ICMCTF2007 Session E3: Tribology of Diamond, Diamond-Like and Related Carbon Coatings/Thin Films

Thursday, April 26, 2007 1:30 PM in Room California

Thursday Afternoon

Start	Invited?	Item
1:30 PM		E3-1 The Role of Substrate Deformation on the Tribological Behavior of Diamond-like Nanocomposite Coated Metallic Substrates J.M. Jungk, S.V. Prasad, J.R. Michael (Sandia National Laboratories) For the case of hard diamond-like tribological coatings deposited on softer metallic substrates, the friction-contact stress relationship can diverge from predicted behavior when the contact stresses generate plastic deformation in the substrate. In order to investigate the relationship between contact stress, accumulated plastic deformation and measured frictional coefficient, diamond-like nanocomposite films were deposited onto metallic substrates with yield stresses ranging 500 - 1300 MPa. Finite element simulations were used to determine the critical load for the generation of plastic deformation in either the coating or metallic substrate beneath a Si₃N₄ sphere. In parallel, experimental indentation and ball-on-disc friction tests were performed with post-experimental characterization utilizing SEM, EDS and focused ion beam (FIB) techniques coupled with electron backscatter diffraction (EBSD) to evaluate the connection between tribological behavior and microstructural damage. A relationship between the generation of plastic damage in the metallic substrate and a dramatic increase in the tribological behavior is shown.
1:50 PM	Invited	E3-3 Tribology of DLC : Industrial Applications and Scientific Aspects H. Ohara (Nippon ITF, Inc., Japan) Among various thin film coating materials, DLC (Diamond-Like Carbon) shows excellent tribogical features, such as low coefficient of friction, superior wear resistance, and less damage in the counterparts. Because of these features, many types of amorphous carbon, which are classified as DLC, have been developed and put in practical use. However, each DLC shows different characteristics according to the hydrogen content, metal content, sp³/sp² ratio, and so on. From the viewpoint of the automotive engine parts, oil-based lubricant is usually used. In such conditions, low friction coefficient of DLC, which is the biggest advantage of DLC, disappears. This is thought to be the reason why the DLC's market has not been expanded explosively in spite of it's excellent properties. If the friction coefficient of DLC decreases remarkably even under the oil lubrications, huge market will be expected. Generally speaking, film properties strongly depend on the film contents. Also, film contents strongly depend on the source material and the principle of deposition process. So, we must use each DLC properly with taking the essential information written above into consideration. For example, it is reported that highly hydrogenated a-C:H shows super low friction under nitrogen gas or high vacuum conditions. It is also reported that hydrogen free ta-C shows super low friction under oil lubrication with some kind of special additives without sacrificing superior wear resistance. In this presentation, some typical examples of industrial application of DLC for proper usage are reviewed in connection with the feature of each DLC from scientific point of view.
2:30 PM		E3-5 Tribological Investigation of Diamond-Like Carbon Films Containing Nanoclusters of Indium, Deposited by Femtosecond Pulsed Laser Ablation J. Fontaine (Ecole Centrale de Lyon, France); F. Garrelie (Université Jean Monnet, France); C. Donnet (Université Jean Monnet and University Institute of France); C. Pareige (Université Jean Monnet, France); M. Belin, T. Le Mogne (Ecole Centrale de Lyon, France); F. Rogemond (Université Jean Monnet, France) Nanostructured coatings of indium-containing diamond-like carbon (a-C:In) have been prepared by femtosecond pulsed laser deposition (PLD). The films have been deposited by ablating sequentially graphite and indium targets under vacuum conditions with an amplified Ti:sapphire laser operating at 1.2 mJ with pulses of 300 femtosecondes. Three indium concentrations (2, 5 and 15 at.%) have been compared. The particular femtosecond laser / matter interaction (power density of 8,6 10¹² W.cm^-2 per pulse) allows to deposit indium metallic clusters (size in the hundred nanometer range) into the carbonaceous matrix. Tribological characterizations have been performed on a reciprocal pin-on-flat tribometer against bearing steel pins, with spatially-resolved measurements of tangential force and electrical contact resistance. Significant lowering of the friction coefficient is observed in ambient air for In-containing films, with stabilized values lower than 0.08 compared to about 0.15 for pure DLC. However, wear of the coatings appeared much higher. The role of the soft In metal nodules on the friction and wear of a-C:In coatings will be discussed, in light of the coating architecture.
2:50 PM		E3-7 Characterization of DLC Thin Film and Evaluation of Machining Forces using Coated Tools in Turning of Al-Si Alloys G.R. Santos (Balzers Balinit do Brasil, Brazil); F.A. Amorim (Pontifical Catholic University of Parana, Brazil); D. Costa (Federal University of Parana, Brazil); R.D. Torres (Pontifical Catholic University of Parana, Brazil) In this work Diamond Like Carbon (DLC) thin films were deposited on an hard metal substrate by PACVD. In the first part of the project DLC thin film characterization was performed. It was determined hydrogen content, nanohardness, friction coefficient and thickness of the DLC coating. The DLC hydrogen content was situated between 10 and 20% while the friction coefficient is 0.25. The DLC nanohardness is around 20 GPA and the coating thickness around 2.5 µm. The roughness of the DLC coated surface was around 37 Ra while the roughness of the uncoated hard metal was around 30 Ra. In the second part of this work cutting and feeding forces were evaluated during turning of Al-Si alloys, using DLC coated and uncoated hard metal tools. In the forces evaluation tests a cutting speed of 450 m/min. and cutting depth of 0.5 mm was adopted. The silicon content of the tested aluminum alloys was 12% and 16% wt. Cutting and feeding forces are higher in the turning of aluminum with 16% wt. of silicon. Using coated hard metal tools reduces both machining forces components no matter what is the silicon content in the aluminum alloy. In the case of turning the Al-12% Si, the feeding force is reduce from 27 N to 23 N using coated DLC hard metal while for the Al-Si 16%, the feeding force is reduce from 47 N to 40 N.
