ICMCTF2000 Session E4/F1-2: Mechanical Characterization - Micromechanical Testing and Modeling

Monday, April 10, 2000 1:30 PM in Room California

Monday Afternoon

Start	Invited?	Item
1:30 PM		E4/F1-2-1 Thermal and Mechanical Contact Stresses in Transversely Isotropic Coatings Z. Shi, S. Ramalingam (University of Minnesota) Hard coatings deposited with PVD or CVD processes for use in tribological systems usually possess a texture which depends on the film deposition conditions used. Columnar structure, for example, is common in the widely used TiC, TiN and Ti(CN), etc., hard coats. In such coated products, the thermal and mechanical properties (thermal conductivity, thermal expansion coefficient, elastic modulus, etc.) in the coating plane differ from those in the direction normal to the coating plane. In contact stress analysis, it is hence more realistic to model the hard coat as transversely isotropic, i.e. the material properties are isotropic in the coating plane, but differ from those in the direction normal to the plane of the coating. In this work, three dimensional contact stress analysis is presented for transversely isotropic coatings on isotropic and transversely isotropic substrates. Temperature and stress fields are determined and presented as a function of anisotropy parameters, contact conditions and coating thickness. Thermal stresses generated in tribo-contacts are compared with stresses due to mechanical loading. The relative importance of thermal stresses in coatings and substrates is examined in detail and their significance is discussed.
1:50 PM		E4/F1-2-2 Stresses in Surface-coated Solids due to Normal and Shear Tractions Applied over an Elliptic Contact Region Z. Shi, S. Ramalingam (University of Minnesota) Contact problems involving surface coated solids have received a great deal of attention in tribological literature. Two dimensional and three dimensional contact problems of layered solids have been studied. However, studies of technologically important problem of elliptic contact in layered solids has so far received little attention (elliptic contact in which the contact area is an ellipse is encountered in rolling element bearings, gears and wheel-rail contact, etc.). This paper is concerned with the calculation of stresses in surface-coated solids produced by normal and shear surface tractions applied over an elliptical region. Fourier transform method is used. Stress fields are analyzed as a function of ellipticity, coating-substrate material properties and coating thickness. Differences in stress distributions in the coating and the substrate due to load sliding along the long and short axes of contact ellipse are examined in detail. Validity of two dimensional contact approximation is evaluated and delimited.
2:10 PM		E4/F1-2-3 Modeling of Contact Stress in Indentation Test of Coatings S.A Senouci, H.Z Zaidi (Faculté des Sciences SP2MI, France); D. Paulmier, M. Schmitt (LPMM-ERMES, CNRS-UMR 7554, France) The contact problem of layered elastic solids is of a considerable interest in many area of tribology. Typical applications include coatings, layered composites and thin films. The analysis of the indentation stress field is important to characterize the mechanical properties of coating. The indentation crack in the coating / indenter contact present two different aspects according to the tool form: (tool without edge, pointed tool).-The tool without edge (ball, cylinder tool...) in contact with coatings produces in first, elastic deformations. These deformations stay elastic until the apparition of a crack with a cone-shaped form. The crack takes in Hertzian mode. The different aspects of this particular mode are developed in this paper.- The tool can be also pointed (Vickers…). The zone of plastic deformation in coating is formed immediately with its contact to the indenter. The dimension and the form of this zone of deformation plastic move when the load applied to the tool increases. When a critical dimension of this zone is reached, cracks appear. The aim of this study is to present the indenter characters of brittle and ductile coating on material , to model the stress field in surface and subsurface.
2:30 PM		E4/F1-2-4 Scratch Test Failure Modes and Performance of Organic Coatings for Marine Applications S.J. Bull, I.P. Gilbert, D. Mitchell, J.R. White (University of Newcastle, United Kingdom) Although the scratch test is widely used for the assessment of thin hard coatings, its use for the testing of organic coatings is much less widespread. This is partly because these organic layers are much thicker than the hard coatings and hence interfacial loadings are much smaller and partly because the low hardness of the coatings means that they will plastically deform considerably during the test. Organic coatings for the protection of marine structures are often based on epoxy-resins or similar materials which are brittle compared to other organic resins. Furthermore, in service these materials undergo photo-oxidation which can increase their brittleness or introduce thin modified surface layers which have poorer properties than the as-received material. Corrosion of the underlying substrate may also lead to changes in coating adhesion. The scratch test is an ideal way of making quantitative comparisons between these materials both in the as-received state and after exposure to UV or salt water. In this study a number of organic coatings and base resins used for marine protection have been assessed by the scratch test. Both through-thickness cracking and interfacial detachment have been observed when the coatings are less than about 400µm thick with mainly plastic deformation for thicker coatings. Interfacial detachment is usually observed as a consequence of through-thickness cracking and initiates behind the moving indenter, contrary to what is usually observed for hard coatings. The critical loads for through-thickness cracking and interfacial detachment change as curing processes and are reduced after exposure to salt water. The use of the scratch test to monitor performance of these coatings will be discussed.
