Papers

ICMCTF2007 Session E1-1: Friction and Wear of Coatings: Lubrication, Surface Effects and Modelling

Monday, April 23, 2007 1:30 PM in Room California

Monday Afternoon

Start	Invited?	Item
1:30 PM		E1-1-1 Improvement of the Slurry Erosion Resistance of an Austenitic Stainless Steel with Combinations of Surface Treatments: Nitriding and TiN Coating A.A.C. Recco, D.M. López (University of São Paulo, Brazil); A.F. Bevilaqua (University of Mackenzie, Brazil); F.B. da Silva, A.P. Tschiptschin (University of São Paulo, Brazil) The combination of different surface treatments for improving the erosion resistance of an AISI 304 stainless steel was studied. Six kinds of sample conditions were tested in a slurry composed of distilled water and SiC particles: high temperature gas nitriding (HTGN), low temperature plasma-nitriding (expanded austenite), high temperature gas nitriding followed by TiN-PVD coating, low temperature plasma nitriding followed by a TiN-PVD coating as well as samples in the solubilized condition. The erosion tests were performed during 6 hours in a jet-like device with normal angle of incidence and impact velocity of 8.0 m/s. Wear rates were assessed by accumulated mass loss measurements made on a five digits scale and through analysis of scanning electron microscopy images of the worn surfaces. The results were related to the microstructure and hardness of the surface to establish a ranking of the different surface treatments. After the first few minutes of testing cutting of the surface occurred in the solubilized, in the HTGN and in the low temperature plasma nitrided AISI 304 samples, whereas TiN coated samples did not show any cutting marks, although some indentation marks could be observed. The TiN coated samples showed wear resistances one order of magnitude greater than the solubilized, HTGN and low plasma nitrided samples.
1:50 PM		E1-1-2 The Critical Conditions for Tribo-Demagnetization of Magnetic Layered Disk in Sliding Contact Against Head J. Liu, D. Diao (Xi'an JiaoTong University, China) The flying height of read/write head sliders over spinning magnetic layered disk surfaces has to be reduced to less than 6 nm in hard disk drives. During the operations, the presence of protruding nano-asperity on the disk surfaces and the shock outside the drives can increase the likelihood of high-velocity intermittent head/disk sliding contacts. The high flash temperature and stress fields at the head/disk interface due to friction can degrade the domain magnetization of the magnetic layered disk, which is known as friction-induced demagnetization. Former studies were not extended to establish the critical conditions of demagnetization from the viewpoint of the tribology and the demagnetization tests. In this paper, therefore, a method based on experiments of tribo-demagnetization test in combination with numerical simulations of temperature/stress is proposed to predict the critical conditions for demagnetization of magnetic layered disk. The critical conditions are investigated by means of the tribotest of a SiC ball sliding against a magnetic disk to erase sectors, the scan of the disk with the magnetic head to detect the erased sectors, and the numerical simulation to calculate the transient temperature/stress distributions in the erased zone. The critical normal load and sliding velocity for the occurrence of demagnetization are measured by the experiments of tribotest and scan, and the critical temperature/stress for the demagnetization are calculated by numerical simulations based upon the critical operating conditions.
