ICMCTF1999 Session EP: EP Poster

Wednesday, April 14, 1999 5:00 PM in Room Atlas Foyer
Wednesday Afternoon

Time Period WeP Sessions | Topic E Sessions | Time Periods | Topics | ICMCTF1999 Schedule

EP-1 Study of r.f. PACVD Diamond-like Carbon Coatings for Space Mechanisms Applications
K. Vercammen, J. Meneve, E.H.A. Dekempeneer (Vlaamse Instelling voor Technologisch Onderzoek - VITO, Belgium); E.W. Roberts (AEA Technology, United Kingdom); M.J. Eiden (European Space Agency, The Netherlands)

The interest in advanced solid lubricant coatings is growing steadily since these materials are able to offer unique combinations of low contact friction and an extended lifetime of the friction couple. This is particularly true for space mechanisms applications, where the use of fluid lubricants is often inadvisable due to losses by evaporation and creep, and the consequent possibility of contamination.

Diamond-like carbon films form an important class of advanced solid lubricant coatings. Since the earliest investigations it was shown that this material could exhibit low friction under vacuum conditions, but in other cases, however, high friction in vacuum was observed. This diversity in results is not surprising since diamond-like carbon represents in fact a wide range of carbon based coatings deposited by a variety of techniques. In this work, the tribological properties in vacuum of a-C:H films produced by RF plasma assisted chemical vapour deposition (RF PACVD) were studied. It was demonstrated that such films deposited at low RF bias voltage show lubricating capacity under vacuum conditions. However, the wear resistance in vacuum of currently used sputtered MoS2 coatings has yet to be achieved.

EP-2 Experimental Study and Numerical Modeling of the Nickel Oxide Coating on the Ni(111) Surface
N. Vallino, L. Gaillet (University of Compiegne, FRANCE); L. Lahoche, V.L. Lorman (University of Amiens, FRANCE); G. Moulin, J.M. Roelandt, M. Viennot (University of Compiegne, FRANCE)

The evolution of the nickel oxide coating developed on the monocrystalline Ni(111) surface was studied both experimentally and by means of numerical modeling. The NiO/Ni system was submitted to a high temperature creep in the oxygen atmosphere. Using O18 diffusion method we were able to observe several deformation modes (diffusional creep, gliding at the interfaces,etc.) and periodic cracks generation perpendicular to the charge application direction. The periodicity of the cracks array depends strongly on the external stress applied to the oxide scale. Two steps numerical modeling of the process was performed using first a simplified 1D model and then the 2D finite elements approach. Modeling procedure takes into account epitaxial deformations due to the scale ordering and to the mismatch of the lattice parameters1, the growth process and the periodic cracks generation. Identification of the visco-plastic material law permits then to obtain the strain (and the stress) distribution in the scale and in the substrate. The comparison of the experimental data with the numerical results allows to formulate several criteria for the oxide scale adherence.

1 Lahoche L. et al, ICMCTF 98, to be published in Surf. Coat.Technology

EP-3 Tribological and Mechanical Properties of Carbon Nitride Films Deposited by Ionised Magnetron Sputtering
Y. Kusano, Z.H. Barber, J.E. Evetts, I.M. Hutchings (University of Cambridge, United Kingdom)

Tribological and mechanical properties were evaluated for carbon nitride films deposited by an ionised dc magnetron sputtering system under various conditions. Inductive plasma was generated between a graphite target and substrates.

Friction measurements were carried out on the films in ball-on-rotating disc tests in laboratory air at room temperature. The mean coefficient of friction was obtained after an initial run-in period. Steady-state coefficients of friction observed were between 0.44 and 0.81 with the inductive plasma, and between 0.36 and 0.60 without the inductive plasma. In each case, the values increased with increasing nitrogen partial pressure in the sputtering gas and then approached a constant value.

The films deposited at a pressure of 2.0 Pa tended to be detached from the substrates more easily than those deposited at 5.0 Pa. The stress and hardness of the films were evaluated and discussed together with the structure and adhesive properties of the films.

