ICMCTF2001 Session D4/E5-1: Mechanical Properties and Applications of Diamond, Diamond-like and c-BN Coatings

Tuesday, May 1, 2001 1:30 PM in Room Royal Palm 4-6

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		D4/E5-1-1 Control of the Tribological Moisture Sensitivity of Diamondlike Carbon Films by Alloying with F, Ti or Si R. Hauert, R. Gilmore (Swiss Federal Laboratories for Materials Testing and Research (EMPA), Switzerland) A specific feature of DLC tribological behavior is the increase of its friction coefficient with increasing ambient humidity levels and the loss of its self-lubricating properties at very high humidity. In a previous study it was shown that alloying DLC with small amounts of Si provided a significant reduction in friction coefficient at high relative humidity and allowed the friction coefficient to be stabilized over a wide humidity range. For example, the addition of about 4 at.% Si allowed friction coefficient to be held approximately constant at 0.08 ±0.01 over the humidity range 5 - 85% R.H. sliding against a steel counterface. In this study, the possibilities for optimizing and tailoring the tribological humidity response of DLC has been further investigated for the alloying elements F and Ti and the results compared with those obtained for Si. The addition of Ti was found to lower friction coefficient slightly both under dry and humid conditions. The addition of F was found to produce a dramatic increase in friction coefficient especially at low humidity, resulting in a friction coefficient as high as 0.9 against steel.
1:50 PM		D4/E5-1-2 Synthesis, Characterization and Properties of: Cr-DLC Films V. Singh, E.I. Meletis (Louisiana State University) Diamondlike carbon (DLC) films, known for exhibiting attractive combination of properties, have been extensively studied in the past. At present, a significant drawback with these films is their relatively low thermal stability above 400° C and low fracture toughness. Carbide formers incorporated into the DLC can possibly stabilize the film structure and have the potential to alleviate some of these problems. The present work focuses on the synthesis, structure characterization and properties of Cr-containing nanocomposite DLC films. Cr-containing DLC films were deposited on Si substrates in an intensified plasma environment using magnetron sputtering of a Cr target with a CH₄ and Ar gas mixture. The effect of Cr content in the DLC films was studied with the percentage of Cr varying up to 20%. The film morphology and composition were characterized by SEM-EDAX. The role of Cr in the DLC structure was analyzed by high resolution TEM. Thermal stability, hardness and tribological behavior of DLC films as a function of Cr concentration were studied by conducting annealing, nanoindentation and pin-on-disc experiments, respectively.
2:10 PM		D4/E5-1-3 Influence of Post Deposition Treatments on the Physical Properties of Cubic Boron Nitride Films Synthesized by PVD Methods M.A. Djouadi (ENSAM, France); O. Banakh (IPA, EPFL, Switzerland); V. Mortet, S. Khandozkho (ENSAM, France); R. Sanjines, F. Levy (IPA, EPFL, Switzerland) Boron nitride films deposited by ion beam assisted deposition (IBAD), triode and magnetron sputtering techniques are studied. The presence of the cubic phase was checked by transmission and reflection infrared spectroscopy. High-resolution cross sectional TEM has confirmed the optical results. The internal stress was measured and found to be proportional to the c-BN content in the films. Values up to 12 GPa were found and the presence of such compressive stress hinders the deposition of thick c-BN films. Attempts to improve the adhesion are undertaken. Firstly, previous work had shown that for h-BN films deposited by IBAD technique the intrinsic stress can always be reduced below -1 GPa by a post deposition annealing [1]. Therefore, annealing experiments were performed in nitrogen atmosphere. The annealing temperature was varied from 200Â°C up to 1000Â°C, after each annealing step, stress, Infrared, Raman analysis and electrical measurements were performed. An improvement of the adhesion and a shift of IR peaks position were observed. Secondly, the deposition conditions have been changed during film growth. The result was a broadening of the window of deposition condition for obtaining the cubic phase but no release of the stress was observed. It appears that the compressive stress within the cubic layer is more related to the mechanical properties of the material rather than the synthesis conditions. 1 M.A. Djouadi, D. Bouchier, V. Stambouli, S. Ilias. Surf. Coat. Technol. 97 (1997) 39.
