ICMCTF2006 Session EP: EP Poster
Thursday, May 4, 2006 5:00 PM in Room Town & Country
Thursday Afternoon
Time Period ThP Sessions | Topic E Sessions | Time Periods | Topics | ICMCTF2006 Schedule
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EP-1 Study on the Theory of Spectroscopic Graze Ellipsometry in Electrochemistry
S.T. Zhang, W.P. Li (Chongqing University, PR China) The mathematical model of the graze ellipsometry has been put forward by combining the model of diffusion layer in electrochemical reaction with graze ellipsometrical experiment. The physical meaning of ellipsometrical parameters δ and ψ has been explained. The influence of the concentration of electroactive substance and the width of the incidence light on δ and ψ is discussed with reference to the experiment results. The results showed that (1) The reason why Graze Ellipsometry can sensitively detect the change of the property of the solution in diffusion layer near the electrode surface is that the change of the concentration of the particles in diffusion layer results in the change of the polarization status of incident light and the change of Ellipsometry parameter δ, ψ reflect that change. (2) Diffusion layer is similar to a phase retarder and an amplitude absorber. Ellipsometry parameter δ demonstrates its function as the phase retarder, and ψ shows its function as the amplitude absorber. (3) δ and ψ are related to the concentration of the electroactive substances and the width of incident light. δ is in linearity with bulk concentration Co and quadraticly linear with width l, while ψ is in exponential relation with Co and quadraticly linear with l. |
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EP-2 Surface Modification of W9Cr4V2Mo High Temperature Bearing Steel by Rare Earth Ion Implantation
F. Jin, P.K. Chu (City University of Hong Kong, PR China); Z. Xu, H. Tong (Southwestern Institute of Physics, PR China) Wear and corrosion are the main failure mechanisms of bearing steels and thus their properties must be improved to prolong their lifetime. Incorporation of rare earth elements have been investigated in processes such as plating, chemical heat treatment, and thermal spray. Ion implantation is an effective technique in the industry but there have been few reports about the use of rare earth ion implantation to improve the wear and corrosion resistance of bearing steels. In this work, rare earth ions including praseodymium, lanthanum and neodymium were implanted into W9Cr4V2Mo high temperature bearing steel specimens using a metal vapor vacuum arc source. Pin-on-disk test, microhardness determination, and potentiodynamic polarization were employed to evaluate the mechanical properties and chemical stability of the treated specimens. The chemical composition and surface morphology of the implanted layers were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results show that the tribological properties and aqueous corrosion resistance of the treated samples were enhanced significantly. The improvement can be attributed to the oxide barriers and increasing cohesive strength of the oxide films. The mechanisms of the wear and corrosion behavior of the implanted specimens are also discussed. |
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EP-5 Dry Machinability of Ceramic-Coated, Cemented Carbide Tools with/without Self-Lubrication via Chlorine Implantation
T.S. Sumitomo (University of Tokyo, Japan); S.Y. Yamamoto (National Institute for Materials Science, Japan); T.A. Aizawa (University of Toronto, Canada) In order to attain low friction and wearing conditions in dry, self-lubrication mechanism must be accommodated to hard protective coating for cutting tools, forming tools and dies. Through our research and development, self-lubrication via chlorine implantation significantly improves the dry-formability and dry-machinability since lubricious titanium oxide films are in-situ formed on the surface of protective coating films. In the solid-lubricated abrasive dry wearing by this self-lubrication, duration of low friction and wear conditions in dry machining might be dependent on the amount of lubricious titanium oxides. In the present study, the effect of titanium resource amount in protective coating and work materials on dry machinability is investigated to describe the self-lubrication process. A turning test was employed to make on-line measurement on the variation of friction coefficient with cutting distance (L) and to evaluate the flank wear for various cutting speeds (v) up to 500 m/min. Two kinds of works materials were used: Al-deoxidized and Ti-deoxidized S45C steels. As a bare tool, WC (Co) with a content of TiC was used; TiCN-coating was also utilized as a titanium resource in coating films. These pairs of coated tools and work-materials with Cl-implantation directly evaluate the effect of titanium in coating and work materials on the dry machinability. Significant reduction of flank wear width (Wf) can be detected with increasing the amount of titanium in the dry cutting condition: e.g. when L = 500 m and v = 400 m/min, Wf = 90 µm for TiCN-WC tools against Al-deoxidized S45C, Wf = 65 µm for Cl-implanted, TiCN-WC tools against Al-deoxidized S45C, and, Wf = 55 µm for Cl-implanted TiCN-WC tools against Ti-deoxidized S45C. |
