ICMCTF1999 Session B1-2: Nanostructure Thin Films
Time Period WeM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF1999 Schedule
Start | Invited? | Item |
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8:30 AM | Invited |
B1-2-1 Tough Crystalline/Amorphous Nanocomposites for Wear Protection
A.A. Voevodin, J.S. Zabinski (Air Force Research Laboratory) Crystalline/amorphous nanocomposite coatings have a number of unique mechanical characteristics. For example, a super-hardness effect was reported for TiN/Si3N4 composites1. More recently, a super-toughness effect was discovered for composites, consisting of 10-50 nm nc:TiC nanocrystals encapsulated in an amorphous diamond-like carbon (a:DLC) matrix2, 3. Carbides and DLC are widely used in wear resistant and low friction coatings. Improvement of their toughness by designing crystalline/amorphous nanostructures is considerd. These novel structures permit initiation of crack deflection on grain boundaries, crack energy dissipation in the amorphous phase, "quasi-plasticity" with nano-grain shifts, etc. The mechanical and tribological properties of the nc:TiC/a:DLC and nc:WC/a:DLC nanocomposites are described, including hardness, scratch toughness, wear rate coefficients, and friction coefficients. Attention is also given to friction mechanisms for crystalline/amorphous coatings. To provide lower friction coefficients, doping with solid lubricants (MoS2 and WS2) was performed. This generated three phase coatings consisting of nanocrystalline carbide, amorphous DLC, and nanocrystalline dichalcogenides. Results are correlated with a review of recent publications, and general concepts for tough, wear resistant crystalline/amorphous nanocomposite coatings are proposed. 1 S. Veprek, S. Reiprich, Tthin Solid Films 268 (1995) 64. 2 A. A. Voevodin, S. V. Prasad, and J.S. Zabinski, J. Appl. Phys., 82 (1997) 855-858. 3 A. A. Voevodin and J. S. Zabinski, J. Mat. Sci. , 33 (1998), 319-327. |
9:10 AM |
B1-2-3 High-temperature Stability of Epitaxial, Non-isostructural Mo/NbN and W/NbN Superlattices
A. Madan, S.A. Barnett, M.U. Guruz, V.P. Dravid (Northwestern University); C. Engstrom, L. Hultman (Linkoping University, Sweden); A. Misra, H. Kung, M. Nastasi (Los Alamos National Laboratory) Non-isostructural Mo/NbN and W/NbN superlattices show an enhanced hardness (~ 30 GPa) as compared to the rule-of-mixtures values (~ 10 GPa). The high-temperature stability of these superlattices is important for elevated temperature applications. Mo/NbN superlattices of varying superlattice periods Λ from 1.4 - 18 nm (~ 40-50% Mo) were annealed in vacuum at 1000 ° C for 1-3 hrs. X-ray diffraction(XRD) results showed gradual formation of a ternary phase (MoNbN) as the annealing time increased. Cross-sectional transmission electron microscopy results for the Λ=18nm annealed Mo/NbN films showed that the structure retained its epitaxial orientation (001)metal||(001)NbN and [110]metal||[100]NbN with sharp interfaces and nearly planar layers. XRD results for the annealed Λ=5 nm (~80% Mo) Mo/NbN superlattice and Λ=3.2 nm W/NbN superlattices (~ 50% W) showed little change in the superlattice satellite intensities indicating little change in the layered structure. Nanoindentation hardness results show that there was either no observable change and sometimes even a slight increase in the hardness of the annealed films. This unusual high-temperature stability is probably related to the mutual immiscibility of these phases and the low-energy coherent (001) interfaces formed between BCC-metals and B1-nitride. |
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9:30 AM |
B1-2-4 The Formation and Characterisation of Nanocomposite a-Si3N4 / nc-TiN Films Synthesized by Ion Beam Assisted Deposition.
