Papers

ICMCTF2009 Session E1-1: Friction and Wear of Coatings: Lubrication, Surface Effects and Modeling

Wednesday, April 29, 2009 8:00 AM in Room California

Wednesday Morning

Start	Invited?	Item
8:00 AM		E1-1-1 Low-Friction and Wear Mechanisms for Sputtered Ti-C-N Coatings M. Rebelo de Figueiredo, G.A. Fontalvo (University of Leoben, Austria); C. Muratore (Air Force Research Lab/UTC, Inc.); R. Franz (University of Leoben, Austria); A.A. Voevodin (Air Force Research Lab/University of Dayton); M. O'Sullivan (Plansee Composite Materials GmbH, Germany); M. Lechthaler (OC Oerlikon Balzers AG, Liechtenstein); C. Mitterer (University of Leoben, Austria) It is known that ceramic coatings with substantial amounts of structurally incorporated carbon (C) show low-friction behavior, in particular at intermediate temperatures. However, the mechanisms behind activation, formation and modification of the required free C in the friction contact are still not fully understood. A previous study focused on the investigation of tribological properties of reactive arc-evaporated Ti-C-N coatings. Dry ball-on-disc tests against alumina were performed at room temperature in different atmospheres in order to elucidate the tribo-chemical mechanisms. A low steady-state coefficient of friction of 0.18 was obtained in moist air, which increased to 0.9 under dry and inert conditions. Only for the test in moist air a significant contribution of C-H oscillations was detected, leading to the conclusion that water absorption and subsequent reactions with C must play a crucial role for the formation and activation of low-friction tribolayers. Since arc-evaporated coatings exhibit macroparticles, which are an obstacle for the study of surface phenomena, TiCN was deposited by dc sputtering from a Ti₂CN target in an industrial deposition plant. The coating is stoichiometric (Ti₅₁C₃₃N₁₅) with a smooth surface. XRD analyses indicated peaks positioned between TiN and TiC giving evidence for the formation of a single-phase TiCN. The synthesized coatings were tested in a tribometer with controlled environment equipped with in-situ Raman and X-ray photoelectron spectrometers, which provided for the analyses of wear track surfaces and detection of the onset of the lubricious tribofilm formation.
8:40 AM		E1-1-3 Tribology of the Head/Disk Interface F.E. Talke (Univ. of California, San Diego) Tribology of the Head/disk Interface Frank E. Talke Center for Magnetic Recording Research and Department of Mechanical and Aerospace Engineering University of California, San Diego In presently available hard disk drives, the head/medium spacing has decreased to less than 10 nm. To achieve a recording density of 1 Tb/inch 2, it is anticipated that the head/medium spacing has to decrease to less than 3 nm. As the spacing between slider and disk decreases, increasingly more emphasis has to be given to the design of the head/disk interface to guarantee reliable tribological performance. At a head/medium spacing of 3 nm, contacts are likely to occur between slider and disk during load/unload and continuous flying. Contacts lead to lubricant migration and wear between slider and disk, which, in turn, is likely to cause failure of the disk drive. In this paper, the tribology of the head/disk interface is discussed. First, the materials and surface characteristics of currently used thin film disk are presented, including the characteristics of the carbon overcoat and the lubricant film used. Then, an overview of currently used magnetic recording sliders is given, including a discussion of thermally activated flying height control heads. The tribology and flying characteristics of the head/disk interface at extremely small spacing will be analyzed for discrete track recording and bit patterned media. In the last part of the talk, the tribological requirements for achieving recording densities of 10 Tbits/inch 2 will be discussed, including the possibility of carbonless magnetic disks; heat assisted magnetic recording; improved lubricants and contact recording.
9:20 AM		E1-1-5 Comparative Study of the Friction Coefficient and Wear Volume with Silane and Carbonitrided Interlayer in 316L Stainless Steel Samples in Hybrid Lubrication Conditions R.P.C.C. Statuti (INPE - Instituto Nacional de Pesquisas Espaciais, Brazil); P.A. Radi, L.V Santos (INPE - Instituto Nacional de Pesquisas Espaciais and Instituto Technologico da Aeronautica - ITA, Brazil); V.J. Trava-Airoldi (INPE - Instituto Nacional de Pesquisas Espaciais, Brazil) This paper reports the results of the tribological study that compares the friction coefficient and wear volume of 316L stainless steel samples, coated and no coated with diamond-like carbon (DLC) films, with silicon and carbonitrided interlayers¹ with and without synthetic oil and distilled water interfaces. The DLC films were grown by using a Pulsed DC Plasma Enhanced Chemical Deposition (PE-CVD) technique². The tests were carried out by using a UMT-CETR ball-on-plate tribometer in the reciprocating mode at 10.0mm.s-1 sliding speeds under 2N and 4N applied load. The sphere wear was measured using a very small pin approach, in agreement with the ASTM G99 norm. The results showed that the friction coefficient and wear dependence with the composition of the fluid and the lubrication regime. Also, the film atomic arrangements and graphitization level before and after tribotests were analyzed by Raman scattering spectroscopy. The surface analyses were studied using WYKO Surface Profilers, NT1100. ¹L.F. Bonetti, G. Capote, L.V. Santos, E.J. Corat And V.J. Trava-Airoldi, Adhesion studies of diamond-like carbon films deposited on ti6al4v substrate with a silicon interlayer, Thin Solid Films, In Press, Available online 20 March 2006 ²Trava-Airoldi, J. V., Santos, V. L., Bonetti, L. F., Capote, G., Radi, A. P., and Corat, E. J., “Tribological and mechanical properties of DLC film obtained on metal surface by an enhanced and low cost pulsed¬ – DC discharge”, (2007).