2:30 PM		D4/E5-1-4 Comparative Study of Hard Carbon Coating Adhesion on Various Materials N. Ali (Manchester Metropolitan University, United Kingdom); Q.H. Fan, J. Gracio, E. Pereira (University of aveiro, Portugal); W. Ahmed (Manchester Metropolitan University, United Kingdom) A modified adhesion test method, which combined indentations with acoustic emission signals was used to compare the adhesion of polycrystalline diamond films deposited on Ti, Cr, Si and Ti coated copper substrates. Further, this technique was used to measure the adhesion of diamond-like-carbon coatings on silicon substrates. We show that indentations in coatings may cause the following failure modes: (a) the substrate cracking, (b) the film cracking and localised detachment, and (c) the film delamination and the delamination propagation. Acoustic emission during indentation loading provides essential information in predicting what mode of failure occurs during film detachment. Combined with the acoustic emission spectra the indentation tests are reliable in comparing the adhesion of diamond films deposited on the same or similar substrate materials. However, the comparison of the film adhesion on very different substrates, like Cu and Ti, is not so straightforward. Acoustic emission spectra also reveal that indentation caused substrate cracking prior to the failure of the film/substrate interface for diamond coatings on Si. In this case, the indentation tests are not valid to compare the coating adhesion.
2:50 PM		D4/E5-1-5 Probing Mechanical Anomalies in TiC/Amorphous Hydrocarbon Nanocomposite Coatings Near the TiC Composition B. Feng, D.M. Cao, W.J. Meng (Mechanical Engineering Department, Louisiana State University); L.E. Rehn, P.M. Baldo (Materials Science Division, Argonne National Laboratory) Ceramic nanocomposite surface coatings exhibit mechanical properties which vary systematically with coating composition and microstructure, and are potentially applicable to a variety of surface engineering situations where "coatings by design" are called for[1]. Stiffness and hardness anomalies in the TiN/amorphous silicon nitride (a-Si:N) nanocomposite coating system near the TiN composition have been reported in the literature[2], mechanisms responsible for which have not been conclusively established. Using a low-pressure, high-density plasma assisted hybrid CVD/PVD reactor[3], we have deposited TiC/amorphous hydrocarbon (a-C:H) nanocomposite coatings near the TiC composition. Detailed coating compositional and microstructural characterizations have been performed with RBS, XRD, and TEM. Coating elastic stiffness and hardness have been measured by instrumented nanoindentation. Measured mechanical responses of TiC/a-C:H coatings near the TiC composition are compared to those expected from macro-mechanical models and to measurements in the morphologically similar TiN/a-Si:N coating system. ¹ W. J. Meng and B. A. Gillispie, J. Appl. Phys. 84, 4314 (1998). ² S. Veprek, S. Reiprich, and Li Shizhi, Appl. Phys. Lett. 66, 2640 (1995). ³ W. J. Meng, E. I. Meletis, L. E. Rehn, P. M. Baldo, J. Appl. Phys. 87, 2840 (2000).
3:10 PM		D4/E5-1-6 The Influence of Surface Roughness and Interlayers on the Nucleation and Adhesion of Cubic Boron Nitride Films R. Freudenstein, A. Klett, W. Kulisch (University of Kassel, Germany) Applications of cubic boron nitride films are, despite their promising properties, hitherto prevented by the low adhesion strength and the high compressive stress of the films. Therefore, in order to solve the stress/adhesion problem and to deposit well-adherent, thick c-BN-layers, an improvement of the adhesion strength is required. New results show that this is possible by the deposition of various adhesion layers such as BCN gradient layers, pulsed laser deposited h-BN layers and boron rich interlayers, but systematic studies are missing. In general, the adhesion strength of a coating depends on the nature of the substrate film interface and is therefore determined by the nucleation process. In order to get insight into the underlaying mechanisms and the delamination behaviour, we investigated the influence of substrate pretreatments and adhesion layers on the surface roughness and the nucleation behaviour, and most importent, on the adhesion of c-BN films. The influence of the precleaning step on the deposition of c-BN has been underestimated up to now. In our contribution, we will show that, depending on the gas phase composition, the precleaning step (sputtering) changes the physical and chemical nature of the substrate, adjusts the surface roughness and influences the nucleation behaviour of c-BN. In order to evaluate the role of surface roughness, we present AFM measurements and discuss the rms roughnesses of substrates, nucleation and adhesion layers. In a second step, the influence of various interlayers (stoechiometric,boron rich, gradient) deposited with different procedures is investigated. It will be shown that interlayers have an extreme influence on the nucleation behaviour of c-BN films and, most important, on the delamination processes or the adhesion, respectively. Optimized processes are proposed for both, the adjustment of the surface roughness and the deposition of interlayers.
