Papers

AVS2001 Session TR-ThM: Tribological Surface Engineering for Lubrication & Wear Resistance

Thursday, November 1, 2001 8:20 AM in Room 132

Thursday Morning

Start	Invited?	Item
8:20 AM		TR-ThM-1 Tribological Surface Engineering for Lubrication and Wear Resistance L.E. Seitzman (Caterpillar Inc.) Tribological Surface Engineering is the art of modifying a materials surface or near-surface by some means in order to achieve a desired friction or wear response of the material. One method available to surface engineers involves the application of metallurgical coatings, grown by one of several plasma-assisted vapor deposition processes. Such metallurgical coatings, usually only a few micrometers thick, have been used to improve the performance of cutting and forming tools and dies for many years. More recently, these coating have been successfully applied to mechanical components in order to extend life or to increase productivity of machines. The performance of the coatings depends on a number of factors, including chemistry, microstructure, surface texture and, of course, adhesion. We will illustrate some of these dependencies for coatings subjected to sliding. As a general rule, metallurgical coatings that provide the best friction reduction exhibit short wear life, and coatings with long wear life rarely reduce friction. The reason for this dichotomy and how it provides direction for the R&D community will be discussed.
9:00 AM		TR-ThM-3 Optimization of Wear-resistant Coating Architecture using Finite Element Analysis T.Z. Gorishnyy, M.S. Aouadi, L. Olson, S.L. Rohde (University of Nebraska - Lincoln) Chromium nitride based single layer, bilayer and multilayer coatings were deposited by unbalanced reactive magnetron sputtering on A2 steel and aluminium substrates. Their wear rates were measured using pin-on-disk testing under normal loads of 4 N and 10 N for Aluminum and A2 steel substrates respectively. Finite element analysis (FEA) was utilized to investigate stress distributions in film-substrate systems under conditions, which related to those of the actual wear tests. Two-dimensional asymmetrical models were created for every coating-substrate architecture tested. The FEA results were compared with analytical solutions for Hertzian contacts with and without frictional effects. A good fit was observed. Fracture mechanics in conjunction with FEA data was used to interpret differences in wear rates for different samples. The following possible causes of fracture were considered: (1) failure in individual layers; (2) delamination of multilayered films due to high in-plane interfacial stresses; (3) failure due to crack propagation at film-substrate interface and (4) failure as a result of film buckling.
9:20 AM		TR-ThM-4 Solution-Assisted Tribological Modification of Surfaces Using an Atomic Force Microscope R. Hariadi, S.C. Langford, J.T. Dickinson (Washington State University) When a surface is subjected to tribological loading, bonds experience time dependent distortions and spatial deformations. In the presence of simultaneous chemical stimulation (e.g., from a solution), this can lead to bond breaking, bond formation, and nuclear rearrangement. We present new studies of combining mechanical and chemical stimuli in model tribological and structural systems, particularly under conditions of solution supersaturation. Thermodynamically, the system tends towards deposition or crystal growth; we show that nucleation and growth on the surface can be controlled on the nanometer size scale using simultaneous mechanical stimulation with an AFM tip. New details of this process are presented with strong support of suggested models using analysis of small perturbations in the frictional force. Careful analysis of the"noise" in the cantilever motion during contact scanning shows that on single crystal surfaces we are very sensitive to the presence of sub-critical cluster formation and re-dissolution, we find that the amplitude of the noise increases by factors of 2-4. We take this as indirect evidence for the presence of these precursors to recrystallization. Furthermore, rich noise spectra are observed on crystal surfaces with low symmetry when one changes the scan directionâ€”we observe modulated signals at frequencies corresponding to calculated times between asperity-lattice row encounters. Again, under supersaturation, the noise levels rise in comparison with pure solvent. Finally, we present structures and surface modifications that can be induced by these mechanical/chemical synergisms.
9:40 AM		TR-ThM-5 Low Frictional Force Coating of Boron Nitride - Copper Complex for Ultra High Vacuum by Magnetron Co-sputtering Technique M. Goto, A. Kasahara, M. Tosa, K. Yoshihara (National Institute for Materials Science, Japan) Boron nitride - copper complex (BN/Cu) coating films were synthesized by a magnetron co-sputter technique. The characteristics of the films such as surface energy, internal stress, surface morphology, elements configuration and adhesion force were measured. Frictional force of the coating films was also measured with a self-made vacuum-friction measuring system from an atmospheric pressure to the pressure of 10-7 Pa. Frictional coefficients of the BN/Cu films as low as 0.1 is achieved in UHV region. It was found that the mixture structure of boron nitride with copper formed under different discharge time was most effective to change the frictional force. This technique is applicable to produce low-frictional force materials for ultra high vacuum system.
10:20 AM		TR-ThM-7 Aging Evaluations of MoS₂-Containing Lubricants¹ D.E. Peebles, M.T. Dugger, W.F. McNamara, J.A. Ohlhausen, E.H. Sorroche (Sandia National Laboratories) Many solid film lubricants and self-lubricating materials utilize MoS₂ as the active lubricant phase. Oxidation of MoS₂ produces MoO₃ and surface sulfate species, which do not possess the same lubrication properties as MoS₂. However, the rate and mechanism for oxidation of MoS₂ is a strong function of the surrounding matrix material and the ambient oxidizing species. This work will review aging studies that have been performed for materials containing MoS₂ particles in polyimide and epoxy resin matrices. This work will illustrate the aging process from the viewpoint of chemical and performance modifications as a function of oxidation in a variety of atmospheric environments. Evaluations of the chemical state of the lubricant material are assessed by detailed surface chemical studies by x-ray photoelectron spectroscopy, while lubricant performance is assessed by pin-on-disk testing. The understanding of lubricant aging mechanisms obtained from these studies is being used to develop age-aware performance models for electromechanical devices. ¹Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.
11:00 AM		TR-ThM-9 Diamond-Like Carbon Nanocontacts R.W. Carpick, J.R. VanLangedon, E.H. Wilson, K. Sridharan (University of Wisconsin - Madison) Wear-resistant low-friction coatings are of interest for a variety of applications from automotive engines to sub-micron machines. One particularly important coating is diamond-like carbon (DLC), which can possess mechanical properties approaching those of diamond. We have used atomic force microscopy to study the nanotribological properties of DLC as a function of preparation to investigate the mechanisms that underlie ultralow friction and wear. Furthermore, we have fabricated nano-asperities by coating the tips of atomic force microscope cantilevers with DLC. The unique coating process, plasma-source ion deposition, produces a high-quality conformal coating of DLC. By placing this asperity in contact with a DLC-coated substrate, we are able to measure, for the first time, the mechanical and frictional properties of DLC/DLC interfaces at the nano-scale. We will discuss the fundamental relations governing friction for this interface.