Papers

ICMCTF2002 Session E3-1: Coatings Resistant to Severe and Unusual Environments

Wednesday, April 24, 2002 8:30 AM in Room California

Wednesday Morning

Start	Invited?	Item
8:30 AM		E3-1-1 Friction and Durability of Monolayer Lubricants for MEMS in Harsh Environments M.T. Dugger (Sandia National Laboratories) Recent developments in surface micromachining (SMM) have resulted in microelectromechanical systems (MEMS) containing actuators, counter-meshing gears and other moving mechanisms that have complex tribological interfaces. Structures with high out-of-plane stiffness can now be fabricated that are much less susceptible to in-process adhesion than previously possible. However, efficient operation of devices with sliding contacts requires surfaces that are tailored to deliver adequate friction and wear performance. Alkylsilane monolayers represent a popular class of lubricants for silicon devices. There has been some research to understand the performance of alkylsilanes as a function of the amount of water vapor in the environment, but the behavior of these surface treatments during and after exposure to harsh environments has not been investigated. In particular, there is a need to investigate quantitatively the effects of harsh environments on the performance of SMM interfaces, rather than simply verifying device functionality. One focus of our research is the development of SMM structures that contain isolated tribological contacts from which quantitative friction forces may be extracted. We use these structures to investigate interface performance and failure mechanisms. Micromachine friction measurement techniques have been used to investigate the performance of alkylsilane monolayers in inert environments, and after exposure to a variety of thermal and radiation environments. Methods of quantifying static and dynamic friction in surface micromachined contacts will be presented. The effects of operating environment and exposure to radiation and thermal treatments on friction and wear in SMM contacts will be discussed.
9:10 AM		E3-1-3 Impact of Variable Loading Conditions on Fretting Wear T. Liskiewicz (University of LODZ, Poland); S. Fouvry (Ecole Centrale de Lyon, CNRS, France); B. Wendler (University of LODZ, Poland) Different kinds of damages have been observed depending on the loading conditions in many engineering situations. The determination of the impact of variable loading conditions allow to predict the material response and the wear rate. Numerous studies have been undertaken to understand the damage created by fretting regime. Some papers explain influence of wide range of displacement amplitude on the wear behaviour. Nevertheless there is no knowledge on materials wear resistance under disproportional amplitude conditions. In this paper, a comparison between variable and constant loading conditions is developed. Energy aspect is one of the main factors that control the wear phenomena. Considering this fact the wear analysis has been quantified using an energy approach linking the total wear volume with the dissipated energy during the fretting cycle. To quantify the impact of disproportional loading, a local dissipated energy approach has been developed and transposed. The wear depth extension is related to the cumulated density of friction work dissipated during the test. Those theoretical results are compared with results obtained for TiC coating deposited on high-speed steel. A ball-against-flat specimen arrangement has been analyzed.
9:30 AM		E3-1-4 ESD Coatings on Small Caliber Gun Barrels C.J. Lindsay (Advanced Surfaces and Processes, Inc.); L. Smeriglio (US Army ARDEC); M. Riley (Surface Treatment Technologies, Inc.) Electro-Spark Deposition (ESD) offers a unique alternative to hard chrome plating currently used for wear and corrosion resistance on the bores of many military small caliber gun barrels. ESD is a micro-arc welding process that uses short duration electrical pulses to deposit a thin layer of electrode material onto metallic substrates. The ESD process, unlike other conventional coating processes, is applicable on small IDâ€™s, creates little or no heat affected zone (HAZ), is environmentally benign and produces a metallurgically bonded coating. The metallurgical bond allows the coating to be formed to a final shape post-application, a key benefit for forming the rifling of the gun barrel. Although the ESD process utilizes a wide range of electrically conductive materials, the primary focus for the development of a wear and corrosion resistant coating included cobalt, nickel and tantalum based materials. This report details the development, manufacturing and testing processes associated with the application and verification of ESD coatings on small caliber gun barrel bores.