EP-4 XPS Study of TiN and Ti+TiN+TiNC Films Deposited by Controlling Feed Gas Flowing Rate
L. Li, L. Xia, X. Ma (Harbin Institute of Technology, P.R. China); Y. Sun (Harbin Institute of Technoogy, P.R. China)
The TiN and Ti+TiN+TiNC films were deposited using filtered vacuum arc deposition apparatus without additional anode ring. N2 . XPS multiplex studies show that an obvious shift of their Ti2p3 peak occurs. Ti+TiN+TiNC films were got by controlling the gas inlet order and the gas flowing rate, a steady increasing of C2H2 gas accompanying with steady decreasing of N2. XPS study showed that the content C was not direct proportion to the increasing of component pressure of C2H2. A small component of N2 gas can prevent the composite of C and Ti effectively.
EP-5 Synthesis of CrC Hard Coatings for Tribological Applications
D.Y. Wang, C.L. Chang (National Chung Hsing University, Taiwan, ROC); K.W. Wong, S.Y. Hwang (National Chung Hsing University); W.Y. Ho (Surftech Corp., Taiwan, ROC)
PVD Coatings such as TiN and CrN have been successfully applied to metal forming industries for their advanced wear improvement. The metal pick-up and sticking problems in certain deep drawing and plastic injection molding processes, however, demand more sophisticated tribological thin films to cope with. In this study, CrC hard coatings synthesized by PVD process were investigated for potential applications in forming and molding operations. CrC thin films of 3-5 ƒÝm in thickness were deposited with both cathodic arc evaporation and unbalanced magnetron sputtering to ensure superior adhesion at interface. Influences of deposition parameters on microstructure and mechanical properties were analyzed by XRD, SEM/EDS, TEM, Vickers Tests, and Tribo-tests. Results indicated that CrC outperformed hard chrome plating and PVD CrN coatings in sliding wear resistance, owing to its process-improved microhardness and interface stability. For low to medium temperatures range, a CrC coating is promising for tribological applications. Details of microstructure analysis and tribological behavior will be discussed.
EP-6 Characterization of MoS2/Ti Multilayered Coatings for Atmospheric Applications
D.Y. Wang, C.L. Chang, Z.Y. Chen (National Chung Hsing University, Taiwan, ROC); W.Y. Ho (Surftech Corp., Taiwan, ROC)
Sputtered MoS2 thin films have provided lubrication and wear resistance to moving components in vacuum and space applications. When exposed to humid environments, however, MoS2 was prone to rapid deterioration by oxidation. In the study, a multilayered coating consisting of interlacing metallic titanium and MoS2 layers were synthesized by unbalanced magnetron sputtering. TEM, XRD, and Raman analysis revealed the amorphous nature of the multilayered MoS2/Ti film containing only short range orders in Ti layers. Ball-on-disk tribo-tests of MoS2/Ti films showed a trend of increased coefficient of friction, endurence, microhardness, and decreased wear debris generation with the thickness of Ti interlayer. The MoS2/Ti multilayered film with 7nm Ti interlayers showed a significant improvement in oxidation resistance, which was attributed to the effective diffusion control of oxygen into MoS2 layers. The interruption of the MoS2 thickness also prohibited the MoS2 from growing into the typical interweaving open structure, which is susceptible to oxidation attack in humid environments. The wear life of Ti modified MoS2 lasted five times more than that of pure MoS2 thin films. This results is reduced the oxidizing reaction of multilayer of MoS2/Ti films.
EP-7 Mechanical and Tribological Properties of CNX Films Deposited by Reactive Magnetron Sputtering
E. Broitman, N. Hellgren (Linköping University, Sweden); O. Wänstrand (Uppsala University, Sweden); M.P. Johansson, T. Berlind, J.-E. Sundgren (Linköping University, Sweden); M. Larsson (Uppsala University, Sweden); L. Hultman (Linköping University, Sweden)

Carbon nitride (CNX) films were deposited by dc reactive magnetron sputtering from a C target in N2/Ar plasma. Films were grown on Si (001), Ni, and steel substrates to thickness of ~1 µm at a constant total pressure of 2.5 mTorr with the N2 fraction varied from 0 to 1, and the substrate temperature, TS, varied from ambient to 500 °C. The influences of the N2/Ar mixture and TS on the surface roughness, hardness, elasticity, adhesion, residual stresses, wear and friction coefficient of CNX films of known microstructure and composition are presented.

