ICMCTF2007 Session E2-1: Mechanical Properties and Adhesion

Wednesday, April 25, 2007 8:00 AM in Room California

Wednesday Morning

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8:00 AM E2-1-1 Centrifuge Technology: A Promising Tool for the Determination of Adhesion and Mechanical Properties!
U. Beck, G. Reiners (Federal Institute for Materials Research and Testing (BAM), Germany); D. Lerche (L.U.M. GmbH, Germany)
The adhesion of coatings and stress-strain properties of materials are of fundamental interest. Because of the huge variety of coating/substrate systems in terms of materials and large thickness range, adhesion tests display the same variety as coating/substrate systems. An overview of conventional adhesion tests (e.g. pull-, scratch-, and rubber-test) is given. Almost all of these tests are generally qualitative rather than quantitative in terms of force per square millimetre. They are hence not comparable. In search of a more general test, the cavitation test is evaluated and the new patented centrifuge test is presented. The centrifuge test as the only quantitative multiple-sample test has manifold advantages compared to the single-sample pull test, i.e. the only quantitative conventional adhesion test. It is advantageous that sample clamping is one-sided for the centrifuge test instead of two-sided for the pull test. The centrifuge technology additionally enables tests under defined climatic (humidity, temperature) or hazardous (gases or liquids) environments. Moreover, supplementary test conditions (alternating loads at various load rates) important to fatigue testing can be easily realised by the variation of the number of revolutions. The use of a test specimen glued to the coating to be tested allows the use of desk-top centrifuges with g-forces of several 1000 g. At present, conventional glues have adhesive strength beyond 50 Newton per square millimetre. A first prototype of a centrifuge for testing the adhesion of coatings and the bond strength of glues equipped with wireless signal transmission is presented. The goal is to apply centrifuge technology to a large variety of mechanical quantities such as adhesion, bond and join strength, and stress-strain parameters. In the long term, centrifuge technology applied to solid-solid systems may have the same importance as it already has for liquid-liquid and liquid-solid phases.
8:20 AM E2-1-2 Comparison Between the Progressive Load Scratch Test and the Mercedes Test and the Effect of the Rockwell Indenter Tip Geometry on the Progressive Load Scratch Test
G. Favaro (CSM Instruments, Switzerland); M. Morstein (Platit AG, Switzerland); R. Consiglio, N. Conte, N.X. Randall (CSM Instruments, Switzerland)

The deposition of thin films and coatings has in recent years prompted significant efforts by ISO and ASTM to standardize tests which can adequately characterize coating adhesion and scratch resistance.

Since 1991 when the VDI 3198 standard appeared, many companies started to use this test method which has since become known as the "Daimler", "Mercedes" or "Rockwell" test method. It consists of making a Rockwell C indentation with an applied load of 1500 N on the coating and evaluating the resultant cracking on a 6-level scale. This test has proved to provide only qualitative information and does not necessarily correlate to coating adhesion. This makes it very limiting when trying to assess the mechanical properties of a coating in a quantitative and reproducible way.

The progressive load scratch test has since proved to be a far better method (ASTM C1624 & ISO 20502) for evaluating coating adhesion in hard ceramic coatings. This paper presents a direct comparison between the Mercedes test and the scratch test on a range of common coatings including TiN, DLC and nanocomposites on Steel and carbide substrate.

In performing tests to compare the Rockwell Test with the Scratch Test it was noticed that the results were significantly influenced by the indenter tip geometry and wear. When using the progressive load scratch test to characterize the mechanical properties of a substrate-coating system, the geometry of the indenter as well as its condition, are very important in obtaining quantitative information and in being able to compare results between different labs.

In order to better understand variations in the measured critical load as a typical indenter becomes worn, we have compared various 200 µm Rockwell indenters, both of natural and synthetic diamond material, from various manufacturers.

