ICMCTF2009 Session EP: Symposium E Poster Session
Time Period ThP Sessions | Topic E Sessions | Time Periods | Topics | ICMCTF2009 Schedule
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EP-1 The Oliver and Pharr Method for Coatings and Physical Scratch Test Analysis for Layered Materials
M. Fuchs, N. Schwarzer (Saxonian Institute of Surface Mechanics, Germany) In the work it will be presented how the classical Oliver&Pharr method, widely used for the analysis of indentation experiments, has to be extended for layered materials. Thereby a completely analytical mathematical approach1 is applied, not only evaluating the substrate effect and correcting it, but also allowing the extraction of the yield strength of the coating material in addition to its Young's modulus. In the second part it will be presented how the extended Hertzian theory1, can be applied to scratch tests on layered materials, in order to extract more physical information from the latter. By taking into account, that with lateral forces additional boundary effects like indenter tilting, mixed loads of sticking-sliding areas are coming into play a much more profound simulation and modelling of the classical scratch test is possible. The methods also work perfectly for multilayer and gradient coatings and in principle allows the extraction of the mechanical parameters of any of the constituents of even very complex coating structures. Especially with a new multi-path scratch method combined with additional classical nanoindentation measurements one can benefit from such a more comprehensive and sophisticated analysis. So, it will be shown how the true initial failure can be detected and clearly defined critical stress values can be assigned to the coating material. The new methods will be demonstrated on a variety of examples in combination with a special new analysing module woven into the software package FilmDoctor2. 1N. Schwarzer: "The extended Hertzian theory and its uses in analysing indentation experiments", Phil. Mag. 86(33-35) 21 Nov - 11 Dec 2006 5153 - 5767 2FilmDoctor: Special version for "next generation surface tester analysis", www.siomec.de/downloads/FilmDoctor |
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EP-2 The Stucture and Properties of Nano-Crystalline ZrTiN Thin Films：Effect of Ratio of Ti/Zr
Y.-W. Lin, J.H. Huang, G.P. Yu (National Tsing Hua University, Taiwan) ZrTiN thin films were deposited by reactive magnetron sputtering based on our previous optimum coating conditions (substrate bias, substrate temperature, system pressure, nitrogen flow etc.) for TiN and ZrN thin films. The ratios of Ti/Zr were tuned by changing target power of Ti and Zr. This study investigated the effect of ratio of Ti/Zr on microstructure and mechanical properties of thin films. With tailoring target power of Ti and Zr to find out the optimum processing parameters, the observed stable nano-crystalline structure and chemically inert characteristic of ZrTiN were the dominant features for the successful demonstration of good properties of thin ZrTiN films. In terms of phase formation, three types of coatings were considered: (a) a ZrTiN single-phase solid solution, (b) ZrTiN interlacing nucleus of TiN or ZrN in the matrix, and (c) nanocomposite ZrTiN films including a significant fraction of TiN or ZrN phase. The films were characterized using X-ray diff raction (XRD), transmission electron microscopy (TEM) and nano-indention. The hardness of ZrTiN film was 37 GPa, and a strong inclination to ZrTiN (111) preferred orientation was observed, when the ratio of Ti/Zr were 1. Furthermore, the target power were 400 Watts and 200 Watts for Ti and Zr, the ZrTiN thin film have been observed to find the X-ray diffraction patterns of ZrTiN (111) and TiN (022), and the film’s hardness was 26 GPa. The thickness of ZrTiN films measured by scanning electron microscope (SEM) was greater than 900 nm. Atomic force microscopy (AFM) was used to measure the surface roughness. The ratio of N/Ti/Zr and composition of ZrTiN thin film were analyzed by X-ray Photoelectron Spectroscopy (XPS) and Rutherford Backscattering Spectrometer (RBS). |
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EP-3 Effect of Surface Polishing on the Abrasion Performance of a Chromium Carbide-Based Coating Deposited by VPS
Z. Marcano (Universidad Central de Venezuela); J. Lesage (University of Lille, France); E.S. Puchi-Cabrera, M.H. Staia (Universidad Central de Venezuela) Thermal sprayed chromium carbide-based coatings are being widely used for a variety of wear resistance applications involving sliding, abrasion and erosion over a wide range of temperatures up to 900°C. The thermal sprayed carbide coatings are in general surface finished by machining or grinding after the coating process. Therefore, it is imperative to understand the influence of the finishing operation on the characteristics and performance of carbide coatings. In the present study, low stress abrasion wear resistance is compared for 6 test conditions: three disc rotation speeds and two surface finishes (as-sprayed and polished coatings). The abrasion