The mechanical and tribological properties of the coatings were evaluated by nanoindentation, laser-induced ultrasonic surface waves method, scratch testing, substrate curvature technique, and pin-on-disk test.

We have shown earlier that TS < 200 °C results in an amorphous phase with properties that are practically not affected by the N concentration. For TS > 200 °C, a transition from a graphite-like to a fullerene-like phase was observed with N incorporated in the film.

For CNX (0X (0S = 350 °C, where a transition from graphite-like to fullerene-like occurs, a dramatic increase in hardness, elasticity and stresses is observed. Furthermore, the rms roughness decreases from 15.0 to 0.4 nm and the film exhibits anisotropic properties. For CNX (0.15S = 350 °C, the fullerene-like phase exhibits high stress levels up to -5 GPa, hardness and elasticity, the latter reaching 90% recovery; the friction coefficient is ~0.2 and the film shows a smooth surface.

EP-8 Damage of Carbon-carbon Composites Surface Under High Pressure and Shear Strain
M. El Mansori, A. Samah, D. Paulmier (ERMES-LPMM CNRS, France)

Under the influence of high contact pressure the tribological performances of the carbon-carbon composite materials essentially depend on the carbon fibres texture and on the properties of the transferred layers.

In this study, employing a combination of scanning electron microscopy and energy dispersive X-ray spectroscopy, the authors explored the friction tracks properties and described the role of the transferred layers in friction and wear of copper/carbon-carbon composite couples in open air of 20-30% relative humidity at room temperature.

Tow multidirectional carbon fibre reinforced carbonaceous matrix material were investigated.

One of the tested composites is based on three directional (3-D) construction consisting of multiple yarn bundles located within the structure with a mail texture, the other is a 2-D array with a taffeta texture.

The results of the tribological tests indicated that the friction coefficient and wear rate decrease when the carbon fibres exhibits a mail texture.

For a 2-D carbon-carbon composite, the contact surface has a rough appearance and fibre surfaces are marked with wear grooves.

Patch of scattered wear debris and worn fibres with longitudinally oriented structure are clearly visible on the contact surface.

The matrix carbon appear to be covered by a very granular layer constituted by a mixture of copper oxide and copper particles as revealed by E.D.S analysis.

The friction track of 3-D carbon-carbon composite is covered with a layer of debris film-like structure

Again, the wear grooves on the carbon fibres are observed.

However, these wear grooves are relatively narrow and shallow compared with the grooves observed on the surface fibre of a carbon-carbon composite with a taffeta texture, which means that the wear rate is lower in this case.

EP-9 Plasma Electrolytic Deposition for Surface Engineering
X. Nie (University of Hull, United Kingdom); A.L. Yerokhin (Tula State University, Russia); A. Matthews, A. Leyland (University of Hull, United Kingdom); S.J. Dowey (Ion Coat Ltd, United Kingdom)

Plasma Electrolytic Deposition (PED) is based on the deposition and modification effects of an electric spark or arc discharge on the surface of an electrode immersed in an appropriate electrolyte. Although the discharge phenomena associated with electrolysis were discovered a century ago, studies of potential industrial applications of PED have been carried out only in the last 20 years, In particular, Micro-arc Discharge Oxidation (MDO) deposition onto aluminium and titanium alloys and Micro-arc Plasma Diffusion (Nitride/Carbide/Boride) treatment of steels have been reported. The results of recent scientific studies are reviewed in this paper, including the physical and chemical fundamentals of plasma electrolysis, the equipment and deposition procedures for coating production as well as the effects of the electrolyte. The metallurgical and tribomechanical characteristics of coatings or layers formed by PED techniques are also described.

