ICMCTF2008 Session E3-2: Tribology of Amorphous and Nanostructured Films

Wednesday, April 30, 2008 8:00 AM in Room California

Wednesday Morning

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8:00 AM		E3-2-1 Micro-Tribological Performance of MoS₂ Lubricants With Varying Au Content P. Stoyanov, R. Chromik (McGill University, Canada) In nanocomposite solid lubricant coatings, such as metal/MoS₂, the coefficient of friction decreases when increasing the normal force. Also, the humidity level has a strong influence on the tribological performance. Therefore, for macroscopic applications, these solid lubricants are used when high contact stress and low humidity levels are expected.¹ The purpose of this research was to investigate the microtribology of Au/ MoS₂ solid lubricants with varying Au content to explore their viability for microelectromechanical systems (MEMS) applications. Using a nanoindentation instrument, the mechanical properties of the coating were measured. Using the same instrument, sliding tests were performed on the Au/ MoS₂ coatings while varying the tip diameter, the normal load, the sliding time, and the humidity level. The results were explained by using an elastic-plastic contact model. Furthermore, the wear volumes and rates were analyzed using an AFM and also using pre/post scanning with the nanoindenter. The combination of the results of the elastic-plastic model, and the wear measurements were used to explore the tribological behavior as a function of the contact stress, humidity and the formation of transfer films and third bodies. super 1@Lince J. R., "Tribology of Co-Sputtered Nanocomposite Au/MoS₂ Solid Lubricant films Over a Wide Contact Stress Range", Tribology Letters, v 17, n 3, 2004, 419-28.
8:20 AM		E3-2-2 Tribological Characteristics of MoS₂ Nb Solid Lubricatn Films in Different Tribo Test Conditions I. Efeoglu, Ö. Baran, F. Yetim (Ataturk University, Turkey); S. Altýntas (Bogazici University, Turkey) MoS₂ coatings lose their lubricating properties through mechanisms that depend on atmospheric conditions. The tribological performance at the different atmospheres of MoS₂ solid lubricant films have been improved by the co-deposition of small amount of another metal. In this study, we investigated tribogical properties of MoS₂ co-sputtered with Nb. MoS₂ Nb solid lubricant composite films were deposited on AISI 52100 steel substrates and silicon wafers by closed field unbalanced magnetron sputtering (CFUBMS). Composition, morphology and structure were analyzed by a variety of techniques including energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM) and X]ray diffraction. Hardness of the films was measured with microindentation. The high temperature friction and wear properties in air and dry nitrogen were determined using pin-on disc tribo-tester. Pulsed-dc sputtered MoS₂ Nb film exibited two types of crystallite orientattion and characteristic dense structure corrosponding to crystallite growth in which the low shear of basal plane of MoS₂ (002) and humidity sensitive NbS₂ phase. MoS₂ Nb coating is displayed good lubricating properties in the oil then distilated water, humid air and in the dry nitrogen conditions respecvialy. The CoF and wear ratio were obtained in dry nitrogen as maximum and in oil as minimum.
8:40 AM		E3-2-3 Friction and Wear Properties of Nanocrystalline Diamond Coatings C.C. Baker, N.D. Theodore (Naval Research Laboratory / North Carolina State University); K.J. Wahl (Naval Research Laboratory) The tribological behavior of nanocrystalline diamond (NCD) coatings was studied under reciprocating sliding conditions. Coatings were deposited by microwave plasma chemical vapor deposition onto Si substrates under varying growth conditions to thicknesses between 1-2 microns. Friction behavior was investigated using reciprocating sliding in a pin-on-flat geometry with both diamond and sapphire counterfaces at contact pressures ranging between 0.09 and 0.9 GPa. Coating microstructure, chemistry, and surface morphology were examined using X-ray diffraction (XRD), micro-Raman spectroscopy, and atomic force microscopy (AFM). Wear volumes of the ball counterface and coating wear tracks were determined with optical interferometry. Steady state friction coefficients for both the diamond-NCD and sapphire-NCD sliding pairs were low, ranging from 0.03 to 0.06. However, large differences in friction during run-in were observed between different NCD coatings, with the number of cycles to run-in from initial high to low friction varying depending both on the counterface material and NCD coating properties. The role of coating microstructure, stresses, wear debris, and transfer film chemistry on the run-in friction behavior of NCD will be discussed.
