ABSTRACTS
The following is a list of the abstracts for papers which will be presented in the SECOND INTERNATIONAL SYMPOSIUM ON ADHESION ASPECTS OF THIN FILMS. The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)
Hard and Elastic Carbon Nitride Films for Tribological Applications
During the last decade, carbon nitrides (CNX) have been discussed as a potential material for many tribological uses because of their particular mechanical properties. Although the synthesis of single-phase crystal films remains a open challenge, amorphous CNX film with low N concentration are already industrially applied and many patents of products using CNX films have been claimed.
A new kind of carbon-based material deposited by PVD, the "fullerene-like" carbon nitride has been recently reported. Due to its particular microstructure, this CNX phase has interesting mechanical properties, such as high hardness (40-60 GPa) and an extreme elastic recovery (90%) in indentation experiments.
In this work, a study of "fullerene-like" CNX films deposited by dc magnetron sputtering on different substrates is presented. The effects of the deposition parameters on mechanical and tribological properties have been investigated; the results are correlated to changes in microstructure and morphology. Adhesion aspects of films deposited on steel substrates are particularly discussed. Furthermore, a novel application for medical implants is also reported.
1) Max-Planck-Institut für Eisenforschung, Düsseldorf, GERMANY
2) DOC GmbH, ThyssenKrupp Stahl, Dortmund, GERMANY
Morphology and Chemical Composition of Interfacial Ultra-Thin Inorganic and Organic Layers at Paint/Metal Interfaces
The development of new environmentally friendly coating systems with tailored properties requires better understanding of the interfacial structure, including the pre-treatment and the adhesion promotion for the subsequent organic coating. New surface-analytical techniques, such as photoelectron spectroscopy and infrared spectroscopy, in combination with microscopic techniques, such as atomic force microscopy and field emission microscopy, enable one to characterise surfaces in detail. Modern electrochemical techniques, such as the scanning Kelvinprobe, can now be applied to measure corrosion processes underneath insulating organic coatings and thus provide insights into the processes that lead to the degradation of the metal/polymer composite.
Plasma polymerisation and chemical vapour deposition will be presented as ways to coat reactive metal surfaces with ultra-thin functional layers to improve the corrosion resistance in conjunction with a standard primer. The ultra-thin layers were characterised by means of reflection absorption FTIR-spectroscopy, photoelectron spectroscopy, atomic force microscopy and high resolution electron microscopy. Deadhesion and corrosion processes at interfaces were studied by means of a Scanning Kelvinprobe and standard corrosion tests.
Defined forming of thin film coated materials and subsequent measurement of the deadhered area by means of high resolution microscopy and surface electrochemistry provides insight into the adhesion and mechanical properties of the thin films relevant for coil coated materials.
The results show that modern CVD and PCVD thin film technology in combination with surface and interface analysis is a promising way to perform successful interfacial engineering in the field of polymer coated metals.
1) Laboratoire de Thermocinétique, UMR CNRS 6607, Ecole Polytechnique de l'Université de Nantes, BP 50609, 44306 Nantes cedex 3, France.
2) Laboratoire de Physique Cristalline, Institut des Matéiaux Jean Rouxel, 2, rue de la Houssinière, 44072 Nantes cedx 03, France
Study of Adhesion and Thermal Contact Resistance of Gold and Copper Films On Alumina Substrates
This work presents a comparative study between the Au/Al2O3 and Cu/Al2O3 films. The pure gold and copper films were deposited by evaporation and d.c. magnetron sputtering respectively. A new photothermal method for measuring the total thermal resistance (Rt) in the interfacial area is presented. The film structure influences considerably the quality of heat transfer in the interfacial area. An increase in the Rt with increasing layer thickness is observed for both systems. The thermal treatment improves significantly and simultaneously the Rt and adhesion as determined by srcatch test. This improvement might be related on one hand to the inter-diffusion of film and substrate, to changes in strain, and on the other to the formation of the new compound in the interface region. It is concluded that there is an important correlation between the evolution of Rt and the adhesion.
Influence of Defects and Internal Stresses on the Adhesion of Nanosized Oxide Coatings on Polymers
Research on the adhesion between oxide thin films and polymers substrates is reviewed, with attention paid to coating defects, internal stresses, and failure mechanisms. Such systems comprise gas-barrier protection for food and pharmaceutical packaging based on silicon oxide coatings/semi-crystalline thermoplastic substrates, and transparent conducting tin-doped indium oxide coatings on polycarbonate substrates developed for optical devices such as flat-panel displays. In these applications, the reliability of the coated component may be considerably reduced by the presence of interfacial defects and high residual stresses generated during the deposition process, particularly when the thickness of the coatings is within the nanometer range. Analyses of failure mechanisms of the coating, including calculations of stress concentrations at defect sites, and of the coating/substrate interface, were developed. The accuracy of the models was tested using substrates with controlled roughness, coatings with controlled levels of internal stress, and structured coatings with small holes of well-defined sizes, whose failure mechanisms under stress was investigated in-situ optical and electron microscopes. These approaches are found to be useful to tailor the deposition process for improved mechanical resistance of the coating and adhesion to the substrate.
Structural Analysis of Hybrid Thin Multilayers on Polymeric Substrates Studied by Transmission Electron Microscopy
The physical properties and adhesion of hybrid thin multilayers on polymeric substrates depend critically on both the designs of the multilayers and the interface structure between the layers. To investigate the layered structure of these hybrid thin multilayers on polymeric substrates by transmission electron microscopy (TEM) in detail, the preparation of thin cross-section of the constituent layers is a key. This is because thin cross-sections of the constituent layers are very difficult to obtain with conventional ion-milling techniques due to the different ion-milling rates among the layers and the ion beam damage of polymeric substrates. Ultramicrotomy, previously limited only to the sectioning of organic substances, is utilized to prepare thin cross-sections of the hybrid thin multilayers on polymeric substrates. It was demonstrated in this study that the cross-sectional TEM studies of the hybrid thin multilayers on polymeric substrates were very useful not only to make clear their layered structure and degradation mechanism but also to disclose the structural characteristics of each layer on an atomic scale.