Micro-arc discharge oxidation operates at a potential above the breakdown voltage of the oxide film growing on the surface of an aluminium (or other light alloy) workpiece, which forms the anode of the electrolytic system. Complex compounds are synthesised inside high voltage breakthrough channels across the growing oxide layer and the coating growth proceeds in both directions from the substrate surface (i.e into the substrate and out from the surface). Micro-arc oxidation of aluminium allows the formation of thick (up to 500µm) and hard (up to 23GPa) surface layers with excellent adhesion to the substrate, by the use of pulsed DC (or AC) power supplies and a suitable aqueous electrolyte. Micro-arc Plasma Diffusion (MPD) is carried out at a potential above the breakdown voltage of the gas bubbles formed on the surface of the workpiece, which in this case forms the cathode of the system. The localised plasma thus created provides reactive and diffusive elements for the substrate and provides intense localised heating of the workpiece. This paper describes 10-20µmthick surface compound layers (1200HV) and 200-300µmdiffusion layers can be produced on steel substrates with excellent mechanical and chemical properties in only 3-5 minutes of treatment by use of MPD nitriding/carburising treatments.

EP-10 Non-Destructive Mechanical and Optical Characterization of Ultra-Thin Films
B. Schoeneich, B. Schultrich, D. Schneider (Fraunhofer Institute for Material and Beam Technology, Germany)
Non-destructive mechanical and optical characterization of ultra-thin films The mechanical properties of ultra thin films in the range of ten nano-meters or even below are of growing interest. Such films include single layers, e.g. for wear protection in thin film heads and multi-layer stacks as well. The reproducible preparation of such films is a high challenge and requires test methods to characterize and to optimize the film quality. In particular, reliably measuring mechanical test parameters, as hardness and Young's modulus of such thin films is still difficult. The laser-acoustic technique based on surface acoustic waves technique is now well established for testing films with micron and sub-micron thickness by measuring the Young's modulus of the film material. The method is shown to may be applied for testing diamond-like carbon films on silicon with thickness less than 10 nm. The films were deposited by a pulsed-arc technology and showed film moduli from 450 to 500 GPa. Stacks of alternating nano-meter layers can also be tested, if they consist of two components. The elastic behavior of one component can be determined, if that of the other one is known. The optical properties of ultra-thin films can be investigated by spectral ellipsometry. Based on TEM supported models, it even allows a quantitative estimation of nano-structured films. The potential of these methods is demonstrated for the characterization of ultra-thin carbon films with different bonding states and different nano-structure.
EP-11 Triode Discharge Assisted Plasma Immersion Ion Implantation Surface Treatment of Cobalt-chromium Alloys
A.D. Wilson, A. Leyland, A. Matthews (University of Hull, United Kingdom)

Biomedical materials generally require good wear resistance and good high cycle fatigue properties. Cobalt-chromium alloys have good corrosion resistance, high strength and surface hardness. However like-against-like sliding contacts under severe sliding wear conditions are prone to adhesive and abrasive wear (hard surface particles are broken off and act as a third-body abrasive.

Plasma immersion ion implantation (PI3) provides a non-directional method of implanting ions into materials using a low temperature plasma. A cathode sheath forms around the workpiece and, by superposition of high voltage pulses, ions from the plasma are accelerated towards the workpiece surface and implanted to shallow depths. Implantation occurs across the whole of the target geometry, alleviating the need to manipulate as in conventional ion beam processes.

In this study triode plasmas were employed with a hot negatively biased tungsten filament providing thermionic-electron plasma support. Low pressure plasmas (5-10mTorr) containing nitrogen and carbon were produced, and pulsed negative bias voltages of between 5 and 20kV (with a varying HV pulse frequency of between 0.1 and 1kHz) were applied to the alloy. Evaluation of the implanted samples by XRD, microhardness testing and dry sliding wear (pin-on-disc) was performed to assess the influence of gas pressure, bias voltage and pulse frequency on treatment effectiveness.

