ICMCTF2007 Session B6-3: Hard and Multifunctional Nano-Structured Coatings

Friday, April 27, 2007 8:00 AM in Room Golden West

Friday Morning

Start	Invited?	Item
8:00 AM	Invited	B6-3-1 Hardening Mechanisms in Multicomponent Coatings W.J. Clegg (Gordon Laboratory, University of Cambridge, United Kingdom) The hardening mechanisms that can occur in multicomponent hard materials are discussed, in particular looking at the effects of planar interfaces on flow. It is shown that the substantial increases in hardness of approximately 30 GPa that have been reported in nitride-based multilayers are not generally observed. Cross-sectional transmission electron microscopy of TiN/NbN multilayers with wavelengths from 2 to 25 nm shows that flow occurs by dislocation motion across the layers and by the compaction of layers if they are porous. Even where dense the hardness of the multilayers tested here is only approximately 6 GPa greater than predicted by a mixtures rule using the hardnesses of the monolithic components, approximately consistent with what might be predicted. The effects on coherency stresses are also described using In-doped GaAs multilayers and also found to be small, sometimes even negative, suggesting that interfacial effects cannot account for the high hardnesses observed. It is tentatively suggested that these are caused by the high levels of internal stress within the films.
8:40 AM		B6-3-3 Ti-B-N Nanocomposite Hard Coatings Synthesized by Reactive Arc Evaporation J. Neidhardt (University of Leoben, Austria); B. Sartory (University of Innsbruck, Austria); M. O'Sullivan (Plansee AG, Austria); C. Mitterer (Montanuniversität Leoben, Austria) Ti-B-N based coating systems have been shown to have a high potential as wear protective coating owing to their outstanding mechanical properties as well as their chemical and thermal stability. Recently it has been demonstrated that these coatings can be synthesized by reactive arc evaporation, which increases their industrial potential. This study reports, thus, on high-rate (30-50 nm/min) TiBN coating deposition by reactive arc evaporation from Ti/TiB₂ compound targets in a commercial Balzers Rapid Coating System. Depending on the level of nitrogen, two different structures can be realized as investigated by XPS, XRD, HRTEM and SAED. At low partial pressures a solid solution of B in fcc TiN is observed, while a saturation in nitrogen content results in the formation of a TiN/BN nanocomposite. The incorporation of B into the TiN crystallites leads to a substantial increase in hardness and wear resistance, which degrade rather rapidly at elevated temperatures. The two phase system, on the other hand, is thermodynamically stable and its properties can be adjusted via the phase fraction of BN. For that reason two target compositions with a Ti/B ratio of 5/1 and 5/3 have been selected to study the effect of the B concentration on structure and mechanical, tribological as well as thermal properties of the resulting coatings. In addition the bias voltage was varied from -20 to -140V to predominantly affect the constitution of the originally amorphous BN phase.
9:00 AM		B6-3-4 The Effect of Pulsed DC Discharges and Pulse Energy on Structure and Properties of Cr-Al-N Coatings Deposited by Pulsed-Closed Field Unbalanced Magnetron Sputtering (P-CFUBMS) J. Lin, J.J. Moore, B. Mishra (Colorado School of Mines); W.D. Sproul (Reactive Sputtering Consulting, LLC); J.A. Rees (Hiden Analytical Ltd); M. Pinkas (CSM Instruments, Switzerland) Pulsing both the magnetrons in the closed field unbalanced magnetron sputtering (CFUBMS) has a significant effect on both ion energies and ion flux within the plasma. The ion energy distributions and the plasma compositions at the substrate position were studied using a Hiden electrostatic quadrupole plasma mass spectrometer (EQP), where the pulsed dc magnetrons were operated at 100 kHz and 350 kHz with different duty cycles in both synchronized and asynchronized modes. Nanocrystallized Cr-Al-N films were also deposited under the above pulsing conditions with the aim of investigating the effect of pulsed dc plasma on the structure and properties of the films. The results show that changing the pulsing parameters different ion energies and ion flux are achieved that can strongly influence the orientation, composition, structure and properties of the films. The increased ion energy and ion flux in the plasma will increase the ion bombardment and ion mobility during CFUBMS deposition, thereby changing the preferred orientation of the Cr-Al-N film from (200) to the more close packed (111), forming a nanocrystallized, dense structure of super hardness and good wear resistance (35-40 GPa, 0.9 H/E ratio, 0.40 to 0.455 COF, and a wear rate of 3.0 to 3.5 x10^-6mm³/Nm). The change in the ion flux effected by pulsing will also change the phase structure and composition of the film. A phase transformation from cubic CrAlN to hexagonal Cr₂N and AlN were observed when pulsing both targets synchronously at 350 kHz. In addition, excessive ion bombardment will increase the internal stress and defect concentration in the films, resulting in a decrease in film toughness and tribological properties.