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EP-6 Effect of Ni Interlayer on the Adhesion Characterization of Mo-Ru Thin Film
C.-Y. Kang, C.-H. Lin (National Tsing Hua University, Taiwan); Y.-I. Chen (National United University, Taiwan); F.-B. Wu (National Tsing Hua University, Taiwan); J.G. Duh (National Tsing Hua Univerisity, Taiwan) Noble metal coatings usually increase lifetime and modify properties of glass molding die. In this study, Mo-Ru coatings with and without Ni interlayer were deposited on tungsten carbide by DC sputtering processes at an elevated temperature of 550 in order to improve the qualities of molding die material. Phase identification was investigated by X-ray diffractometry (XRD).The surface morphology and surface composition were evaluated by atomic force microscopy (AFM) and field emission electron probe microanalyzer (FE-EPMA), respectively. Mechanical characteristic, such as surface hardness of the Mo-Ru films, was measured by nanoindentation testing. In the aspects of adhesion mechanism, failure modes with and without interlayer appeared comparable. Nevertheless, the different thickness of interlayer resulted in various kinds of fracture configurations during scratch. Besides, conventional scratch test exhibited chipping failure between substrate and layer at load as low as 3N.However, nanoscratch technique showed only ductile scratch because the channel depth was so shallow such that the scratch was merely affected by top layer's intrinsic behavior. |
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EP-7 Wear Behavior of Several PVD Coatings Against Stainless Steel
A.E. Reiter (Balzers Ltd., Liechtenstein); M. Rebelo de Figueiredo, C. Mitterer (University of Leoben, Austria) During the last ten years, the usage of stainless steel materials increased continuously in various industrial applications. However, the machineability of these materials is difficult, especially austenitic stainless steels. Tools like blind hole taps, punches or deep drawing molds are often exposed to severe wear by machining these materials, mainly due to their tendency of cold-welding. Additional to the intensive abrasive wear, the material build-up causes adhesive wear which results in a distinctive reduced tool life. In this study, ball-on-disc experiments were carried out in ambient air at room temperature, 150°C and 250°C. The high-speed steel (HSS) discs were coated with TiN, CrN, TiAlN, AlCrN with three different compositions, CrC, TiCN, WC/C and DLC. The coatings were worn against an austenitic stainless steel ball (DIN 1.4301). Characterization of the wear track was done by SEM, Raman spectroscopy and an optical 3d profiling system. Emphasis of the analysis was to achieve a comparison regarding the abrasive wear behavior and the tendency to material build-up. Especially AlCrN based coatings, TiCN and DLC are demonstrating sufficient abrasive wear resistance whereas the results obtained on DLC suffer due to increased sticking of counter part material. This build-up was found to be lowest for CrN and also minor for AlCrN based coatings. However, the abrasive wear for CrN and CrC was severe for all tested coatings. Increasing test temperature entails increasing abrasive and adhesive wear. |
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EP-8 Measurement of Friction and Wear of PVD Coated Pistons
K. Bobzin, E. Lugscheider (RWTH Aachen University, Germany); H. Murrenhoff (Institute of Fluid Power Drives and Controls (IFAS), Germany); N. Bagcivan (RWTH Aachen University, Germany); S. Scharf (Institute of Fluid Power Drives and Controls (IFAS), Germany); N. Goebbels (Surface Engineering Institute, Germany) Hydrostatic displacement units have a sophisticated design that enables a high level performance in combination with specially developed mineral oil based fluids. In order to use biologically degradable fluids based on native esters, fluids based on mineral oil have to be replaced. That means that functions, which had been realised with mineral oil based fluids by adding chemical substances, have to be substituted. The reason is that these chemical substances are mainly environmentally toxic and thus have to be avoided. Within the Collaborative Research Center 442 at Aachen University the aim is to replace these functions by providing components of tribological contacts with PVD coatings, that hydrostatic displacement units, bearings and gears can perform with biologically fast degradable fluids based on native ester. The pistons are coated with a carbon based