EP-12 The Influence of Nitrogen Based Triode Plasma Treatments Compared to PVD TiN, CrN Duplex Coatings, and Ion Implantation on the Dynamic impact and Abrasove Wear Resistance of Ti-6Al-4V
A.D. Wilson, A. Leyland, A. Matthews (University of Hull, United Kingdom)

The mechanical and tribological properties of plasma thermochemical heat treatments have been compared with PVD TiN, CrN coatings and nitrogen ion implantation of the titanium alloy Ti-6Al-4V using a rubber-wheel-type abrasion tester and a pneumatic impact tester. Using a thermionic triode plasma assisted system, a hot filament supported glow discharge was produced with different compositions of nitrogen, carbon and hydrogen for the plasma treatments (substrate temperature 700-750°C). The duplex system consisted of plasma nitriding followed by plasma-assisted physical vapour deposition (PA) PVD of TiN ("Nitron"). Two groups of nitrogen implanting regimes were chosen for the study. An increased nitrogen ion dose and higher pre-implant temperature was used, to produce a larger diffused layer of nitrogen ions into the substrate to enhance load support.

At elevated temperatures and increased process times the surface roughness of the alloy was found to increase significantly, although this roughening effect was reduced by depositing a thin titanium layer by (PA) PVD, prior to the plasma treatment. In this study we describe how it is possible to increase the substrate/surface load support with surface microhardnesses of >1500Hk and investigate this effect on the abrasion and impact resistance of the titanium alloy. The plasma diffusion treatments all increased the load support provided by the substrate but provided limited improvement in the abrasive wear resistance compared to the (PA) PVD CrN coating and the "Nitron" duplex system.

EP-13 Abrasion and Corrosion Behaviour of Micro-arc Discharge Oxidation Coatings on Aluminium Alloys
X. Nie, A. Leyland (University of Hull, United Kingdom); A.L. Yerokhin (Tula State University, Russia); A. Matthews (University of Hull, United Kingdom)
Plasma Electrolytic Deposition (PED) processes are a relatively new family of techniques by which thick ceramic oxide, nitride and carbide layers can be rapidly and cost-effectively produced on metal surfaces. One particular variant is Micro-arc Discharge Oxidation (MDO), which can be used to harden aluminium alloy parts for engine components, hydraulic and textile machinery, etc, and is also a highly promising technique for use in pumps, valves and seals, which often suffer from abrasive wear and corrosion by aggressive gases and liquids. Thus the abrasion and corrosion behaviour of MDO coatings is of increasingly significant scientific and technical interest. In this work, various MDO coatings deposited on aluminium alloy substrates were characterised by a variety of mechanical and tribological methods, including micro-hardness testing and wet/dry rubber wheel abrasive wear tests. A Solatron 1286 ECI system was employed for assessment of corrosion resistance. SEM with EDAX was employed to observe the abraded and corroded surfaces, and X-ray diffraction analyses were also performed, using a Siemens D-5000 diffractometer with glancing-angle attachment. The results indicated that MDO treated aluminium alloys can provide much higher abrasion resistance and better corrosion performance than (for example) stainless steels, whilst giving significant weight-saving benefits for practical applications.
EP-14 Influence of the Heat Treatment on the Tribological Behavior of a Ni-P-BN(h) Autocatalytic Composite Coatings
M.H. Staia (Central University of Venezuela); O.A. León (UNEXPO, Venezuela); H.E. Hintermann (University of Neuchatel, Switzerland)
Pin on disc tests have been performed in order to evaluate the influence of the heat treatment temperature on both friction coefficient and wear resistance of a Ni-P-BN(h) composite coating on a 316L stainless steel substrate. The "as deposited" samples have been heat treated for 1 hour at 200, 300 and 4000C in Argon atmosphere. X-ray diffraction analysis has been employed in order to study the phase transformations produced during heating , meanwhile the coating morphology and wear mechanism were studied by Scanning Electron Microscopy. Microhardness values for the coatings with and without heat treatment are also reported.
EP-15 Performance of a Rotating Gear Pair Coated with an Amorphous Carbon Film Under a Loss-of-Lubrication Condition
M. Murakawa (Nippon Institute of Technology, Japan); T. Komori (Kyouiku Gear Mfg, Co., Ltd., Japan); S. Takeuchi (Nippon Institute of Technology, Japan); K. Miyoshi (NASA Lewis Research Center)
The ability of gear boxes to complete their missions following the loss-of-lubrication is an important parameter in design criteria for various machines. This paper shows the results of the actual gear performance test conducted using a gear testing machine which was subjected to a loss-of-lubrication condition immediately after a short operating period under fully lubricated condition. The result showed that a gear pair subjected to an initial shot peening process and a subsequent PVD process to deposit an amorphous carbon film (WC/C film) could endure for very long before it failed or seized (more than 107 times of repeating rotational meshing) even under a very severe loading condition, i.e., under a Lloid's K factor of 4 MPa thus demonstrating the utility of gears coated with an amorphous carbon film.
EP-16 Influence of Magnetic Field on Aluminium / XC48 Tribological Behaviour
Z.H. Zaidi, A.S. Senouci (Laboratoire de Mécanique des Solides, France)