9:20 AM		B6-3-5 Metastable Single-Crystal AlCrN Thin Films; - The Influence of Crystallinity on Age-Hardening H. Willmann, M. Beckers, J. Birch (Linköping University, Sweden); P.H. Mayrhofer, C. Mitterer (Montanuniversität Leoben, Austria); L. Hultman (Linköping University, Sweden) Metastable ternary nitrides have found widespread industrial use as protective hard coatings for cutting and forming applications. TiAlN as the most used compound is relatively well characterized, whereas for others, as the emerging AlCrN, the knowledge of structure-property relations as well as thermal phase stability is still evolving. Here, we report on characterization of cubic AlCrN films epitaxially deposited onto MgO (001) and MgO (111) substrates by reactive magnetron sputtering. The effects of varying the Al content was studied by changing composition of compound targets. Rutherford backscattering spectroscopy revealed stoichiometric nitrides with Al/Cr ratios close to the compound target composition. High resolution x-ray diffraction (HR-XRD) showed epitaxial growth of NaCl structured single-phase AlCrN (001) and AlCrN (111) films for the respective substrate orientations whereas an initial strained epitaxial layer was observed for the (001) orientation. The degree of crystallinity was higher for the AlCrN (001), demonstrated by XRD rocking curves. Films on MgO (111) show higher mosaicity and lower x-ray intensity pointing towards changed growth conditions due to decreased adatom mobility compared to the (001) substrate. Temperature-dependent transmission electron microscopy (TEM) investigations show the influence of grain boundary density on the precipitation of nanometer-sized hexagonal AlN. The results have impact for understanding age-hardening in arc-deposited AlCrN coatings.
9:40 AM		B6-3-6 Microstructure and Mechanical Properties of Cr-B-N and Cr-B-Al-N Coatings by Unbalanced Magnetron Sputtering, W.C.M. Moerbe, J.J. Moore, B. Mishra (Colorado School of Mines) A range of Cr-B-N and Cr-B-Al-N coatings were deposited using unbalanced magnetron sputtering from CrB₂ and Al targets in a reactive argon-nitrogen atmosphere. The structure and properties of the films were investigated using analytical techniques that included XRD, FE-SEM, XPS, nano-indentation, micro-tribometry, potentiodynamic testing, and DTA. The nitrogen content in the Cr-B-N films has a prominent effect upon the mechanical properties. Hardness and Young's modulus decrease as a function of increasing nitrogen content and increasing amorphous phase content in the films. The friction coefficients of the Cr-B-N coatings were in the range of 0.35 to 0.45 and the wear factors were in the 10-6 mm3 N-1 M-1 range. The addition of Al to the Cr-B-N films generally lowers the friction coefficient and improves the overall oxidation resistance.
10:00 AM	Invited	B6-4-7 PVD Oxide Deposition by Enhanced Electron Emission J. Ramm, M. Ante, T. Bachmann, W. Kalss, B. Widrig, C. Wohlrab (OC Oerlikon Balzers Ltd, Liechtenstein) Pulsed enhanced electron emission is a new approach in PVD technology for the deposition of metal oxides. The process is dedicated to the formation of alumina-based and other metallic oxide layers and comprises high current pulse technology for the arc sources as well as for the substrate bias. The technology allows a deposition of hard alumina-based coatings at substrate temperatures of about 550°C and even below. Reproducibility and deposition rates were demonstrated in a production system and proved to be comparable with arc ion plating processes for standard PVD nitride coatings. The high flexibility of the process allows an easy control of the reactive gases, smooth and abrupt transitions between the layers in multi layer structures and the combination of metals, oxides and nitrides in layer systems deposited in one single process in a batch-system. Layers of up to 15 µm thickness and above have been deposited showing an excellent adhesion. Cutting tests for inserts with respect to turning and milling show promising results compared to standard PVD layers as well as in comparison with CVD deposited layers. A number of different oxide layers were prepared with this new technology illustrating the enormous potential for the design of layer systems in wear resistant coatings. The layers were characterized with respect to mechanical properties, film morphology, crystal structure, stoichiometry and chemical stability.