3:30 PM		D4/E5-1-7 BN Coating Adhesion on Ion Implanted and Plasma Treated Polymer Surfaces R Checchetto, A Miotello, M Adami, LM Guzman (University of Trento, Italy) Due to their excellent physical and chemical properties, coupled with their low cost and easy processibility, polymers frequently replace traditional engineering materials such as metals, glasses and ceramic. However the good bulk properties of polymers are often compromised by unfavoured surface characteristics such as low hardness value and low resistance to abrasion and scratching. Among the different techniques which can improove the surface characteristic of polymers the deposition of a thin coating layers is very attractive for its effectiveness, flexibility and environmentally friendly character. Ceramic thin films are assuming a great importance as surface coatings of polymeric materials in applications such as food packaging, optics and microelectronics. The most important limit to their wide application is the poor adhesion to the plastic surface due to the high intrinsic stresses in the coating and/or the low wettability exhibited by untreated plastic substrates. In this paper we present a study on the adhesion of BN thin films deposited by r.f. magnetron sputtering on plasma treated and ion implanted polymer surfaces. We have examined two different polymeric substrates, polycarbonate (PC) which is a plastic where ion irradiation gives rise to crosslinking effect and polytrifluorochloroethylene (PTFE) where ion irradiation only produces the polymeric chain scission. Ion implantation was carried out at room temperature with 160 keV N⁺ion energy for doses between 1.0E15 and 4.0E15 N/cm². The coating adhesion was analysed by scratch-testing and Scanning Electron Microscope. It was observed that, without ion pretreatment, the coatings are poorly adherent: due to the high level of stresses developed in the BN films, the deposited layers on unimplanted samples appear delaminated. On the contrary, the adhesion of the coatings on implanted polymer surfaces is appreciably better. This effect is attributed to the superior mechanical properties exhibited by the implanted polymers and to the enhanced wettability induced by energetic ion bombardment. Scratch tests show also an optimised tribological behaviour for the treated polymer surfaces.
3:50 PM		D4/E5-1-8 Stress Redistribution and Microstructural Evolution of Diamond Coatings, Submited to an External Stress M Ignat (LTPCM - INP Grenoble - CNRS, France); I De Wolf (IMEC); L. Vandenbulke, C Met (CNRS - LCSR, France) The application of diamond coatings depends strongly on their intrinsic mechanical properties, as for example: the residual stresses (generated by the deposition conditions and by the coating/substrate thermoelastic mismatch), the rupture strengths and the critical debonding strains.nowadays, it is well established that the mechanical response of coating on substrate systems will change, depending on the coating microstructure, which is controlled by the obtention conditions (deposition parameters, nature and preparation of the substrate...etc). We present an attempt to correlate the mirostructural evolution of diamond coatings, under the effects of an applied external stress.this is performed by microtensile experiments and in-situ Raman spectroscopy. As a matter of fact, we pulled coating/substrate systems, consisting on diamond coatings obtained with different deposition conditions, on metallic substrates.simultaneously with the applied stress, we followed the evolution of the Raman peak. From the micromechanical experiments the critical parameters for the film cracking with or without debonding were deduce; while the in-situ Raman peak evolution shows evidence of microstructural changes induced by the applied stress.besides, the micro Raman scanning allows to analyse the stress redistribution during the evolution of the cracking of the film. Our experimental results are discussed with respect to the deposition conditions internal stresses, and calculation of the stress evolution in a cracked film.
