ICMCTF2002 Session B3-2: Structure and Properties of Hard Coatings

Wednesday, April 24, 2002 8:30 AM in Room Golden West

Wednesday Morning

Start	Invited?	Item
8:30 AM		B3-2-1 Growth and Characterization fo Single Crystal Ti₃SiC₂(0001) Thin Films J.P. Palmquist (Uppsala University, Sweden); T. Seppanen, J. Birch, P.A. Persson, J. Oden, J. Neidhardt, J. Emmerlich (Linköping University, Sweden); P. Isberg (ABB Group Service Center, Sweden); U. Jansson (Uppsala University, Sweden); L. Hultman (Linköping University, Sweden) The combination of useful properties, such as high stiffness, machinability, low friction, thermal stability, and electrical and thermal conductivity has triggered materials research on the so-called MAX-phases during the last decade. These are nano-layered materials with a chemical composition M_nAX_n-1 (M=early transition metal, A=A-group element, and X is either C or N) with Ti₃SiC₂ being the most well characterized MAX-phase, although it has, until now, only been synthesized as polycrystalline bulk material. We report here on the first synthesis of single phase and single crystal Ti₃SiC₂ thin film material. The films were grown using two different PVD deposition processes onto an epitaxial TiC-seed layer on MgO(111) substrates. The first method is co-sputtering of Ti and Si from individual magnetron sources with C supplied by C₆₀ evaporation. The second method is sputter deposition from a stoichiometric Ti₂SiC₂ target. At substrate temperatures above 900°C, XRD as well as HR-TEM showed single phase single crystal Ti₃SiC₂ formation on the substrate, with the epitaxial relationships Ti₃SiC₂(0001)//TiC(111)//MgO(111) and T₃SiC₂[1000]//TiC[101]MgO[101], using both processes. At 800°C, the C₆₀ based process yielded a mixture of epitaxial Ti₃SiC₂ and Ti₄SiC₃. Homogenous stoichiometric films were formed under all deposition conditions as measured by energy filtered TEM and XPS depth profiling. Friction measurements, using a Hysitron triboscope, have been performed and will be reported on and nano-indentation measurements indicate hardness and elastic modulus values up to 20 Gpa and 350 GPa, respectively, independent of deposition method. These findings have implications for wear-protective low-friction coatings on a range of components, not the least electrical contacts.
8:50 AM		B3-2-2 Wear Protective Coatings Consisting of TiC-SiC-C Deposited by Magnetron Sputtering J. Matthey (EICN, Le Locle, Switzerland); T. Zehnder (EMPA, Dübendorf, Switzerland); A. Klein, P.-A. Steinmann (EICN, le Locle, Switzerland); J. Patscheider (EMPA, Dübendorf, Switzerland) Hard coatings of the composition TiSi_xC_y have been deposited with the aim of depositing self-lubricating Ti₃SiC₂. Two groups of films were prepared by physical vapor deposition: one set from elemental targets and ethine in a reactive UBM configuration and another set from a compound target of the composition Ti₃SiC₂. The coatings are composed of nanocrystalline TiC and, according to the deposition method and the various compositions, of amorphous carbon and amorphous silicon carbide. Nanohardness values of up to 45 GPa could be obtained for coatings with friction values well below that of TiC. Low friction coefficients against steel were measured for higher concentrations of amorphous carbon at hardness values of about 28 GPa. Preliminary experiments indicate that improved temperature stability can be obtained due to silicon incorporation. Results will be presented and discussed in terms of the nanostructure of the coatings.
9:10 AM		B3-2-3 Properties of TiSiN_x Deposited by Concurrent Cathodic Arc Evaporation and Magnetron Sputtering P.J. Martin, A. Bendavid (CSIRO, Australia) Thin films of TiSiN_x have been synthesised by the concurrent reactive deposition of Ti with a cathodic arc source and Si with a magnetron sputter source. The films were found to have a microhardness of up to 60 GPa and a grain size of 15 nm whilst the stress was reduced from 3.5 GPa for pure TiN to 1.8 GPa for Si contents of 5 atomic percent or higher. The films were found to be nanocomposite in structure confirmed by the amorphous nature of the SiN_x and increased mechanical properties relative to TiN.
9:30 AM		B3-2-4 Microstructure and Mechanical Properties of Nanostructured Ti-Si-N Coatings W.J. Meng, R.C. Tittsworth, X.D. Zhang, B. Shi (Louisiana State University); L.E. Rehn, P.M. Baldo (Argonne National Laboratory) The microstructure and atomic bonding environment of Ti-Si-N coatings, synthesized by high-density inductively coupled plasma (ICP) assisted sputter deposition, have been characterized in detail by Rutherford backscattering spectrometry (RBS), transmision electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). The mechanical properties have been measured by instrumented nanoindentation. The elastic stiffness and hardness of Ti-Si-N coatings are correlated with observed coating microstructure, and related to recent experiments reported in the literature.
