ICMCTF2002 Session E4/F1-2: Mechanical Characterization. Micromechanical Testing and Modelling

Monday, April 22, 2002 1:30 PM in Room California

Monday Afternoon

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1:30 PM		E4/F1-2-1 Practical Issues Associated with the Development of an ASTM Standard Scratch Hardness Test P.J. Blau (Oak Ridge National Laboratory) While ASTM consensus standards for quasi-static indentation hardness testing, none exist for single-point scratch testing despite its importance as a characterization tool for bulk materials, surface treatments, and coatings. Three years ago, ASTM Subcommittee G02.30 on Abrasive Wear created a task group to look into the matter. The objective of the group was to develop a straightforward, quantitative, and repeatable procedure by which to determine the resistance of a surface to damage from a hard stylus moving along it under non-zero load. The measurement of coating adhesion was intentionally excluded from the scope of this group. After several rounds of inter-laboratory testing, a draft scratch hardness test standard was eventually prepared, and it is being balloted for final approval. This talk will describe the practical metrology issues associated with creating a standard test method for scratch hardness and the problem of establishing the conditions for which the test is valid and invalid. These issues involve how to specify stylus characteristics, selecting from among several types of width measurement methods, coping with edge deformation and fracture issues, addressing the transition between the spherical tip and the conical portion of the stylus, and even defining what is meant by the basic term scratch width. The current status and the form of the scratch hardness standard will be discussed.
1:50 PM		E4/F1-2-2 Properties and Performance of Commercial TiCN Coatings; Part 1; Coating Architecture and Hardness Modeling S.J. Bull (University of Newcastle, United Kingdom); D.G. Bhat (University of Arkansas); M.H. Staia (Central University of Venezuela) Several PVD and CVD TiCN coatings on a cemented carbide substrate have been obtained from commercial suppliers and subjected to a range of analysis and characterization techniques in order to determine the effects of coating composition and architecture on performance. The majority of suppliers produce coatings with the C/N ratio approximately equal to 1 although one supplier increases this to 2. For all the PVD coatings the supplier initially deposits a layer of TiN to promote adhesion and then gradually increases the nitrogen content of the process gas to make TiCN with a graded composition running from pure TiN to TiCN over a few microns of coating growth. This graded layer may or may not be capped with a layer of TiCN with fixed composition. The hardness behaviour of these layers is more complex than a simple single layer on the substrate. In this study an existing predictive hardness modeling analysis developed at Newcastle has been extended to deal with coatings of graded composition. The potential for optimizing the hardness of TiCN coatings by changing coating architecture will be discussed.
2:10 PM		E4/F1-2-3 Properties and Performance of Commercial TiCN Coatings: Part 2; Tribological Performance S.J. Bull (University of Newcastle, United Kingdom); D.G. Bhat (University of Arkansas); M.H. Staia (Central University of Venezuela) Friction and wear testing has been carried out on a range of commercial PVD and CVD TiCN coatings deposited on WC/Co which were characterised in detail in part 1 of this paper. Single pass scratch tests were used to characterise adhesion and pin-on-disc testing was used to determine friction coefficients and wear rates. The critical load for coating detachment depends on coating thickness as expected for arc evaporated coatings and there is no systematic variation between coatings deposited by different processes. The friction coefficient against WC and sapphire balls varies considerably between coatings produced by different processes as does the wear rate. These results are discussed in light of the different coating architectures used.
2:30 PM		E4/F1-2-4 Study of Adhesion of Thin Films Using Acoustic Emission During Indentation O.G. Lysenko, N.V. Novikov, V.I. Grushko (Institute for Superhard Materials, Ukraine); V.J. Valuisky (UDACHA-Diamond, Ukraine) Because of the availability of commercial adhesion testing machines and the minimal time required for data acquisition, indentation method has some advantage in comparison with the most known methods of the adhesion evaluation. Using the load on the indenter at the moment of delamination as a measure of adhesion strength under such tests one can evaluate the thin films adhesion degree. The disadvantage of this technique is that the uneven change of the both load on the indenter and the value of standard deviation can occur with crack initiating on the specimen. For accurate determination of the moment of peeling off a film from a substrate authors have developed the technique of the analysis of AE signals by processing the initial signal. A special feature of this technique is that the AE transducer plays the role of a basis surface. The tested sample is installed directly on a working surface of the sensor preliminary greased with a thin layer self-hardening lubricant. The amplified signal is transmitted to the oscilloscope and computer. Results for a range of carbon films on different substrates is presented to demonstrate the method.