2:10 PM		E1-1-3 Novel Tribological Systems Using Shape Memory Alloys and Thin Films Y. Zhang (Michigan State University); Y.T. Cheng (General Motors Research and Development Center); D.S. Grummom (Michigan State University) Thin film and bulk shape memory alloys are shown to have robust indentation-induced shape memory and superelastic effects, where indents can recover upon martensite-to-austenite phase transformations. Since many tribological contact conditions are similar to those under indentations, we have, in recent years, explored novel tribological applications of the micro- and nano-scale shape memory and surface elastic effects using thin film and bulk NiTi shape memory alloys. First, we show that superelastic NiTi thin films as interlayers between hard coatings and aluminum substrates can improve coating adhesion and wear resistance. The NiTi interlayers are sputter deposited onto 6061 T6 aluminum substrates. Chromium nitride (CrN) and diamond-like carbon (DLC) hard coatings are deposited by unbalanced magnetron sputter deposition. X-ray diffraction and nanoindentation are used to characterize NiTi interlayers. Wear and scratch tests show that superelastic (austenitic) NiTi interlayers significantly improve tribological performance of hard coatings on aluminum substrates. Second, we show that the indentation-induced two-way shape memory effect can be realized in thin film and bulk NiTi alloys, where spherical indents exhibit two-way reversible depth change with heating and cooling temperatures. Furthermore, reversible surface protrusions are realized after the indents are planarized (a polishing procedure to restore a flat surface). Micro- and nano- scale circular surface protrusions arise from planarized spherical indents in thin film and bulk NiTi alloy; line surface protrusions appear from planarized scratch tracks. Surfaces with patterned reversible indentations and protrusions can exhibit unusual tribological behavior that may be used for controlling friction in tribological systems.
2:30 PM		E1-1-4 Low Earth Orbit Space Environmental Effects on MoS₂/DLC Lubrication Films M. Tagawa, K. Yokota (Kobe University, Japan); K. Matsumoto (Japan Aerospace Exploration Agency, Japan); M. Belin (Ecole Centrale de Lyon, France) In order to eliminate unexpected molecular contamination from lubricating oils or greases, solid lubrication is preferred in critical space applications. However, effects on extreme space environment on solid lubricants have not been fully understood. Especially, reaction of ground state atomic oxygen (O³P), which is a dominant atmospheric composition in the upper atmosphere of Earth, is one of the major concerns on solid lubricating films directly exposed to low Earth orbit (LEO) space environment. Ground-based studies of hyperthermal atomic oxygen reaction with solid lubricant surfaces can only be performed by a laser-detonation acceleration technique. In this method, collision energy of atomic oxygen with spacecraft surfaces (5 eV or 7.5 km/s) can be simulated in a ground-based facility. Reproduce such high collision energy of atoms is essential to simulate atomic oxygen reaction in LEO and is practically difficult by the other methods. In this presentation, recent knowledge on atomic oxygen reactions with molybdenum disulfide (MoS₂) and diamond-like carbon (DLC) lubricating film obtained by a laser-detonation atomic oxygen facility will be surveyed. Change in tribological properties as well as chemical reaction pathways will be presented. A part of this work was supported by Grant-in-Aid of Scientific Research and SAKURA Project from JSPS and Nanotechnology support program of JASRI (BL23SU, SPring-8) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. RBS/ERDA measurement was carried out by 5SDH2 accelerator at Kobe University.
3:10 PM		E1-1-6 Growth, Structure and High Temperature Friction Behavior of Titanium Doped Tungsten Disulphide Films A. Rajendran, T.W. Scharf (The University of North Texas) This study describes the synthesis, structure and tribological behavior of titanium doped tungsten disulphide (Ti-WS₂) solid lubricant films grown by co-sputtering. Thin films varying in thickness from 300 to 500 nm were deposited on silicon at room and 300°C in situ substrate temperatures. Films were studied by cross-sectional scanning and transmission electron microscopies and X-ray diffraction to determine the coating structure and crystallinity as a function of varying titanium atomic percent and sputtering power. X-ray diffraction confirmed that the films grown at room temperature and 300°C were crystalline with hexagonal texture. Basal planes with c-axis predominantly orientated parallel to the substrate surface [(100) and (101) reflections] were observed in all films. Regardless of orientation to the substrate surface, these basal planes when sheared at high contact pressures imparted low friction with a steady-state friction coefficient of ~0.2 in ambient air environments using room temperature and high temperature (500°C) pin-on-disk tribometry. The coatings exhibited non-Amontonian friction behavior, with friction coefficients decreasing with an increase in Hertzian contact stress. The formation of smooth transfer films (third bodies) during sliding provided low interfacial shear stresses between the Ti-WS₂ film and the couterface, thus achieving low friction and wear. Electron microscopy was used to examine the structure and composition of the wear surfaces and cross-sectional focused ion beam cuts were made inside and outside the wear tracks to determine the sub-surface deformation behavior as a function of Ti-WS₂ film growth temperature and atomic percent Ti in the film.
