ICMCTF2009 Session B6-3: Hard and Multifunctional Nano-Structured Coatings

Friday, May 1, 2009 8:00 AM in Room Golden West

Friday Morning

Start	Invited?	Item
8:00 AM	Invited	B6-3-1 Progress in the Development of Adaptive Nitride-Based Coatings for High Temperature Tribological Coatings S. Aouadi, B. Luster, P. Kohli (Southern Illinois University Carbondale); C. Muratore (Air Force Research Laboratory/UTC, Inc.); A.A. Voevodin (Air Force Research Laboratory) Adaptive tribological coatings were recently developed as a new class of smart materials that were designed to adjust their surface chemical composition and structure as a function of changes in the working environment to minimize friction coefficient and wear between contact surfaces. This presentation provides an overview of the current research developments in this field, including: (1) Chameleon nanocomposite coatings which are produced by depositing a multi-phase structure whereby some of the phases provide mechanical strength and others are lubricious; (2) Micro- and nano-textured coatings which consist of ultra-hard nitride films with highly ordered micropores and nanopores that are subsequently filled with solid lubricants using various techniques such as lithography, reactive ion etching, laser texturing, pulsed air arc treatment, and ceramic beads as placeholders for sputter deposition; and, (3) Carbon and nitride nanotubes that are filled electrochemically with solid lubricants. The frictional and wear properties of the above three classes of newly developed adaptive structures, tested in various controlled environmental conditions (temperature, humidity), will be discussed in detail.
8:40 AM		B6-3-3 Influence of the Chemical Composition on Tribological Properties of Nitride-Based Nanocomposite Coatings P. Dessarzin (ETH Zurich and PLATIT AG, Switzerland); P. Karvankova, M. Morstein (Platit AG, Switzerland); N.M. Renevier (University of Central Lancashire, United Kingdom); N.D. Spencer (ETH Zurich, Switzerland) As a consequence of the increased use of dry machining strategies such as high-speed cutting (HSC), high-performance cutting (HPC) and hard turning, modern tool coatings are constantly challenged by severe environments, combining oxidative, abrasive and adhesive wear. In order to evaluate the role of coating chemical composition in related high-temperature situations, this study compares friction, wear and oxidation behaviour of different conventional and nanocomposite PVD coatings, deposited using the rotating arc cathodes technology. At room temperature, dry-sliding experiments were carried out in dry air on coated HSS plates against metalloid (WC-Co) and ceramic (Si₃N₄) counterparts. For both pin materials, a distinct decrease of the coating wear coefficient was found upon addition of carbon, silicon or chromium to the Ti_1-xAl_xN base system. In contrast, the coefficient of friction remained essentially unchanged except for the case of carbon. SEM investigations showed that the wear was dominated by an abrasive mechanism, with only few cases of ball material transfer to the friction track. Neither fracture nor delamination of the coatings were observed. High-temperature pin-on-disk tests of coatings on cemented carbide plates against alumina balls revealed early failure of carbon-containing coatings due to their low oxidation resistance. Most nitride and oxynitride coatings were able to withstand the conditions with only minimum oxide scale formation, yet the beneficial effect of Cr addition on the wear resistance was found to be less pronounced. The wear volume at 600°C correlated well with dry milling tests in steel, however not strongly with room-temperature nanomechanical properties of the coatings. Therefore, the hot hardness and -modulus of selected coatings were measured in situ, using a special indenter setup.
9:00 AM		B6-3-4 Development and Properties of Advanced Nitride Coatings for Tooling Applications M. Lechthaler, F. Neff, E. Plesiutsching (OC Oerlikon Balzers AG, Liechtenstein); R. Franz (University of Leoben, Austria) Advanced manufacturing technologies such as high performance cutting augment the requirements of wear protective coatings for tooling applications. Within this work, recent investigations in industrial coating development of arc evaporated coating applications are presented. In order to achieve superior coating properties, additional alloying elements including Si and B as well as transition metals were added to the highly investigated Al-Cr-N coating system. Moreover, the improvement of the coating properties due to fine tuning of deposition parameters is discussed. This allows the design of new coatings with tailored coating properties leading to superior performance in machining applications. Furthermore, investigations are highlighted on innovative promising material systems for new wear resistance coatings such as AlNbN. X-ray diffraction and scanning electron microscopy as well as transmission electron microscopy analyses were carried out to investigate the microstructure and morphology of the coatings. The mechanical properties are characterized by nanoindentation measurements, whereas annealing tests in ambient atmosphere served to determine the oxidation resistance. Finally, the correlation between mechanical properties and the application performance of these coatings is evaluated in cutting tests. The comparison to state-of-the-art coatings allows the estimation of the potential of these coatings for future industrial use.