9:50 AM		E3-1-5 Reduction of Tool Wear in Metal Cutting Using External Electromotive Sources M El Mansori (LMPF, France); D. Paulmier (ERMES Group, France) Metal cutting is the process of shaping materials into finished products by removing excess material. The removal of unwanted material involves physical contact between cutting tool and the processed material with attendant friction and wear. Excessive wear imposes limits on the efficiency of cutting tools and their subsequent loss of function. Friction and wear control is, therefore, critical to the success of materials cutting process. The most well established methods to achieve this are based either on process optimization, application of lubricant or use of surface coatings to provide wear resistant and low friction coatings. Nevertheless, improved performance of cutting tools to give lower wear and extended tools lifetime can be accomplished by making use of favorable effect of external electromotive force (EMF) sources ( e.g. magnetic filed ) on friction and wear This paper is intended to highlight this trend in the area of cutting processes@ Thus firstly substantial results of studies concerned with the mechanisms of the action of EMF sources in magnetized sliding contacts (MSC) are discussed. Then various applications for turning and drilling processes are comprehensively presented.}sd
10:10 AM		E3-1-6 Some New Perspectives on Gun Bore Erosion Mechanisms Using Laser Pulse Heating P.J. Cote, G. Kendall, M. Todaro, M. Witherell (Benet Laboratories, Watervliet Arsenal) Prior work¹ has shown that laser pulse heating can reproduce many of the important degradation effects at chromium coated gun bore surfaces. Among these effects are recrystallization and grain growth in the chromium, development of major cracks in the chromium, development of a heat-affected zone in the substrate steel, and rapid oxidation of the steel at the chromium crack tips. The present report describes further studies using the laser method to include cyclic thermal pulsing under controlled atmospheres of air, argon, oxygen, nitrogen, and hydrogen. The observed features relate to surface roughening, melting, surface cracking (heat checking), interface degradation, and high temperature gas-metal reactions. Computer modeling of the laser pulse process was performed for the specimen configuration used in these experiments. Comparisons of laser pulse heating experiments on uncoated and coated steel with data from damaged surfaces of fired gun barrels offer several new perspectives on gun bore degradation mechanisms. ¹ . P.J. Cote, G. Kendall, M. Todaro, Proceedings of ICMCTF 2001, April, 2001, San Diego, CA.
10:30 AM		E3-1-7 Corrosion Behaviour of Amorphous Al-Cr and Al-Cr-(N) Alloys Deposited by dc Magnetron Sputtering on Mild Steel Substrate. F. Sanchette (CEA Grenoble, France); J. Creus (Universite de La Rochelle, France); V. Benevent (CEA Grenoble, France); A. Billard (Ecole des Mines de Nancy, France) Physical vapour deposition (PVD) Al alloys films are potential alternatives to conventional electrochemically deposited coatings for sacrificial protection of steel substrates. Even though the structure-mechanical relationships have ever been studied for Al-Cr or Al-Cr-(N) coatings, there is no published data on the corrosion behaviour of these alloys deposited on mild steel substrates. Al-Cr or Al-Cr-(N) coatings were deposited by dc magnetron sputtering of Al-Cr large size targets with different Ar-N2 mixtures in an industrial PVD system. In this paper, the influences of both chromium and nitrogen contents on the substrate/coating galvanic coupling behaviour in 3%NaCl solution are studied. In a general way, only single-phased amorphous films have been synthesized and the microhardness can reach about 9 GPa. The results of electrochemical tests are discussed and linked to coatings composition. It is shown that 20 at% chromium in Al-Cr coatings is the limit above which galvanic corrosion of steel substrates occurs. Nitrogen incorporation seems to influence the coatings passive layer and favours its pitting resistance. The salt bath results (more than 800 hours without corrosion for Al-Cr 18at%Cr) are in agreement with electrochemical behaviours. The effect of a plasma polymer top layer to prevent galvanic coupling at the growth defects has also been investigated.
10:50 AM		E3-1-8 Corrosion Behavior of Unbalance Magnetron Sputtered TiN Films on 304 Stainless Steel G.P. Yu (National Tsing Hua University, R.O.C.) Titanium nitride (TiN) was deposited on AISI 304 stainless steel using an unbalance magnetron sputtering (UBM) technique. Corrosion behavior of the TiN-coated stainless steel was studied on the specimens with controlling TiN film thickness. After deposition, the thin film structure was characterized by X-ray diffraction (XRD) and field-emission-gun scanning electron microscopy (FEG-SEM). The composition depth profiles of TiN films were determined using a secondary ion mass spectrometer (SIMS). The N/Ti ratios were measured using both X-ray photoelectron spectrometer (XPS) and Rutherford backscattering spectrometer (RBS). From the results of RBS, packing factors of the TiN films can be obtained. An atomic force microscope (AFM) was used to measure the roughness of the thin films. The corrosion resistance was evaluated by standard salt spray test, and by potentiodynamic polarization scan of the specimens in 1N H2SO4 + 0.05M KSCN solution. The surface morphology of the specimens after corrosion tests was observed using both FEG-SEM and optical microscope. The corrosion resistance was correlated to film thickness, packing factor, and thickness Ã— packing factor. There is a good agreement between the results of salt spray test and potentiodynamic polarization scan. There is a critical film thickness observed, as the film thickness is smaller than the critical thickness, the corrosion current density increased abruptly. It is also found that the value of thickness Ã— packing factor is larger than a critical value, there is only minor increase in corrosion resistance for the TiN coated specimen.