2:50 PM		E4/F1-2-5 Comparison of Elastic Modulus of Very Thin Diamond-Like Carbon Films Deposited by FVA and r.f.-PACVD J.-W. Chung (Korea Institute of Science and Technology, Korea); C.S. Lee (Korea Institute of Science and Technology and Yonsei University, Korea); D.-H. Ko (Yonsei University, Korea); J.-H. Hahn (Korea Research Institute of Standards and Science, Korea); K.-R. Lee (Korea Institute of Science and Technology, Korea) As the requirement for the very thin film increases in various industrial applications, the mechanical properties of the thin film become increasingly important. For example, the protective layer for hard disk should be less than 5 nm due to the reduced magnetic spacing between the magnetic layer and the read/write head. The mechanical property of the protective layer is thus one of the major concerns in the development of hard disk. Diamond-Like Carbon (DLC) film is one of the candidate materials. However, in the film made by radio frequency plasma assisted chemical vapor deposition (r.f.-PACVD), it is observed that the elastic modulus of very thin film was smaller than that of the thick film in some deposition conditions. In the present work, we investigate the elastic modulus of very thin DLC film deposited by filtered vacuum arc (FVA) process and r.f.-PACVD. Biaxial elastic modulus of very thin DLC film could be measured by recently suggested free overhang method. Because the substrate was removed to obtain sinusoidal free overhang of the DLC film, the measured value is not affected by the mechanical property of the substrate. In r.f.-PACVD, it is observed that the elastic modulus is independent of the film thickness only at the optimum ion energy. However, in ta-C films deposited by FVA process, the elastic modulus of very thin film is not varied with the film thickness, regardless to the deposition condition. This result showed that the mechanical property of very thin film is strongly dependent on the deposition method and the deposition conditions.
3:10 PM		E4/F1-2-6 Progress Towards Standardisation of Ball Cratering M. Gee (National Physical Laboratory, United Kingdom) The ball cratering (micro-abrasion) test is becoming popular as a method for the abrasion testing of surface engineered materials. It possesses many advantages over more conventional abrasion tests including the ability to test small volumes of material and thin coatings, its perceived ease of use and the low cost of the test equipment, and its versatility. Standards are now being drafted both in the USA and in Europe on ball cratering, but further work is needed before this work can be completed on the effect of test variables and the choice of measurement method on the results that are achieved. This paper discusses these aspects of the test and its relevance to industrial wear problems, and describes the results of a preliminary interlaboratory exercise that has been conducted in the UK to determine the effectiveness of the test method. The paper will also give an outline of a new EU funded project that has the aim of validating the test and which brings together a consortium of 10 research partners from 4 European countries.
3:30 PM		E4/F1-2-7 The Effect of the Substrate on the Mechanical Properties of TiN Coatings S.V. Hainsworth, W.C. Soh (University of Leicester, United Kingdom) TiN coatings are commonly used in industry to impart improved friction and wear performance. It is widely recognised that the substrate plays an important role in determining the mechanical properties and wear resistance of such coatings. TiN coatings are usually applied to hard tool steels where there is substantial load support from the substrate. However, there are many applications where it may be desirable to apply the coatings to softer substrates, for example where the strength-to-weight ratio of the substrate material is important. Coatings can still be used effectively in these applications. However, it is then critical to understand the transitions between where the load is contained solely in the coating, or where it is a combination of coating/substrate properties that are important in determining the overall mechanical response of the system. This paper therefore reports on a systematic investigation of the effect of substrate on the mechanical response using a range of mechanical testing te hniques. A TiN coating has been deposited using ion assisted PVD onto a number of substrates with differing combinations of modulus and hardness. The substrate materials include steel, stainless steel, titanium, copper and brass (i.e. a range of E/Y ratios). The mechanical properties of these coatings has been investigated using nanoindentation, microindentation, scratch testing and micro-abrasion wear testing. The deformation observed around the indentations at different loads has been observed using scanning electron microscopy and atomic force microscopy. The scratch displacement and the amount of pile-up around the scratches has also been investigated and the wear has been observed using scanning electron microscopy. The results from indentation and wear testing are correlated to investigate the critical depth to coating thickness ratio where coating-only properties can be obtained.
