Papers

ICMCTF1999 Session B1-2-2: Nanostructue Thin Films

Wednesday, April 14, 1999 1:30 PM in Room Golden West

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		B1-2-2-1 Elastic and Plastic Properties of Sputtered Nanostructured Ceramic Coatings Evaluated by Nanoindentation M. Odén, L. Hultman (Linköping University, Sweden); H. Ljungcrantz (Impact Coatings AB, Sweden) Nanostructured coatings are an emerging class of functional materials. In contrast to homogeneous coatings these materials are tailored on the nanoscale level that leads to improved mechanical properties. Included in this class of materials are layered ceramics such as the transition metal nitride superlattices and nanocomposites. Enhanced hardness of up to 100% compared to single-layered materials is observed for nitride superlattices with a periodicity of 5-10 nm, both for single-crystal and polycrystalline coatings. Fundamental knowledge of elastic and plastic processes is essential to the understanding of the potential hardness enhancement. For example, results show that elastic-moduli differences of the constituting layer materials are a critical factor determining the enhancements in hardness, yield stress, and tensile strength. It has also been proposed by Koehler that for small period superlattices, yield stress enhancements are determined by calculating the stress required to move individual dislocations across the layers. For large period superlattices, the yield stress is believed to be limited by operation of dislocation sources and dislocation glide within layers. In both cases, it is necessary to know the operating dislocation glide systems as well as correct values for the shear moduli (i.e., dislocation line energies). In this presentation, we will review nanoindentation experiments carried out on various nanostructured ceramic coatings and present results for sputter-deposited single-crystal TiN/NbN superlattices. The superlattice indentation response is compared to homogenous single-crystal TiN and NbN layers and discussed in terms of observed different plastic behavior. Deformation mechanisms are evaluated by electron microscopy and atomic force microscopy.
2:10 PM		B1-2-2-3 Performance of Cemented Carbide Tools Coated with Single and Multilayered TiN/TiAlN Films Deposited by Sputtering and Cathodic Arc T.I. Selinder, C. Strondl, A. Nordgren (AB Sandvik Coromant, Sweden) Cemented carbide cutting tools coated with single and multilayered TiN and TiAlN films were evaluated in machining tests. The performance of the tools was correlated to the physical properties and the morphologies of the coatings. The wear resistance of the tools was tested in longitudinal turning of steel and the coating adhesion was characterized in flaking tests. All films were deposited on cemented carbide substrates by physical vapor deposition (PVD), using the unbalanced magnetron sputtering or the random cathodic arc methods. These two different methods are known to produce coatings with different properties with respect to surface morphology, adhesion and droplet density. The properties are found to be critical parameters for the film adhesion, particularly when there is a pronounced interaction between the chip and the tool, i.e., the film surface. The choice of deposition method also affects the residual stress and the chemical composition of the films. These properties were studied by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS), respectively.
2:30 PM		B1-2-2-4 Elastic and Plastic Energies in Sputtered Multilayered TiN Films Estimated by Nano-Indentation N. Kikuchi, M. Kitagawa, A. Sato, E. Kusano, H. Nanto, A. Kinbara (Kanazawa Institute of Technology, Japan) Recently microhardness enhancement of 30% in comparison with that of monolithic TiN films was observed in compositionally modulated TiN films at a modulation period of 10 nm (E. Kusano et. al, JVST A16,1272 (1998) and J. Nano-struct., in publishing), and difference in the elastic and plastic behavior of the films on the modulation period under indentation had also reported (E. Kusano et al., MRS proc. Vol.505). In order to understand the hardness enhancement on some modulation period, we had measured the elastic and plastic energies for deformation of compositionally modulated TiN films with multilayer structure using the load-displacement curves of nano-indentation measurement. Compositionally modulated TiN films were deposited by reactive dc sputtering on glass substrates with thickness of 400 nm. Range of the modulation period for the films were from 7 nm to 80 nm. Nano-indentation measurement was carried out to evaluate not only microhardness but also the elastic and plastic energies for deformation of the films. XRD patterns and internal stress were also measured. Compressive stress was observed in all films, irrespective of the modulation period. XRD patterns of the films with the period of 6.7 and 10 nm showed only TiN phase. The dissipated energy, which is assumed to be equal to the plastic energy, showed the minimum of 0.36 pJ at a modulation period of 10 nm. Dependence of the dissipated energy on modulation period was consistent with that of the hardness. On the other hand, the elastic energy also showed the minimum value of 0.93 pJ at the same modulation period. We had demonstrated that the plastic and elastic components of the deformation process in the TiN films can be separated. It is assumed that this method is an effective process in order to analyze the mechanism for the hardness enhancement of the multilayered films.
2:50 PM		B1-2-2-5 Growth and Structural Studies of Magnetron Sputtered Si-C-N Films T. Berlind, N. Hellgren, M.P. Johansson, L. Hultman (Linköping University, Sweden) Si-C-N thin films with a Si/C ratio of up to 2 were deposited by reactive co-sputtering of C and Si targets in a mixed Ar/N₂ (60/40) discharge at a total gas pressure of 3 mTorr. Films were grown to a thickness of ~1.5 µm on Si(001), pyrolytic carbon, HSS (ASP 30), and NaCl substrates held at 300 °C and a negative floating potential of ~10 V. In order to vary the composition of the film, the deposition rate varied between 200 and 400 nm/h, by controlling the target power of each magnetron between 20 W and 200 W. As-deposited films were analysed with respect to composition, structure, mechanical properties and surface energies by RBS, XPS, TEM, SEM, XRD, nanoindentation, and wetting techniques. For films with low Si concentration, the XPS N1s peak indicated the presence of an amorphous C-N network. A narrower N1s peak for films with increasing Si content gave an indication of more nitrogen bonded in a Si-N configuration. This was also consistent with the changes observed for the C1s and Si2p peaks. High resolution transmission electron microscopy revealed a predominantly amorphous-to-graphite-like microstructure. The films grown with a low Si content (< 10%) also contained widely dispersed fullerene-like aggregates, similar to what has been observed for CN_x films deposited under similar conditions. However, no diffracting intensities could be detected by XRD indicating X-ray amorphous material.