This study was carried out using the standard operating procedures as outlined in the ISO 20502 and ASTM C1624 standards, including up to 100 scratches per indenter on a standard DLC-coating of thickness 2 µm. The results to be presented show very clearly the importance of regular quality control of a scratch test indenter and the influence of its wear on the measured critical load. Some recommendations will also be made on the best ways of achieving this in the modern industrial environment.

9:00 AM E2-1-5 The Effect of the H/E Ratio on the Adherence of TiN And TiC Coatings Deposited on an AISI H13 Tool Steel
A.A.C. Recco (University of São Paulo, Brazil); I.C. Oliveira, M. Massi, H.S. Maciel (Instituto Tecnológico de Aeronáutica, Brazil); A.P. Tschiptschin (University of São Paulo, Brazil)
Reactive Magnetron Sputtered TiN and TiC films were deposited over H13 tool steel and silicon, under nitrogen plus argon or methane plus argon reactive plasma. Depth sensing techniques were used to assess the mechanical properties of the films, namely hardness and Young's modulus using a load of 7 mN. The ratio H/E increases when the amount of nitrogen in the atmosphere is increased for nitrogen contents between 3 and 38 wt%. On the other hand when the methane content of the reactive atmosphere is increased the ratio H/E increases reaching a maximum when the methane content is 12 wt%. Further increases of the methane content in the atmosphere lead to a decrease in the H/E ratio of the TiC films. The adherence of the films to the substrate was evaluated using a conic Rockwell indentor with 0.3 mm radius and varying loads of 10, 15, 30, 60, 100, 125, 150 and 250 kgf. The adherence of the film to the substrate is greater when the H/E ratios of the film and of the substrate are similar.
9:20 AM E2-1-6 Adhesion Energy of Cu/Polyimide Interface in Flexible Printed Circuits
S. Kamiya, H. Furuta (Nagoya Institute of Technology, Japan); M. Omiya (Tokyo Institute of Technology, Japan)

For the case of flexible printed circuits, peel tests have been commonly used to determine the strength of adhesion. However the estimated strength usually depends on the thickness of adhered films due to the plastic dissipation energy. It is expected that extrapolation of the results toward zero thickness may exclude the influence of plastic deformation, which resulted in 250 J/m2 for a Cu/Polyimide sample studied in this paper. Kinloch1 tried to estimate the effect of plastic deformation on the basis of beam bending theory. His theory yielded the adhesion energy 100 J/m2 when applied to the same sample. However, there still remains plastic deformation on the substrate side and at the interface crack tip which was not taken into these considerations.

In this study, instead of peel test, an experimental technique recently developed by Kamiya et al.2 was applied, where interface crack was effectively extended by a local load with a minimum amount of deformation. Elastic-plastic finite element model was calculated to simulate the interface crack extension process and to obtain the amount of plastic deformation. The sum of the increments of elastic strain energy and plastic dissipation energy was found not to agree with the work done by the external load. The difference was consumed to separate the interface and thus defined as the interface fracture energy. The same amount was obtained by calculating the work done by the nodal force in the vicinity of interface crack tip. This concept concluded the interface fracture energy of the system mentioned above to be 35 J/m2 and is expected as a new reliable scheme to determine the strength of adhesion independent of plastic deformation in film-substrate systems.

1A.J.Kinloch, C.C.Lau, J.G.Williams, Int. J. Frac., 66(1994), 45-70.

2S. Kamiya, H. Nagasawa, K. Yamanobe, M. Saka, Thin Solid Films, 473(2005), 123-131.