How Residual Stresses and Mechanical Properties of Organic Coating Applied onto Metallic Substrate Interphases Do Affect Practical Adhesion
Residual stresses (s), Young's modulus (E), and the practical adhesion, characterized by either ultimate parameters (Fmax or dmax) or the critical strain energy release rate (Gc), of organic layers made of DGEBA epoxy monomer and IPDA diamine hardener were determined. The prepolymer (DGEBA-IPDA) was deposited both as thick coatings and as a mechanical stiffener onto degreased or chemically etched aluminium alloy (5754). To understand the influence of real gradient properties within the interphase layer, a three-layer model (bulk polymer/interphase/metallic substrate) was used for a quantitative determination of the critical strain energy release rate (Gc). The particular characteristic of this model was to consider residual stresses developed within the entire three-layer system leading to an intrinsic parameter of practical adhesion between a polymer and a metallic substrate. Residual stress intensities are found to be maximal at the interphase/substrate interface leading to an adhesional (interfacial) failure. Moreover, residual stresses act as a potential deformation energy in bonded system. Obviously as soon as this potential deformation energy is higher than the intrinsic adhesion energy of the coating, a spontaneous coating delamination will occur. The determination of the critical strain energy release rate by the flexure three-point test (ISO 14679-1997) shows that residual stresses cannot be neglected. From one surface treatment to another, the effect of the Young's modulus of the interphase ant residual stresses on the (Gc) values will be discussed.
A Study of Intrinsic Residual Stress in Silver Films Deposited by RF Magnetron Sputtering
All physical vapor-deposited coatings are characterized by residual stresses, that are particularly sensitive to energetic particle bombardments (ions or neutrals) in terms of sign and magnitude, so that an increase of particle bombardment can make tensile stresses change into compressive ones.
In this work we investigate the dependence of residual stress on the deposition parameters of silver coatings, through a comparison with the structural and optical properties. The coatings were grown by radio frequency magnetron sputtering on (100)-oriented silicon substrates; in addition, several sets of samples were produced varying the sputtering pressure (0.15-0.9 Pa) and changing the sputtering power supply in the range 25-100W. The results obtained indicate that Ag films are polycrystalline with a moderate [111] texture. The compressive in-plane stress was measured for all the investigated samples. The stress behavior as to the varying of particle bombardment (neutrals), can be summarized as follows: the compressive stress value increases up to a very pronounced maximum, then reaches a saturation value.The experimental results have been explained in the frame of the theory of the "thermal spikes".
Adhesion Aspects of Thin Films in the Field of Micro Reaction Technology
Micro reaction technology is getting increasingly important in the chemical process technology. Especially in the field of liquids and gases micro reactors can be used advantageously. Reactions which are difficult to handle with common known equipment as glasses or flasks can be carried out very save using micro reactors. Another advantage is the possibility of continuous flow reactions in several types of micro reactors. Expensive chemicals can be used in the desired amount and it is possible to save costs, too. Especially pharmacy and biotechnology have great benefits using micro reactors. Most of these devices are made of glass, silicon or polymers. While at the beginning of the development micro reactors contain just a few micro channels one can consider presently growing demands on the wall materials. Often the basic materials do not meet the requirements. Thin film deposition technologies are a relatively simple way to adapt wall materials onto the demands. Chemical as well as physical properties of the wall materials are getting more into the focus of the research activities. Deposition and structuring methods as well as adhesion aspects influence the selection of the materials.
The report gives a survey about material demands and possible solutions. One main focus is the adhesion of different thin films on selected areas of micro reactors made of silicon.
National Institute of Advanced Industrial Science and Technology(AIST)
1-1, Hirate-cho, Kita-ku, Nagoya 462-8510, JAPAN
Improved Adhesion of Ti-O Film deposited onto Titanium-based Alloy
by Reactive Sputtering with Ti/O Compositional Gradient
Coating of titanium-based alloy(Ti-6Al-4V) with Ti-O compositionally gradient films was carried out by reactive DC sputtering, in order to improve not only the biocompatibility of the alloy[1] but also the adhesion between the deposited film and the alloy substrate with preserving the high hardness of Ti-O films[2]. The effects of Ti/O compositional gradient on adhesion of the film to the alloy substrate were investigated by comparing the adhesion of Ti-O compositionally gradient films to the alloy substrates with that of Ti-O compositionally constant films to the alloy substrates. The compositional gradient was realized by varying continuously the oxygen content in Ar-O2 sputter gas mixture during the sputter-deposition.
According to AES in-depth profiles, the oxygen(O) concentration in the deposited film decreased gradually in-depth direction from the surface toward the substrate, confirming that a film with Ti/O compositional gradient, i.e., a Ti-O compositionally gradient film had formed on the alloy substrate, and thereby expecting that the stress concentrated at the interface between the deposited film and the alloy substrate could be relaxed. Based on indentation-fracture tests, it was found the compositionally gradient films were more adhesive to the alloy substrates than the compositionally constant films, concluding that the Ti/O compositional gradient improved the adhesion of the deposited Ti-O films to the alloy substrates.
References
[1] T.Kitsugi et al., J. Biomed. Mater. Res. 32,149(1996).
[2] A.Dubertret and P.Lehr, Compt. Rend. 263,591(1996).