Papers

ICMCTF2009 Session B6-2: Hard and Multifunctional Nano-Structured Coatings

Thursday, April 30, 2009 1:30 PM in Room Golden West

Thursday Afternoon

Start	Invited?	Item
1:30 PM		B6-2-1 Metal Carbide/Amorphous C-Based Nanocomposite Coatings for Tribological Applications J.C. Sanchez-Lopez, D. Martinez-Martinez, M.D. Abad, A. Fernandez (Instituto de Ciencia de Materiales de Sevilla, Spain) This paper tries to assess the factors governing the tribological behaviour of different nanostructured or nanocomposites films composed by metallic carbides (MeC) mixed with amorphous carbon (a-C). Different series of MeC/a-C coatings (with Me: Ti(B) and W) were prepared by magnetron sputtering technique varying the power applied to the graphite target in order to tailor the carbon content into the films. A deep investigation of the chemical and structural features at the nano-scale is carried out for each family of coatings by many different spectroscopic, microscopic and diffraction techniques in order to establish correlations with the tribological properties measured by a pin-on-disk tribometer in ambient air. The analysis of the counterfaces by Raman confocal microscopy after the friction tests is used to follow the chemical phenomena occurring at the contact area responsible of the observed friction behaviour. The importance of determining the nanocrystalline/amorphous ratio is highlighted as a key-parameter to control the tribological properties. A comparative analysis of the mechanical and tribological performance of the three systems (TiC/a-C, TiBC/a-C, WC/a-C,) is revised and conclusions are obtained concerning the friction and wear mechanism involved.
2:10 PM		B6-2-3 XPS Analysis of Binary and Ternary TiC-Based Alloy and Nanocomposite Coatings E. Lewin (Uppsala University, Sweden); M. Gorgoi (BESSY GmbH, Germany); U. Jansson (Uppsala University, Sweden) Through thin film techniques a continuously growing amount of meta-stable phases and microstrucures are synthesised and proposed for use in a diverse field of applications. A commonly used technique to analyse these coatings with regards to chemical composition and bonding is X-ray photoelectron spectroscopy (XPS) coupled with sputter etching using an ion gun to attain information below the outermost surface. For carbide based systems XPS is presently often used to determine relative amount of carbide and free carbon phases, well as the sp²/sp³ ratio of the free carbon phase. This analysis is often performed after sputter-etching. Although it is well known that sputter etching can cause damage to the analysed sample and interfere with the results, it is often not thoroughly investigated as one moves from well known systems such as TiC to alloyed or nanocomposite systems such as (Ti,Me)C and nc-TiC/a-C. We here present an analysis of binary and ternary TiC-based alloy an d nanocomposite coatings in the Ti-Ni-C and Ti-Cu-C systems. We have used angle-resolved XPS with different sputter energies (acceleration voltages) and compare these results with results attained by use of high kinetic energy (HIKE) XPS, which has a larger sampling depth, of undamaged samples. We observe substantial sputter damage (strongly dependent on sputter energies), specially for the case of alloyed carbides such as (Ti,Ni)C. This clearly limits the use of XPS together with sputter-etching as a tool to understand the structure of meta-stable coatings. In the light of these results we discuss when and how one can use XPS as a reliable analytical tool.
2:30 PM		B6-2-4 Fabrication and Tribological Properties of Composite Coatings Produced by Lithographic and Microbeading Methods J.E. Krzanowski (University of New Hampshire) Nanoscale multiphase and composite coatings have been the subject of intensive research and are being proposed as the next generation of tribological coatings. This research has been driven by the need for coatings to function in extreme, as well as multiple, environments. However, fabrication of coatings with distinct phases and appropriate microstructure remains a challenge. One approach is to pattern a coating by external intervention. These methods include masking, laser drilling of holes, and lithographic methods. Our recent work has focused on lithographic methods, as well as a new masking approach which we refer to as microbeading. In the latter method, microscopic ceramic or glass beads are used to decorate the surface before deposition, and act as placeholders. After deposition, these beads are removed leaving behind a random arrangement of holes. The surface is then coated with a solid lubricant, and during wear the holes act as microreservoirs for lubricant s torage. Evaluation of microreservoir-containing coatings fabricated by the microbeading method was carried out by depositing a TiN film, and then using graphite as the solid lubricant. Pin-on-disk tests using an alumina counterface showed that substantial reductions in friction coefficients were obtained for the larger bead sizes (5-10 microns). Examination of the wear tracks using optical microscopy showed that the graphite lubricant was successfully trapped by the microreservoirs during the pin-on-disk test running. The microbeading coating method was also implemented on cutting tools for machining where indium was used as the solid lubricant. Turning tests were conducted by high-speed machining of hardened 4340 steel. TiN-In coated inserts were tested by measuring flank wear in lubricated (cutting fluids used) machining, and showed up to 4 times longer wear life than a TiN coating without indium. TiN, TiN with an In topcoat, and TiN with In and 5 micron microreservoirs we r e also tested in dry machining, and the coating with the 5 micron microreservoirs exhibited the least wear for most of the test period. XPS analysis confirmed the presence of the indium near the tool tip, where the chip flows on the rake face. In addition, samples with microreservoirs showed greatly reduced crater wear on the rake surface. These results demonstrate that the use of indium with microreservoir-patterned coatings can be beneficial in dry machining of steel.