tests were carried out using a three-body solid particle rubber wheel test rig using silica grits as the abrasive medium. A commercially available Cr20Ni9.5C coating powder (1376T, Praxair) was deposited industrially by means of a vacuum plasma spraying (VPS) system. The incremental volume wear loss of the coating deter mined as a function of time shows that lower values were obtained for the polished coatings in comparison with the as-sprayed Cr3C2-NiCr coatings. The results also prove that the abrasive wear volume increases with the rotation speed of the disc. The SEM study of the worn surfaces revealed that the wear was mainly due to the selective removal of the binder as consequence of both plastic deformation and fatigue, due to the repeated action of the abrasive particles followed by the undermining of the carbide particles, resulting in their eventual pullout. Some evidence of microcutting could also be noticed, indicating the removal of the binder phase by this mechanism. Also, very little carbide grain fracture and material removal by delamination were observed. |
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EP-5 A Study of the Reciprocating Sliding Wear Performance of Plasma Surface Treated Titanium Alloy
G. Cassar (University of Sheffield, United Kingdom); J.C.A. Batista-Wilson, S. Banfield (Tecvac Ltd); J. Housden (Tecvac Ltd.); A. Leyland, A. Matthews (University of Sheffield, United Kingdom) The use of accelerated wear tests, particularly on laboratory test machinery, is extremely popular within the surface engineering research community. The level of success of novel tribological coatings and treatments is often assessed by one or more of the following techniques: pin-on-disk, rubber-wheel abrasion, block-on-ring, micro-abrasion (free and fixed ball), ball-on-plate impact and reciprocating-sliding wear tests. Many of the available test devices and methodologies are described in the international or national standards such as ISO, DIN or ASTM. However, many of these techniques owe their origin primarily to the characterisation of bulk materials with relative uniform hardness and elastic properties and may therefore be less applicable to functionally-graded and surface-engineered materials, particularly in the case of materials with intrinsically poor tribo-mechanical properties. Linearly reciprocating sliding wear testing of duplex treated Ti-6Al-4V alloys was carried out in this study. Wear volumes were correlated to changes in friction force (and the resultant measured coefficient of friction) which are often indicative of breakdown of the surface treatment. Surface micro profilometry and both optical- and electron- microscopy were used to characterize the wear scars produced. The analysis of test parameter variability (depending on the different surface treatment processes investigated) is presented. The results obtained suggest that the use of total material volume lost (after a pre-set period), of time in order to obtain average wear rates, may be incompatible with the tribo-behaviour of (particularly) duplex-treated substrates. The results obtained here indicate that, in order to differentiate and assess the relative improvements (or lack of) in wear behaviour attained by using surface treatments it is insufficient to compare linear wear rates alone. A clear comparison is only possible if testing is carried out in steps of increasing sliding distance, until the treated/deposited layers have been completely removed. Also, it is shown that the number of repeated tests necessary (for a given treatment and chosen test condition) to evaluate clearly the treatment and/or coating can vary substantially depending on the observed test progression; typically this necessitates the greatest number of repeats around the point of wear at which the ball counter-face contact area is in transition from the treated layers to the bulk. |
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EP-6 In-Situ Raman Tribo-Spectrometry Technique for High Temperature Sliding Contacts
J. Bultman (UDRI/Air Force Research Laboratory); C. Muratore (Air Force Research Laboratory/UTC, Inc.); A. Safriet (UDRI/Air Force Research Laboratory); A.A. Voevodin (Air Force Research Laboratory) An in situ Raman tribo-spectrometer was designed and constructed for use during high-temperature wear tests with ambient temperatures of up to 800°C. The instrument was used to determine the oxidation thresholds for common solid lubricants such as MoS2 and WS2, and to identify the reaction pathways in novel, temperature-adaptive coating materials that rely on catalysis and/or tribo-oxidation to provide low friction contact interfaces throughout a broad temperature range. The probe was also useful for identifying wear mechanisms in multilayered coatings. Finally, the system was compatible with smart tribological coatings for use at high temperature, which use rare earth-doped diffusion barrier layers to produce a characteristic spectral signature when illuminated by laser light to indicate the extent to which the coatings have been worn while in use. The key element of the Raman system was a remote, high-temperature probe with temperature-resistant focus ing and collection optics consisting of two quartz lenses coupled to a commercial Raman spectrometer via fiber optics. The probe allowed focusing of the laser light on the wear track and collection of scattered light from the surface with the same optics, which were air-cooled to reduce aberrations (mirage effects) due to extreme heating. The probe was suitable for use in a variety of wear test geometries, or for use in actual applications in addition the pin-on-disc tests that were the focus of the current work. Advantages and limitations of the technique with examples of its use for MoS2, WS2, chameleon YSZ-MoS2-Ag, and smart Er and Sm doped YSZ/MoS2 coatings are provided. |