9:40 AM		E1-1-6 How Can H Determine the Tribological Behavior in Lubricated Contact of Cu/W – C:H Sputtered Coatings M. Evaristo (SEG-CEMUC, University of Coimbra, Portugal); T. Polcar (SEG-CEMUC University of Coimbra & Czech Technical University - Prague, Portugal); A. Cavaleiro (SEG-CEMUC University of Coimbra, Portugal) C-based coatings are being used in many mechanical contacts without any type of lubrication, however, in many applications the presence of liquid lubricants is required. Tribological studies carried out under oil lubrication conditions for DLC coated contacts showed that the final results are better neither than uncoated materials nor with non-lubricated coated contacts. In this study, carbon coatings were doped with W or Cu, elements with different affinities for C. A Teer Coatings sputtering device with four magnetron was used for the depositions in reactive (Ar+CH₄) and non reactive (Ar) atmospheres. W-C:H coatings were deposited by co-sputtering form individual carbon targets and a carbon target with W pellets placed in the preferential erosion zone. The coatings were with (~10 at.%) and without W, with (~25 at.%) and without H contents. Similar procedure was carried out for the Cu-C:H system but in this case co-sputtered was performed using individual C and C targets and a Cu target. Similar Cu and H contents were introduced in the C-based films. In all cases, prior to the deposition a Ti interlayer of approximately 100 nm was deposited for improvement the adhesion of the coatings. All depositions were done with substrates rotation with an angular speed high enough to avoid the formation of a multilayer structure. A negative substrate bias of -50V was applied to the substrates during deposition. After basic characterization of the coatings, the influence of the W and H contents on the tribological behavior in dry and lubricated contacts will be studied. The lubricants are commercial oils with and without additives. Selected worn samples will be further studied by Raman spectroscopy and scanning electron microscopy in order to understanding the sliding mechanisms influencing the friction coefficient and the wear rate.
10:00 AM		E1-1-7 In Orbit Tribological Tests of a Novel Solid Lubricating Film at the International Space Station M. Brizuela, A. Garcia-Luis (INASMET-Tecnalia, Spain); J.I. Oñate (Fundacion INASMET-Tecnalia, Spain); I. Garmendia (INASMET-Tecnalia, Spain); C. Martinez, R. Fernandez-Sanz (INTA, Spain) MoS₂ is a broadly accepted solid lubricant for space mechanisms. However, a drawback of MoS₂ is its tribo-sensitivity to atmospheric water vapor which renders the film unsuitable for use under high humidity levels at air conditions. This recommends precautions during ground qualification testing and storage of solid lubricated space mechanisms. Recently, coupling a need of extending space mechanisms’ life with advances made in PVD technology, efforts have been made in developing more wear resistant MoS₂ and low friction films capable of both: vacuum and atmospheric application. Alloying the MoS₂ films with metals has been reported by several researchers with varying success. This contribution reviews the work carried out at INASMET-Tecnalia on the development of novel WC alloyed MoSx solid lubricant films. Pin on disk vacuum tribology tests of these films, at 0.75 and 0.95 GPa contact stress, have shown friction coefficients similar to those obtained for conventional MoS₂ films, but with a significant improvement in durability up to about 1 million wear cycles. Tribo-performance of these films under atmospheric conditions, at various humidity levels (40 to 75 % RH) has also been very good, with average friction coefficients as low as 0.07 and a durability as high as 220,000 wear cycles. XPS analyses have shown that the WC-MoS_x films consist mainly of a MoS_x lubricating matrix in which a carbidic wear resistant WC phase is embedded. This combination ensures a low friction behaviour while providing a higher wear resistance. Finally, these novel WC-MoS_x coatings are being tested in orbit at TriboLAB, in the International Space Station (ISS). TriboLAB is a tribology laboratory installed in the EuTEF (European Technology Exposure Facility), fixed to Columbus laboratory from ESA. Tests in progress within the TriboLAB experiment at the ISS have shown that the solid lubricating film maintain very low friction levels of 0.04 and reach a maximum of 1,011,000 wear cycles when tested on a ball on disk geometry at 0.75 Gpa, demonstrating a similar behaviour to that experienced on ground under laboratory conditions.