3:10 PM		B6-2-6 Microstructures and Corrosion Resistance of Pulsed DC Reactive Magnetron Sputtered nanocomposite Zr-Si-N Thin Films Y.-B. Lin, J.-W. Lee (Tungnan University, Taiwan); L.-C. Chang (Mingchi University of Technology, Taiwan) The nanocomposite Zr-Si-N thin films with various Si contents have been deposited by a bipolar asymmetric pulsed DC reactive magnetron sputtering system. The Zr-Si- N thin films with Si contents ranging from 1.5 at.% to 8 at.% were achieved. The structures of Zr-Si-N films were characterized by XRD. The surface and cross sectional morphologies of thin films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface roughness of thin films was explored by atomic force microscopy (AFM). The nanoindentation, nanoscratch and nanowear tests were adopted to evaluate the nanomechanical properties of Zr-Si-N coatings. The electrochemical test in 3.5 wt.% NaCl aqueous solution was conducted to evaluate the corrosion performance of each coating. The amorphous structure was observed when the silicon content reached 7 at.% in Zr-Si-N thin films. In general, the corrosion resistance of the coating increased with increasing Si content. A high hardness and good corrosion resistance were found in the Zr-Si-N thin film with around 3 at.% Si in this work.
3:30 PM		B6-2-7 Hard and Decorative Coatings Based on Al-N + Au Nanocomposite Structures A. Cavaleiro, C. Louro, N. Figueiredo (University of Coimbra, Portugal) One of the most interesting aspects of the metals clusters when placed in a dielectric matrix is that their optical properties depend strongly upon the particle size and shape. Metals with free electrons (essentially Au, Ag and Cu) possess plasmon resonances in the visible spectrum, which give rise to intense colour in this situation. The main objective of this research is to produce new decorative coatings by dispersing nanocrystals of gold in a dielectric and transparent matrix (e.g. Al-O). Simultaneously, it is expected that the coatings have suitable mechanical properties for being wear resistant. Al-N+Au coatings were deposited by sputtering from an aluminium target embedded with thin gold plates, in a reactive environment containing nitrogen. The N2 flow was high enough for working in compound mode producing transparent dielectric films. The Au content was varied from 0 up to 15 at.%. Subsequently, the films were treated to promote the segregation of metallic nano crystals of Au in the dielectric matrix. The precipitation process was followed by high-temperature X-ray diffraction. For selected temperatures, samples were annealed in a furnace in order to produce samples to be optically and mechanically characterized. In this work, only the results concerned the optical properties, evaluated by colorimetry and UV-Vis spectroscopy, and the mechanical properties, hardness and Young´s modulus, will be presented as a function of the Au content, before and after annealing at increasing temperatures up to 1000ºC.
3:50 PM		B6-2-8 Microstructure – Property Relationships in Nitride-Based Coatings on Steel Substrates Prepared by Pulsed Laser Deposition A. Jahja, P. Munroe (University of New South Wales, Australia) A range of sub-micron thick TiN coatings were deposited on a H13 hot worked tool steel substrate via pulsed laser deposition as a function of processing condition. The coatings were subject to detailed microstructural characterization, including cross-sectional TEM studies. Coatings prepared at high substrate temperatures (450°C) and reactive gas conditions exhibited nanoscale grain sizes, whilst slightly coarser structures were prepared in inert environments. Mechanical behaviour was assessed through nanoindentation using a spherical indenter. The coatings exhibited high hardness values and significant resistance to cracking, even at high loads. Examination of the indented layers revealed intercolumnar cracks within the TiN coatings, together with shear steps at the coating-substrate interface, whilst inclined cracks were observed at the periphery of the indentations.
4:10 PM		B6-2-9 Chromium-Aluminum Oxide Coatings Deposited by Reactive Magnetron Sputtering P. Eklund (Linköping University, Sweden); K. Pedersen (University of Aarhus, Denmark); K.P. Almtoft, L.P. Nielsen (Danish Technological Institute, Denmark); M. Sridharan, M. Sillassen, J. Bottiger (University of Aarhus, Denmark) Chromium oxide and aluminum oxide thin films were deposited by reactive inductively coupled plasma magnetron sputtering at substrate temperatures from room temperature to 700°C. X-ray diffraction and electron microscopy showed that the as-deposited chromium oxide coatings crystallized in a corundum structure, while aluminum oxide thin films deposited at low ion flux during growth were amorphous in the substrate-temperature range 200 to 450°C. A higher ion flux and/or temperature resulted in predominantly crystalline γ-alumina¹. For Cr₂O₃, the hardness was 29 GPa, while the hardness values of the as-deposited alumina films varied from 8–20 GPa, with the highest values corresponding to larger crystalline volume fractions. The growth of α-alumina at 450°C could be promoted by depositing onto chromia templates, a result consistent with previous findings². In contrast, we observed a strong texture effect with extended growth of α-Al₂O₃ at a substrate temperature of 450°C using a predominantly <104>-textured Cr₂O₃ template layer, while only limited α-Al₂O₃ nucleation was seen on a <001>-textured Cr₂O₃ template³. The texture of the chromia templates could be controlled from a <001> texture due to competitive growth to an ion-bombardment-induced <104> texture, to a mixed <110>-dominated texture at high ion bombardment. Codeposition of chromia and alumina onto <104>-textured templates yielded corundum-structured films and a slight hardness increase as compared to pure chromia, possibly due to phase separation of Cr₂O₃ and Al₂O₃. Further, alumina films were deposited in a large-scale industrial coating facility employing pulsed dc sputtering and a range of pulsed dc bias. The morphology and density of the alumina coatings could be controlled by bias modulation and ramping, with columnar growth obtained for negative bias of 30 to 65 V. A dense, featureless, insulating alumina was obtained for bias above 70 V. ¹M. Sridharan et al Surf. Coat. Technol. 202 (2007) 920. ²J. M. Andersson et al J. Vac. Sci. Technol A 22 (2004) 117, and references therein. ³P. Eklund et al Thin Solid Films 516 (2008) 7447.