ICMCTF2009 Session E1-2: Friction and Wear of Coatings: Lubrication, Surface Effects and Modeling

Wednesday, April 29, 2009 1:30 PM in Room California

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		E1-2-1 Interfacial Scratch Adhesion Behavior of Multilayered Ti(BN):Ti(MoS₂) Based PVD Coatings I. Efeoglu (Ataturk University, Turkey); B. Prakash, J. Hardell (Luleå University of Technology, Sweden) Interfacial adhesion is critical property of multilayered thin films used in micro-electromechanical systems, ceramic capacitors, wear resistant coatings. In the present investigation, Ti(BN)+Ti(MoS₂) solid multilayered-composite solid lubricant coatings were deposited by magnetron sputtering from separate Ti, TiB2, and MoS₂ target. X-ray diffraction, microhardness tester, and scratch tester were used to evaluate structural, mechanical and interfacial adhesion properties. In the work, described here changes in the adhesion of intercoat exhibited by nine different coatings deposited under variants of deposition parameters have been investigated. It is found that the crack propagates alternatively between the two interfaces with thinning of the interlayer.
1:50 PM		E1-2-2 Optimization of AlN Coatings for Tribological Applications A. Rojo (ITESM-TOL, Mexico); J. Oseguera, O. Salas, J. Solis (ITESM-CEM, Mexico) Several modes of injection of nitrogen during reactive magnetron sputtering of aluminum where carried out in order to optimize the AlN layer structure for tribological applications. The injection methods used were: convectional injection of Ar + N₂ mixture away from the substrate varying the amount of nitrogen, Ar + N₂ mixture away of the substrate with extra nitrogen near the substrate and direct injection of N₂ near the substrate, the resulting coatings where analyze by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and tribological characterization in a pin-on disk machine. The injection method that results in a richer nitrogen atmosphere seems to produce better results. Adhesion of the coatings to the substrate is central for the tribological behavior.
2:10 PM	Invited	E1-2-3 Surface Chemical Mechanisms of Lubricants Under Sliding Conditions W. Tysoe (UW-Milwaukee) Chlorine- and sulfur-containing compounds are commonly added to the base fluid to synthesize lubricants used under extreme pressure (EP) conditions. Analysis of the resulting tribological films on iron reveals that chlorinated hydrocarbons thermally decompose forming a layer that consists of iron chloride (FeCl₂) or iron carbide (Fe₃C), depending on the additive. Carbides are formed most easily when carbon tetrachloride is used as an additive. Similar analyses of films formed from sulfur-containing additives reveal that dialkyldisulfides and carbon disulfide thermally decompose to form a tribological film that consists of FeS and Fe₃C. The surface chemistry leading to the formation of these tribological films is explored on clean iron in ultrahigh vacuum using d.c. molecular beams of the reactant impinging on the surface. In order to better understand the role of thin films in reducing friction, their tribological properties were investigated in ultrahigh vacuum. This strategy eliminates contamination and allows films of known composition and structure to be grown on well-characterized substrates. It is found that a single layer of the film causes a substantial reduction in friction so that a monolayer of KCl on iron reduces the friction coefficient from its clean-surface value of ~2, to 0.27, while a layer of FeCl₂ reduces it to ~0.08. The friction coefficient increases once again as the film becomes thicker and this effect can be modeled using Greenwood-Williamson theory. Systematically varying the nature of the film and the substrate allows the limiting friction coefficient of the monolayer to be related to the mechanical properties of both the films and the substrate.