I.F. Brunell, R. Valizadeh (University of Salford, United Kingdom); J.S. Colligon (Manchester Metropolitan University, United Kingdom) Nanocomposite a-Si3N4 / nc-TiN films 400nm thick were synthesised in various compositions by using ion beam sputtering with concurrent nitrogen and argon ion bombardment. The substrate temperature was varied from 80 C to 750 C. The ion assist beam energy was varied from 300 eV to 700 eV for various ion/atom arrival ratios ranging from 0.5 to 3. The film composition was controlled by varying the area of a silicon strip overlayed on a Ti target and determined by RBS. Film morphology was characterised by glancing incidence X-ray diffraction (GXRD) and TEM; hardness was determined by nanoindentation. The hardness was found to depend upon film morphology, which in turn depended on the film composition and deposition parameters. The average TiN crystal size varied from 1.6nm to 8.6nm as determined by analysis of peak broadening of GXRD data, which was confirmed by TEM. The crystal size was seen to increase with ion/atom arrival ratio, reach a maximum, and then decrease at a given substrate temperature. Hardness varied with composition and a maximum of 48 GPa was achieved with a 9.25% Si content, at a substrate temperature of 500 C. |
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9:50 AM |
B1-2-5 Mechanical Properties and Oxidation Resistance of Nanocomposite TiN/Si3N4 PVD Thin Films
M. Diserens (EMPA Dübendorf, EPFL, Switzerland); J. Patscheider (EMPA Dübendorf, Switzerland); F. Lévy (EPFL, Switzerland) Thin films of TiN/Si3N4 coatings have been prepared by reactive unbalanced magnetron sputtering from two opposite Ti and Si targets. The silicon concentration in the deposited films was varied between 0 and 15 at.%. As evidenced by X-ray diffraction, XPS measurements and TEM micrographs, the deposited films are composed of TiN nanocrystallites in an amorphous Si3N4 matrix. These composite coatings exhibit improved mechanical properties in comparison to TiN deposited under the same conditions. As the hardness measured by nanoindentation is about 24 GPa for TiN, 37 GPa are reached in TiN/Si3N4 films containing 5-6 at.% Si and decreases to the values of amorphous Si3N4 at silicon concentrations above 15 at.%. Beside higher hardness values and improved wear resistance, these composite coatings are superior to TiN in their resistance against oxidation. The oxidation resistance is gradually enhanced with increasing silicon concentration. The oxidation rate of TiN/Si3N4 films containing 12 at.% Si at 700°C in air is 10 times lower than that of TiN. It is shown that in the TiN/Si3N4 composite structure the oxidation along the grain boundaries is limited by the presence of the amorphous Si3N4 phase. |
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10:10 AM |
B1-2-6 Characterization of Ti1-xSixNy Nanocomposite Films Prepared by Reactive Magnetron Sputtering
F. Vaz (University of Minho, Portugal); L. Rebouta (Universidade do Minho, Guimarães, Portugal) Nanocomposite thin films consisting of both nanosized solid solutions or nanosized polycrystalline materials embedded in various amorphous matrix materials thus provide a great potential for future mechanical devices. In this respect, films resulting from additions of Si to TiN matrix and prepared by r.f. reactive magnetron sputtering, will be prepared and characterised in this paper. Structural properties such as growing characteristics (type of matrix, texture, grain size) and mechanical properties such as hardness and adhesion were analysed. Both conventional transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM) were used for the structural characterisation, while ultarmicrohardness test and scratch test were chosen for the mechanical characterisation. The atomic composition of the samples was obtained by Rutherford Backscattering Spectrometry (RBS). X-ray diffraction (XRD) experiments were used in order to obtain texture factors (rocking curves) and microstress states by the sin2Ψ method. The deflection method was used to evaluate the macroresidual stress states. All properties will be characterised and discussed as a function of the Si content in the Ti1-xSixNy matrix and several relations will be made regarding important parameters such as texture factor, grain sizes, stress states and specially the type of matrix developed. Regarding the preliminary results, the samples with a composition of Si between 5.9 and 10.6 at. % show higher hardness values (about 50 GPa). This region is also the one where the most oriented films grow (220 cubic fcc orientation) together with the smallest grains observed. The highest critical adhesion loads are also obtained in this region. Relations within these results, together with those of residual stresses will be made and discussed in detail. |
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10:30 AM |
B1-2-7 Properties, Internal Stress and Thermal Stability of nc-TiN/a-Si3N4 and nc-(Ti1-yAlySix)N Superhard Nanocomposites.