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EP-9 Solid Particle Erosion Performance of HVOF WC-Co and WC-Co-Cr Coatings Deposited onto SAE 1045 Steel
Y.Y. Santana, J.G. La Barbera-Sosa, A. Bencomo, E.S. Puchi-Cabrera, M.H. Staia (Universidad Central de Venezuela) Thermally sprayed cermet coatings have emerged as a viable solution for a wide range of wear resistance applications. The tungsten carbide coating is frequently used for many applications related to systems such as gas and steam turbines, aero engines, etc. in order to improve the service life of their components. Solid particle erosion under extreme conditions, i.e. high hardness and strength of abrasives, high velocity and pressure, etc. is a serious problem for the industrial equipment. The main objective of this paper is to study the solid particle erosion behavior of both WC-12Co and WC-10Co-4Cr coatings deposited by HVOF thermal spray technique. A detailed microstructural and mechanical characterization study of these coatings was carried out in order to relate their morphology, roughness, hardness, fracture toughness and residual stresses to their tribological performance. X-ray diffraction techniques were used to determine the surface residual stresses of the co atings, whereas the incremental hole drilling technique allowed the analysis of the non-uniform through-thickness residual stresses present in the coatings. Dry erosion tests were carried out at 30° and 90° angle of impingement, respectively, using as erodent SiC particles with ~ 60 µm of diameter, at a velocity of 83.4 m/s and a feed rate of 2 g/min, according to the ASTM G-76 standard. The eroded surfaces were examined so that the erosion mechanisms of the coatings could be determined. It was found that the erosion rate for both coated systems was higher when the erosion test was carried out at an angle of 90°, leading to a brittle wear type mechanism. The results also indicate that, for the experimental conditions carried out in the present study, the WC-10Co-4Cr coating exhibited a higher erosive wear resistance as consequence of a smaller W2C brittle phase content and a higher through-thickness residual compressive stresses values, wh e n compared to the WC-12Co coating. |
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EP-12 Impact Properties of TiN, TiAlN and TiSiN PVD Coatings at Ambient and Elevated Temperatures
K.-D. Bouzakis, M. Pappa, S. Gerardis, G. Katirtzoglou, S. Makrimallakis, G. Skordaris (Aristoteles University of Thessaloniki, Greece); R. M'Saoubi (Seco Tools AB) The impact behavior of TiN, TiAlN and TiSiN coated cemented carbide inserts at ambient and elevated temperatures was investigated. Nanoindentations were conducted, supported by FEM algorithms to determine the stress-strain constitutive laws of the examined films. Moreover perpendicular impact tests at various temperatures were carried out. The impact imprints were evaluated with the aid of scanning electron microscopy graphs and a developed algorithm to determine the coating failed area ratio. Thus the change of the impact behaviour of the examined coatings at various temperatures was established. The experimental results indicate a non-linear PVD film wear resistance versus the applied temperature. By FEM-based simulation of this procedure, taking into account the test conditions and duration up to the film damage initiation, the critical stresses associated with the coating fatigue strength were calculated. According to the obtained results, the TiAlN film possesses a n enhanced impact resistance compared to the TiN coating. Moreover, TiSiN coatings show a significantly improved capability to withstand effectively the applied loads, compared to TiAlN films, even at elevated temperatures during the impact test. |
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EP-13 Production of a Multicomponential Layers on a 99.8% Purity Iron by the Two State Boro-Nitriding Process: Microstructural and Mechanical Characterization