PVD coating. Graded zirconium carbide (ZrCg) has shown a big potential for reduction of wear and friction. Due to its graded hardness and carbon distribution along coating thickness ZrCg enables self adjustment tribological systems. This paper deals mainly with the research of wear and friction of coated pistons in axial piston units on the one hand and with the investigation of the mutual influence of biologically degradable fluids and coatings on the other hand. For this purpose contact angle measurements with different fluids and materials are performed in order to conclude on wetting behaviour and surface energy of coatings and fluids. Furthermore piston contour will be changed in order to investigate its impact in combination with the ZrCg coating. This includes experimental results with a new designed test facility as well as simulations for calculating pressure distributions within friction contacts. |
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EP-10 Fracture Mechanics of Diamond-Like Carbon (DLC) Films Coated on Flexible Polymer Substrates
D. Tsubone (Keio University, Japan); T. Hasebe (Tachikawa Hospital, Japan); A. Kamijo (University of Tokyo Hospital, Japan); T. Suzuki, A. Hotta (Keio University, Japan) Diamond-like carbon (DLC) films have been widely used for many industrial applications due to their high hardness, wear resistance and biological compatibility. The DLC films coated on polymer substrates have also been extensively used and investigated because recently, quite a few applications for the use of these DLC-polymer composites have been proposed and actively discussed. The applications range from DLC-coated Polyethylene Terephthalate film (DLC-PET), through DLC-coated Polycarbonate (DLC-PC) to other DLC-coated rubbers. In this work, thin DLC films coated on several polymer substrates of different chemical structures, crystallinities and Young moduli were introduced. The DLC-polymer composites (films) were stretched to different strains and the extended surface was investigated by optical microscope to study the fracture mechanics of the DLC-coated polymer films. Anomalous horizontal and vertical micro-cracks and micro-curled surfaces were observed, constructing unusual micro-lattice patterns on the surface of the DLC-polymer composites. |
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EP-11 Tribological Properties of Superhard TiSiCN-Based Nanocomposite Coatings
E. Bousser, L. Martinu, J.E. Klemberg-Sapieha (Ecole Polytechnique de Montreal, Canada) Recent advances in the area of aerospace, automotive and biomedical industries require new surface-engineered materials combining enhanced tribological properties, excellent corrosion protection and high temperature stability with controlled thermal conductivity, fouling-resistance, aesthetic appearance and other characteristics. In the present work, we study novel nc-TiCxNy/a-SiCN nano-composite coatings, obtained by plasma enhanced chemical vapor deposition (PECVD), consisting of 5-10 nm size TiCN particles incorporated in an amorphous matrix of SiCN. Such films exhibit a very high hardness (H > 50 GPa), a Young's modulus of E ~ 300 GPa, an elastic rebound of 80 %, and a very high H3/E2 coefficient of 1.8 GPa. We particularly investigate the tribological properties of coatings deposited on martensic stainless steel and titanium-based alloy substrates, such as those typically used in aerospace applications. This includes the effect of the film/substrate interface or interfacial regions modified by nitriding, carburizing, and by applying homogeneous and inhomogeneous intermediate layers. We specifically correlate adhesion, wear-, scratch- and corrosion resistance with the film elasto-plastic properties. Detailed multitechnique microstructural and chemical characterizations using SEM, TEM, AFM, XRD, XPS and ERD are used to assess the wear and corrosion mechanisms, and their correlation to a new modified microstructural model postulating a network of interconnected non-ideal (defect-containing) electrically conducting nanoparticles with dielectric SiCN inclusions. |
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EP-12 Tribological Characterization of a Ni-P-35%BN(h) Composite Autocatalytic Coating