3:50 PM		E4/F1-2-8 The Fracture Toughness Properties of Borided Some Tool Steels U. Sen, C. Bindal, S. Sen (Sakarya University, Turkey) In this study the fracture toughness of boride layer of two borided cold work tool steels has been detailed. Boriding was carried out in salt bath consisting of borax, boric acid, ferro-silicon and aluminum. Boriding temperature was between 850°C and 950°C, and duration was 1-8 hours. The presence of boride phases was clarified by x-ray difraction. Hardness and fracture toughness measured via Vickers indenter. Increasing of boriding time and temperature lead to reduction of fracture toughness. Metallographic examination showed that boride layer formed on cold work tool steels were homogenous and smooth.
4:10 PM		E4/F1-2-9 Fatigue Studies of Microscale Structures for MEMS Applications Using Nanoindentation Techniques X. Li, B. Bhushan (The Ohio State University) Mechanical property evaluation of microscale structures is necessary to help design reliable microelectromechanical systems (MEMS) devices since most material properties are known to be size-dependent and such properties of microscale structures have not been well characterized. Fatigue properties of microscale beams were studied using a depth-sensing nanoindenter with a harmonic force. The contact stiffness was monitored continuously throughout the test. The abrupt decrease in the contact stiffness indicates fatigue damage has occurred. The critical load amplitude, below which no fatigue damage occurs, was identified. Failure mechanisms of the beams during fatigue are also discussed in conjunction with the hardness, elastic modulus, fracture toughness, and fabrication processes. The dynamic nanoindentation fatigue test used in this study can be satisfactorily used to simulate and study fatigue damage in MEMS devices.
4:30 PM		E4/F1-2-10 Analysis of Depth-sensing Indentation Test Data for Functionally Graded Materials. A.C. Fischer-Cripps (CSIRO, Australia) This paper presents a method of analysis of data obtained from sub-micron indentation testing performed on materials whose elastic modulus varies with depth from the specimen surface. Conventional methods of analysis assume that the elastic modulus of the specimen material is a constant. The present work describes a correction to the conventional methods that take into account the variation of modulus with depth of penetration of the specimen.
4:50 PM		E4/F1-2-11 A New Model for the Composite Hardness of Thin Films B. Pertuz (Laboratory of Mechnics, LML URA CNRS 1441, France); A. Roman (Université de Franche-Comté, Montbéliard, France); K. Chicot (Laboratory of Mechanics, LML URA CNRS 1441, France); E.S. Puchi, M.H. Staia (Central University of Venezuela); H. Shi (University Tsing Hua, Beijing, China); P. Démarécaux (School of Hautes Etudes Industrielles, Lille, France); J. Lesage (Laboratory of Mechnics, LML URA CNRS 1441, France) Measuring Hardness of thin films, namely films of less than 10 μm thick, using standard microhardness testers is a very complicated task. The values that are obtained for this range of micro-indentation loads are in fact the results of contribution by both the film and substrate. In order to determine the hardness of the film it is necessary then, to separate the two contributions by means of a mathematical model. Numerous models can be found in literature but their application requires the introduction of constants that have to be deduced from other experiments or from results already published in literature. These models are generally based on a linear additive law expressing the measured "apparent" hardness in function of the hardness of the film and of the substrate. The objective of the present work is to propose a new model that does not require the introduction of a constant. The idea that is developed here is to combine a series law and a parallel law in order to calculate the hardness of very thin films for which only the thickness, hardness of the substrate and the apparent hardness are known. The methodology was applied to various Ti, TiN, TiC, and DLC films and the results have been discussed in the light of other well in use models. It is shown that this model gives similar values to the of Jonsson and Hogmark model, using a constant C = 0.5.