I. Campos, O.A. Gómez-Vargas (Instituto Politécnico Nacional, México); U. Figueroa-López (Tecnológico de Monterrey, México); M. Ortiz-Domínguez (Instituto Politécnico Nacional, México) Nowadays, there are a number of termochemical processes for improving surface mechanical properties. Boriding have been positioning as a one of the processes which report high performance in the improvement of mechanical properties (hardness and wear strength) as well as corrosion resistance on several alloy systems; i.e. ferrous and non ferrous alloys1,2. It has been seen that paste boriding process can be used in high production lines in comparison with the powder-pack boriding2. On the other hand, surface treatment by nitriding can produce a set of high surface hardness and good wear resistance2. However, it is not recommended to apply this treatment in some high carbon steels because the carbon tends to diffuse at the surface of the sample, and the nitride layer formed on the substrate leads to flaking and spalling when a mechanical load is applied. This study analyzed the production of multicomponential boro-nitriding layers at the surface of 99.8% high purity iron3 by two stage process consisting of paste boriding step followed by a powder nitriding process. Characterization of the boro-nitriding samples were made by Knoop microhardness testing, Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM). The diffusion of boron and nitrogen in the two stage process depends of several factors, although in the boriding stage boron potential seems sensible to the preparation of boriding paste as well as the particle size. Additionally, the preparation of the sample before and after of boriding stage plays an important role because is possible to minimize surface imperfections and unnecessary compound on the surface after boriding stage. The product consist of a well define FexBy/BxNy/diffusion zone multicomponential layers which seems as a interesting system where a combination of wear and corrosion strength are main properties in service. 1I. Campos, R. Torres, O. Bautista, G. Ramirez, L. Zún˜iga., Appl. Surf. Sci. 252 (2006) 2396-2403. 2I. Campos, G. Ramirez, U. Figueroa, J. Martinez, O. Morales Appl. Surf. Sci. 253 (2007) 3469-3475. 3Fan-Shiong Chen, Kuo-Liang Wang. Appl. Surf. Sci. 115 (1999) 239-248. |
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EP-14 Effect of Spraying Distance on the Microstructure and Mechanical Properties of a Colmonoy 88 Alloy deposited by HVOF Thermal Spraying
J.G. La Barbera-Sosa, Y.Y. Santana (Universidad Central de Venezuela); N. Cuadrado, J. Caro (CTM Centre Tecnològic, Spain); P.O. Renault, E. Le Bourhis (Université de Poitiers, France); M.H. Staia, E.S. Puchi-Cabrera (Universidad Central de Venezuela) The present work has been conducted in order to determine systematically the influence of the spraying distance on the microstructure and mechanical properties of a Colmonoy 88 alloy deposited by means of HVOF thermal spraying onto a SAE 1045 steel substrate. The spraying distance varied between 380-470 mm and the evaluation of the deposits characteristics and properties was carried out both on their surface and on cross section. The microstructural study was conducted by means of SEM and image analysis techniques, which allowed the characterization of the unmelted particles volume fraction and the apparent porosity of the coatings. Also, X-ray diffraction techniques were used to determine the surface residual stresses of the coatings employing the sin2ψ method. For this purpose, an analysis of the (311) plane of the dominant Ni phase, at an angle of 2θ~ 93.2°, was conducted. On the other hand, both the hardness and elastic modulus of the coati ngs were determined according to the analysis earlier advanced by Oliver and Pharr (1992; 2004), employing the indentation load versus penetration depth curves derived from instrumented indentation tests conducted with a Berkovich indenter. The yield strength of the coatings was also estimated from the above curves following the methodology suggested by Zeng and Chiu (2001), as well as from spherical indentation tests and the Hertz equations commonly used in contact mechanics. The microstructural analysis indicated a significant increase in the unmelted volume fraction as the spraying distance increases. Such particles were found to give rise to a decrease in the lamellas cohesion and the development of interlamellar microcracks, leading to a decrease in the elastic modulus of the coatings. Both hardness and elastic modulus showed an anisotropic behavior. Such properties were found to be higher on the cross section of the coating than on the deposition plane. A satisfactory c omparison between the predicted and experimental values of the coatings yield strength was observed for all the conditions investigated. |
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EP-15 Effect of Damage Accumulation in Co-Depletion Layer on the Fatigue Debonding Behavior of Diamond Coated WC-Co