O.A. León (UNEXPO, Venezuela); M.H. Staia (Central University of Venezuela); L.E. Gil (Corrosion Studies Center, Venezuela); H.E. Hintermann (University of Neuchatel, Switzerland) Sliding wear experiments at room temperature were performed, using a pin-on-disc configuration, in order to study the tribological performance of a Ni-P-BN(h) composite autocatalytic coating with 35 volume percent of BN(h) in as-deposited and heat treated conditions (200, 300 and 400°C by a hour). Substrate used for the autocatalytic deposition was AISI 316L stainless steel. Coating was tested against AISI 52100 steel balls. The coating with 35 volume percent of BN(h) was obtained by dispersing BN(h) of an average particle size of 5.16 µm in a sodium hypophosphite based autocatalytic bath with enhanced agitation and surfactant addition. Scanning Electron Microscopy and 3-D perfilometry techniques were employed for to study the wear scars. Knoop microhardness, structure, roughness, thickness, chemical composition, friction coefficients and wear resistance of the coating for all experimental conditions are also reported. The results obtained indicate that the composite coating present a wear resistance two orders of magnitude higher that conventional Ni-P coating in all experimental conditions. Composite coating heat treated at 400°C by a hour presents the better tribological performance. Wear mechanism present at the wear scars of the composite coating is a mild adhesive wear mechanism (adhesive ploughing) which is different to the mixed wear mechanism (adhesive and abrasive) reported for conventional Ni-P autocatalytic coatings. |
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EP-14 Wear and Corrosion Behavior of Duplex Coatings Deposited on AISI 316L Austenitic Stainless Steel
M. Flores, B. Rubio, I. Rodriguez (Universidad de Guadalajara, Mexico); E. de las Heras, D. Egidi, P. Corengia (INTI, Argentina); E. Andrade (IF-UNAM, Mexico) There are applications as biomaterials, where are needed resistant materials simultaneously to corrosion and wear. Some materials and coating characteristic, such as the grain size, have opposite effects on the corrosion and wear behavior. Metal-ceramic multilayers can improve both properties simultaneously, however, if the total thickness is a few microns it could suffer from brightness fracture under local loads, as in the abrasive wear. Duplex treatments consist of plasma nitride plus metal-ceramic multilayers deposited by magnetron sputtering were deposited with the aim of overcome these problems. In this work we present results of wear and corrosion tests performed on AISI 316L stainless steel samples, nitrided and coated with TiN/Ti multilayers. The abrasive wear tests of the samples nitride, coated with multilayers and with duplex treatments were made with a ball cratering system and the corrosion with potentiodynamic polarizations in an electrolyte of NaCl 0.5 M. Analysis and discussion of results show that plasma nitriding and multilayers improves the wear resistance of the austenitic stainless steel and the corrosion results indicate that the porosity of the coated should be low to improve the corrosion resistance. The microstructure of the films was characterized by XRD analysis. Ion Beam Methods (RBS) were used to obtain the atomic composition profiles and the TiN/Ti multilayer thickness. The results obtained for the periodic multilayers were compared with commercial and laboratory monolayer films. |
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EP-15 Microstructure and Mechanical Properties of Al-Cr-N Films Deposited by CFUBMS
S.Y. Lee, G.S. Kim, B.S. Kim (HanKuk Aviation University, Korea) For a long time, binary transition metal nitride films have been widely used as protective and wear resistant hard coatings for cutting and forming tools due to their high mechanical and tribological properties. However, in spite of their excellent properties, binary systems are still inadequate for high temperature applications due to their low oxidation temperature. During service at the high temperatures above 700°C, their mechanical properties are degraded rapidly by the formation of porous oxides at the film surface. In order to overcome these problems, ternary nitride coating system was explored and until now, various ternary nitride coatings such as Ti-Zr-N, Cr-Al-N, Zr-Al-N and Ci-Si-N have been unflaggingly developed In this paper, Al based Al1-xCrxN films with 0 X 0.69 were synthesized by closed field unbalanced magnetron sputtering with vertical magnetron sources and their chemical composition, crystalline structure, morphology and mechanical properties were characterized by Auger electron spectroscopy (AES), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation and wear tests. Also, the thermal stability of films was evaluated by hardness measurement after annealing treatments at temperatures between 600 and 1000 in air for 30 min. From the experimental results, it could be noticed that the Al1-xCrxN films (excluding X=0) formed solid solution and exhibited crystalline phases of fcc B1 type structure with strong (111) preferential orientation. Depending on the Cr content (X value), the hardness values of Al1-xCrxN films were ranging from 31 to 41 GPa and the residual stresses were in the range of 5.6 to 4.5 GPa. As compared to other films, the most excellent mechanical and thermal properties were observed from the film with the Al1-xCrxN films with X=0.29. The detailed analysis results of films will be presented. |
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EP-16 Tribological Behavior of Cr-Zr-N Films Synthesized by Closed Field Unbalanced Magnetron Sputtering