9:40 AM E2-1-7 Controlling the Adhesion Between Diamond-Like Carbon (DLC) Film and High-Density Polyethylene (HDPE) Substrates
T. Hoshida, D. Tsubone, K. Takada (Keio University, Japan); H. Kodama (Kanagawa Academy of Science and Technology, Japan); T. Hasebe (Tachikawa Hospital and Keio University, Japan); A. Kamijo (The University of Tokyo Hospital, Japan); T. Suzuki, A. Hotta (Keio University, Japan)
High-density polyethylene (HDPE) is the most fundamental polymer as well as one of the most commonly used semi-crystalline plastics. Nevertheless, one of the difficulties for its implementation lies in the adhesion of the HDPE, especially when it is used for a complex with other materials. Here in this paper, we will discuss the adhesion of HDPE with thin diamond-like carbon (DLC) films. The DLC films were deposited on HDPE substrates by plasma enhanced chemical vapor deposition (CVD). We will also discuss the effect of the fluorine content in DLC films on the adhesion between HDPE and DLC. The adhesion force between the two materials was measured through modified T-peel testing. The adhesion force was then plotted against peel length to measure the averaged adhesion force and the total adhesion energy between HDPE and DLC.
10:00 AM E2-1-8 Effect of Substrate Plasticity on the Buckling Phenomenon of Coated Materials
F. Foucher, C. Coupeau, J. Colin, A. Cimetiere, J. Grilhe (LMP-CNRS, Poitiers University, France)

Buckling and wrinkling of thin objects, such as sheets or rods, are well known phenomena, studied from wide to fine-scale in micro-electronic or bio-mechanic for instance. Using continuum mechanics, buckling of thin sheets has been studied by Foppl and Von-Karman at a macroscopic scale as far back as the beginning of 1900s. Since the 1980s, the reduction to the microscopic scale of experimental observations has allowed us to study thin film buckling phenomena in the same framework. Taking advantage of the high resolution offered by scanning probe microscopy, the fine structure of buckling patterns is now intensively investigated at a nanometre scale. It has been demonstrated that a thin film sustaining a stress greater than a critical value may buckle into different patterns, such as circular blisters, straight-sided wrinkles or telephone cords. The influence of substrate morphology and elasticity has been also investigated. However, the effect of the crystalline substrate plasticity has not yet been considered on the buckling instability phenomenon.

It is the purpose of the present paper to report experiments where dislocations coming from the substrate and emerging at the interface modify the further buckling structures of the thin film. Formation of straight-sided blisters just above step structures resulting from the dislocation emergence process is experimentally shown and explained in the frame of the Foppl/Von-Karman theory of thin plates. A new critical stress above which the buckling may occur has been determined and asymmetry of the resulting blisters has been also explained. Finally, the role of the crystallographic angle of the emerged steps with respect to the interface has been quantified and appears to be a relevant parameter in the study of the mechanical behaviour of the film.

10:20 AM E2-1-9 Finite Element Analysis of Radial and Tangential Stresses Developed During the Indentation of Coated Steels
T. Pachler, R.M. Souza, A.P. Tschiptschin (University of São Paulo, Brazil)

Previous analysis on the Rockwell C indentation of systems with titanium nitride (TiN) films and high-strength tool steel substrates indicated the formation of circular and radial cracks at the film surface. Further analysis indicated that the radial cracks propagated after the unloading step of the indentation process, since they were only observed in the outer region of indentation.

In this work, a Finite Element Analysis was carried out to simulate the penetration of Rockwell conical and spherical indenters in coated systems and to study the intensity of the peaks in radial and tangential stresses at the indentation edge, during the loading and unloading steps of the indentation. The objective was to determine the conditions where the peak in tangential stresses overcomes the peak in radial stresses near the edge of indentation mark, favoring the formation of radial cracks. In the simulations, the behavior of the substrate and the film were considered to be elastic-plastic and different values of substrate yield stress were considered.

The results indicated that, during loading, the peak in radial stress at the indentation border is higher than the peak of tangential stress. During unloading the peak of tangential stresses increases, while the peak of radial stresses decreases, favoring a change in the crack pattern. Results have indicated that the lower intensity of the peak in radial stresses is due to a change of film curvature when the system is unloaded.

The rate at which the peaks in radial and tangential stresses increase was lower for substrates having higher yield stresses. Substrates with higher yield stresses also showed a larger decrease in the peak of radial stresses during the unloading step. The results were similar for both conical and spherical indenters.

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