2:50 PM		E4/F1-2-5 Adhesion of Copper on Polyimide Deposited with Arc Enhanced Deposition T. Lux (Fraunhofer Institute Manufacturing Engineering and Automation, Germany) Polyimide foils have been coated with Copper using Arc Enhanced Deposition known as VALICO technology. At this deposition process the metal is evaporated from a crucible and can be partly ionized by an electron beam extracted from a cathodic arc. This coating technology allows different magnitudes of ionization of the metal vapour by setting the currency of the electron beam. The influence of the ionization on the adhesion has been studied. Adhesion measurements have been made by pull test and by peel test on coatings which are electroplated to 25 µmm thickness. The foils were pretreated by plasma with different gases. AFM measurements have been made on pretreated and coated substrates.
3:30 PM		E4/F1-2-7 Cladding of Copper with Modified Hard-Facing Alloys Using High Power Lasers B.S. Medres, G. Rik, L.V. Shepeleva, M. Bamberger, I. Etsion (Technion - Israel Institute of Technology, Israel); B.L. Mordike, S. Mordike (Institute für Werkstoffkunde und Werkstofftecnik, Germany) The high thermal conductivity of copper makes it an interesting material for applications involving heat removal, e.g., in casting molds. But due to the low abrasive and impact wear resistance of copper and its alloys, their applications in industry are limited Cu substrates were laser-clad with a Ni and Co-based powder with different particle sizes. The laser clad was carried out of 10 kw laser RS 10 000. A comprehensive analysis of the laser cladding for the determination of its tribological characteristics and cylical impact load were performed. Some correlation was found between the cladding thickness and the tribological properties of clad powders due to thickness induced defects in the cladding layers. The high hardness and wear resistance of the Ni and Co-based cladding, resulting from its microstructure consisting mainly of dendrites and borides, allows for an increase in the abrasive and impact wear resistance of copper components for casting dies.
3:50 PM		E4/F1-2-8 On The Residual Stress Of TiN And CrN PVD Coatings J.R.T. Branco (Fundação Centro Tecnológico De Minas Gerais- Cetec, Brazil); M. Vieira (Universidade Estadual de São Carlos, Brazil); E.K.L. Barroso (Fundação Centro Tecnológico De Minas Gerais- Cetec, Brazil) Coating thickness and the corresponding mechanical properties, adhesion and wear behavior of coated parts depend on the residual stresses imposed by PVD processes. However, there is not enough information available about the interrelationship between residual stresses, substrate surface preparation and interlayer thickness, in special for CrN. To better understand this point and to improve control over the variability of PVD coatings behavior, this investigation was carried out. TiN and CrN coatings were deposited by electron beam and arc evaporation ion plating on AISI M2 high-speed steel and AISI 304 stainless steel. The substrates were finished to 0,4 and 0,1 µm and placed at different positions in a BAI 640 R coating chamber. The effect of two levels of Cr interlayer thickness was also investigated. The residual stresses were determined by measuring the deflection of both strip and disc shape samples with a profilometer.
4:10 PM		E4/F1-2-9 Characterisation of Hard Coatings Produced by Filtered Cathodic Arc Deposition Processes J.R. Tuck (University of Newcastle upon Tyne, United Kingdom); D.G. Bhat (UES Arcomac, Inc.); A.M. Korsunsky (University of Oxford, United Kingdom); S.J. Bull (University of Newcastle, United Kingdom) Wear-resistant PVD coatings are becoming increasingly harder and thinner as manufacturers optimise and improve deposition processes. However, a complex interdependence exists between the individual properties of the coating and substrate on the one hand, and those of the coated system on the other. Hence, for example, there is no good reason to assume that for any given application a harder coating is necessarily better than e.g. a softer one deposited to a greater thickness. There is a great need for quantitative modelling methods so that the design of coatings and multilayered systems can be improved, and the choice of materials optimised. In the present study, various hard coatings produced by filtered cathodic arc deposition in the form of both mono- and multi-layer systems were characterized by micro-hardness and nanoindentation methods, and scanning electron microscopy. The fracture behaviour of these coatings is critical in dictating their hardness performance. Hardness testing results were analysed using a work-of-indentation model that was recently developed and applied to a range of coated systems at Newcastle University. This model allows fitting of empirical data, and yields values for the coating hardness and a dimensionless materials parameter k. The parameter k is related in a complex way to the ductility and fracture toughness of the thin film, as well as the substrate's yield strength and hardening behaviour. As a general trend, a higher value of k indicates lower fracture toughness. The variation of the k parameter within a family of coatings produced by the filtered arc deposition and other techniques will be discussed.