B.S. Kim, S.Y. Lee, G.S. Kim (HanKuk Aviation University, Korea) For many years, binary transition metal nitride films such as TiN, CrN, ZrN and HfN have played an important part as hard protective and wear resistant coatings in the tool and forming industries. Among these films, CrN together with TiN has been the most extensively studied and frequently used in various industries due to its high thermal stability and good wear resistance as well as superior corrosion resistance. However, in spite of its excellent properties, CrN still shows inadequate properties for some applications such as high speed machining and high temperature conditions above 700°C because of the limitations of binary system. In order to overcome these problems, ternary nitride system with the addition of another elements into binary system was explored. It is well known that ternary nitride coatings exhibit usually superior mechanical and chemical properties compared with binary nitride films. Recently, various Cr based ternary nitride coatings such as Cr-Ti-N, Cr-Al-N, Cr-W-N and Cr-Si-N have been unflaggingly developed and their excellent properties are reported in many papers. In this work, Cr1-xZrxN films were synthesized in order to improve the mechanical properties of CrN coating and their crystalline structure, morphology and mechanical properties as a function of Zr content were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation and wear tests. The experimental results reveal that the structure and mechanical properties of films were found to depend strongly on the Zr content. As the Zr content increases, the more dense and compact microstructure is developed and the surface roughness is highly decreased. Also, the mechanical properties including hardness (maximum hardness: 34 GPa) and wear property are largely improved in comparison with CrN film. Detailed analysis results will be presented. |
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EP-17 Mechanical Fatigue Properties of Diamond Deposited on Silicon Substrate
S. Kamiya (Nagoya Institute of Technology, Japan); J.C. Madaleno (University of Aveiro, Portugal); H. Hanyu (OSG Corporation, R&D Center, Japan); G. Cabral, J. Gracio (University of Aveiro, Portugal); H. Sekino, H. Takeuchi (Nagoya Institute of Technology, Japan) Chemical vapor deposited (CVD) diamond is already used in a wide range of applications, from electronic devices to anti-wear protection coatings. However, there isn't still enough knowledge on the mechanical strength of CVD diamond products and the reliability issue still remains in these products, being critical to some of them. To ensure the integrity and estimate the life time, it is necessary to know about fatigue properties. However, mechanical fatigue test has been rarely performed on CVD diamond up to now, and common understanding is not yet established. For example, Brookes and Zhang[1] reported that both single crystal diamond and CVD diamond on WC-Co substrate were susceptible to fatigue cracking, while Davies et al.[2] found recently that cyclic loading never decreased the strength of free standing CVD diamond samples in normal environment. When diamond films on substrates are subjected to cyclic loading, strength degradation due to fatigue may occur not only in the film but also in the interface and substrate. Therefore details of fatigue behavior should be further surveyed from the view point of the material systems composed of film, substrate and their interface. In the present study, diamond films deposited on silicon substrate are repeatedly loaded with spherical indenter at a frequency of 0.5 kHz and damage accumulation process is observed in detail in order to accumulate basic knowledge of possible fatigue degradation mechanisms in such a materials system. Interface delamination was clearly observed during the fatigue process. The electronic behavior of the system is also characterized in terms of current-voltage (I-V) relationship for the possibility to sense fatigue degradation of system integrity. [1]c. A. Brookes, L. Y. Zhang, Diamond Relat. Mater., 8(1999), 1515-1521. [2] A. R. Davies, J. E. Field, K. Takahashi, K. Hada, Diamond Relat. Mater., 14(2005), 6-10. |
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EP-18 In Situ Formation, Surface Characteristics and Interfacial Adhesion of Poly(imide siloxane)/Tantalum Oxide Hybrid Films