S. Kamiya, A. Ueda (Nagoya Institute of Technology, Japan); H. Hanyu (OSG Corporation, Japan); J.C. Madaleno, J. Gracio (University of Aveiro, Portugal) Cobalt-cemented tungsten carbide (WC-Co) coated with chemically vapor deposited (CVD) diamond is one of the most common styles of diamond tools. This technique allowed the realization of precise and complex tool geometries with the extreme wear resistance against severely abrasive materials. The most serious drawback of such tools could be sudden debonding of diamond coating after a certain period of use in machining even without any trace of wear, which causes unacceptable damage to the workpieces. However, no clear observation on the mechanism of such delayed debonding was reported at this moment. Therefore there is no efficient method to predict the lifetime before such sudden debonding of diamond coatings. In the previous studies, we surveyed fatigue debonding behavior of CVD diamond films deposited both on silicon1 and WC-Co2 substrates and subjected to repeated mechanical loading. In the former case, fatigue cracks were found on the substrate surface whenever debonding was observed. In both cases, stress-fatigue lifetime before debonding (S-N diagram) appeared to be independent of film thickness when appropriate stress components were plotted to represent the state of damage on the substrate surface. Therefore the attention in this study is newly focused on damage accumulation in the Co-depletion layer on the WC-Co substrate surface, which has to be introduced for a successful diamond deposition and should be the most susceptible to fatigue. The elastic plastic properties of Co-depletion layer are surveyed by indentation on the bare substrate surface. Fatigue damage of substrate surface under repeated indentation loading is also investigated and correlated to the debonding behavior of diamond coatings with different film thicknesses. Finally, possibilities for fatigue lifetime prediction on the basis of substrate surface damage accumulation process and optimization of Co-depletion layer for a longer fatigue lifetime is discussed. 1S. Kamiya, H. Sekino, H. Hanyu, J. C. Madaleno, J. Gracio, Surface and Coatings Technology, doi:10.1016/j.surfcoat.2008.08.031 (2008). 2S. Kamiya, H. Sekino, A. Ueda, H. Hanyu, J. C. Madaleno, J. Gracio, The 11th International Conference on Plasma Surface Engineering, September 15-19 (2008), Garmisch- Partenkirchen, Germay. |
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EP-16 Effect of Microstructure on the Mechanical Properties of In-Situ Deposited Carbon Monolayer on the Si(100) at High Temperature Under Ultra High Vacuum
C.K. Chung, S.T. Hung, C.W. Lai (National Cheng Kung University, Taiwan) In this article, the effect of substrate temperature on mechanical property of carbon nanofilms using nanoindentation in dynamic contact measurement mode (DCM) was investigated. The carbon monolayer was deposited on the Si (100) substrate at room temperature and at high temperature of 400 to 700°C by ultra high vacuum ion beam sputtering (UHV IBS). Raman spectroscopy was utilized to characterize bonding behavior of carbon monolayer for the variation of graphite peak (G-peak) and disorder-induced peak (D-peak). The amorphous C microstructure is stable up to 500°C. However, ID/IG ratio increases with increasing substrate temperature from RT to 500 °C due to graphitization effect for the increases sp2 bonds. The new phase of c-SiC was formed together with the remained C at 600°C. Complete C and Si reaction was found at 700°C from Raman spectra without any C peak. The formation of SiC at higher substrate temperature on the surface of carbon monolayer leads to hardne ss enhancement. Also, a nanoweb-like morphology of the c-SiC was observed on the surface of film from the SEM image. With regard to the mechanical properties, the hardness and Young’s modulus of films decrease with increasing substrate temperature from RT to 500°C due to more sp2 bonding formed. And then the hardness and Young’s modulus of films increase with increasing substrate temperature from 500 to 700°C due to the formation of nanostructured SiC phase. |
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EP-17 Effects of Si Addition on the Mechanical Properties and Cutting Performance of Nanocrystalline Cr-Si-C-N Coatings Prepared by a Hybrid Coating System
M.C. Kang, J.H. Jeon, K.H. Kim, J.S. Kim (Pusan National University, Korea) Hard coatings are known to improve the performance of cutting tools in aggressive machining applications, such as high-speed machining. Unfortunately, the development of cutting tool for high-speed machining is not enough in machining of difficult-to-cut materials. The Cr–Si–C–N coatings, characterized as a nanocomposite nanosized (Cr and Si)(C and N) crystallites embedded in amorphous phase of Si3N4 and SiC, was successfully synthesized on WC-Co substrates by a hybrid coating system of AIP and sputtering method. Microhardness value of the Cr–Si–C–N coatings by nanoindentation was ¨43 Gpa, which was a much largely increased one compared with Cr–C–N coatings and Cr–Si–N coatings. In addition, the average friction coefficient of the Cr–Si–C–N coatings largely decreased with increasing Si content and compared with CrN, Cr(C, N), and Cr–Si–N coatings. The cutting performances of Cr-Si-CN coated tool for the high-hardened material (AISI D2 steel; HRC50) were investigated under various high-spindle speeds. The reliable on-the machine system for measurement of tool wear was introduced in this work. |
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EP-19 Mechanical and Tribological Properties of Graded Ti(BN-MoS2) Based PVD Coatings
