ICMCTF2008 Session E1-2: Friction and Wear of Coatings: Lubrication, Surface Effects and Modeling

Monday, April 28, 2008 1:30 PM in Room California

Monday Afternoon

Start	Invited?	Item
1:30 PM		E1-2-1 Mechanical and Tribological Properties of Duplex and Non-Duplex Cr-Al-N Coated AISI 4140 Steel S. Goulart-Santos, C. Godoy, R.D. Mancosu (Universidade Federal de Minas Gerais, Brazil); A. Leyland, A. Matthews (University of Sheffield, United Kingdom) In this work, the influence of plasma diffusion and coating treatments on the wear resistance of steel, including cavitation erosion and micro-abrasion, was investigated. In order to improve the wear resistance of AISI 4140 low alloy steel, two surface engineering techniques were applied: plasma nitriding and plasma-assisted PVD coating. The wear resistance of uncoated, Cr-Al-N coated and nitrided/Cr-Al-N coated AISI 4140 steel was investigated, with two different plasma nitriding times and two coating thicknesses being examined. Cavitation erosion tests were performed according to the ASTM G32-03 standard. Mass loss plots as function of cavitation exposure time were obtained and statistical analyses were applied in order to evaluate the cavitation erosion wear rates. Micro-abrasion tests were also carried out, to assess the wear coefficients. The systems under investigation were also characterised by Rockwell C adhesion tests, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), 3D profilometry and instrumented indentation hardness testing. Correlation between hardening depth and wear performance are discussed.
1:50 PM		E1-2-2 Gradient Cr(C,N) Cathodic Ac PVD Coatings G.G. Fuentes (Centro de Ingeniería Avanzada de Superficies de AIN, Spain); J.A. García (Centro de Ingeniería Avanzada de Superficies AIN, Spain); R. Martínez (AIN, Centre of Advanced Surface Engineering, Spain); R. Bueno, M. Rico (Centro de Ingeniería Avanzada de Superficies AIN, Spain); M.J. Díaz de Cerio (AIN, Centre of Advanced Surface Engineering, Spain); R.J. Rodríguez (Centro de Ingeniería Avanzada de Superficies de AIN, Spain) This work reports on recent advances in Arc-discharge Physical Vapor processing for low friction coefficient coating deposition. The study has evaluated the mechanical and tribological performance of engineered PVD coatings based on complementary carbon/nitrogen gradient concentrations through the film thickness. Traditional arc-discharge (Ti,Cr)N based coatings show overall good mechanical performance specially for cutting applications. However in forming applications, they still exhibit some undesired effects of excessive material transfer (galling), or reduced surface finishing quality, as due to relatively high friction coefficients (0.7-0.8)and high tendency to metal adhesion. To overcome these pernicious effects, a set of arc-discharge PVD gradient Cr(C,N) coatings were produced. The coatings exhibited friction coefficients down to 0.2-0.3 against Cr-steel, and similar mechanical strength than CrN. It is worthy to note that these values of the friction coefficients are reachable at industrial scale principally by sputtering methods such as MoS₂, or WC:H films. The microstructure and chemical composition properties of the coatings were evaluated by x-ray diffraction and spectroscopic techniques, whereas the mechanical properties were measured by ultra-micro-hardness, wear coefficient, and adhesion tests. Metal adhesion during sliding friction of CrCN coated tools were monitored using pin-on-disc experimental set up. Preliminary results evidenced the low tendency of the deposited films to pick up particles from the counter steel friction surfaces, with respect to other conventional arc-PVD films.
2:10 PM		E1-2-3 The Effect of Oxygen Content on the Temperature Dependent Tribological Behavior of Cr-O-N Coatings M. Urgen, V. Ezirmik, M.K. Kazmanli (Istanbul Technical University, Turkey) Increase of the temperature from room temperature to 100°C generally increases the wear and friction of the hard nitride coatings. This increase can be very distinct even if the temperature of the environment increases only to 40-50°C. Temperature dependent wear behavior of CrN coatings has been recently investigated and the temperature dependent wear behavior has been correlated with the character and structure of the tribofilm formed on the contact zone¹. The results of this study showed the important role of non-stochiometric oxynitrides on the temperature dependent wear behavior. In this work we have explored the possibility of producing Cr-N coatings that are able to exhibit temperature independent wear behavior (between 25-150 C) by introducing oxygen into their structure. CrN coatings with different oxygen contents were produced with cathodic arc PVD. The results of this study showed that it is possible to design Cr-O-N coatings showing temperature independent wear behavior, in the temperature range of 25-150 C, by introducing oxygen into their structure. ¹V. Ezirmik, E. Senel, K. Kazmanli, A. Erdemir and M. Ürgen, Effect of copper addition on the temperature dependent reciprocating wear behaviour of CrN coatings, Surface and Coatings Technology, In Press, Corrected Proof, Available online 24 May 2007, doi: 10.1016/j.surfcoat.2007.05.049.