M.-H. Tsai, C.-J. Ko (National Chin Yi Institute of Technology, Taiwan) A new poly(imide siloxane)/tantalum pentoxide (PIS/Ta2O5) hybrid nanocomposite material has been successfully fabricate through the in situ formation of Ta2O5 within a poly(imide siloxane) matrix by sol-gel process. The hybrid thin films are prepared from 4,4'-oxydiphthalic anh.ydride (ODPA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane(BAPP), α,ω-bis(3-amnopropyl)polydimethyl siloxane (APPS) and p-aminophenyltrimethoxysilane (APTS). The APTS is employed to provide bonding between the PIS and Ta2O5 phase and controls the poly(amic acid siloxane) block chain length. Through sol-gel process and imidization reaction, the Si-O-Ta crosslinked structure of PIS/ Ta2O5 hybrid film are formed. The object here is to correlate the properties with the Ta2O5 content, the polyimide block chain length and the crosslinking density. The effect of composition of the PIS/Ta2O5 hybrid thin films on their surface morphology, thermal stability, thermal expansion coefficient and dynamic mechanical properties are investigated. To improve the adhesion strength between the PIS/Ta2O5 hybrid films and copper system, the modification of plasma treatment is also applied to the hybrid films. The more detail will be presented in the conference. |
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EP-20 DLC Films Deposited on TigAL4V Substrate as Spatial Sliding Parts
L.V. Santos, V.J. Trava-Airoldi, L.F. Bonetti, G.C. Rodrigues, E.J. Corat (INPE/MCT-Instituto Nacional de Pesquisas Espaciais, Brazil) High hardness and low friction coefficient of diamond-like carbon (DLC) films give itself significant advantages in terms of lifetime and several kinds of trybological applications, including space devices for sliding and anti-cold welding surfaces. However, low friction coefficient of hydrogenated DLC films (a-c:H) deserves special attention because of the growth parameters dependence with the sliding environment. In this work very high adherent a-c:H films on Ti6Al4V polished surface has been obtained by using 13.56 Mhz RF discharge, allowing us to apply it on space device requiring sliding between parts. Low stress was obtained with growth rate as high as 2.5 µm/h. In order to get high adherence special interlayer of amorphous silicon between the a-c:H film and the substrate was used. The adherence and the hardness were evaluated by micro scratching and micro indentation, respectively. Friction coefficient in air and ultra-high-vacuum environment was measured in several speeds by pi-on-disc. An additional characterization technique as Raman scattering spectroscopy has been also used in order to evaluate the film quality. Novelty: Hard, thick, very adherent and low friction coefficient a-c:H films on Ti6Al4V substrate for space sliding parts. |
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EP-21 High Temperature Tribological Behavior of PVD AlCrN Coatings on Cemented Carbide and Steel Cutting Tools
D.G. Bhat (University of Arkansas); M.H. Staia, E.S. Puchi-Cabrera (Central University of Venezuela); M. Cruz (University of Venezuela); G. Haley (University of Arkansas); D.T. Quinto (Balzers, Inc.) The recent developments in the deposition of ternary metal nitrides by physical vapor deposition methods have led to the synthesis of a number of high-performance hard coatings, which have demonstrated superior resistance against wear, corrosion, chemical attack and other harsh operational environments. In this regard, the recent studies on the deposition of (Al,Cr)N coatings have highlighted the beneficial effect of Al addition to CrN, along the lines of similar effects observed in the development of AlTiN coatings in the past. The incorporation of Al into the CrN films deposited by arc evaporation and magnetron sputtering techniques is expected to improve the hardness and wear resistance of the ternary nitride film, as well as its oxidation resistance at high temperatures. Recent studies on arc-evaporated AlCrN films has shown that the tribological and oxidation behavior of these films depends on the Al:Cr ratio in the film. In the present work, the high-temperature wear behavior of AlCrN films deposited on high-speed steel and cemented tungsten carbide substrates was tested both at room temperature and at elevated temperatures in the range of 200-600°C, against alumina ball in a high-temperature tribometer. The hardness of the film was also evaluated using a model for the composite hardness of the coated system, which was determined by Vickers microindentation at different loads. The results of these studies are presented and discussed from the perspective of performance in metal-cutting applications. |
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EP-22 Electrical Endurance of Noble and Non Noble Coatings Under Automotive Connector Contact Loadings