The application of magnetic field alters significantly the plastic properties of crystal and surface oxidation.

The action of magnetic field on sliding surfaces: ferromagnetic steel XC48/aluminium may cause a surface modifications and then the friction and wear behaviour modifications.

Aluminium and steel surface modifications induced by the magnetic field during sliding test are analysed and performed by Vickers Microhardness, Optical Microscopy, Scanning Electron Microscopy, EDS analysis and by the oxidation ratio measurement.

This paper presents a study of the surfaces modification, the wear and friction behaviour of aluminium in non feroomagnetic, aluminium/ferromagnetic XC48 steel sliding contact in magnetic field.

EP-17 Subsurface Stress Field Modifications Owing to the Presence of Isolated Crack in Elastically Loaded Bi-Layers : A Boundary Element Study in Ball on Flat Contact Geometry
C. Comte, R. Kouitat, J. von Stebut (Ecole des Mines, France)

The presence of pre-existing crack in a layer structure is expected to modify the subsurface contact stress field owing to elastic contact. In case of brittle failure the presence of such cracks is likely to lower the critical stress required to trigger crack propagation and/or nucleate new cracks. In the present study boundary element method is retained to model such effects. This numerical technique has been shown to be especially well adapted for modelling of contact-induced elastic subsurface stress fields. In addition, this technique is very economic in terms of required computer performance and can be easily implemented on a standard P.C..

In a first part we consider a homogeneous, isotropic solid half-space placing the crack at various depths with aH/10 < t < 3aH (aH being the hertzian contact radius). We show that for the upper limit the presence the presence of a crack has practically no effect anymore.

In a second part we consider layered composites with a coating to substrate modulus ratio of roughly 2 and the inverse situation. Here again the position of the crack is modified : within the coating, at the interface and in the substrate. The object is to show the effect of crack in relation with the unperturbed stress distribution.