3:30 PM		E1-1-7 Mechanical and Tribological Properties of CrAlN-Ag Self Lubricating Films P. Basnyat, S.M. Aouadi, B. Luster, S. Stadler, Z. Kertzman (Southern Illinois University, Carbondale); S.R. Mishra, J. Xu (University of Memphis) This paper reports on the investigation of the mechanical and tribological properties of reactively sputtered CrAlN-Ag composite nanostructures. These films were co-sputtered from three individual targets of Cr, Al, and Ag onto Si(111) and stainless steel SS-440C substrates. Three sets of samples were produced by varying: (1) the power to the Ag target (P_Ag); (2)the power to the Al target (P_Al); and, (3) substrate temperature. The elemental composition was deduced from Rutherford Backscattering and was found to be influenced by P_Ag and P_Al. The crystal structure and film architecture were evaluated using x-ray diffraction and transmission electron microscopy. The films were found to consists of nanocrystal of Ag embedded in a solid solution of CrAlN with a pattern typical of the NaCl structure. The CrAlN grain size was found to decrease with the increase in silver content in the film. The hardness and elastic modulus of each sample were measured by nanoindentation. Finally, the coatings were worn against ball-bearing steel using a ball-on disc tribotester. Characterization of the wear tracks were performed by profilometry. A low wear coefficient of 1.7x10^-7mm³/s was obtained for a load of 2N.
3:50 PM		E1-1-8 Synthesis of a Rhenium Based High Temperature Tribological Coating System C.C. Baker (North Carolina State University); K. Wahl (US Naval Research Laboratory); A.A. Voevodin (Air Force Research Laboratory) The synthesis of a novel nanocomposite coating system which includes the ability to impart low friction in ambient as well as high temperature environments has been investigated. The coating system includes: hexagonal boron nitride (BN) for low friction in atmospheric conditions, rhenium for friction in elevated temperatures and space environments, and aluminum oxide (Al₂O₃) for hardness and wear resistance. The use of rhenium in the system represents a novel approach to high temperature lubrication. Research on the friction and wear properties of rhenium has had a very limited amount of activity in the past due to its rarity. Rhenium is, however, an exciting candidate due to its exceptional properties such as the third highest elastic modulus and melting point of any element, ductility at room temperature, and a hexagonal structure with a high c/a ratio of 1.615 which is considered to be close to the ideal value for low friction materials. The coatings were produced using the technique of magnetron sputtering pulsed laser deposition (MSPLD). The procedure consists of magnetron sputter deposition of a rhenium target used along with pulsed laser deposition of sectioned BN and Al₂O₃targets. The coatings were deposited in several multilayer approaches. Chemical and structural analysis of the coatings included x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), transmission electron microscopy (TEM), and micro-Raman spectroscopy. Coating hardness was investigated using nanoindentation tests. The coefficient of friction for all samples was evaluated in a pin-on-disc tribometer in air from room temperature to 700Â°C. The coatings were found to have low coefficients of friction and wear resistance at all temperatures.
4:10 PM		E1-1-9 High Temperature Tribological Behavior of Sputtered NbN_x Thin Films G.A. Fontalvo, V. Terziyska (University of Leoben, Austria); C. Mitterer (Montanuniversität Leoben, Austria) In the present study, the tribological behaviour of NbN thin films was investigated in ambient air at temperatures up to 600°C by using ball-on-disc tests and alumina balls as counterfaces. The films were deposited on high speed steel substrates by reactive magnetron sputtering. The crystal structure and microstructure of the films were varied by changing the N₂ partial pressure and the substrate bias potential. Coatings were characterised by x-ray diffraction, scanning electron microscopy, and nanoindentation measurements. Wear tracks on the samples were characterized using Raman spectroscopy, scanning electron microscopy and white light profilometry. The crystal structure of the films changes from hexagonal Nb₂N for coatings deposited at 6% p_N2 to a mixture of hexagonal and cubic NbN for higher nitrogen partial pressures, reaching a pure cubic phase for 40% p_N2. The hardness and Young's modulus strongly depend on the crystal structure. The coefficient of friction decreases slightly with increasing temperature, presumably due to niobium oxide formation on the surface during the heating step.