9:50 AM		B3-2-5 PVD Grown (Ti,Si,Al)N Nanocomposite Coatings and (Ti,Al)N/(Ti,Si)N Multilayers: Structural and Mechanical Properties S. Carvalho, E. Ribeiro, L. Rebouta (University of Minho, Portugal); P. Renault, J. Pacaud, P. Goudeau, J.P. Riviere (University of Poitiers, France) In last few years a considerable effort has been undertaken in order to optimise the production techniques of thin films and improve their quality. In this work nanocomposite films resulting from Si additions to (Ti,Al)N matrix have been prepared by rf and/or dc magnetron sputtering and with deposition rates varying from 0.2 µm/h to 4 µm/h. Rutherford backscattering (RBS)and Electron microprobe analysis (EMPA) were used in order to obtain the chemical composition as well as the density. Results of X-ray diffraction (XRD) in both θ-2θ and α-2θ scans showed the development of a two-phase system for samples prepared with low deposition rates. One phase with 0.427 nm as lattice parameter is indexed to bulk TiN and develops for low Si content. In case of low surface mobility and high Si content a fcc metastable Ti-Si-Al-N phase (a≥0.417 nm) is developed, where Si and Al atoms are occupying Ti positions within TiN. Concerning texture evolution, there is some variations in preferencial growth, which changed from (111) for the (Ti,Al)N and low Si additions to (200) at intermediate Si additions and finally to a week (200) and (220) texture for large Si addition. From XRD asymetric experiments the degree of the misorientation from the (200) reflections can reach ± 7° compared with to ± 2.3° (from (111)) for low Si content and ± 3° for (Ti,Al)N from (111). High-resolution transmission electron microscopy (HR-TEM) micrographs revealed a columnar growth as well the fcc-type structure for both phases. Small crystallites with a size of ±5 nm were observed. (Ti,Si)N/(Ti,Al)N multilayers with modulation periods of approximately 10 nm were obtained, as shown by HR-TEM results, when the samples were prepared with a deposition rate of 4 µm/h. The average ultramicrohardness can be as high as 50 GPa.
10:10 AM		B3-2-6 Structure and Mechanical Properties of Superhard Thin Films O. Durand-Drouhin (Swiss Federal Institute of Technology (EPFL), Switzerland); A.E. Santana (Swiss Federal Institute of Technology (EPFL)); A. Karimi (Swiss Federal Institute of Technology (EPFL), Switzerland); A. Shuetze (Balzers Ltd., Liechtenstein) The paper deals with the relationships between nanostructure and nanoscale mechanical properties of multicomponent thin films in particular titanium aluminium carbon nitride multilayer. By changing chemical composition and deposition parameters, various nanostructured films were produced. The structure of coatings was investigated using electron microscopy (SEM, TEM) and X ray diffraction measurements. Growth morphology, texture and bilayer effect will be discussed in more details in the paper. Mechanical properties, including Young's modulus and hardness were extracted from the load displacement curve of nanoindentation measurements. A particular attention is devoted to hardness measurements analysis for such superhard materials, as well as the contribution, which could arise from the substrate. The existing analytical model will be discussed. The paper presents also the experimental results concerning the failure modes generated by nanoscratch and nanoindentation tests. The formation of radial and interfacial cracks will be showed versus film structure and substrate hardness. Also, as well as fracture toughness and energies calculated for these cracks will be given. All the obtained results will be discussed in terms of structure and chemical composition.
10:30 AM		B3-2-7 Tough Nanocomposite Coatings: Design and Testing A.A. Voevodin, J.J. Hu, T.A. Fitz, J.S. Zabinski (Air Force Research Laboratory) Material is generally considered tough if it withstands high levels of loading (tensile, compressive, shear, etc.) and can dissipate strain energy without brittle fracture. In addition, interfacial toughness is particularly important for thin films where delamination, even if the substrate is plastically deformed, must be avoided. In conventional tough materials, plastic deformation with dislocation activity causes strain relaxation and suppresses crack growth, promoting ductility as opposite to brittle fracture. This approach deteriorates material hardness since it reduces both yield strength and elastic modulus of the material. An alternative approach is to embed hard nanocrystalline grains into a stiff amorphous matrix and rely on grain boundary sliding for strain relaxation at loads above the yield strength. This maintains composite hardness and elastic modulus at a high level yet introduces ductility at very high loads, preventing brittle fracture. Toughness is further enhanced by a large volume fraction of crystalline/amorphous boundary interfaces, where cracks are deflected and eventually terminated. Design concepts of tough nanocomposite coatings are discussed together with examples within the TiC/DLC, WC/DLC, and YSZ/Au material systems. Particular attention is paid to the methods of coating toughness evaluation, where various approaches are suggested and compared.