P. Jedrzejczyk, C. Rapiejko, K. Kubiak, S. Fouvry (Ecole Centrale de Lyon, France) Micro displacements at the contact interface (fretting) of electrical connectors damage the contact area and disturb the electrical signal. Such phenomenon is widely observed in numerous automotive application inducing specific loading conditions like temperature, relative humidity and specific gaseous atmospheres. To increase the connector endurances numerous thin soft coatings been applied. However due to the complexity of the phenomena it is still very difficult to compare and predict their respective durability. A specific device to test micro contacts with low normal forces and very small displacement amplitudes, high frequencies, controlled atmosphere and elevate temperature, representative of an automotive engine condition, has been developed. The electrical contact resistance as well as the wear is measured. Hot-dipped tin, heat treated tin, gold and silver coatings over a bronze substrate have been tested. A strong relationship between the fretting sliding condition and the electrical behavior is found. Under partial slip conditions the stick zone maintains a very good conductance independently of the coatings. Under larger sliding conditions, involving gross slip conditions, the electrical conductance of the contact is highly connected to the wear and debris oxidations properties. For noble coatings, wear through of the coating rules the electrical behavior since the debris are not oxidized. For non noble coatings the electrical endurance is drastically reduced since the electrical behavior is directly related to the oxidized third body formation. Taking into account such phenomena, a local wear/third body activation approach is developed to modelize the electrical conductance of the studied palliatives under such severe contact and ambient conditions. |
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EP-24 Structural Characterisationof W/Cu Multilayers by X-ray Diffraction
B. Girault, P. Villain, P.O. Renault, Ph. Goudeau, F. Badawi, V. Pelosin (Universitat de Poitiers, France) Interfaces contribution becomes preponderant in nano-sized crystals yielding deviations from the average mechanical behavior of bulk material. Multilayer structures offer the opportunity for studying the mechanical properties of low dimension systems (in one direction). In order to analyze the elastic behavior of nanostructured W layers, W/Cu multilayers with period thicknesses ranging from 24 down to 1.7 nm and different W/Cu thickness ratios have been prepared by ion beam sputtering and characterized using X-ray reflectometry, X-ray diffraction, instrumented indentation and energy dispersive analysis in a scanning electron microscope. W and Cu are non miscible elements, but EXAFS measurements indicated that interface alloying may occur in tungsten sub layers for the lowest periods and for equiatomic composition. The mechanical elastic behavior of the W layers was observed to depend on the period and the W/Cu thickness ratio of these multilayers as well. Elastic response is observed to be well below that expected from a simple rule of mixture. The interface alloying may induce the change in the elastic behavior. In order to understand more precisely the mechanical properties of these multilayers, the elastic behaviors of both tungsten and copper sub layers have been analyzed using a method combining X-ray diffraction and tensile testing. Indeed, X-ray diffraction is phase selective and allows measuring the elastic deformations both in W sub layers and Cu sub layers. The first results for a multilayer composed of 10 bilayers of 6 nm W and 18 nm Cu and the microstructural evolution, i.e. texture evolution, of WCu multilayers as a function of period will be presented and discussed. |
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EP-25 Nanoceramic Based Coatings of High Lubricity and Low Friction Formed by Plasma Spray Processes
X. Ma, D. Xiao (Inframat Corporation) This work has investigated the behavior of friction and wear of a nanocomposite coating that was formed in a process of plasma spray. A solid-state lubricant phase iron sulfide (FeS) was chemically converted from iron disulfide (FeS2), and incorporated in a wear-resistant nano-aluminia/titania matrix in the process of plasma spraying. The nanocomposites also have been fabricated into lubricant coatings with a functionally graded structure in plasma spray processes. The nanocomposite coating exhibited a low coefficient of friction and low wear rate. Tribological test results for the nanocomposite coatings demonstrated dramatic increases in both sliding wear resistance and abrasive wear resistance, potentially for the applications that require a solid lubricant surface. |
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EP-26 Didactically Optimized Training Tools for Mechanical Thin Film Design
