ICMCTF2003 Session E3/F1-1: Mechanical Properties and Adhesion

Wednesday, April 30, 2003 10:30 AM in Room California

Wednesday Morning

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10:30 AM		E3/F1-1-7 Nanotribological Studies of the Dendrimer-mediated Metallic Thin Films X. Li, M. Curry, G. Wei, J. Zhang, S.C. Street, M.L. Weaver (University of Alabama) The studies on the ultra-thin Au films on the dendrimer-mediated substrates reported recently [1,2] show that the nanohardness of thin films was increased significantly by the presence of dendrimer monolayer, which is attributed to the supposed enhanced adhesion and superior flatness of Au metal films as well as the confined nature of the dendrimer layer. This paper presents extensive nanotriobological studies on the 10 nm Ti and Al thin films deposited onto the PAMAM dendrimer mediated Si wafer using DC sputtering. Nanoindentation was made using a Hysitron TriboScope Â® nanomechanical system, while the ramped and constant load nanoscratch testes were performed using a Nano Indenter II system. AFM and SEM were used to measure the nanoindents and the scratch wear tracks, and XPS was used to investigate the chemical interaction. TEM cross-sectional experiments were performed on the inverstigation of the film/dendirmer/substrate interface. It has been found that the nanohardness and elastic modulus of the Ti and Al thin films were influenced by the dendrimer interlayer. The nanoscratch surface and friction coefficient profiles of the thin films indicate that the critical load for the film delamination is increased by the presence of dendrimer interlayer, which is related to the adhesion and interface binding strength. It also shows that the nanoscratch behavior is different for G4 and G8 dendrimer interlayer, which can be corresponded to the different correlation lengths of the thin films on them. The deformation and delamination mechanism was discussed through the AFM analyses of the indents and scratches with and without a dendrimer interlayer and compared with the abrasive wear behavior of the dendrimer mediated Cr and Cu ultra-thin films [3]. These results are important for the developments and potential applications of the polymer mediated metallic thin film tribomaterials.
10:50 AM		E3/F1-1-8 Nanoindentation Assessment of Aluminium Metallisation; the Effect of Creep and Pile-up S. Soare, S.J. Bull, A.G. O'Neill, N.G. Wright, A.B. Horsfall, J.M. Dos Santos (University of Newcastle, United Kingdom) The continuing drive towards deep sub-micron silicon technology has been stimulated by the demand for higher operating frequencies, greater circuit complexity and lower power consumption. As gate lengths approach 250nm and below there is a demand for interconnect widths to decrease to similar dimensions. At such scales the mechanical properties of the lines are considerably different from those of larger sizes and this could affect the reliability of the metallisation, particularly under conditions of thermal cycling. The elastic modulus, yield stress and creep behaviour are all likely to be important and these can, in principle, be determined by nanoindentation. However, the deformation mechanisms are significantly more complex for a thin layer on a harder, stiffer substrate when compared to a thicker, more bulk, coating. In particular, the effect of pile-up on measured mechanical properties becomes more significant as the coating thickness is reduced. In this study a combination of nanoindentation testing, atomic force microscopy, and finite element modelling has been used to investigate the mechanical properties of aluminium metallisation as a function of layer thickness. The effect of line thickness and lateral dimensions on the validity of data determined from indentation experiments will be discussed.
11:10 AM		E3/F1-1-9 Indentation Study of Microscopic Shape Memory and Superelastic Effects in Shape Memory Alloys and Thin Films W. Ni, Y Cheng (General Motors Research and Development Center); D.S. Grummon (Michigan State University) Although shape memory alloys were discovered more than 50 years ago, there is a growing interest in shape memory thin films and coatings for applications ranging from MEMs to tribology. While the macroscopic shape memory (SM) and superelastic (SE) behavior of NiTi alloys are well known, very few studies have been conducted to investigate the SM and SE effects at the micro- and nano-meter length scales. In this work, instrumented indentation experiments with spherical and Berkovich indenters were employed to study the mechanical behavior of NiTi alloys and thin films at the micro- and nano- meter scales. The indentation load-displacement curves for the shape memory and superelastic NiTi were obtained under a range of indentation conditions. The SM effect was quantified by the depth recovery ratio of the indents measured by a surface profilometer; the SE effect was determined by the ratio of reversible work to total work. We show that SM and SE effects exist under both spherical and pyramidal indenters for a wide range of indentation loads and depths. However, the magnitude of these effects depends strongly on indenter geometry. These observations were rationalized using the concept of representative strain and maximum stress under the spherical and Berkovich indenters. These studies provide new insights into the mechanisms of SM and SE effects at multiple length scales.
11:30 AM		E3/F1-1-10 Indentation Behavior of PVD Multilayer Coatings. Analysis of their Fracture Mechanisms by Cross-sectional Electron Microscopy N.J.M. Carvalho, B.J. Kooi (University of Groningen and Netherlands Institute for Metals Research, The Netherlands); J.Th.M. De Hosson (University of Groningen, The Netherlands) Contact-induced fracture in coated systems is a complex phenomenon and controlled by the coating material itself, the substrate upon which the coating is deposited, and the interface(s) which bond the system together. In order to predict their performance in service the fracture modes of the coatings subjected to nanoindentation testing, with sharp and spherical indenter geometries, were investigated. In this study, amorphous multilayer of tungsten carbide/carbon (WC/C) and polycrystalline multilayer of titanium nitride/titanium-aluminum nitride (TiN/(Ti,Al)N) both deposited by physical vapor deposition onto steel substrates were considered. The cracking mechanisms were explored using a new technique for cross-sectional electron microscopy of the nanoindentations. The information retrieved with this technique has been combined with the analysis of load-displacement (P-δ), load-displacement squared (P-δ²), and load-contact stiffness squared (P-S²) curves in order to identify the load capacity and the transitions between the different deformation regimes of the coatings. The MTS Nano Indenter XP with a continuous stiffness module (CSM) and a high load cell has been also used to probe the variation of hardness and modulus with the indenter displacement. The outcome of this study has permitted to understand in more detail the dissimilarities in deformation modes of amorphous and polycrystalline multilayer coatings.
11:50 AM		E3/F1-1-11 Nanoindentation of a Thermal Barrier Coating at High Temperature A.C. Fischer-Cripps, C. Comte (CSIRO, Australia) Nanoindentation is typically used to measure mechanical properties of small volumes of materials such as found in thin film applications. The technique is usually applied at room temperature. However, the in-service temperatures are often several hundreds of degrees greater than this. Indeed, coatings are often designed to protect the underlying substrate from high in-service temperatures. The mechanical properties of the coating can be quite different at elevated temperatures compared to room temperature. The present work shows how nanoindentation testing can be performed at elevated temperatures through the use of a special tip heater. Results are shown for a thermal barrier coating at room temperature and an elevated temperature.