I. Efeoglu, A. Çelik, A. Alsaran, I. Kaymaz, F. Yetim (Ataturk University, Turkey) In the present investigation, Ti(BN)+Ti(MoS2) graded solid lubricant coatings were deposited by magnetron sputtering from separate Ti, TiB2, BN, and MoS2 target. X-ray diffraction, microhardness tester, scratch tester and pin-on-disc tribometer were used to evaluate structural, mechanical, frictional, and adhesion properties. In the work, described here changes in the adhesion and friction-wear life exhibited by nine different coatings deposited under variants of deposition parameters have been investigated. It is found that there is good correlation between the critical loads and friction-wear life of the deposited thin films under different deposition parameters. |
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EP-20 Effect of the Target Shuttering on the Characteristics of the Ta-Si-N Thin Films by Reactive Magnetron Co-sputtering
C.K. Chung, T.S. Chen, N.W. Chang, S.T. Hung (National Cheng Kung University, Taiwan) The nanocomposite Ta-Si-N coatings were deposited using a reactive magnetron co-sputtering with and without alternating shutter control at different N2 flow ratios (FN2% = FN2 / (FAr+FN2)) of 3-20%. The evolution of microstructure, composition, surface morphology and nanomechanical properties of different Ta-Si-N thin films were characterized by X-ray diffraction, energy dispersed spectrum (EDS), scanning electronic microscopy (SEM) and nanoindentation, respectively. The microstructure of nanocomposite Ta-Si-N thin film with and without target shuttering is amorphous-like which has nanocrystalline grains embedded in an amorphous matrix at 3-10 FN2%. The amorphous-like Ta-Si-N without target shuttering control is transformed into the polycrystalline phase at 20 FN2% while the Ta-Si-N film with target shuttering is still in amorphous-like microstructure due to the increased silicon content. The morphology of amorphous-like Ta-Si-N films is smoother than the polycrystallin e Ta-Si-N film at 20 FN2%. The nano-hardesses of all Ta-Si-N films measured by nanoindentation were between 10.3 and 18.5 GPa. The hardness of Ta-Si-N films without shutter control increases with increasing FN2% to 10 % and then drop at 20 FN2%. In contrast, the hardness of Ta-Si-N films with shutter control was increased with increasing FN2% to 20 %. The maximum hardness of Ta-Si-N films without shutter control occurs at 10 % while that with shutter control is at 20 %. Amorphous-like Ta-Si-N films have much higher hardness and smooth morphology compared to polycrystalline films. |
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EP-21 Mechanical Properties Characterization of Multilayered Nano Thin Films by Atomistic Simulations
J.-C. Huang (Tungnan University, Taiwan) The molecular dynamics simulation method was used to investigate the mechanical characteristics of multilayered nano thin films. The NPT ensemble principle and COMPASS potential function were employed in the simulation. The multilayered nano thin film contained the Cu and Ni thin films in sequence. The average elongation of the Cu/Ni multilayered nano thin film in different axis was simulated under different applied stress. The corresponding stain could be obtained when the elongation was divided by the original lattice constant. Similarly, the strains under different stress field were also achieved. The ideal stress-strain relationship of the Cu/Ni multilayered nano thin film in different axis can be calculated based on the classical mechanics linear law. The Young’s modulus of thin film in different axis was also obtained based on the slope of the simulated stress-strain curves. It was concluded that the Young’s modulus of Cu/Ni multilayered nano thin film differe d in different axis. |
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EP-22 Phase Analysis of Alumina Coating by X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM), Secondary Electron Microscopy (SEM) and Micro Indentation
W. Engelhart (Walter AG, Germany); W. Dreher (NMI Natural and Medical Sciences Institute, Germany); V. Schier (Walter AG, Germany); O. Eibl (Eberhard Karls University Tübingen, Germany) Bulk alumina has a lot of structural degrees of freedom. This gives a variety of different phases which are well studied. The thermodynamically most stable phase is defined by the minimum of the Gibbs Energy. This function depends on a variety of external variables e.g. the interaction energy with the substrate, the energy of grain borders, or even the external pressure. The well known alpha phase is not the minimum of the Gibbs energy for all ambient conditions. Some of these phases are synthetically fabricated with physical vapor deposition (PVD). The growing process depends sensible on the depositions conditions. For the design of the coating are special phases and grain size selected to increase the lifetime of cutting tools. A detailed phase analysis is necessary for the understanding of the wear mechanism. However it is a challenge to indentify the nanostructure clearly and in