ICMCTF2009 Session B5-2: Properties and Characterization of Hard Coatings and Surfaces

Tuesday, April 28, 2009 1:30 PM in Room Golden West

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		B5-2-1 Structure, Stability and Bonding of Ternary Transition Metal Nitrides P. Patsalas, G.M. Matenoglou, L.E. Koutsokeras, Ch.E. Lekka (University of Ioannina, Greece); G. Abadias (Universite de Poitiers-CNRS, France); C. Kosmidis, G.A. Evangelakis (University of Ioannina, Greece) Nitrides of the group IVb-VIb transition metals have been well known for their unique combination of exceptional mechanical and electrical properties sharing high hardness values and electrical conductivity. Ternary transition metal nitrides have lately gained special attention (with TixZr1-xN being the most widely studied) in an effort to improve further these properties. In this work we present a comparative study of a very wide range of ternary transition metal nitrides of the form: TixMe1-xN (Me=Zr,Hf,Nb,Ta,Mo,W) and TaxMe1-xN (Me=Zr,Hf,Nb,Mo,W) over the whole x range (0
1:50 PM		B5-2-2 Ab-Initio Calculations of the Effect of Si and C on Elastic Properties of Metal Nitrides J. Houska, J.E. Klemberg-Sapieha, L. Martinu (Ecole Polytechnique de Montreal, Canada) In this contribution, we report extensive ab-initio calculations of elastic properties of Ti(Si)N(C) and Cr(Si)N(C) materials. Atom cores and inner electron shells are described by Vanderbilt-type pseudopotentials, and Kohn-Sham equations for valence electrons are expanded using a wave-basis set. In fcc metal nitride networks, up to 1/8 of metal atoms are replaced by Si, and up to 1/4 of N atoms by C. For various material compositions, bulk modulus (B) and lattice constant (a₀) is calculated by fitting the Birch equation on total energies calculated at different lattice parameters (94-106 % of the lowest energy value), and elastic tensor (C_ij) is derived using energy changes resulting from small volume-preserving strains and shears (up to 6% and 6 deg., respectively). Young's modulus (E), Poisson's ratio (ν) and shear modulus (G) are calculated from C_ij. We examine dependence of density of unpaired spins on material composition and on the strains applied. We find that small Si or C contents in materials lead to decreasing G, increasing E₁₀₀, decreasing ν and slightly increasing a₀, and calculate slopes of the changes. Furthermore, B decreases after addition of Si while there are no changes in B after addition of C. Dependence of electrical conductivity on material composition is examined by calculating electronic density of states. The results, compared with experimental data and explained using the changes in valence electrons wavefunction, can be used to estimate properties of the previously deposited and simulated nanocomposite structures. The calculated lattice constants can be used to estimate compositions of crystals examined by x-ray diffraction.
2:10 PM	Invited	B5-2-3 Growth Behavior and Microstructure of Arc Ion Plated Titanium Dioxide C.-J. Chung (Central Taiwan University of Science and Technology, Taiwan); H.-I. Lin, P-Y. Hsieh, K.-C. Chen, J.-L. He (Feng Chia University, Taiwan); A. Leyland, A. Matthews (University of Sheffield, United Kingdom) Titanium dioxide (TiO₂) films have been prepared using physical vapor deposition (PVD) processes for several decades. It is often considered as a material for applications such as photocatalysis, self-cleaning and antimicrobial purposes. However, numerous questions regarding the growth behavior and microstructure remain unanswered. This study aims to clarify, using microstructural characterization techniques and optical emission spectroscopy (OES), the conditions under which rutile or anatase phase constituents appear in films deposited by PVD arc ion plating (AIP), to give a better understanding of TiO₂ films deposited using different deposition processes. The experimental results show that the calculated free energy for rutile phase growth is lower than for anatase, and that the rutile phase grows preferentially if thermodynamically satisfactory oxygen supply (in terms of oxygen partial pressure) is present, although less activation energy is required for anatase growth. However, OES studies reveal that, with further increased oxygen partial pressure and extended deposition time, oxidation occurring at the cathode surface generates a higher amount of neutral titanium atoms and, consequently, the metastable anatase phase grows. Detailed TEM microstructural characterization of the deposited TiO₂ films in this study also explicitly shows that films identified as XRD amorphous actually contain very fine rutile nanocrystallites within the amorphous structure, whereas films revealed by XRD as composed predominantly of the anatase phase are actually as a consequence of later growth, preceded by rutile growth in the initial stage.