10:50 AM		B3-2-8 Mechanical Properties and Tribological Behavior of Al/Al₂O₃ and Ti/TiN Multilayer Nanocomposite Thin Films Z.Q. Qi (Louisiana State University); X. Nie (Louisiana State Universtiy); E.I. Meletis (Louisiana State University) The effects of layer thickness on the mechanical properties of the Al/Al2O3 and Ti/TiN multilayer nanocomposite systems were investigated in the present study. The multilayers were deposited on Si wafers using an electron-beam physical vapor deposition (EB-PVD) method. Three series of multilayers were synthesized for each nanocomposite system. In the first group, the metallic and ceramic layers were of the same thickness (10-50 nm), in the second group, the thickness of the metallic layer was kept constant (40 nm) while the thickness of the ceramic layer changed from 10 nm to 40 nm; and in the third group, the ceramic layer thickness was kept constant (40 nm) and the thickness of metallic layer changed from 10 nm to 40 nm. Monolithic metal and ceramic thin films were also deposited for comparison. The total thickness of each film was about 1 Âµm. Transmission electron microscopy (TEM) was employed to characterize the microstructure of the multilayer thin films. Nanoindentation tests were performed to determine hardness and elastic moduli of the composites and to analyze thickness effects. Pin-on-disc wear tests were also performed to investigate the tribological behavior of the thin films as a function of layer thickness. Key Words: EB-PVD, Multilayer thin films, Nanoindentation, Tribology, TEM.
11:10 AM		B3-2-9 Effect of the Substrate Bias on the Microstructure of Polycrystalline CrN/NbN Superlattice Coatings Grown by the Combined Cathodic Arc / Unbalanced Magnetron Sputtering Method Q. Luo, B.D. Lewis, P.Eh. Hovsepian, W-D Münz (Sheffield Hallam University, United Kingdom) Polycrystalline CrN/NbN superlattice coatings have been grown by the combined steered cathodic arc / unbalanced magnetron sputtering deposition method, which exhibit excellent corrosion resistance and tribological properties. A characterisation of the microstructure of the nano-scale architectured coatings is presented, using transmission electron microscopy and X-ray diffractometry. The study has been concentrated on the influence of substrate bias on the structure evolution so as to illustrate the relationship between the growth mode and the enhanced ion bombardment. It has been found that, the superlattice period of the CrN/NbN decreased from 5nm to 3.3nm as the substrate bias increased from -75V to -150V. The inter-columnar voids are eliminated together with increasingly flat front of each CrN/NbN columnar grain leading to smooth coating surface. Meanwhile, the preferred growth orientation changes between (200) and (111) texture as a result of the varied substrate bias. Variation of texture has also been observed, through cross-sectional TEM, along the longitudinal direction at each coating. Additionally, residual compressive stresses have been found to increase from 2.14 to 7.07 GPa as the substrate bias increased from -75V to -150V.
11:30 AM		B3-2-10 Corrosion Resistance of CrN/NbN Superlattice Coatings Grown by Various Physical Vapour Deposition Techniques P.Eh. Hovsepian, Q. Luo, B.D. Lewis, W-D Münz (Sheffield Hallam University, United Kingdom) This work presents results from the corrosion and tribological performance of CrN/NbN superlattice coatings deposited by unbalanced magnetron sputtering (UBM), steered cathodic arc evaporation and combined steered cathodic arc / unbalanced magnetron sputtering (known also as Arc Bond Sputtering: ABS) techniques. Potentiodynamic polarisation in 3% aqueous NaCl solution revealed significant differences both in the passivation behaviour and in the corrosion current measured during the tests. The UBM deposited coatings showed poor passivation and pitting occurred already at a potential as low as 200 mV. Furthermore, the UBM coatings showed high corrosion current densities in the range between 10^{- 4} to 10^-5 A. cm^-2. A clear passivation in the current density range between 10^-6 to 10^-7 A. cm^-2 with first pitting events occurring at 380 mV was observed with CrN/NbN deposited by steered arc evaporation. No pitting up to 800 mV and low corrosion current densities ranging between 10^-7 to 10^-8 A. cm ^-2 were detected with the ABS coatings, where the substrate was exposed to a 3.6 keV metal ion implantation. The highest hardness of HK 3700 and scratch adhesion critical load values of Lc= 62 were measured for the ABS deposited coatings, compared to HK 3600, Lc= 46 and HK 3400, Lc = 18 for the steered arc and UBM coatings respectively. The UBM grown CrN/NbN coatings showed mediocre tribological properties with high friction coefficient of 0.95 and high dry sliding wear coefficient of Kc= 3.4 10^-12 m² N^-1. Although the friction coefficient of steered arc deposited coatings was the lowest, 0.3, inferior wear resistance (Kc=8.2 10^-13 m² N^-1) was observed. The tribological properties of ABS CrN/NbN were superior to both UBM and steered arc coatings. For these coatings, friction coefficient of 0.9 and the lowest dry sliding wear coefficient of Kc= 5.10^-15 m² N^-1was measured, compared to Kc= 5.8 10^-14 m² N^-1of electroplated Cr. XTEM, SEM, XRD and EDX analysis provided explanation of the behaviour of the PVD coatings, demonstrating the major structural and compositional differences both at the coating substrate interface and the bulk of the coatings as well as differences in the type and density of the defects in the coatings inherited by the deposition method.