detail. The one micrometer thick coating on tungsten carbide is a nalyzed with x-rays in the gracing incidence geometry (GIXRD). The FWHM of the diffraction pattern gives a number for the correlation length for one crystallographic orientation. The peak to background ratio is taken into account to evaluate the x-ray diffraction data. The combination of TEM bright and dark field images gives a microscopic picture of the real space structure and a first understanding of the homogeneity of the growing process. For industrial applications the film homogeneity is one of the basic demands. For a local analysis of the chemistry energy dispersive x-ray (EDX) in the SEM and TEM is the suitable method. We analyzed several different positions and compared the intensity ratio of the signal for special lines. The structure and the change of the structure is studied with selected area diffraction. As a result a model for the film is given. The model correlates with the mechanical properties, e.g. the hardness measured by micro indentation experiments. |
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EP-23 Galling and Wear Characteristics of Some Commercial PVD Coatings as Evaluated by Tribological Testing
J. Ericsson, M. Olsson (Dalarna University, Sweden) The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with galling in sheet metal forming operations. Galling is a tribological phenomenon associated with transfer of material from the steel sheet to the tool surface during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency to galling in sheet metal forming, including the development of new dry lubricants, new forming tool steel grades and improved surface engineering treatments such as the deposition of low friction CVD- and PVD-coatings. In the present study the potential performance of a number of commercial PVD coatings, including CrN, (Ti,Al)N and various DLC-based coatings, in the forming of hot and cold rolled high strength steel as well as electro and hot-dip galvanized high strength steel has been evaluated using pin-on disc testing and mono and multi pass sliding tests under dry as well as lubricated contact conditions. Post-test examination of the tribosurfaces using FEG-SEM and EDX analysis was performed in order to evaluate the mechanisms controlling the tendency to material transfer and wear. |
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EP-24 Tribological Properties of Cr2N Ceramic Films with Tungsten Dopants
C.S. Wu (National Kaoshiung University, Taiwan); C.W. Chu (University of I-Shou, Taiwan) With the miniaturization of the dimensions of the current micro-drill for machining flexible printed circuit board (PCB) , the rotational speed has reached up to 30 krpm.The miniaturization of the micro-drill makes the rework of itself become more and more difficulty. Surface coating is one of the methods to prolong the service life of the micro-drill and Cr2WN is a prominent material for the protective coating which could apply on the micro-drill due to its excellent oxidation and adhesive resistance properties.Some experimental data use the UCψ0.25×4.0 D2 as the drill sample are in the following: the hardness increased with the increase of the W content,the hardness increased from 17.76GPa to 26.0Gpa.However,when W contents increased，the hardness values also increase. Experimental results show that when W content increased，the wear rate、grain size、contact angle and the mechanical properties of the Cr2WN coating are superior to those in other W contents It will have the minimum flank wear and the tool life is 4 times longer than those of the uncoated samples. |
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EP-25 Microabrasion Wear Testing of PEO Coatings on 2024 Aluminium Alloy
A. Pilkington, H.X. Cheng, A. Yerokhin, A. Matthews (University of Sheffield, United Kingdom) Plasma electrolytic oxidation (PEO) attracts increasing interest as an environmentally friendly technology to improve the wear resistance of Al alloy surfaces. The conventional PEO process suffers from a low growth rate, microstructural defects such as shrinkage cracking and voids which limits the effectiveness of the oxide ceramic coating on Al alloys. A recently introduced higher frequency pulsed bipolar (PBP) PEO treatment enables faster production of oxide coatings with refined morphology based on gamma alumina. This created a requirement to evaluate the wear resistance of the new PEO coatings with greater sensitivity than conventional wear tests (e.g. Tabor test). It is also useful to discriminate between wear rates of the well known outer porous layer and denser inner regions of PEO coatings. A microabrasion test can discriminate between local wear rate variations due to hardness or morphology within a thin surface coating. It also offers greater freedom from self abrasion. The microabrasion test was used to investigate the wear coefficients of a series of PBP PEO coatings on 2024 aluminium alloy. A 25mm AISI 52100 steel ball was used with 1200 grit SiC slurry. Normal loads in the range 0.1-0.3N were used for between 50-1000 cycles. Wear scars were examined by optical microscopy and surface profilometry. Apparent wear volumes measured by the two techniques were compared. The effective ball diameter was estimated from the wear scar profile data. SEM imaging was used to investigate the wear mechanism. The wear coefficients obtained are discussed in relation to the coating morphology, hardness and phase composition. |