3:10 PM		E3-8 Effect of Counterpart and Substrate Materials on Tribological Properties of DLC Film for Space Applications K. Matsumoto (Japan Aerospace Exploration Agency, Japan); M. Belin, J. Fontaine, T. Le Mogne (Ecole Centrale de Lyon, France) Recently, good tribological characteristics in vacuum have been reported for DLC films. However, in order to apply DLC film to space applications, much data and scientific interpretation are needed. Especially, influence of metallic counterpart and substrate materials on friction properties remains unclear. In this study, friction tests with pin-on-flat configuration were carried out for DLC films with various metallic substrate and counterpart materials. The materials used for counterparts and substrates were stainless steel, bearing steel, Ti alloy and Al alloy. The tests were performed not only in a vacuum environment but also in dry nitrogen gas and ambient air. Whatever the counterpart materials, friction coefficient in air showed higher values than in nitrogen gas. Ti alloy showed good repeatability and its friction coefficient was stable and low, approximately 0.02 in nitrogen gas and 0.05 in air, except at the beginning of the tests. Al alloy also showed low and stable friction coefficient in air. However, higher value than other materials was obtained at the beginning. Friction coefficient for two types of steel showed high value at the test-start and then gradually decreased compared to Ti and Al alloy in air. Difference in friction between the two types of steel was not clearly observed. Significant differences in color and aspect of transfer film between counterpart materials were observed after the tests in gas environment. Influence of counterpart material and environment on friction coefficient will be discussed, emphasizing the difference in tribofilm build-up on metallic counterparts.
3:30 PM		E3-9 Friction-Induced Gas Desorption on Hydrogenated Amorphous Carbon Films A. Rusanov, J. Fontaine, T. Le Mogne (Ecole Centrale de Lyon, France); R. Nevshupa (Bauman Institute, Russia); J.M. Martin (Ecole Centrale de Lyon, France) Diamond-Like Carbon (DLC) coatings present exceptional tribological properties in various environments. Highly hydrogenated amorphous carbon (a-C:H) films are known to exhibit extremely low friction coefficient under high vacuum or inert environment, known as "superlubricity" or "superlow friction". The use of such lubricant coatings for industrial vacuum-based process seems thus promising, providing outgasing of sliding surfaces remains negligible. Nature of outgasing could also provide information on the friction and degradation mechanism of the coatings. Desorption of various a-C:H films has been studied by mass spectrometry during sliding in an ultra-high vacuum tribometer. While in superlow friction regime, no increase can be detected for the 0-50 mass range. However, for a-C:H film with lower hydrogen content, the superlow friction regime ends after few hundreds of cycles, with a drastic friction increase. During this loss of superlubricity, significant increase of several masses is observed, especially mass 2 and 16, corresponding respectively to H₂ and CH₄ gases. In light of these results, tribological mechanisms of superlubricity and its loss will be discussed.
3:50 PM		E3-11 Effect of Hydrogen Content on Tribological Behaviour of DLC Coatings Under Fretting Mode I at Room and High Temperature T. Van der Donck, S. Achanta, W.Z. Eddine, M. Muchlado (Katholieke Universiteit Leuven, Belgium); N.J.M. Carvalho (Bekaert Advanced Coatings, Belgium); J.-P. Celis (Katholieke Universiteit Leuven, Belgium); V. Libermn (Bekaert Advanced Coatings) DLC coatings with different H-content were investigated for their tribological behaviour in a fretting mode I regime. Their tribological behaviour was tested in ambient air at 23°C and 50% relative humidity, and at higher temperatures of 100 and 150°C. The tests were done at different normal loads and on sliding against corundum and DLC coated steel balls. Fretting tests on DLC/corundum couples at 23°C revealed a lowering of the coefficient of friction (COF) at increasing normal loads. For the coating with the highest H-content, the COF reduced from 0.14 at 2 N down to 0.04 at 15 N normal loads. This effect was attributed to an accelerated graphitisation taking place in the sliding contact at high normal loads. The COF for the DLC/DLC couple was even lower compared to the DLC/corundum couple. The effect of temperature on graphitisation was investigated by performing fretting tests at 100°C and 150°C. A lowering of the COF at increasing fretting test temperature was noticed. This effect was most pronounced for the DLC/DLC couple, where the COF decreased from 0.09 at 23°C down to 0.01 at 150°C. Nevertheless, this decrease in COF was accompanied with an increasing wear of the coating. The result confirms that a severe degradation of the DLC is induced by graphitisation at higher test temperatures. An interesting finding was that the fretting tests performed at 23°C but after a thermal treatment at either 100 or 150°C, showed an identical friction and wear behaviour to the ones recorded on the non heat treated samples. The wear volume on the coatings was found to vary linearly with the cumulative dissipated energy. A decrease in the wear rate coefficient was noticed with increasing H-content. The improved friction and wear performance under fretting mode I conditions of DLC coatings with increasing H-content may thus be linked to a stabilization of the sp³ bonds.