P. Heuer-Schwarzer (ESAE, Germany); N. Schwarzer (Saxonian Institute of Surface Mechanics, Germany) When the properties of a layered material shall be improved, the following three steps must be taken: First of all, the material needs to be characterized carefully with a suitable measurement instrument and an appropriate analysis software. It is a well known fact, that the characterization of the mechanical parameters constitute the basis for a successful optimization. Nevertheless, many people do not pay enough attention to this matter and are often content with rather poor results. The very advanced measurement techniques and instruments that exist on the market need to be supported by didactically edited material such as training videos or audiovisual presentations to ensure an optimal application for the user. In the second step, the exact use of the material must be analyzed. Is its surface exposed to small, sharp contacts or rather to large and blunt contact counterparts. The question about the mechanical loads needs to be answered as well as the kind of contact and damage that occurs. Those concrete contact conditions lay the foundations for a simplified model-contact-system that will, like an idealized experiment, illustrate possible solutions. Finally, the optimization of the actual mechanical layer can be approached: The characteristics of the layer and surface can be designed in a way that the material is protected optimally against the mechanical stresses and contact loads that do occur during the normal use. The full understanding of these three steps contributes crucially to a successful mechanical thin film design. Thus, this paper will present a specialized didactic strategy for training tools for thin film design models, which include associations, motivate the user and is optimized with respect to the later application. |
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EP-27 Automated Analysing of Thin Film Nanoindentation Data Using the Concept of the Effectively Shaped Indenter
N. Schwarzer (Saxonian Institute of Surface Mechanics, Germany); L. Geidel (TU Chemnitz, Germany) Recently developed analysing techniques applying the concept of the effectively shaped indenter allow a much more comprehensive analysing of nanoindentation data of thin films1. The new analysing procedures have even been successfully applied in the case of very thin coatings well below 100nm thickness. Important physical mechanical parameters like Young's modulus, critical stresses for phase transition and Yield strength can be determined2. From the theoretical point of view, also fracture toughness (critical stresses for cracks of various fracture modes) and intrinsic stresses should in principle be determinable. However, as the mathematical apparatus for such analysing procedures is rather complex and the performance of the evaluation very cumbersome and difficult to learn, it seems reasonable to develop software tools providing features for a rather automated calculation process. The present study is about the principle feasibility of such analysing tools and the state of their realisation. 1 N. Schwarzer, T. Chudoba, G. M. Pharr: "On the evaluation of stresses for coated materials during nanoindentation with sharp indenters", Surface and Coatings Technologies, in press, Corrected Proofs, doi:10.1016/j.surfcoat.2005.01.011 2 N. Schwarzer, T. Chudoba, F. Richter: "Investigation of ultra thin coatings using Nanoindentation", Surface and Coatings Technology, in press, accepted July 2005. |
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EP-28 Fretting Wear of TiCx and TiNy PVD Coatings Under Variable Relative Humidity Conditions - Development of a 'Composite' Wear Law
R. Rybiak, T. Liskiewicz, S. Fouvry (Ecole Centrale de Lyon, France); B. Wendler (Technical University of Lodz, Poland); P. Kudlacek (University of West Bohemia, Czech Republic) Fretting wear is defined as a small oscillatory displacements between two contacting bodies. The interface is damaged by debris generation and its ejections from the contact area. It is well-known that the application of hard coatings is potentially a solution against fretting wear. For this study TiC and TiN hard coatings manufactured by a PVD method have been selected and tested against polycrystalline alumina smooth ball. A fretting test programme has been carried out at the frequency of 5Hz, 100N normal load, 100µm displacement amplitude and at five values of a relative humidity (RH): 10, 30, 50, 70 and 90% at 296K temperature. The intensity of a wear process is shown to be significantly dependent on the environmental conditions. A dissipated energy approach has been employed to quantify wear rates of hard coatings. This approach is stable to predict wear kinetics under constant medium relative humidity. However, an increase of the relative humidity promotes the formation of hydrate structures through the interface and modifies the third body rheology. This phenomenon has been characterised by the evolution of wear kinetics associated to a significant variation of the corresponding energy wear coefficient (α). In this work a 'composite' wear law integrating the wear energy coefficients as a function of the relative humidity is introduced. It permits to predict the wear responses under variable relative humidity varying from 10 to 90% within a single fretting test. The stability of this approach is demonstrated by comparing various variable relative humidity sequences. |