11:10 AM		E3-1-9 Performance of Nanoscale CrN/NbN PVD Coatings on Mild Steel in Various Corrosion Tests T.J. Savisalo, R. Akid, W-D. Münz (Sheffield Hallam University, United Kingdom) The influence of the thickness of a metallic Nb barrier layer on the corrosion performance of CrN/NbN PVD coatings on mild steel substrates was studied comparing different corrosion measurement techniques. Potentiodynamic polarisation tests were considerably affected by the local defects inherent to the PVD coatings. When small measuring area was used the random distribution of the defects caused considerable variation with in the results measured from the same sample. Larger measurement area reduced the variance producing more reliable results. CrN/NbN coatings themselves showed considerably electrochemical stability when an inert Ta substrate was used. Linear Polarisation Resistance technique was shown to be effective in determining the corrosion rate of the coating/substrate system. Since the test does not use external potential to speed up the corrosion, the results are more representative of the real corrosion performance of the coating. This can be seen by comparing the results with the visual inspection and salt spray tests. We also experienced better sensitivity and less variance than with salt spray tests. Open potential measurements correspond well with the LPR results. AC-impedance can be used to determine corrosion mechanisms. This measuring technique was used to distinguish the effect of diffusion through the minute pores, inherent to most PVD coatings, from other electrochemical reactions in the system. This technique should be used with care due to the uncertainties in the interpretation of the results.
11:30 AM		E3-1-10 The Tribological Performance of Ultra-Hard Ceramic Composite Coatings Obtained Through Micro Arc Oxidation L. Ramakrishna, K.R.C. Somaraju, G. Sundararajan (International Advanced Research Centre for Powder Metallurgy and New Materials, INDIA) Micro Arc Oxidation (MAO) also called Plasma Electrolytic Oxidation (PEO) and Spark Anodisation (SA) is an emerging coating technology capable of producing thick, ultra hard coatings on alloys of Al, Ti, Mg and Zr. The MAO is also an environmentally friendly coating technique. A MAO coating unit, designed and built by the authors, has the capability to deposit dense Al₂O₃ based coatings up to 100 µm thick on a variety of Al alloy substrates/components. In the present work, an Al-7075 alloy has been chosen as the substrate and the influence of process parameters such as current density, electrolyte temperature and inter-electrode distance on the kinetics of the ceramic layer growth has been studied. Simultaneously, the evolution of coating roughness, hardness and phase distribution during the course of the coating deposition has also been investigated. The above results have been utilized to understand the mechanism of coating formation during the MAO process. The tribological performance of the ceramic coated Al-7075 samples has also been evaluated and compared with the performance of detonation sprayed Al₂O₃ coatings and also cold isostatically pressed and sintered high purity alumina. In particular, pin-on-disc sliding wear test (with SiC as the disc and MAO coated pins), dry sand abrasive wear test (with SiO₂ and SiC as erodent) have been carried out. The results of the above study will be presented and a correlation between the mechanical and structural properties of the MAO coatings and their tribological performance will be attempted.
11:50 AM		E3-1-11 Composite Bearing Based on Metal - Polymer - Soft Metal - Ceramics Composition M.V. Kireitseu (Institute of Machine Reliability, Belarus) To improve customer properties it has to develop and to use new composite sliding bearing. In the paper developed composite bearing like alumina-aluminum-polymer-steel substrate have been investigated. Both Al and polymer layers were produced by thermal flame spraying process because by this processing the layers reshape the surface profile reaching strong adhesion. Finally, Al layer was transformed into alumina by micro arc oxidizing process. Study of technological aspects reveals semi-empirical relations to calculate thickness of Al and polymer layers of composite bearing providing rational balance between strength and adhesion. An analysis of structure and porosity in depth of alumina revealed that the structure of the layer contains α, γ phases of aluminum oxides, porosity ranges in 5-11 %. Microhardness of the layer reaches 12-15 GPa, that is very high result to be achieved for alumina layer on sprayed aluminum in contrast to traditionally produced on cast aluminum alloys. Applied soft intermediate composite layer of aluminum and polymer provide both rigid and adaptive structure of the composition that, however, is deformed under applied load, but preventing the hard coatings from ultimate failure. In result, the composition has both strength and ability to adapt under applied localized contact pressure and sliding speed while friction. The frictional behavior of the bearing composition and the same but hardened by CrC have been reviewed. It was found that CrC-alumina prevents significant increase in coefficient of friction during initial sliding and it stabilizes process of friction while the work.