2:50 PM		B5-2-5 Structure-Property Relations of arc-Evaporated Al_xNb_1-xN Hard Coatings R. Franz (University of Leoben, Austria); M. Lechthaler (OC oerlikon Balzers AG, Liechtenstein); C. Polzer (PLANSEE Composite Materials GmbH, Austria); C. Mitterer (University of Leoben, Austria) Ternary MeAlN hard coatings, especially TiAlN and AlCrN, have been intensively studied during the past 20 years. Due to the incorporation of Al into the crystal lattice, superior mechanical properties and improved oxidation resistance were obtained. Similar effects can be expected by alloying NbN with Al. However, the Nb-N system is of higher complexity as compared to Ti-N and Cr-N since several different phases can be formed. The aim of the present work was to synthesise Al_xNb_1-xN coatings with the face-centered cubic structure of δ-NbN and to investigate the influence of the Al content on the crystal structure evolution as well as the mechanical properties and the oxidation resistance. All coatings were deposited in an Oerlikon Balzers arc-evaporation system using powder-metallurgically prepared AlNb targets with different Al to Nb ratios. The target composition is roughly mirrored in the metal ratio of the coatings as it was obtained by energy-dispe rsive X-ray spectroscopy. With the aid of X-ray diffraction analyses, the formation of the face-centered cubic structure could be evidenced. Only at very high Al contents hexagonal phases are formed as well. The mechanical properties were assessed by nanoindentation and biaxial stress measurements. Annealing experiments up to 1000°C in ambient air revealed an onset temperature for oxidation in the range of 700-800°C for the coatings with a low Al content. The increase of the Al content is beneficial in terms of oxidation resistance as it leads to higher onset temperatures. In summary, incorporating Al into NbN improves the coating properties and the presented Al_xNb_1-xN hard coating family seems to be promising for industrial applications.
3:10 PM		B5-2-13 Wear Resistant Coatings Via Directed Vapor Deposition S. Eustis, D. Hass (Directed Vapor Technologies International, Inc.) To protect components from a wide range of wear related failure mechanisms, advanced coatings and coating deposition approaches are sought which impart improved wear resistance to increasingly complex components. For these applications, wear resistant coatings must have good ductility, excellent adhesion, and not detrimentally affect the properties of the substrate material. Flexible coating systems having a range of properties that can be individually tailored to meet the needs of both the substrate and the application are therefore of high interest. Here, nano-composite coating systems (such as Cu-Cr-N) having a controllable elastic modulus, yield strength and hardness have been deposited with a Directed Vapor Deposition (DVD) approach to form enhanced wear resistant coating systems. The DVD process operates in an elevated pressure processing environment that employs a supersonic gas jet to “direct” vapor atoms onto substrates. This results in highly efficient, high rate deposition of controlled coating compositions onto complex substrate geometries, including those having non line-of-sight regions. Using the DVD approach, nano-grained coatings were created by co-evaporating materials in a manner which resulted in multiple phase coatings being formed during deposition. By tuning the deposition conditions, the composition and the properties of the coating could be modified. Combinatorial synthesis approaches were used to identify specific coating compositions having mechanical properties in a desired range. The composition, microstructure, mechanical properties and wear properties (pin-on-disc) of the DVD deposited films are reported. Results indicate increased wear resistance when compared to conventionally applied TiN and hard chrome coating compositions.
