Papers

ICMCTF2001 Session B3-1: Synthesis/Structure Relationship in Nano Structured Films

Tuesday, May 1, 2001 8:30 AM in Room Golden West

Tuesday Morning

Start	Invited?	Item
8:30 AM		B3-1-1 Structure-Properties-Performance Relations in Nanocomposite Hard Coatings J. Patscheider, T. Zehnder (EMPA Dübendorf, Switzerland); M. Diserens (EMPA Dübendorf and IPA, EPF, Switzerland) Classical hard coatings like TiN, TiC and others can be improved with respect to their performance by combining these single-phased materials with certain suitable materials on a nanometer scale. In particular, multilayers and nanocomposites proved successful in promoting hardness, oxidation resistance, wear behavior and other properties relevant for wear-reducing coatings. Examples encompass combinations of crystalline hard phases with each other, of hard crystalline and amorphous phases and also combinations of hard and soft phases. Despite some fundamental differences, similarities between multilayer structures and nanocomposites are found. When the typical dimensions of the constitutents are of the order of 5 to 20 nanometers, the properties of these multiphased materials are determined by interactions between the phases; the role of phase boundaries is therefore in the focus of interest. However, certain preconditions such as phase composition, single layer thickness and crystallite size have to be met in order to obtain improved properties of nanostructured coatings. Various examples of different nanostructured hard coatings will be presented and the existing models, which explain the properties, will be discussed.
9:10 AM		B3-1-3 Synthesis and Tribological Properties of TiN/SiN_x Superlattice Coatings with an Equiaxed Microstructure, Increased Hardness, and Reduced Internal Stress Y.H. Chen, K.W. Lee, Y.-W. Chung (Northwestern University) TiN coatings are commonly used in various tribological applications for their wear resistance and inertness to steels. However, TiN coatings predominantly grow with a columnar grain structure. These columnar grain boundaries become the usual sites for crack initiation, resulting in early failure of TiN coatings. In our research, TiN/SiNx nanolayered superlattice coatings are developed to suppress the columnar structure. SiNx is primarily used to periodically interrupt the columnar structure and renucleate the growth of TiN. In addition, the amorphous layers serve to suppress the transmission of dislocations from one TiN layer to another, thereby enhancing the hardness of the coating. Cross-sectioned TEM studies verified that the columnar structure was totally suppressed and showed the equiaxed structure. These TiN/SiNx nanolayered superlattice coatings also showed better mechanical and tribological properties than those of TiN coatings, such as higher hardness (45GPa), lower friction coefficient (half of TiN coatings), and better nanoscratch resistance. Block-on-ring wear tests showed that the wear rate of TiN/SiNx superlattice coatings was three times better than that of TiN coatings. The correlation between microstructure and mechanical properties of these coatings will be presented. .
9:30 AM		B3-1-4 CrN/NbN Superlattices Grown by Cathodic Reactive Arc Deposition S. De Rossi, C. Pecchio (Istituto Scientifico Breda S.p.A., Italy) CrN/NbN superlattice coatings, approximately 3 µm in thickness, have been deposited on tool steel samples by reactive cathodic arc evaporation technique in an industrial-size chamber. Superlattice deposition was achieved by triggering alternatevly on Cr and Nb cathodes and the superlattice period is varied ranging from 3 to 30 nm changing the alternating cathodes time. The relative thickness of CrN layer with respect to the total period thickness was also varied in order to optimise the coating characteristics. All coatings were mechanically characterised with respect to their hardness, adhesion, dry sliding and abrasive wear resistance. Analytical techniques including X-ray diffraction, scanning and transmission electron microscopy and energy dispersive X-ray analysis were used for the phase composition, microstructure and chemical composition measurements. A CrN coating was used as a reference throughout the investicgation since CrN/NbN superlattice coating has been developed as a potential alternative to the CrN one. X-ray diffraction showed for the CrN coating a (220) preferred orientation while all superlattice samples displayed a strongly preferred (200) orientation with a lattice parameter intermediate the CrN and the NbN one depending on the Cr/Nb ratio. It was found that the mechanical and tribological properties of the superlattice CrN/NbN coatings were, in general, superior of those of homogeneous CrN.
9:50 AM		B3-1-5 Study of Mechanical and Tribological Properties of Ti/TiC and Cr/TiC Multilayer Films Deposited by Magnetron Sputtering Assisted Pulsed Laser Deposition R.P. Ayalasomayajula, J. Kraznowski (University of New Hampshire); J. Nainaparampril (Systran Corp.) Metal/ceramic multilayers have the potential to provide high fracture toughness in thin-film coatings. In this paper we present the results an investigation on the effects of multilayer structures of compositionally modulated Ti/TiC and Cr/TiC films on mechanical properties and microstructure. Compositionally modulated Ti/TiC and Cr/TiC films were deposited onto Si (111) and 440C steel substrates at 400°C using the magnetron sputtering assisted pulsed laser deposition (MSAPLD) method. The metal component (titanium or chromium) was deposited by DC sputtering while the carbon was deposited by laser ablation. The film hardness was measured by nano-indentation, while x-ray photoelectron spectroscopy (XPS) was used to estimate the film composition using depth profiling. Film morphology and roughness were measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques, respectively. The residual stress of the deposited multilayers was measured by 2D-area General Area Detector Diffraction System (GADDS). Modulation periods examined in this investigation were 20, 10, 5, 2.5 nm of Ti and Cr with 50nm TiC maintained constant in the deposited multilayers. Films of TiC only were also deposited by MSAPLD for comparison. It was found that the film with lower modulation periods yielded a lower hardness value than single layer TiC, which may be due to compressive stress inside the deposited films. The results obtained in this investigation indicate that the hardness of compositionally modulated Ti/TiC and Cr/TiC multilayer films strongly depend on modulation frequency. Tribological properties performed on steel substrates were also studied and will be discussed.