EP-20 Improvement of Tribological Properties of 9Cr18 Bearing Steel Using Metal and Nitrogen Plasma Immersion Ion Implantation
Z.M. Zeng (City University of Hong Kong and Harbin Insitute of Technology, China); T. Zhang (City University of Hong Kong); B.Y. Tang, X.B. Tian (City University of Hong Kong and Harbin Institute of Technology, China); P.K. Chu (City University of Hong Kong)
Employing an improved cathode arc plasma source, metal plasma immersion ion implantation (PIII) is performed on 9Cr18 bearing steel. Titanium and Tantalum ions are implanted into the 9Cr18 samples followed by nitrogen plasma immersion ion implantation to result in a modified surface layer with superior wear resistance. The surface properties of the 9Cr18 bearing steel samples are evaluated by measuring the microhardness, wear property, coefficient of friction, as well as elemental depth profiles and chemical composition of the modified layer. The results show that the wear resistance of the samples implanted with Ti+ + N+ is enhanced to a larger degree than that of the samples undergoing nitrogen PIII alone. The XPS results indicate that many nitride phases such as CrN, TiN and TaN have been formed in the implanted layer. In this paper, we will also discuss the new improvements on the metal and source arc source and experimental protocols. Using the new procedures incorporation both metal ion and gas PIII, the surface properties of 9Cr18 bearing steel is significantly improved.
EP-21 Investigation of Dose Uniformity in Industrial Parts with Interior and Exterior Races and Grooves Treated by Plasma Immersion Ion Implantation
Z.M. Zeng (City University of Hong Kong and Harbin Insitute of Technology, China); T.K. Kwok (City University of Hong Kong); B.Y. Tang, X.B. Tian (City University of Hong Kong and Harbin Institute of Technology, China); P.K. Chu (City University of Hong Kong)
Plasma immersion ion implantation (PIII) prolongs the working lifetime of industrial components and is an effective surface treatment technique. However, the lateral implantation dose uniformity is usually not very good particularly for samples with an irregular shape. In this work, we focus on real industrial bearings possessing grooves and races both on the inside and outside and investigate the PIII dose uniformity. The sheath expansion around the inner and outer races is simulated using a time-dependent, two-dimensional fluid mode. The angular distribution of the incident ions and retained dose along the irregular surface are derived. It is found that the retained dose is highest on the bottom of the arc trench along both the inner and outer races. The minimum retained dose is observed near the corner of the groove due to the more glancing ion impact as a result of the evolution of the ion sheath. Our results indicate that the nonuniformity can be minimized by reducing the implantation pulse duration.
EP-22 Mechanical Characterization of Diamond-like Films Using the Combination of the Methods of Nanoindentation and Acoustic Emission with an Improved Tunnel Microscope
N.V. Novikov, O.G. Lysenko, V. Grushko, S. Dub (V.Bakul Institute for Superhard Materials, UKRAINE)
A method, which couples nanoidentation experiments and imaging procedures, has been developed. Piezoelectric elements are used to move an improved tip of a tunnel microscope. A three-sided pyramidal (Berkovich) diamond tip has been used to obtain a load-displacement curve with residual depth of the order of 0.1 nm. The same tip has been used to generate topographic images, while the sample remains stationary. A second tip is used for noncontact measuring of acoustic emission waves during indentation. Results obtained on diamond-like thin films are presented as to illustrate the method
EP-23 Electrometallization and Plasma Coatings Modification Under Laser Action
A.V. Pokhmurska (Institute of Applied Problems of Mechanics and Mathematics, Ukraine)
atings have been obtained by electric arc spraying and plasma spraying of powder wire. Powder wire mixture consists of different refractory components. Some of them are not completely melted in electric arc and almost do not come into reaction with shell material. Laser treatment has been carried out in such a regime in which the coating and a thin layer of a base are being alloyed. The strength of a coatings increases after laser treatment. A porosity after laser treatment decreases from 10 to 0 %, making it possible to apply such coatings as corrosion resistant ones. Corrosion resistance evaluation of samples with electrometallization coatings carried out by analysis of polarization curves shows that due to surface laser treatment corrosion current essential decrease is observed. The wear resistance of both electrometallization and plasma sprayed coatings is improved too.
EP-24 Acoustic Emission Monitoring of Single Cracking Events by Means of Novel Dedicated High Speed Electronics
J. von Stebut, F. Lapostolle (Ecole des Mines, France); H. Vallen (Vallen Systeme GmbH, Germany)