9:00 AM		E3-2-4 Coating Chemistry and Run-in Friction of Nanocrystalline Diamond Coatings N.D. Theodore, C.C. Baker, K.J. Wahl (Naval Research Laboratory) Tribology studies were performed on three nanocrystalline diamond coatings to correlate compositional, structural, and chemical bonding differences to their friction performance. Microstructure and surface morphology were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), and optical interferometry. All the diamond coatings were nanocrystalline with crystallite sizes ranging from 8 to 40 nm. These nanocrystalline diamond coatings could be differentiated from each other by their visible wavelength Raman absorption bands. One coating had a strong peak at 1332 cm^-1 typical of crystalline diamond bonding; the second had strong peaks at 1340 cm^-1 and 1580 cm^-1 characteristic of the D and G peaks in sp² hybridized carbon; and the third had D and G peaks along with peaks at 1135 cm^-1 and 1470 cm^-1, which are commonly attributed to polyacetylene bonding. Transmission Fourier transform infrared (FTIR) microscopy was also used to examine the coatings and wear tracks. Reciprocating sliding tests using sapphire and diamond counterfaces in ambient environments resulted in similar friction values, between 0.03 and 0.06, for all coatings. However, while initial friction coefficients were high for all coatings, the number of cycles required to run-in to low friction on each sample varied between 30 - 600 cycles. Shorter run-in periods were correlated with higher amounts of sp² carbon content or carbon-hydrogen bonding. Potential mechanisms for wear and tribochemical reactions at the nanocrystalline diamond surface will be presented, and their role in friction will be discussed.
9:20 AM		E3-2-5 Wear Behavior in SiC-TiX Nanocomposites A.R. Beaber, J. Hafiz, J.V.R. Heberlein, W.W. Gerberich, S.L. Girshick (University of Minnesota) SiC-TiX (X includes oxide, carbide and elemental forms) nanocomposites were deposited through a hybrid process of nanoparticle impaction and chemical vapor deposition. Reactants are injected into a thermal plasma and undergo a rapid expansion through a converging nozzle, resulting in gas-phase particle nucleation and hypersonic impaction onto a substrate. While film growth is composed primarily of nanoparticles, excess vapor from the particle nucleation process forms a reactive boundary layer above the substrate and supports CVD growth. Embedded particles both inhibit grain growth in the matrix material during the deposition and enhance fracture toughness under compression. Consecutive deposition of SiC and TiX creates a multilayered film with SiC particles embedded in a SiC matrix and a Ti/TiO₂/TiC/TiO composite. Both layers show an increased hardness without a change in the modulus compared to bulk samples. While residual tensile stresses at the TiX-SiC interface show weak interlayer adhesion, the independent performance of the layers with respect to H3/E*2 suggests unique microstructural benefits inherent to the deposition process. These results demonstrate the potential for high strength nanocomposites with enhanced wear properties.
9:40 AM		E3-2-6 Effect of Microstructure on the Erosion Resistance of Cr-Si-N Coatings E. Bousser, M. Benkahoul, P. Robin, L. Martinu, J.E. Klemberg-Sapieha (École Polytechnique de Montréal, Canada) Erosion by solid particle impact can cause severe damage to critical components of airplanes, helicopters and other applications affecting their overall performance, costs and most notably safety. In our search for novel high performance erosion resistant coatings, Cr-Si-N coatings have been studied. In this work, 10 µm thick films were deposited on AISI 410 stainless steel substrates by DC reactive dual magnetron sputtering using Cr and Si targets. Microstructure, composition and mechanical properties were studied as a function of silicon content (C_Si) using XRD, ERDA, EDS, and depth sensing and Vickers indentation techniques. A maximum hardness of 24 GPa was found for Cr-Si-N with C_Si = 2.3 at.%, while that of pure CrN is 18 GPa. Previous work has shown that this increase can be explained in terms of the solid solution hardening mechanism rather than by the nanocomposite effect. Solid particle erosion (SPE) tests were performed according to the G76-02 ASTM standard on a test rig developed by our laboratory. Al₂O₃ particles with an average size of 50 µm were projected onto the coating surface, with a mean velocity of 90 m/s and incidence angles ranging from 15 to 90°. The 90° erosion rate of Cr-Si-N with C_Si = 2.3 at.% was found to be 4.2x10^-3 mg/g, one order of magnitude lower than that of pure CrN and 50 times lower than that of the substrate. In this work, we correlate the SPE behaviour of Cr-Si-N coatings with respect to their mechanical (hardness, Young’s modulus and toughness) and microstructural (texture and morphology) characteristics.