10:30 AM		B3-1-7 Structure and Properties of Al-Ti-Si-N Coatings Prepared by the Cathodic Arc Ion Plating Method for High Speed Cutting Applications Y. Tanaka, N. Ichimiya, Y. Onishi, Y. Yamada (MMC Kobelco Tool Co., LTD., Japan) Al-Ti-Si-N coatings with several Al/Ti/Si ratios were deposited on WC-Co substrates by the cathodic arc ion plating method. Morphology and compositions of the local parts of the films were investigated by using transmission and scanning electron microscopy with EDS. The films seemed to have the same columnar structure of (Al,Ti)N films with smaller column size. The crystal structure, hardness and oxidation resistance were investigated, and Al-Ti-Si-N films with cubic B1 crystal structures had higher hardness than (Al,Ti)N films. Similarly, the Al-Ti-Si-N films displayed much improved oxidation resistance at elevated temperatures of up to 1150 °C in air. Cutting performance of (Al,Ti,Si)N coated carbide endmills were evaluated and offered significantly better performance in the machining of hardened steels with higher cutting speeds. Wear mechanism and cutting characteristics were discussed with the film properties.
10:50 AM		B3-1-8 Microstructure and Properties of Low Friction TiC-C Nanocomposite Coatings Deposited by Magnetron-Sputtering M. Stueber, H. Leiste, S. Ulrich, H. Holleck, D. Schild (Forschungszentrum Karlsruhe, Germany) The object of nanocomposite coatings combining hard and lubricant phases is the development of advanced multifunctional protective thin films showing abrasion resistance, and, simultaneously, low friction. Up to now no clear relation between constitution, microstructural properties and performance of such nanocomposite coatings based on dry lubricants like carbon or MoS2 has been evaluated. Deposition techniques, constitution, properties and performance of magnetron-sputtered nanocomposite coatings in the system TiC-C will be reported. The Vickers hardness could be optimized to values of polycrystalline TiC thin films, and, at the same time, low friction coefficients against steel, similar to diamond-like amorphous carbon, could be realized. The mechanical properties and the tribological behaviour of these thin films will be related to the chemical composition and the microstructure of these advanced materials, characterized by electron microprobe analysis, Auger electron spectroscopy, x-ray photoelectron spectroscopy, x-ray diffraction, and, high resolution transmission electron microscopy.
11:10 AM		B3-1-9 Microstructure and Mechanical Properties of Hydrogenated WC-C Nanocomposite S.J. Park (Korea Institute of Science and Technology and Yonsei University, Korea); K.-R. Lee (Korea Institute of Science and Technology, KOREA); D.-H. Ko (Yonsei University, Korea); J.H. Han (Korea Research Institute of Standard Science, Korea); K.Y. Eun (Korea Institute of Science and Technology, Korea) WC-C nanocomposite film was deposited by using a hybrid deposition system of r.f.-PACVD and magnetron sputtering of W. W concentration in the film was varied from 5.2 to 42 at.% by changing the composition of Ar/CH₄ gas mixture. The film was deposited at the self bias voltage of 150 V and pressure 1.33 Pa. The composition and structure of the film was characterized by RBS, XRD, TEM and Raman spectroscopy. The content of WC phase increased with increasing W concentration. The mechanical properties of the film were dependent on the size and distribution of the WC phase embedded in the hydrogenated amorphous carbon matrix. When W concentration is larger than 13 at.%, the residual stress and hardness was significantly increased with increasing W concentration. This behavior could be explained by the interlink of WC phases in the matrix.
11:30 AM		B3-1-10 Hardness, Toughness, and Wear Resistance of TiC-Cr and TiC-Ti Multilayer Films Developed to Simulate Nacreous Microstructures R.W. Obbard, T.S. Gross, J.E. Krzanowski, A.R. Phani (University of New Hampshire) Other investigators have reported that multilayer metal-carbide or metal-nitride films can have increased hardness and toughness. We have produced a series of one micrometer thick multilayer metal-TiC films by sputter deposition and by pulsed laser deposition with the intent of providing more information on the effect of these structures on wear resistance and toughness. The metal interlayers were either Ti or Cr and the thicknesses were 5 nm, 10 nm, 25 nm, and 50 nm. Films were produced with 5, 10, and 15 interlayers. We have evaluated the mechanical behavior and wear resistance of these films using nanoindentation, scratch testing, wear testing, and macroscopic deformation using a unique strain gradient specimen.
11:50 AM		B3-1-11 Thermal Stability of Nanostructured Boride/Nitride Films R.A. Andrievski, G.V. Kalinnikov, A.E. Oblezov (Russian Academy of Sciences, Russia) Boride/nitride films were prepared by non-reactive magnet-ron sputtering using different targets such as TiB₂, TiN, and TiB₂ + (25, 50, 75 wt%)TiN ones. As-deposited and annealed up to 1000°C films were characterized by XRD, AES, and TEM analyses as well as by measuring of hardness and electric resistivity. The evolution of structure and properties is discussed in detail. The attention is also focused in the grain-size distribution and presence of very small crystallites with the size of 1 nm and lower.