10:40 AM		B6-4-9 Phase Formation, Microstructure and Properties of Nanostructured Hard Coatings of the Material System Cr-Al-N-O M. Stüber, U. Albers, H. Leiste, C. Ziebert, S. Ulrich (Forschungszentrum Karlsruhe, Germany) The phase formation and microstructure evolution of magnetron-sputtered coatings was examined for the Cr-Al-N-O material system. A combinatorial material science based approach by sputtering from a segmented target with a Leybold Z 550 machine was applied for the deposition experiments. The target was composed of two pieces, one made of bulk, hot pressed (Cr, Al)N and the other of a commercial Al₂O₃ plate. Both non-reactive and reactive deposition was applied. In each experiment six coatings of different composition and microstucture were obtained simultaneously by placing 6 substrate samples in individual positions below the target. The coatings, as-deposited and thermally annealed in vacuum up to 750°C, were characterized by Electron Probe Micro Analysis, X-Ray Diffraction, and Transmission Electron Microscopy. The microhardness was measured by the Vickers method. Non-reactively as-deposited coatings exhibited a nanocrystalline structure independent of the chemical composition and moderate hardness values between 1000 and 1200 HV0.05. A strong increase in the crystallite sizes of these coatings was observed at annealing temperatures above 600°C. This crystallization was accompanied by a significant increase in the microhardness up to 1500 HV0.05 at lower Cr:Al and higher O:N concentration, and up to 2000 HV0.05 at higher Cr:Al and lower O:N concentration. The brittle, ceramic behaviour of these coatings increased clearly with increasing annealing temperature. The reactive deposition in nitrogen atmospheres resulted in the synthesis of nanocrystalline coatings with a significantly higher hardness and ductility. The Vickers microhardness of as-deposited films was in the range of 2250 to 2500 HV0.05 and no brittle cracking of the coatings was observed. Annealing in vacuum however did not result in a remarkable change of the hardness values but in a change of the crystalline structure of the coatings.
11:00 AM		B6-4-10 Al-Si-N Transparent Thin Films as Protective Coatings: Structural, Optical and Mechanical Properties A. Pélisson, M. Parlinska-Wojtan (EMPA, Switzerland); F.-J. Haug (University of Neuchatel, IMT, Switzerland); H.-J. Hug, J. Patscheider (EMPA, Switzerland) Transparent nanostructured coatings of Al-Si-N were deposited by reactive DC magnetron co-sputtering of Al and Si targets in an Ar/N₂ atmosphere at 200 and 500°C. The chemical composition was varied from pure AlN to Al-Si-N with 30 at.% of Si. The coatings were investigated by UV-Visible spectroscopy, nanoindentation, XPS, TEM and XRD. For Si concentrations below 13 at.% the coatings consist of nanocrystalline h-AlN with substitutionally incorporated silicon, as suggested by a shift in the h-AlN (002) X-ray diffraction peak. At Si concentrations above 13 at.% the coatings are X-ray amorphous, which may be interpreted as the solubility limit of silicon in AlN. In contrast to known silicon-containing ternary nitrides and to available thermodynamical data for the Al-Si-N system, this material shows no phase segregation during deposition into nc-AlN/a-SiN_x ; a metastable Al_1-xSi_xN solid solution is formed instead. From XRD and TEM analysis it follows that the crystalline material consists of elongated grains; the crystallite size decreases from 60 nm to about 10 nm upon addition of silicon. The average optical transparency of 1 micron thick coatings in the visible range of light approaches 100%. The hardness exceeds 30 GPa, with a weak maximum at 8-12 at.% of Si. This maximum corresponds to the lowest internal stress in the coatings (≤ 0.5 GPa). The elastic strain to failure H/E, or resilience, is increased by 50% by the addition of silicon to AlN. Owing to its excellent optical transparency and improved hardness, Al-Si-N is identified as a promising candidate for wear protection of surfaces requiring optical transparency, such as architectural glass or scratch-sensitive decorative coatings.
11:20 AM		B6-4-11 Combinatorial Studies of Co-Sputtered Carbon-Incorporated Titania Films as Visible Light Photocatalyst M.S. Wong, C.W. Weng, T.K. Chen, K. Koteswara Rao (National Dong Hwa University, Taiwan) A series of carbon-incorporated titanium dioxide (TiOxCy) films were prepared by combinatorial method using dual-cathode co-sputtering of Ti metal and graphite targets in argon and oxygen plasma. The composition spread of the TiO_xC_y films ranges from near-pure TiO₂ to carbon. The effect of carbon content on the structures and properties of the films were explored. XPS, Raman, TEM and UV-Vis spectroscopy studies show that carbon is present both in the form of substituted Ti-C bonds as well as free graphitic nature. The absorption edge of the TiO_xC_y films shifts from ultraviolet to visible region about 450 nm with intense absorption shoulder beyond 800 nm as the carbon content is increased. The carbon-containing titania films possess a unique structure of carbon-covered (along grain boundaries) columnar grains of carbon-doped (inside the grains) titania phase. The content and the nature of carbon as well as the titania crystallinity dominate the visible-light induced photocatalytic activity of the TiO_xC_y films.