9:20 AM		B6-3-5 Influence of B on Structural, Mechanical and Tribological Properties of Arc Evaporated Al-Cr-N Thin Films C. Tritremmel, P.H. Mayrhofer (University of Leoben, Austria); M. Lechthaler (OC oerlikon Balzers AG, Liechtenstein); C. Polzer (PLANSEE Composite Materials GmbH, Austria); C. Mitterer (University of Leoben, Austria) Al-Cr-N is a well-established hard coating system with excellent mechanical and tribological properties. Structure and mechanical properties of transition metal nitrides like TiN or CrN can be further improved by boron addition; thus we systematically investigated its effect on Al-Cr-N. Coatings were synthesized by cathodic arc evaporation in pure N₂ atmosphere at 3.5 Pa and 500°C in an industrial-scale Oerlikon Balzers Innova deposition system. The B content in the targets was varied between 10 and 20 at% at constant Al/Cr atomic ratio of 1.8. X-ray diffraction revealed that all coatings exhibit a face-centered cubic structure in the as-deposited state. Texture and mechanical properties of the coatings are, however, slightly changed by varying substrate bias and nitrogen pressure. Residual stress measurements indicated a low compressive stress level (-1.2 GPa) even at high substrate bias. Nanoindentation experiments revealed a significant hardness enhancem ent in comparison with B-free Al-Cr-N coatings, where a hardness maximum of 43 GPa was found for Al-Cr-B-N synthesized using the target with 10 at% B. Tribological ball-on-disc tests confirmed that B addition is a promising attempt for further improvement of Al-Cr-N coatings, yielding wear coefficients in the range of 1x10^-17 m³/Nm at room temperature.
9:40 AM	Invited	B6-3-6 From Understanding the Growth Mechanism to the Design and Fabrication of High-Performance Functional Coating Architectures L. Martinu (Ecole Polytechnique de Montreal, Canada); A. Amassian (Cornell University); E. Bousser, S. Hassani, J. Houska, R. Vernhes, J.E. Klemberg-Sapieha (Ecole Polytechnique de Montreal, Canada) Recent advances in the technological sectors of aerospace, automotive, biomedical and pharmaceutical applications as well as in energy and environment control stimulate research on high performance functional coatings. In many cases, the ever increasing requirements involve an “ideal” combination of the mechanical, tribological, corrosion, thermal and other characteristics that can only be satisfied by using specifically tailored film architectures including nanocomposite, nanolaminate, multilayer and graded layer systems. In this presentation, we will outline approaches that allow one to design and fabricate high-performance protective coatings based on understanding the film growth mechanisms, on the lessons learned in the area of optical coatings such as optical interference filters, and on the use simulation techniques. We will briefly describe our recent studies of the ion-surface interactions in plasma environments (bias- and pulse-controlled PECVD and PVD techniques) using a methodology combining in situ real-time spectroscopic ellipsometry and different complementary microstructural and chemical analysis methods, while specifically addressing selected nanostructured systems such as Ti-Si-N, Ti-Si-C-N and Cr-Si-N coatings. We will show examples in which the modeling approach helped us to enhance our understanding of the growth-structure-property relationships, and that allowed us to predict functional behavior of different coating combinations; this includes: (i) Dynamic Monte-Carlo simulation of the ion bombardment effects on subplantation and interfacial mixing; (ii) Molecular dynamic simulations of the nanocomposite structures capable of predicting the experimentally observed superhardness; and (iii) Finite element design of film architectures for the prediction of enhanced resistance to solid particle erosion. Finally, we will discuss new opportunities and surface engineering strategies leading to attractive technological solutions in the areas of protective coatings for aerospace, biomedical and optical applications.