S. Veprek (Technical University Munich, Germany); A. Niederhofer (Technical University Munich, Germany); P. Nesladek, H.-D. Mánling (Technical University Munich, Germany); M. Jilek (SHM LTD, Czech Republic) As reported earlier, the crystallite size, d, of the nc-TiN/a-Si3N4 nanocomposites prepared by plasma CVD varies between ~3 nm and ≥10 nm depending on the Si3N4 content. A comparison of the crystallite size determined from the Scherrer formula using either the integral width or FWHM of the Bragg reflection and by Warren-Averbach analysis of the peak profiles will be presented. Films of pure TiN and those with a low Si3N4 content show (200) preferential orientation which changes to almost random for Si3N4 content of about 20 mol. %, where the highest hardness of about 50 GPa is achieved. The biaxial compressive stress of ≤5 µm thick films is ≤ 0.3 GPa and it increases with the thickness to ≤0.5 GPa for ~10 µm. Also the random strain determined from the Warren-Averbach analysis is fairly low. With a number of films we have confirmed the high thermal stability of the superhard nanocomposites with the crystallite size of ~3 nm, which show neither recrystallization nor change of the hardness under isochronal annealing up to ≥1100°C for 0.5 hr. However, the recrystallization temperature (at which also the hardness decreases) monotonously decreases with increasing crystallite size to ~800°C for d≥7 nm. We shall report on the dependence of all these properties on the Si3N4 content (0 - 45 mol. %), film thickness (up to 15 µm) and discharge current density during the deposition. The results show that whereas the thermal stability depends on the crystallite size, the superhardness can be achieved also at a larger crystallite size of 6 - 9 nm if the Si3N4 content is about 17 - 23 mol %. Similar results will be reported for (Ti1-yAlySix)N nanocomposites prepared by plasma PVD and a combined plasma PVD/CVD technique. |
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10:50 AM |
B1-2-8 The Influence of Si Addition on the Characteristics of (Ti,Al)N Films
L. Rebouta, F. Vaz (University of Minho, Portugal); A. Cavaleiro (ICEMS - Departamento de Engenharia Mecânica - FCT da Universidade de Coimbra, Portugal); E.J. Alves (ITN, Sacavém, Portugal) Recently there has been increasing interest in the deposition of composite films in searching for new materials. One of the most recent materials is the nc-TiN/a-Si3N4 system. As the TiAlN already demonstrated significant improvement in hardness and heat resistance over conventional binary metal nitrides, the influence of Si adittion on TiAlN coatings was studied. In this work we report the preparation and characterisation of (Ti,Al,Si)N films with different Ti; Al and Si contents, deposited onto silicon and polished high-speed steel substrates by rf and dc reactive magnetron sputtering technique. Compositional studies were carried out by Rutherford Backscattering Spectrometry (RBS), while crystallographic orientation and grain size were obtained by X-ray diffraction (XRD). The deflection method was used to evaluate the residual stress states. Microindentation tests to evaluate hardness and dynamic indentation experiments to evaluate critical adhesion behaviour are also reported and related to the Si content of the films, process parameters such as temperature and working gas pressure, and developed residual stress states. |
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11:10 AM |
B1-2-9 ZrN/Cu Nanocomposite Film - a Novel Material of the Type Nanocrystalline Metal Nitride/Soft Metal Matrix
J. Musil, P. Zeman (University of West Bohemia, Czech Republic) Recently, new superhard (> 40 GPa) coatings in a form of superlattices of metal nitrides , e.g. TiN/VN, and nanocomposite coatings composed of nanocrystalline metal nitrides embedded in hard amorphous matrix, e.g. nc-TiN/a-Si3N4, were developed. These materials exhibit very high hardness up to 50 GPa but they are also very brittle due to their low plasticity at loads exceeding their elastic limit. However, in many applications hard coatings with higher toughness are needed. Such a requirement meet nanocomposite coatings of the type nc-MeC/a-C and also nanocomposites of the type nc-MeN/soft metal matrix (e.g., Cu, Ni, Mo, Co, Ag, etc.) The paper reports on properties of ZrN/Cu films, i.e. on a new class of hard coatings based on nitrides of copper based alloys. The ZrN/Cu films were prepared by d.c. reactive magnetron sputtering of an alloyed target ZrCu (70/30 wt.