10:00 AM		E3-2-7 Tribological Performance of Superhard Nanocomposite Ti-Al-Si-N Coatings at Elevated Temperature P.W. Shum, Z.F. Zhou, K.Y. Li (City University of Hong Kong) Nanocomposite Ti-Al-Si-N coatings (Al content ranging from 0 to 18 at.% and Si from 0 to 12 at.%, respectively) were prepared on hardened M42 tool steel substrates at 500 °C by reactive close-field unbalanced magnetron sputtering in an Ar-N₂ mixture. These coatings were characterized and analyzed by a variety of techniques such as x-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), optical interference method, nanoindentation measurements, scanning electron spectroscopy (SEM) and scratch tester etc. In particular, the wear behavior was analyzed by a ball-on-disk wear tester at temperature up to 400°C, while the fatigue strength was studied by an impact tester up to 800°C. It was found that the tribological behaviours of the Ti-Al-Si-N coatings at high temperature depended strongly on the variation of Al and Si content in the coatings. The wear resistance of the quaternary Ti-Al-Si-N coatings was improved significantly when compared to ternary Ti-Si-N and Ti-Al-N coatings at temperature of 400°C. The Ti-Al-Si-N coatings could endure longer impact cycles before the coating failure. The enhanced tribological performance at elevated temperature can be explained by the combination of improved structure and mechanical properties of the Ti-Al-Si-N coatings.
10:20 AM		E3-2-8 Mechanical and Tribological Properties of Nanocomposite and Nanomultilayered Ti-B-N Thin Films K. Chu, Y.H. Lu, Y.G. Shen (City University of Hong Kong) Two different types of nanocomposite TiBN-related thin films, monolayer TiBN and nanomultilayer nc-TiN/a-TiBN, were fabricated by reactive unbalanced dc-magnetron sputtering using Ti and TiB₂ targets in Ar-N₂ mixture. The mechanical and tribological properties of the films were characterized and analyzed by microindentation measurements, an optical interference method, a pin-on-disk tribometer, an optical microscope and a scanning electron microscope. The results indicated that the microstructure and the bilayer thickness (λ) were the key factors affecting the mechanical properties, which resulted in obvious difference in wear behavior between TiBN and nc-TiN/a-TiBN films. In TiBN monolayer, the hardness increased with addition of boron was due to the densified microstructure, whereas the hardness enhancement in nc-TiN/a-TiBN multilayer with decreasing λ was explained by the Koehler’s theory. In tribological tests, both friction coefficient and wear rate in TiBN monolayer decreased with the increase of amorphous matrices, which was contributed to a change in wear mode from abrasive to dominant adhesive. An inverse trend occurred in the wear rate when additional h-BN phase was formed. The formation of nanomultilayer greatly decreased the friction coefficient and wear rate. Both friction coefficient and wear rate of nc-TiN/a-TiBN increased with increasing λ. It was believed that bilayer interfaces hindered the nanocrack propagation during dry sliding and the presence of h-BN phase in small λ also lowered the friction coefficient and wear rate. The difference of wear mechanisms between the monolayer and multilayer is also discussed.
10:40 AM		E3-2-9 Wear Evaluation of WC Inserts Coated With TiN/TiAlN Multinanolayers J.C. Caicedo (Universidad del Valle, Colombia); F. Martinez (Universidad de la Havana, Colombia); L.H. Moreno (Universidad del Valle, Colombia); T.S. Batallaille (Universidad de la Havana,, Colombia); P. Prieto (Universidad del Valle, Colombia) TiN/TiAlN multilayers were deposited by r.f. reactive magnetron sputtering using titanium and aluminum targets with 10 cm diameter and 99.99% purity in an argon/nitrogen atmosphere, applying a substrate temperature of 300°C. WC inserts were used as substrates to improve the mechanical and tribological properties of TiN/TiAlN multilayers coatings against other types of coatings like TiAlN monolayers and manage greater efficiency of these coatings in different industrial applications such as drilled, milling, mechanized, extrusion. Their physical, mechanical, and tribological characteristics were investigated, including cutting tests with steel AISI 4340 hardened (50HRC) to assess wear as function of the period and number of bilayers. A comparison of the properties of TiCN-Al₂2O₃-TiN nanoestructure monolayer and the [TiN/TiAlN]₃₀₀heterostructure with individual layer thicknesses of 10 nm revealed an increasing in the machining lengths around of 36% and wear resistance improvement around 14% for coatings with 300 bilayers. These also showed better machining properties onto hardened AISI 4340 steel like pieces to mechanize, as compared to not coated WC inserts. These results open the possibility to use [TiN/TiAlN] multilayers as a new coating for tool machining with excellent industrial performances. ¹Acknowledgements: This work was supported by COLCIENCIAS, and by the Excellence Center for Novel Materials, CENM, under the RC-043-2005 contract.