3:30 PM		B5-2-8 Development of B4C Sputter-Deposited Coatings for Mechanical Applications C. Patacas, C. Louro, J.C. Oliveira, A. Cavaleiro (University of Coimbra, Portugal) Boron carbide (B4C) is one of the hardest materials and has the highest known dynamic elasticity. These properties, along with its high melting point, low mass density, high wear resistance and high thermal stability, explain the great interest in depositing this material as thin protective coatings. Boron carbide has a complex structure consisting of icosahedral arrangements of twelve atoms at the vertices of a rhombohedral unit cell connected with three-atom chains along the main diagonal. This structure is stable within a large carbon content range, extending from 8.8 to 22 at.% C, mainly due to the atomic similarity of boron and carbon atoms. Within the phase homogeneity range, B4C is believed to form several polytypes at room temperature such as B12(CCC), which consists of 12 boron atom icosaedras and 3 carbon atom chains, or B11C(CBC). Several studies have shown that different polytypes most likely coexist at the same chemical composition. Very recently, it was a lso shown that the mechanical properties of boron carbide can be improved by doping with silicon, mainly by the suppression of the B12(CCC) polytype. In this study, B-C and B-C:Si thin films were deposited by r.f. magnetron sputtering from a hot-pressed B4C polycrystalline target. In the first step of the work, simple B-C coatings were optimized by varying the bias, target power and coil current. After, the coatings were incorporated with Si contents up to 7 at.%. The EPMA analysis revel that with the exception of the unbiased film (high C/B ratio), all the other coatings were overstoichiometric in relation to carbon (~22 at.% C). The films exhibited poor crystallinity with only a broad XRD peak close to the main reflection of the boron carbide. Thus, in order to achieve long-range order, the coatings were thermally annealed in a protective atmosphere (Ar+5% H2) up to 1200ºC. The results concerning structure, chemical composition and hardness will be presented as a function of the annealing temperature as well as the Si content. Further results obtained by Raman, FT-IR spectroscopy and TEM analysis will be also presented for understanding both compositional and thermal effects on boron carbide-based coatings.
3:50 PM	Invited	B5-2-9 Influence of the Chemical Composition, Electronic Structure and Phase Evolution on the Electric and Optical Behaviors of Decorative Zirconium Oxynitride Thin Films F. Vaz, P. Carvalho, L. Cunha (Minho University, Portugal); N. Martin (Institut FEMTO-ST, France); J.P. Espinós, A.R. González-Elipe (Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Spain) This work is devoted to the investigation of decorative ZrO_xN_y films. Film's color changed from metallic-like to very bright yellow-pale and golden yellow, for low oxygen contents to red-brownish for intermediate oxygen amounts. Associated to this color change, there is a significant decrease of brightness. With further increase of the oxygen content, the color of the films changed from red-brownish to dark blue. The films deposited with high oxygen amounts showed only apparent colorations due to interference effects. This change in optical behavior from opaque to transparent (transition from metallic to insulating materials), revealed that significant changes were occurring in the films structure and electronic properties. In fact, the variations in composition disclosed the existence of four different types of films, which were also correlated to the structural features. For the so-called zone I, XRD revealed the development of films with a B1 NaCl face-ce ntered cubic zirconium nitride-type phase. Increasing the reactive gas flow, the structure of the films changed to an over-stoichiometric nitride phase, similar to that of Zr₃N₄, but with some probable oxygen inclusions within nitrogen positions. This region was characterized as zone II. Zone III was indexed as an oxynitride-type phase, similar to that of γ-Zr₂ON₂ with some oxygen atoms occupying some of the nitrogen positions. Finally, occurring at the highest oxygen amounts, zone IV was assigned to a ZrO₂ monoclinic type structure. The composition/structure variations were consistent with the chemical bonding analysis carried out by XPS, which showed a continuous decrease of density of states near the Fermi level associated to an increase of transference of d electrons to the p band. The electronic properties of the films exhibited significant changes from zone to zone. Resistivity measurements revealed a very wide range of values, varyin g from relatively high conductive materials (for zone I) with resistivity values around few hundreds of μΩcm, to highly insulating films within zones III and IV, which presented resistivity values in the order of 10¹⁵ μΩcm. Regarding zone II, corresponding to oxygen doped Zr₃N₄-type compounds, the observed behavior revealed resistivity values increasing steeply from about 10³ up to 10¹⁵ μΩcm, indicating a systematic transition from metallic to insulating.