11:50 AM		B3-2-11 Synthesis, Characterization and Properties of Ti₃SiC₂ Thin Films Deposited by PLD J.J. Hu, J.E. Bultman, S.T. Patton, J.S. Zabinski (Air Force Research Laboratory) Ti₃SiC₂ is a ternary phase ceramic with high strength, high toughness, oxidation resistance, and good electrical / thermal conductivity, which makes it promising for tribological applications. It has a layered structure of double TiC-like blocks, separated by planes of silicon where the atoms are in six-fold coordination along the c-axis. The weak Van der Waals bonding between repeating layers suggests a similarity to the well-known solid lubricants MoS₂ and graphite. In this work, pulsed laser ablation of Ti₃SiC₂ targets was used to grow Ti₃SiC₂ crystalline films for studies of their tribological properties. Deposition conditions, in particular substrate temperature, were controlled to adjust film microstructure and chemistry. X-ray diffraction and transmission electron microscopy showed that coatings grown at 100^oC were composed of about 5 nm diameter crystallites, and that increasing the deposition temperature to 300^oC increased crystallite size to 10 nm. Coating elemental compositions were determined by X-ray photoelectron spectroscopy (XPS) and X-ray energy-dispersive spectrometry (EDS) microanalysis. XPS showed that the coatings were nearly stoichiometric and EDS showed that the films were uniform. The hardness and adhesion of the films were evaluated using nanoindentation and scratch tests, respectively. Friction coefficients as low as 0.1 were observed for the first 15 cycles and stabilized around 0.2 after about 700 cycles on a ball-on-disk tribometer. Films of transferred coating material were identified on the ball after 10,000 cycles suggesting that friction was in part due to Ti₃SiC₂ rubbing against itself. The films were also analyzed using scanning electron microscope and atomic force microscope. Correlations among coating chemistry, microstructure, and tribological performance will be discussed.
12:10 PM		B3-2-12 Effect of Ultra Dispersed Diamonds on Mechanical Properties of Alumna Composite Coatings S.G. Yerakhavets, M.V. Kireytseu, M.V. Istomin (NAMATEX System Division, Institute of Machine Reliability, Belarus) Structure and mechanical properties of composite materials and coatings that contain of 5 to 25 % (vol.) of ultra-dispersed diamonds, different alumna phases, and components of silicon carbide, aluminum nitride, aluminum or glass-bundle have been investigated. Material was formed by impulse pressing. Some components of the coatings were formed by thermal flame spraying, micro arc oxidizing, PVD, pyrolisys, ion sputtering or combination of the technologies. Diamonds of 10-90 angstroms was produced by a detonation synthesis method. Developed materials belong to the class of wear resistant, hard materials. The material has variable-porosity, high density, microhardness of up to 27-30 GPa and good load rating. XRD analysis shows that the structure includes the diamond phase. The particular cluster of material compounds non-metallic high-melting compounds interacted with the diamonds that form ultra fine structure as well. Structure, grains morphology, presence of pores and their distribution, interaction zones were investigated with SEM, X-ray-phase analysis and micro-X-ray-spectral analysis. To investigate load rating of the material Hertzian contact was used. As result of work we revealed an effect of ultra-dispersed diamonds on mechanical properties and quality of composite coatings. Another effect is an optimal amount of diamonds per volume of thin coatings (up to 500 micron in thickness) to improve overall load rating. And the last is an effect of size, number of diamond particles, its structure and properties on strength, microhardness of material.