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EP-26 Influence of Nitrogen Ion Implantation on Hard Coating Layer to Improve Adhesion Strength Using Combined Surface Modification
G.C. Jeong (Korea Polytechnic University, Korea); Y.H. Sohn (University of Central Florida); S. Kwun (Korea University, Korea) In order to improve the durability and pefermance of molds and tools, diverse methods of surface modification are used, including PVD. In this method adhesion strength between a substrate and coating plays an important role. To improve adhesion strength, a combined surface modification method is ofen utilized. In this study, on substrate(STS420), a various combination of ion-nitriding, Cr intermediate layer, CrN coating layer and nitrogen ion-implantation was examined. Phase constituents, microstructure, adhesion strength and hardness of coating-substrate system with combined surface modification was examined by using opical microscopy, X-ray diffraction, transmission electron microscopy, scratch test, and nano-indentation. Highest adhesion strength was observed when CrN coating was formed by Nitrogen implantation on ion-nitrided substrate with a Cr-intermediate layer. Influence of processing sequence and combination is related to microstructural observations and adhesi on strength. |
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EP-27 Ti(C,O,N)-Based Coatings for Biomedical Applications: Influence of Composition and Structure om the Mechanical/Tribological and Biological Behaviour
N. Jordão, S. Ribeiro (Universidade do Minho, Portugal); J.C. Sanchez-Lopez, M.D. Abad (Instituto de Ciencia de Materiales de Sevilla, Spain); F. Vaz, M. Henriques, R. Oliveira (Universidade do Minho, Portugal); R. Escobar-Galindo (Instituto de Ciencia de Materiales de Madrid (ICMM -CSIC), Spain); S. Carvalho (Universidade do Minho, Portugal) Application of thin films in the biomedical engineering field represents an attractive challenge due to the multiple situations where they may improve or even functionalize a certain parts of human body. Implants are one of such cases, representing one of the most active fields within the so-called biomaterials R&D. Implant failure is a huge problem for both the patient and governmental agencies, once it involves repeated surgeries and consequently considerable economical resources. This failure can be attributed to excessive wear and wear debris and also to microbial infection. Byway, the use of several kinds of nitride-based this films has been carried out in the group, with some promising results. Thus, the main aim of the present work is to study such nitride-based thin films, namely in what concerns to C and O additions to well-known TiN thin films. The obtained Ti(C,O,N) based coatings where then characterized in terms of surface biofilm formation in order to acqu ire knowledge to use them in several medical devices. The thin films were deposited by DC unbalanced reactive magnetron sputtering. Mechanical/tribological resistance of the films was achieved by hardness testing as well as by friction and wear measurements. The tribological response was studied under biological fluid, using reciprocating and pin-on disk configurations. An improvement of the wear rate is observed by application of a bias voltage during film preparation and also for reduced oxygen contents in the films. Regarding biological properties, it was noticed that all samples showed similar ability for Staphylococcus epidermidis biofilm formation, although it was reduced in comparison to the control (stainless steel without coating). However, concerning with fibroblast viability, it was possible to verify that sample coated with TiON had a lower effect that samples with other coatings. |
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EP-28 Tribological Behaviour of PT and PtNx Coatings Deposited by Magnetron Sputtering
M. Flores, E. Rodriguez, J. Garcia (Universidad de Guadalajara, Mexico) During the last 10 years there has been a growing interest on the synthesis and characterization of new nitrides with low friction coefficients and high hardness, due to their technological and fundamental importance. The aim of this work is to report the tribological behavior of Pt and PtNx coatings on 316L stainless steel, deposited by magnetron sputtering using a target of Pt and an atmosphere of nitrogen plus argon; the gas mixture was varied to obtain different nitrogen contents in the deposited coatings. The structure and tribological behavior of Pt and PtNx films was studied by means of XRD analysis and a tribometer with pin-on-disk and reciprocating features respectively. The tribological performance of the coatings is reported and discussed as a function of nitrogen content and film structure. |