10:20 AM		B6-3-9 Combinatorial Approach to the Growth of α-(Al,Cr)₂O₃ Solid Solution Strengthened Thin Films by Reactive r.f. Magnetron Sputtering M. Stueber, D. Diechle, H. Leiste, S. Ulrich (Forschungszentrum Karlsruhe, Germany); V. Schier (Walter AG, Germany) The development of superior coatings for high performance cutting tools is a key factor for significant advances in metal working. Aluminum oxide thin films deposited by chemical vapor deposition (CVD) methods are industrially well-established since years. Recently, the physical vapor (PVD) synthesis of aluminum oxide and derivative coatings is attracting large scientific and technical interest. Especially aluminum-chromium oxide coatings are promising candidates for offering simultaneously thermal stability, chemical inertness, excellent high temperature toughness and hardness with regard to their mixed ionic and covalent bonds. A combinatorial approach to the growth and microstructure evolution of Al-Cr-O thin films by means of reactive r.f. magnetron sputtering is presented. A segmented target consisting of two half plates of Al and Cr was used for the deposition experiments carried out under stationary conditions in a laboratory scale PVD coater (Leybold Z 550). Opposite to the cathode five substrate samples (commercial cemented carbides, silicon wafers) were placed in equidistant positions. The r.f. cathode power was set to 500 W and the total gas pressure was kept constant at 0.65 Pa for all experiments with a fixed oxygen to argon gas flow ratio. The substrate temperature was varied between 180°C and 600°C, while the r.f. substrate bias voltage was varied systematically between 0 V and -400 V. Detailed results on the coatings composition, constitution, microstructure and properties will be presented. XRD and TEM studies clearly show that the growth of well adherent, nanocrystalline, stoichiometric, metastable corundum-like solid-solution strengthened (Al_1-x,Cr_x)₂O₃ thin films with a high degree of crystallinity and Vickers hardness up to 2600 HV0.05 is possible at non-equilibrium conditions already at low substrate temperatures of 500°C.
10:40 AM		B6-3-10 Dense Nanostructured Oxide Coatings Made By Plasma Spray and Conventional Consolidation Processes M. Gell (University of Connecticut, United States); E.H. Jordan, J. Wang, C. Muoto (University of Connecticut) Dense oxide coatings are traditionally used in wear, environmental and functional applications. There is an increasing body of research that demonstrates that superior properties for these applications can be obtained if the grain size is reduced into the nano-scale range (<100 nm). In this study, magnesis-yttria nanoscale powder, with a grain size of about 50 nm, is produced by a combustion synthesis process. This powder is then consolidated using a variety of methods, including vacuum hot pressing, hot isostatic pressing, spark plasma sintering, and suspension plasma spraying. The powder is also agglomerated so that it can be directly plasma sprayed. The microstructure and hardness of the resultant coatings made from the various processes will be described.
11:00 AM		B6-1-9 Nano-Structured CrN/AlN Superlattice Coatings Synthesized by Pulsed Closed Field Unbalanced Magnetron Sputtering J. Lin, B. Mishra (Colorado School of Mines); M. Pinkas (Nuclear Research Center, Israel); J.J. Moore (Colorado School of Mines); W.D. Sproul (Reactive Sputtering, Inc.) Chromium nitride/aluminum nitride (CrN/AlN) superlattice coatings were prepared using a pulsed closed field unbalanced magnetron sputtering system from pure Cr and Al targets. The bilayer periods of the coatings were obtained between 2.0 to 15 nm by controlling the target powers and the substrate rotation speed. The effects of the bilayer period (especially in the 2-7 nm range) on the structure and properties of the CrN/AlN coatings were characterized by means of low angle and high angle X-ray diffractions, scanning electron microscopy, transmission electron microscopy, nanoindentation, Rockwell C indentation, and ball-on-disk wear tests. All CrN/AlN superlattice coatings synthesized in the current study exhibit a single phase face-centered cubic structure. Compared with the homogeneous Cr_0.4Al_0.6N coatings, significant improvements on the hardness and wear resistance were achieved in the CrN/AlN superlatice coatings. The CrN/AlN superlattice coatings exhib it super hardness above 40 Gpa in a wide range of bilayer period of 2.7~4 nm, where the highest hardness of 45 Gpa was achieved when the bilayer period is at 2.7 nm. When the bilayer period is between 2.7 to 5.5 nm, the nanolayered coatings also showed low coefficient of friction in the range of 0.3 to 0.35 and low wear rate in the 10^-7 mm³N^-1m^-1 range. The CrN/AlN superlattice coatings also exhibit lower residual stress, improved adhesion and toughness as compared to those of the homogeneous CrAlN coatings.