4:30 PM		E1-1-10 Nanocomposite Coatings Demonstrating Adaptive Lubrication Over Multiple Thermal Cycles from 25-700°C C. Muratore, J.J. Hu (UTC Inc./Air Force Research Laboratory); A.A. Voevodin (Air Force Research Laboratory) Adaptive "chameleon" nanocomposite coatings demonstrate low friction throughout broad ranges of temperature, humidity, and other environments. In the current work, temperature adaptation was explored by integrating noble metal diffusion for the formation of easy-to-shear surface tribofilms, together with tribochemical formation of lubricious surface oxides to cover sliding temperatures from 25 to 700°C. Results from diffusion studies were used to propose novel YSZ/Mo/Ag nanocomposite coating architectures, incorporating TiN diffusion control layers either as a porous surface mask to control vertical silver transport, or as solid interlayers to guide lateral silver transport. Knowledge of the diffusion parameters allowed theoretical prediction of the wear life of TiN/YSZ-Ag-Mo coatings at different temperatures, which was longer than our current test equipment could measure (>50000 cycles over more than 12 hours at 500°C). Lateral lubricant transport was also explored as an "on demand" lubricant supply concept, in which silver diffusion toward worn areas is triggered only when the diffusion barrier in subsurface coating volume is worn through. In parallel to the diffusion mechanism studies, lubricious oxide formation at high temperature by tribochemical reactions was also investigated. It was found that MoO₃ (easily sheared >500 C) was readily produced in the contact, but silver-molybdate compounds, expected to provide lubrication at moderate temperatures, did not. Addition of sulfur to the system promoted Ag₂Mo₄O₇ formation resulting in friction coefficients of < 0.2 from 25-700 C. Multilayered coatings demonstrated repeated diffusion, tribochemical and catalytic adaptive mechanisms to provide low friction over multiple thermal cycles.
4:50 PM		E1-1-12 Studies on the Thin Film Characteristics of Zirconium-Based Metallic Glass with Slight Addition of Silicon Using Magnetron Sputtering Process C.W. Chu (I-Shou University, MIRDC, Taiwan) The priority for the development of the new metallic materials includes toughness "wear resistance" "light weight" "high plasticity" high temperature resistance and environmental friendly. The currently developed metallic glasses possess these advantages. Based on the references of the research projects that the addition of the various contents of the smaller atomic radius metalloid element boron on the Zr₆₅Al_7.5Cu_17.5Ni₁₀ based alloy Zr_65-xAl_7.5Cu_17.5Ni₁₀B_xO_0.2 ~ 1.0 mm thick amorphous alloy using the rapid melt-spinning and gravity casting processes can be obtained. Preliminary results indicate that the amorphous alloys with the addition of boron has similar glass transition temperature (Tg~ 650 K), however othe crystallization temperature has the raising tendency with the increase of the boron content. Comparisons of the various characteristics of the Zr65-xAl_7.5Cu_17.5Ni₁₀B_x thin film to the current TiN and Cr₂N thin films are as follows: for the contact angle, 940>850>800, for wear resistance (Pin-On-Disk):0.35>0.5>0.55, for hardness testing 32Gpa>30Gpa>26Gpa, for the microstructure using X-ray and TEM the metallic glass of Zr_65-xAl_7.5Cu_17.5Ni₁₀B_x thin film is amorphous while the TiN and Cr₂N thin films are crystalline form. Metallic glass has better mechanical performance and is easy to be manufactured into amorphous and nano-materials. In addition to its excellent engineering characteristics, such as high tensile strength, high elasticity, high impact toughness and excellent corrosion resistance, the addition of boron could promote the thermal stability of the alloy, therefore the alloy could maintain in metallic glass state for longer time.