10:40 AM		E1-1-9 Low Earth Orbit Space Tribometer B. Krick (University of Florida); J.G. Jones (Air Force Research Laboratory/RXBT); J.K. Lenoff (Air Force Research Laboratory/RXBN); A.A. Voevodin (Air Force Research Lab/University of Dayton); W.G. Sawyer (University of Florida) The requirements for increased reliability, minimization of friction losses, and extending lifetime of space deployed and operated mechanisms in both commercial and military systems place stringent demands for solid lubricant solutions. The challenge is multiplied by a need for lubricant survivability over harsh environments both in space (vacuum, atomic oxygen, radiations, particle bombardment, temperature spans) and on ground during system tests, storage and launch. Gold and molybdenum disulfide based coatings are traditional solid lubricants for space with performance data accumulated over decades of their use. However, they do not meet the increased design challenges, hindering new concepts for large space deployed antennas, solar panel structures, fast response re-positioning telecommunication and sensor platforms. A number of new materials have been recently developed which show considerable benefit over traditional lubricants in laboratory tests, but they were not flown in space to create a confidence of their use. To resolve this, a set of 8 portable pin-on-disk sliding tribometers was designed and built to space qualify such candidate materials in the frame of Materials International Space Station Experiment (MISSE) program. In collaboration with personnel from Boeing, NASA, NRL, Air Force Research Laboratory (AFRL), and the University of Florida (UF) the tribometers have been integrated in a Passive Experimental Carrier (PEC) and are awaiting shuttle delivery in October, 2009 to the International Space Station (ISS). Suited up astronauts will place the PEC mounted tribometers outside the ISS where it will remain for more than 12 months, allowing space exposure in front and back of ISS (different degree of atomic oxygen and radiation exposure). The new coatings based on PTFEE composites, adaptive chameleon solid lubricants, and low friction carbon originated from recent fundamental studies in the Extreme Environment Tribology programs supported by the Air Force Office of Scientific Research will be space tested against the base line standards of Au and MoS2 materials. This paper provides information on the MISSE tribological experiment design and compares laboratory data for the selected coatings scheduled for space experiments. Seventh in a series, MISSE 7B will re-utilize existing PEC hardware, refurbished for flight. With the retirement of the shuttle program, this is expected to be the last MISSE project for at least 5 years. The miniature and yet fully controllable design by UF with control and data acquisition developed by AFRL allow the tribometers to also be used in a variety of vacuum chamber tests on the ground, including in-situ SEM, XPS, and Auger surface analyses experiments.
11:00 AM		E1-1-10 Role of Transfer Phenomena on Tribological Behaviour of of Al-Cu Thin Films M. Ruet (Ecole Centrale de Lyon, France); T. Duguet (Ecole des Mines de Nancy, France); J. Fontaine (Ecole Centrale de Lyon, France); V. Fournee (Ecole des Mines de Nancy, France); K. Ito (Ecole Centrale de Lyon, France); J. Ledieu (Ecole des Mines de Nancy, France); M. Belin (Ecole Centrale de Lyon, France) Adhesive phenomena are controlling friction and wear of metallic contacts, which are usually poor tribological materials without lubrication. In this study, thin films of Aluminum-Copper alloys have been deposited by magnetron sputtering followed by annealing. Regular alloys (Al, θ-Al₂Cu...) as well as approximant phases (ζ-Al₃Cu₄, γ-Al₄Cu₉) were obtained, as observed by XRD. The tribological behaviour of these different coatings has been evaluated against steel ball on a linear reciprocating tribometer allowing electrical contact measurements. Two different behaviours can be distinguished. Pure metal and regular alloys exhibit high friction (> 0.3) and evidence of strong adhesive phenomena with massive transfer to the counterface, finally leading to removal of the coating. Approximant phases exhibit lower friction (< 0.3), with less material transfer to the ball, but coating failure arises from brittle fracture when coefficient of friction is higher than about 0.2. Nevertheless, surprisingly low friction (< 0.1) was observed for ζ-Al₄Cu₉ phase, with mild wear and build-up of insulating tribofilm on the ball. When the insulating character of the tribofilm is lost, friction starts to increase, leading to tensile cracks on the coating surface. The role of transfer phenomena and adhesive interactions between sliding surfaces will be discussed, attempting to account for such significant differences in tribological behaviour of Al-Cu alloys.