4:30 PM		E4/F1-2-10 Testing and Design of Tool Coatings with Properties Adapted to the Use of Biodegradable Cutting Fluids F. Klocke, T. Krieg (Laboratory for Machine Tools and Production Engineering (WZL), RWTH-Aachen, Germany); E. Lugscheider, K. Bobzin (University of Technology Aachen, Germany) For machining processes which cannot be run without the use of cooling-lubricants, the application of not water miscible and biodegradable fluids is a means for realising an environmentally compatible production. However, compared to conventional cooling-lubricants technological limitations concerning tool wear exist: The lubrication effect decreases due to the reduction of the additive content. Parallel, the thermal tool loadings increase due to diminished heat removal as compared to conventional emulsions. These restrictions necessitate a technological concept to preserve the process performance. This includes: - The definition of suitable fields of application (finishing and light roughing operations), - A systematic adaption of the tools through PVD coating technology by the means of tribological methods and - The systematic development of the fluids. The paper focusses on the definition of demands on tool coatings to be developed aiming at the use of biodegradable cutting fluids. New coating systems and research results on necessary coating functionalities are presented that are in line with the aforementioned technological demands. A coating development including a tribological test scheme for the realisation of high tribo-oxidation stability is part of the presentation. Scopes for improving the anti-adhesive functionality of coatings for drilling tools are presented. This covers the physical characterisation of surface polarity and surface energy of PVD hard coatings and the behaviour of nano-layered WC/C-coatings in drilling of austenitic stainless steel.
4:50 PM		E4/F1-2-11 Surface Reconstruction of Alumina Surfaces J.W. Mintmire (U.S. Naval Research Lab) The (0001) basal plane surface of α-alumina has been known since the late 1960's to reconstruct preferentially at higher temperatures to several larger scale structures, including the (√3x√3) rotated 30°, (3√3x3√3) rotated 30°, and (√31x√31) rotated ±tan^-1(√3/11) reconstructions. All three of these structures are in registry with the underlying (1x1) structure. In earlier work using atomic-scale molecular dynamics techniques to simulate nanoindentation on alumina we found that the nanoindentation process was sufficient to create a lower energy amorphous surface structure apparently related to these reconstructions. We have examined these families of surface reconstructions with our ES+ empirical potential that explicitly includes variable ionic charge. We discuss the relative energetics of these reconstructions, as well as simulations of nanoindentation on aluminum and alumina substrates. This work was supported by the U.S. Office of Naval Research, both directly and through the U.S. Naval Research Laboratory. Computational support was provided under a DoD HPCMP grant.
5:10 PM		E4/F1-2-12 The Role of Physical and Mechanical Factors on the Adhesion Strength of Chemically Vapor Deposited (CVD) Diamond Coatings on Cemented Carbide Inserts M.A. Taher (Materials and Manufacturing Research Laboratory (MRL), Department of Mechanical Engineering, University of Arkansas); W.F. Schmidt, A.P. Malshe (Materials and Manufacturing Research Laboratory (MRL), University of Arkansas) In this study, the role of physical and mechanical factors on the adhesion strength of chemically vapor-deposited (CVD) diamond coatings on cemented carbide inserts was investigated. The changes that occurred in the substrate residual stress due to pretreatment were measured by x-ray diffraction. A drop in the stress values of the substrates was found to occur after the chemical etching and annealing processes. It was shown that the initial compressive residual stress present in the substrate always dropped as a result of the CVD diamond deposition process. A scraper-testing fixture was designed to examine the adhesion strength of diamond coatings on cemented carbide substrates. The adhesion was found to be extremely poor when the surface of the substrate was mechanically polished or seeded with a layer of nano-crystalline sized diamond particles. Diamond coatings having a thickness higher than 12 µm immediately failed after completion of the CVD process. Glass blasting the substrate prior to CVD diamond deposition and etching with a HF-HNO₃ mixture improved the adhesion strength of the diamond coatings when tested by the use of a scrapper test. Qualitative results show that the diamond coatings deposited on the samples treated by glass blasting and HF-HNO₃ etching did not flake off during the scraping action.