2:50 PM		E1-2-7 Expanding the Range of Temperature-Adaptive Solid Lubricant Coatings Beyond 25-700°C with the Aid of In Situ Wear and Surface Analysis Techniques C. Muratore, J. Hu, J. Bultman (Air Force Research Laboratory); A.A. Voevodin (Air Force Research Lab/University of Dayton) Nanocomposite coatings demonstrating multiple temperature adaptation mechanisms have been deposited with a hybrid physical vapor deposition process to provide solid lubrication from room temperature to over 700°C. These coatings generally rely on diffusion of low shear phases to the surface and tribo-oxidation mechanisms to yield moderately low friction coefficients of 0.4 over this broad temperature range. Catalyst elements can be added to the coatings to promote chemical interaction between the metal phases and produce compounds with layered atomic structures with a lower shear stress than the pure metals or their oxides, resulting in a reduction of the friction coefficient to less than 0.2 from 25-700°C and potentially higher temperatures. Multilayered coatings consisting of pure ceramic and metal adaptive lubricant layers separated by diffusion barriers to inhibit segregation and oxidation of the buried lubricant material allowed adaptation in those layers to oc cur only upon exposure by wear, which resulted in longer wear lives both at static temperatures and over multiple thermal cycles. Further studies of the multilayered coating architecture described above were carried out to demonstrate a novel in situ wear measurement and failure warning system consisting of buried layers known to produce distinctive luminescence spectra when exposed to laser illumination and located at different depths throughout the thickness of the solid lubricant coating. One example employed erbium- and samarium-doped (1 at. %) yttria stabilized zirconia (YSZ) films as sensor layers. The YSZ-Er material was placed approximately midway through an adaptive coating, and the YSZ-Sm layer was located at the coating/substrate interface. Placement of the luminescent coatings in these positions allowed detection of wear depth and provided a clear warning of impending coating failure during testing. With the wear detection system in place, luminescence spectroscop y was also performed in situ on high temperature sliding interfaces to allow identification of the onset and mechanisms of changes in surface chemistry at elevated temperature during sliding without artifacts introduced by chemical reactions and crystal growth during cooling after testing and prior to analysis. This technique also provided a means of identifying the role of sliding in altering surface chemistry.
3:10 PM		E1-2-8 Optimization of the Coating Parameters for Micro Arc oxidation of Cp-Ti Y. Vangolu, A. Alsaran, E. Arslan, Y. Totik (Ataturk University, Turkey) TiO₂ coatings were formed on the surface of CP-Ti by AC pulse micro arc oxidation. The structural, mechanical, tribological and corrosion properties were analyzed by using XRD, SEM, microhardness tester, surface profilometer, pin-on-disk tribotester and electrochemical polarization unit. Voltage, electrolyte components, concentration, frequency and duration time were chosen as the coating parameters and three levels for each parameter were determined. By determining the wear, surface hardness and corrosion behaviors, the optimum working conditions were determined by using a Taguchi design of experiment. After micro arc oxidation, the aim is to minimize the friction coefficient, the wear rate and the corrosion resistances and to maximize surface hardness after micro arc oxidation. While the optimum conditions were determined, due to existance of more than one goal, a trade-off among goals was considered. First of all, each goal was optimized separately, and then all the goals were optimized together, considering the priority of the goals. Keyword: AC pulse micro arc oxidation, Taguchi method.
3:30 PM		E1-2-10 Effects of Sicking-Sliding Zones on the Tool Wear and Coating Delamination When Machining Hard Materials S. Bahi, A. Moufki, M. Nouari (Ecole Nationale Supérieure des Mines de Nancy, France); M. El Mansori (Arts et Métiers Paristech, France); A. Molinari (Ecole Nationale Supérieure des Mines de Nancy, France) To minimize tool wear and coating delamination processes, it is necessary to understand the nature of interactions between chip flow, tool and coating materials. In this paper, a hybrid analytical-numerical approach is performed for the orthogonal cutting process. The modelling of the thermomechanical material flow in the primary shear zone, the tool-chip contact length and the sliding-sticking zones is obtained from an analytical approach. In addition, the Finite Element method is used to solve the non linear thermal problem in the chip. At the chip-tool interface, the friction condition can be affected by the important heating induced by the large values of pressure and sliding velocity. In spite of the complexity of phenomena governing the friction law in machining, a reasonable assumption is to consider that at the sliding zone the mean friction coefficient is primarily function of the average temperature at the tool-chip interface. The objective is to propose an ap proach which can easily be used to identify the main parameters governing tool wear and to explain the experimental trends. The effects of cutting conditions and material behaviour on the sliding-sticking zones and on the temperature distribution along the tool-chip interface are evaluated. It has been found that the sliding-sticking zones at the tool chip interface strongly control the local conditions of stress, velocity and temperature. Experimental analyses of the sticking-sliding zones and their evolution at the tool-chip interface have been used to identify tool wear modes and coating delamination process for different cutting conditions. A qualitative comparison between the model and the experimental results is also provided.