%) in Ar+N2 gas mixture at the total pressure of 0.7 Pa using a circular planar magnetron 100 mm in diameter. Mechanical properties of the ZrN/Cu film, i.e. its hardness, elasticity and plasticity, can be controlled by substrate temperature Ts, substrate bias Us, substrate ion current density is and partial pressure of nitrogen pN2. The film hardness can be continuously increased from low values of about 10 GPa to very high values up to 55 GPa. While the ZrN/Cu film with a relatively low hardness of about 10 GPa exhibits a high (40%) plasticity and low (60%) elastic recovery, the superhard ZrN/Cu film with hardness of about 50 GPa, on the contrary exhibits high (80%) elastic recovery and low (20%) plasticity. The mechanical properties of ZrN/Cu films are closely connected with their structure. XRD patterns from superhard (> 40 GPa) ZrN/Cu films show a well developed high intensity ZrN(111) reflection only; no reflection from Cu is observed. It means that the superhard films are composed of several nm ZrN grains embedded in amorphous Cu matrix. On the contrary, the ZrN/Cu films with a lower (20-30 GPa) hardness and higher (40-30%) plasticity are two phase nanocomposite films composed of small ZrN and Cu grains. The XRD patterns from these films exhibit reflections from two crystalline phases ZrN(111) and Cu(111); the intensity of ZrN(111) reflection is considerably lower than that from the superhard ZrN/Cu film. A phase composition of the ZrN/Cu film can be controlled by energy delivered to the film during its growth at a constant substrate temperature Ts. The superhard ZrN/Cu films are formed at Ts = 400 °C and pN2 = 0.05 Pa when larger amount of energy is delivered to the growing film by bombarding ions, i.e. when is ≥ 1 mA/cm2 is used. To prepare hard ZrN/Cu films with higher toughness the substrate ion current densities is < 1 mA/cm2 are sufficient. These films can be produced even in absence of both the substrate heating and ion bombardment, i.e. at Ts = RT and Us = Ufl, but higher values of pN2 = 0.3 Pa has to be used. The XRD patterns from these films exhibit broad, very low intensity ZrN(200) and ZrN(111) reflections. It means that hard ZrN/Cu films sputtered on unheated substrate at Us = Ufl have a very fine grained structure with the grain size below 5 nm. |
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11:30 AM |
B1-2-10 Nanocomposite nc-TiN/BN Coatings: Their Applications on Cemented Carbide Substrates and Results of Cutting Tests
P. Holubar, M. Jilek, M. Sima (SHM LTD, Czech Republic) Nanostructured nc-TiN/BN coatings were deposited on cemented carbide indexable inserts by a combined plasma CVD/PVD technique. Structural properties were analyzed by means of X-ray diffraction (XRD) and composition of the coating was analyzed by means of scanning microscope/wave dispersive analysis (SEM/WDX), in order to determine the correlation between these properties and the deposition conditions. The boron content was varied in the range of 10 - 30 at. %. The resulting size of the TiN nanocrystallites was in the range of 3 - 7 nm. The microhardness of these coatings, measured by the microindentation method under the maximum load of 70 mN, was in the range of 6000 - 7000 kg/mm2. The performance of nc-TiN/BN coatings of a different composition deposited on indexable inserts made of cemented carbide were tested in cutting tests under real industrial conditions. Wear of coated cemented carbide indexable inserts was evaluated and compaired. Cutting tests were aimed especially to the machining of hardened steel and cast iron with a higher cutting speed than the standard PVD coatings allowed. There is a discussion of the results. |
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11:50 AM |
B1-2-11 Friction and Wear of Nanostructured Multilayers Deposited by Reactive Sputtering
G. Sorensen, H. Jensen, J. Sobota (Aarhus University, Denmark) Nano-structured multilayer films containing niobium nitride and carbon nitride have been deposited by reactive sputtering. Reactive gas was controlled with a high precision, and deposition rates at various specific deposition conditions were measured showing a ratio between the NbN and the C-N layer varying from 0.08 to 3.1. Multilayer adhesion was measured with the acoustic schratch test technique, and the reproducibiliy of this will be discussed. Different multilayer structures were deposited by varying the power of the sputtering cathodes and the rotation speed of the substrate holder, and particularly friction characteristics in dry sliding against a reciprocating ball of silicon nitride was investigted for multilayers on WC and Si. The wear scar after 14 m of reciprocating dry sliding with a load of 5 N was also measured, and it was shown that friction and wear could be reduced by more thana factor of three and thirty respectively, when comparing with a sputter deposited film of NbN. An apparatus for measurement of dynamic impact wear was constructed, and the performance of multilayers deposited at different deposition conditions will be reported. Finally it will be discussed whether it is possible to deposit nanostructured multilayer coatings for applications in dry sliding operations combining a reduction in friction with a low wear. Possible applications of wear resistant low friction coatings will be discussed. |