4:10 PM		D4/E5-1-9 The Effect of Modified Initial Layer on the cBN Growth by Unbalanced Magnetron Sputtering H.S. Kim (Korea Institute of Science and Technology, Korea); I.H. Choi (Korea University, Korea); Y.-J. Baik (Korea Institute of Science and Technology, Korea) We modified an intermediate layer between Si substrate and cubic boron nitride (cBN) layer intentionally to investigate its effect on the nucleation of cBN phase. Films were deposited by unbalanced magnetron sputtering using hBN as target material with argon - 10% nitrogen mixed gas. For a substrate bias, we connected a direct current (DC) and high frequency (HF) power supply to the substrate. The RF power and the target-substrate distance were fixed at 400 W and 100 mm respectively. Either amorphous BN or turbostratic BN was deposited on Si substrate at low bias voltage as intermediate layers, and then the substrate bias was increased where cBN would be grown at normal growth condition. Residual stress was measured for all samples. We considered the thickness, roughness, microstructure, and mechanical properties of intermediate layer, which has the possibility to influence the cBN nucleation. The thickness and microstructure of intermediate layers influenced the growth and adhesion of cBN films. The high content cBN films, deposited on intermediate layers, have shown critical residual stress above roughly 8 GPa. The cBN films, deposited on amorphous BN intermediate layer, were very adhesive. In addition, the DC and HF substrate bias showed different behavior of cBN deposition on intermediate layer.
4:30 PM		D4/E5-1-10 Composite Electoless Diamond Coatings M.D. Feldstein (Surface Technology, Inc.) Electroless nickel is a key segment of the metal finishing industry. Its properties are widely recognized and utilized in a broad array of industrial applications. The inclusion of diamond particles within electroless nickel deposits can be a powerful enhancement of the coating's inherent characteristics, and also add new properties to the nickel layer. This paper demonstrates how the inclusion of diamond particles within electroless nickel produces exceptional hardness, wear resistance, impact resistance, and thermal transfer with uniformity and economy. Moreover, these composite electroless nickel coatings are truly non-line of sight coatings applicable to even the most complex geometries including internal diameters. These coatings are suitable for all metals and numerous non-conductors. Also presented are descriptions of the newest advances in the field of composite electroless plating.
4:50 PM	Invited	D4/E5-1-11 Relevance of Structure and Properties on the Tribological Behaviour of Carbon-Based Coatings O. Massler, R. Herb, H. Karner, H. Eberle, M. Grischke (Balzers Limited, Liechtenstein) Modern mechanical tribological systems run under higher loads, speeds and temperatures and have to deliver smaller energy consumption, longer life and increased environmental friendliness. The already high importance of wear in the tribological systems becomes even more important by these developments. Where modifications of the materials are not being considered due to performance, cost or time reasons, a modification of the surface by coatings can be regarded to deliver an improvement of the demanded behaviour without design changes or system modifications. For tribological systems in the industrial practice, especially the area of general and automotive engineering, carbon based coatings become more and more known to enhance the performance regarding wear life, energy consumption and cost effectiveness. Carbon-based coatings deliver advantages regarding friction behaviour, dry and lubricated running, abrasive wear resistance, resistance against scuffing and seizure, and corrosion. The members of the family of carbon based coatings cover and combine a wide range of properties, from abrasive wear resistance, increased resistance against adhesive wear under lubricated conditions to a reduced friction coefficient under dry conditions. The most important members in modern machine applications are the metal containing Me-C:H coatings and the metal-free amorphous a-C:H-coatings. Me-C:H Coatings have remarkable frictional properties. The base for this is the nanolayer structure of the coating. This type of coating is widely distributed in industrial applications. Protection against adhesive wear, scuffing and seizure, increase of lifetime and improvement of sliding behaviour are the demands mostly required by industrial applications. The Me-C:H coating with its integration of low friction coefficient, moderate hardness and fracture toughness and sufficient abrasive wear resistance proves its performance in many modern applications. The metal-free a-C:H coatings (DLC) have a higher hardness than Me-C:H-coatings, high internal stresses and do not show a nanolayered structure, since the growth mechanism is significantly different from the Me-C:H-process. The high hardness gives the base for a much higher abrasion resistance in tribosystems with highly abrasive tribocomponents. Me-C:H and a-C:H systems show significant differences regarding structure, properties and behaviour. The coating structure is a very important parameter for the performance of the coating in a tribosystem. The relationship between structural features of the coating families and the tribological behaviour in selected tribological systems is discussed on the basis of analytical investigations and results from tribological tests.