4:30 PM		B5-2-11 Sub-Microstructure and Surface Topography of Reactive Unbalanced Magnetron Sputtered Titanium and Titanium Compound Thin Films S.D. Carpenter (Manchester Matropolitan University, United Kingdom); P. Kelly (Manchester Metropolitan University, United Kingdom) Physical vapour deposition techniques (PVD) are non equilibrium processes that often produce non equilibrium microstructures. Nucleation occurs at many sites in close proximity over the substrate surface and is similar to electro deposition within an electrolyte in this respect. Thin film growth advances from the substrate to form a dense columnar structure with a growth direction parallel to the flux of incident energetic particles. Growth is usually along one of the preferred close packed crystal directions and results in a high degree of crystallographic texture within the deposit. Titanium was sputtered with varying nitrogen flow rates to vary the film composition from Ti to stoichiometric TiN. The thin films were grown at different DC pulse frequencies ranging between 100 kHz to 350 KHz using an Advanced Energy Pinnacle Plus power supply. For comparison purposes, films were also grown in DC mode. The substrates were RF biased using an Advanced Energy RFX-600 supply. Electron microscopy revealed that TiN and titanium metal grow as individual crystallites within sub stoichiometric TiN. Furthermore the growth direction of these crystallites was found to be influenced by deposition conditions. It was also found that the growth direction alters radically for cylindrical substrates rotated in front of a titanium cathode target. The results indicate that growth occurs by a ledge mechanism for rotated substrate and by a spiral growth mechanism for fixed substrates.
4:50 PM		B5-2-12 Effect of Substrate Positioning for TiAlN Films Deposited by an Inverted Cylindrical Magnetron Sputtering System H.H. Abu-Safe (Lebanese American University, Lebanon); M.H. Gordon (University of Arkansas) TiAlN films up to 300 nm thick were deposited on glass substrates at three different positions within an inverted cylindrical magnetron sputtering system. Titanium and aluminum targets were used and one substrate was located near the titanium target, another near the aluminum target, and third centered between the targets. In addition at each location, substrates were positioned at three different angles (0, 45, and 90). The sputtering power during deposition was maintained at 2 kW with constant Argon and nitrogen gas flow rates. The Films chemical and elemental composition at different elevations and tilts with respect to the targets was analyzed using Energy dispersive X-Ray diffraction. A preferred 200 crystal orientation was noticed in all samples. However, the peak intensity at this orientation varied with substrate tilt. This indicates the effect of surface exposure to the confining magnetic field on the arrangements of atoms during deposition. The scanning electr on microscope images showed variation surface textures with position and tilt for all samples. A model of the deposition mechanism at different position inside the sputtering chamber is presented.
5:10 PM		B5-2-7 Carbon Occupancy of Interstitial Sites in Vanadium Carbide Films Deposited by Reactive Magnetron Sputtering E. Portolan, C.L.G. Amorim, G.V. Soares, C. Aguzzoli, C.A. Perottoni, I.J.R. Baumvol, C.A. Figueroa (Universidade de Caxias do Sul, Brazil) Hard coatings are widely used in surface engineering for wear protection and friction reduction of mechanical components. Numerous different coatings are currently available for specific applications. Among these coatings, vanadium carbide (VC) thin films show high hardness, high melting point, and good chemical stability. However, the crystalline structure of VC thin films is still open to investigation. On one hand, stoichiometric VC is an interstitial compound, where vanadium forms the principal lattice and carbon occupies the octahedral interstitial sites¹. On the other hand, the equilibrium phase diagram of the V-C system is complex and many phases with different stoichiometries coexist².Although order-disorder phase transformations were already observed, the migration of carbon atoms associated with these transformations is still unclear³. In this work, vanadium carbide thin films were deposited on Si substrates by reactive magnetron sputtering f rom a V target in a Ar/CH₄ plasma, varying the Ar/CH₄ partial pressure ratio and substrate temperature. The films were characterized by glancing angle X-ray diffraction and Rutherford backscattering spectrometry. Better defined crystalline structures were obtained at higher CH₄ content than 13%. The increase of substrate temperature diminishes slightly the film thickness and substantially the C/V atomic ratio. The intensity ratio of the Bragg peaks (111)/(200) decreases as a function of substrate temperature. The results are discussed in terms of a proposed mechanism for interstitial diffusion of carbon atoms in vanadium carbide thin films with fcc-like crystalline structure and the carbon occupancy of tetrahedral or octahedral interstitial sites as a function of substrate temperature. ¹V. N. Lipatnikov, A. I. Gusev, P. Ettmayer, and W. Lengauer, J. Phys.: Condens. Matter 11, (1999) 163. ²J. Hu, C. Li, F. Wang, and W. Zhang, J. Alloys Compounds 421, 120 (2006). ³V.N. Lipatnikov, W. Lengauer, P. Ettmayer, E. Keil, G. Groboth, and E. Kny, J. Alloy and Comp. 261, 192 (1997).