced at elevated substrate temperatures.
3:30 PM	Invited	B3-7 Mechanical Properties in Transition Metal Nitrides F. Lévy, P. Hones, P.E. Schmid, R. Sanjines, M. Diserens, C. Wiemer (Ecole Polytechnique Fédérale de Lausanne, Switzerland) Thin films of hard materials are of prime importance for resistant, protective and decorative coatings. Beside adhesion, hardness is the most often quoted requirement, even if doubts remain on the experimental determination of the hardness values of thin films and on their theoretical interpretations. Transition metal interstitial compounds are extensively used because of their broad range of functional properties in machining, microelectronics, decoration, etc.. The article presents a summary of recent relevant results on the structural, mechanical, electronic and optical properties of fcc TiN, VN, CrN, NbN, MoN, WN and some ternary nitrides in the form of sputtered thin films. The process parameters, e.g. the reactive gas partial pressure and the substrate bias, strongly influence the film properties. The composition and growth parameters influence the morphology, the stress state and other physical properties. The systematic investigation of the electronic density of states in valence and core states of comparable nitrides provide indications of the degree of covalency in the chemical bonding in relation with properties such as cohesive energy and hardness. For example in molybdenum nitride, the low stability of the cubic MoN phase is related to an increase in the charge transfer of Mo d electrons to nitrogen with increasing stoechiometric ratio N/Mo. Ellipsometric measurements of the dielectric function interpreted in relation with details of the band structure measure the variation of the density of conduction electrons. Since vacancies and interstitials give specific numbers of electrons to the conduction band, this analysis allows to differentiate the type of defects at various compositions in TiN films, for exemple, for which the reported hardness values spread over a wide range.}
4:10 PM		B3-9 Taylored a-C:H Coatings by Nanostructuring and Alloying R. Hauert, L. Knoblauch, G. Francz (Swiss Federal Laboratories for Materials Testing and Research (EMPA), Switzerland); A. Schroeder (ETH Zurich, Switzerland) We present our results on different types of nanostructured and alloyed a-C:H coatings reflecting a technology for the design of optimized coatings for a wide range of applications. Multilayered a-C:H films, composed of a 60 nm Si-a-C:H adhesion layer and 300 nm (hard/soft) multilayer structure have been deposited on 100Cr6 steel by a periodical variation of the sample self-bias voltage during deposition. The single layer thickness has been varied from 4 to 20 nm. The wear rate (determined by pin on disk measurement against a steel ball) of multilayer structures having a single layer thickness in the range of 11 nm to 15 nm, showed a drastic decrease by one decade down to 4 x 10^-18 m³/Nm, compared to the multilayer systems composed of thicker or thinner single layers. Amorphous hydrogenated carbon films containing titanium in different concentrations (a-C:H/Ti) were deposited on glass substrates by a combined rf-PACVD and DC magnetron sputtering process. By adding titanium to the carbon matrix, cellular reactions like tendential differentiation of osteoblast cells together with a reduced osteoclast cell activity, compared to pure a-C:H or pure Ti, could be obtained . This makes a-C:H/Ti a valuable coating for bone implants, by enhancing bone ingrowth through osteoblast differentiation while reducing bone resorption through osteoclast inhibition.
4:30 PM		B3-10 Structure and Thermal Stability of Nanocomposite DLC Films E.I. Meletis, K.S. Kim, V. Singh (Louisiana State University) Diamondlike carbon (DLC) films have been extensively studied in the past since they exhibit an attractive combination of properties. A significant drawback however with these films is their relatively low thermal stability. The present work focuses on the development and study of nanocomposite DLC films with additions of carbide formers such as Si, Ti and Cr, that offer the potential to stabilize the tetrahedral diamondlike structure and extend their high temperature application range. Nanocomposite DLC films with Si, Ti and Cr additions were developed using a combination of plasma-assisted and sputter deposition techniques. The produced films were characterized by SEM-EDAX, TEM, and FTIR. Thermal annealing experiments were conducted at various temperatures and in parallel with FTIR analysis and microhardness measurements to study the thermal stability of the films as a function of the level and type of the carbide former addition.
4:50 PM		B3-11 Size Effect in Nanostructured Hard Films R.A. Andrievski (Laboratory of Special Inorganic Synthesis, Russia) Nanostructured films on the base of high-melting point compounds such as carbides, nitrides and borides attract the great attention because of their unique physical-mechanical properties. These films are characterized by small crystallite sizes (L>10-20 nm) and can be prepared by different PVD methods. The main attention is focused in the crystallite size effect on physical-mechanical properties of films such as hardness, elastic modulus, and electrical resistivity as well as features of fracture. The crystallite size determination by TEM, SEM, XRD, and AFM is also discussed in detail. The important influence of nonthermal vacancies on elastic and electrical properties of films is noted taking as an example TiN and TiB2 films. Properties of multilayered nitride films are also characterized. Two types of film fracture under a Vickers indentor connected with homogeneous and inhomogeneous deformation are describing.