2:30 PM	Invited	E1-2-4 Coatings for Tribological Applications in Aerospace and Application-Close Testing N. Schupp, F.J. Gammel, M. Meyer (EADS Innovation Works, Germany) An overview of contacts relevant to tribological load in aerospace is presented including examples from airplanes, helicopters and satellites. The specific requirements for different aircraft and space applications are explained. This study places emphasis on the approach how to solve tribological problems (e.g. fretting, wear) in aerospace applications. The main focus relies on coatings for aerospace components. However tribological functions are also important for tools for the manufacturing of aerospace parts. In the frame of this approach different test methods with increasing level of complexity are used to determine the solution candidates. A preselection of coatings can be made considering the process parameters of the coating deposition. It is mandatory to avoid changes of the substrate properties (hardness, microstructure, fracture toughness). These changes can be caused by temperature, special process gases or the coating material. Evaluation of the key parameters like loads, movements, contact partners, temperatures and environment during the use of the component enables the selection of relevant materials and/or coatings to be tested in standard lab-tests (e.g. pin-on-disc, Taber® Abraser). The results obtained from these tests give basic information (coefficient of friction, wear) under clean laboratory conditions with special contact geometry. Based on the results from laboratory testing a custom-built component test is designed with contact geometry and loads (surface pressure, vibration frequency) comparable to the real application. This test gives information about the behaviour of the coating or surface treatment under application related conditions. The reliability of the component test is investigated employing the materials in its initial stage as a reference (e.g. without coating). Coatings or surface treatments which meet the requirements are considered for flight tests. Two examples of laboratory and component test equipment for fretting and long amplitude wear are shown. Furthermore some practical examples from different aerospace applications are discussed, which demonstrate the use of various coating technologies (PVD, hybrid coating, galvanic process, special grease) to work against existing tribological challenges.
3:10 PM		E1-2-8 TiN-Ag Nanocomposite Coatings: Deposition Process and Tribological Characterisation J. Barriga, A. Alberdi, M. Marin, I. Ciarsolo, X. Fernandez (Tekniker, Surface Physics and Technology, Spain) Combined cathodic arc and sputtering Physical Vapour Deposition (PVD) techniques were used to produce wear resistant nanocomposite coatings on steel substrates. These low wear coatings consisted of nanometric silver solid lubricant clusters embedded into a hard titanium nitride matrix. The nanocomposite coatings were characterised by atomic force microscopy, confocal microscopy, optical and scanning electron microscopies, and EDS micro-analysis. This analysis showed that the silver nanoclusters were about 40-60 nm in diameter. Reciprocating ball-on-disc tribological tests under dry conditions were carried out to determine the influence of density, size and distribution of the nanometric silver clusters on wear resistance. Load was increased progressively during the tests. Improvement up to six times higher load were obtained with these TiN-Ag nanocomposite coatings when these were compared to conventional TiN simple coatings.
3:30 PM		E1-2-10 Nanotribology Simulations of Self-Assembled Monolayers Using Realistic AFM Tips M. Chandross (Sandia National Laboratories); C.D. Lorenz (Kings College, London, United Kingdom); J.M.D. Lane, M.J. Stevens, G.S. Grest (Sandia National Laboratories) We present the results of massively parallel molecular dynamics simulations of realistic AFM tips in contact with silica surfaces coated with self-assembled monolayers (SAMs). Detailed analysis demonstrates that the commonly applied JKR and DMT models do not accurately predict the contact mechanics of these systems. Shear simulations reveal the effects of varying tip radius (from 3 to 30 nm) and the addition of a SAM coating to the tip itself. We show that small applied loads are sufficient to damage the SAM, enabling the penetration of water which leads to further debonding of the coating. Our simulations of coated and uncoated tips additionally provide evidence supporting a recently proposed plowing mechanism of energy dissipation¹. Sandia is a multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. ¹ E.E. Flater, W.R. Ashurst, R.W. Carpick, Langmuir, in press (2007).
3:50 PM		E1-2-7 Impact Stress Absorption and Load Spreading in Multi-Layered Erosion-Resistant Coatings S. Hassani, J.E. Klemberg-Sapieha, L. Martinu, M. Balazinski (École Polytechnique de Montréal, Canada); M. Bielawski, W. Beres (National Research Council Canada) Aerospace industry seeks to develop high performing coatings for the protection against solid particle erosion in different components of aircraft engines. The development of such erosion-resistant coatings requires understanding of impact stress propagation under complex conditions. In the present work the finite element method approach is proposed to investigate whether the resistance of protective coatings to erosion by solid particles can be enhanced by appropriate stress management. In particular, the role of residual stress in compensating the impact stresses is investigated. In such cases, the Young’s modulus graded design is introduced to optimize the impact energy spreading inside the coating system. From the standpoint of tensile stress reduction and energy absorption, a multi-layer configuration with a varying Young’s modulus and residual stress distributions along the coating depth, is suggested as an optimal coating architecture. Guidelines and design principles for erosion-resistant coatings are discussed in the paper.