A detailed study on optimisation of single cracking events in three point bending, indentation and scratch testing of brittle coatings is presented. In the two latter situations, best results are obtained with a resonant piezo transducer on the indenter shaft and newly developed high speed electronics allowing for detection of single cracks with tuneable holding times of the instan- taneous AE event peak voltage. Wave forms are seen to contain only information on the crack energy and the instant of nucleation. The latter is exploited for precise synchronisation of all test-specific parameters with the real image of the cracking failure. With this approach it is possible to do advanced failure mechanism analysis of test-induced surface damage. For depth sensing indentation, cracking is seen to occur in the elastically strained region outside of the real contact area (size of the plastic indent). In a first order approximation the shape of the plastic indent is unmodified by the elastic recovery on unloading. In scratch testing, clear correlation between high energy AE pulses and cracking failure is achieved and first attempts to analyse prevailing failure mechanisms are presented. Various case studies of typical scratch failure are presented illustrating the major break through of this new method as compared to the generally adopted black box approach with RMS filtering, available on most commercial scratch testers.
EP-25 The Effect of Electric Field on High Temperature Oxidation of Copper in Air
N. Parkansky, B. Alterkop, S. Goldsmith, R.L. Boxman, Yu. Rosenberg, Z. Barkay (Tel-Aviv University, Israel)
Two copper disks of 99.95 purity and 1 mm thick were connected as capacitor electrodes. A potential difference of 500 V d.c. was applied between the disks, which were spaced 2 mm apart. The capacitor was placed in an air furnace at temperatures of 400, 500 and 600 0C. The surface structure of the disks was examined by XRD, SEM, and EDX . After 1 h of annealing XRD showed the presence of Cu and Cu2O phases and a smaller amount of CuO. The relative concentration of the various phases depended on the electrode polarity. The ratio of Cu to O atomic concentration was 3:2 on the anode and 2:1 on the cathode at 500 0C. The CuO phase was not observed at temperatures lower than 600 0C . At 600 0C SEM and EDX analyses indicated the existance of regions on the anode with a 1:1 atomic concentration of Cu and O. Grain size in these regions was approximately 2.2 microm. The intensity of the XRD lines of CuO on the anode was greater than that of the cathode. Grains with a Cu:O atomic concentration ratio of 2:1 were observed on the cathode with the grain size of approximately 4 microm.
EP-26 Surface Modification of Polymer Materials by High-dose Ion Implantation for Protection from Severe Oxidative Environments
Z. Iskanderova (University of Toronto Institute for Aerospace Studies, Canada); H. Kleiman (Integrity Testing Laboratory, Inc.,, Canada); Y. Gudimenko (Integrity Testing Laboratory, Inc., Canada); R.C. Tennyson (University of Toronto Institute for Aerospace Studies, Canada); W.D. Morison (University of Toronto Insitute for Aerospace Studies, Canada)
A new approach is presented for protection of polymers and carbon-based composite materials from severe low Earth orbit space environment. The protection from erosion and oxidation by atomic oxygen, combined with VUV radiation, is achived by high-dose ion implantation with specially selected species and following oxidative conversion to ceramic or oxide(s)-based new surface structures. Middle-energy monoenergetic single, dual, or tripple ion implantation, treatment by a MEVVA ion source, as well as plasma immersion ion implantation have been used at specially selected regimed, derived from the results of computer simulation. Testing of the implanted advanced polymers and carbon fiber reinforced composites have been performed in a Space Simulator for accelerated testing, by exposure to fast (E~2-3eV) atomic oxygen beam, and the same beam combined with VUV radiation. After an intermidiate stage of surface conversion, the treated materials did not show any mass loss and surface morphology change, that are indications of high-quality protection from the severe Space environment. A variety of complementary surface analysis techniques, such as RBS,SIMS,XPS,SEM etc have been used for examining the surface content and structure of the modified subsurface layers. Based on the unique newly developed surface structures on polymers, the opportunities are discussed for the tecnology transfer from Space to terrestrial applications, such as polymeric biomaterials and advanced sensors with improved stability to oxidation.
EP-27 Finite Element Analysis of the Effect of Roughness and Strength at Interface on Coating Delamination
D.F. Diao (Shizuoka University, Japan)
Interfacial roughness and adhesion strength are very important!!factors for coating design and tribology. In this paper, the stress distribution in the coating and the substrate is analyzed by using finite elemnt method under considering the influence of the roughness at the interface between coating and substrate and the adhesion strength of the interface. Also, the relationship among the roughness, adhesion strength and the coating thickness at the viewpoint of affecting the coating delamination is cleared. Finally, a quantitative evaluation of the coating delamination zone or the no-delamination zone under sliding contact is given in a map.
EP-28 Determinationof the Adhesion Strength of HVOF-coating by a Shperical Indentation Technique
L. Deneuville, K. Ravi-Chandar, K.W. White (University of Houston)
A hybrid numerical experimental method has been developed to determine the adhesion strength of the thermally sprayed HVOF-coating. The elastic mismatch between the coating and the substrate, upon unloading of the indentation cycle, gives rise to a tensile stress normal to the interface. This stress may cause interfacial debonding. After having obtained the critical load for delamination, by performing spherical indentation experiments with increasing load, a finite element model which simulates the indentation cycle is used to predict the observed delamination behavior. The bond strength obtained from the model is compared with the adhesion strength resulting from the ASTM test.
Time Period WeP Sessions | Topic E Sessions | Time Periods | Topics | ICMCTF1999 Schedule