Papers

ICMCTF2008 Session B6-2: Hard and Multifunctional Nano-Structured Coatings

Monday, April 28, 2008 1:30 PM in Room Golden West

Monday Afternoon

Start	Invited?	Item
1:30 PM		B6-2-1 Realising the Potential of Thin Hard Coatings for Tribological Exploitation P.A. Dearnley (University of Leeds, United Kingdom) Thin hard coatings produced by plasma assisted technologies have found widespread use in metal forming and metal cutting applications for several decades. Although the potential of such coatings for use in the wider tribological applications, like automotive engine power train and orthopaedic implant bearing surface components has been appreciated for some time, actual take-up has been sporadic, due to unpredictable performance. This has been for a combination of reasons but a lack of cohesive and adhesive toughness has been a major factor. The proposed paper will present an overview of the current status of established interstitial compound and doped DLC coatings developed specifically for the wider tribological sector. The potential for improving tribological component performance by applying protective coatings based on intermetallic compounds and metastable doped metals, will also be described.
2:10 PM		B6-2-3 Multilayered Adaptive Coatings for Friction and Wear Reduction Under High Temperature Cycling A.A. Voevodin (Air Force Research Laboratory); C. Muratore (Air Force Research Laboratory (AFRL/RXBT)/UTC, Inc.); J. Hu (University of Dayton Research Institute); J.G. Jones (Air Force Research Laboratory (AFRL/RXBT)) Aircraft and space applications involve a variety of mechanisms and surfaces which need to be protected from wear during operations in extreme environments, especially high temperatures. In previous years we have reported on the concept of "chameleon" wear protective coatings which change their surface chemistry and structure to adapt to the extremes of operational environments. This paper presents the most recent developments with multilayer chameleon coating architectures for multiple high temperature cycles in air. The coatings are made with 200-300 nm thick layers nanocomposites materials incorporating ceramics, metals, and dichalcogenides, such as YSZ/Mo/Ag/MoS₂ and YSZ/Mo/Ag/WS₂, which are interlaced with approximately 100 nm thick diffusion barrier layers of TiN or other materials. The separation of adaptive lubricating layers with TiN diffusion barriers prevents segregation and oxidation of the buried lubricant material, allowing adaptation in those layers to occur only upon exposure by wear. The coatings were tested by sliding against Si₃N₄ balls in air over temperature ranges from 25 to 700°C. At temperatures below 500°C, noble metal phases embedded in a nanocrystalline-amorphous ceramic matrix segregate and coalesce at the coating surface, forming a continuous layer and providing a low-shear interface at the friction contact. At temperatures above 500°C, the noble metal layer softens and is pushed away to allow oxidation of the transition metal additions buried under the surface. Sulfur was found to promote chemical interaction between metal phases and produce oxide compounds that reduce friction coefficient to less than 0.2. The multilayer structures were optimized to control metal diffusion in testing with temperature cycling between room and 500°C in air. Friction and wear rates of the coatings are reported, which show promise for aerospace applications.
2:30 PM		B6-2-4 Microstructure and Tribological Properties of CrN-Ag Nanocomposite Coatings C.P. Mulligan (Benet Laboratories, U.S. Army Armament Research); T.A. Blanchet, D. Gall (Rensselaer Polytechnic Institute) CrN-Ag composite layers were deposited by reactive magnetron sputtering on Si(001) and 304 stainless steel substrates in a 0.4 Pa pure nitrogen atmosphere and at growth temperatures of T_s = 500, 600, and 700 °C. The 3-to-5-µm-thick layers had compositions ranging from pure CrN, to 3, 12, and 22 at. % Ag, as controlled by adjusting the relative power to 5-cm-diameter Ag and Cr targets. A combination of x-ray diffraction and cross-sectional transmission electron microscopy analyses show that the pure CrN develops a columnar microstructure with ~200 nm-wide columns, while the columns decrease in width and continuity for composites of increasing Ag content and increasing growth temperature. In 22% specimens, Ag segregates to form aggregates with an average width that increases from 10 to 200 to 1500 nm for T_s = 500, 600, and 700°C. At high T_s, the aggregates extend along the surface plane to form horizontal lamellae that cause grain renucleation and, in turn, a disruption of the columnar microstructure. The layers were vacuum annealed at 700°C for t_a = 5, 20, and 60 minutes, to study the temperature activated Ag transport to the free surface. Quantitative plan-view elemental mapping of the annealed surfaces by scanning electron microscopy and energy dispersive spectroscopy suggests rapid Ag surface segregation that will ultimately lead to the depletion of the Ag in the CrN matrix. Nanoindentation measurements indicate that the Ag has only a minor effect on the mechanical integrity of the CrN matrix. The high temperature friction coefficient µ, measured using a pin-on-disc tribometer, is initially considerably lower for the composite coating (µ = 0.2) than for pure CrN (µ = 0.4) grown under identical conditions. This composite coating system offers potential for adaptive high-temperature lubrication.
2:50 PM		B6-2-5 Mechanical and Tribological Properties of CrN/Ag and CrSiN/Ag Nano scale Multilayers Deposited by Reactive Magnetron Sputtering M. Baraket, D. Mercs (LERMPS-UTBM, France); V. Demange (LSGS-Ecole des Mines Nancy, France); C. Coddet (LERMPS-UTBM, France) CrN and CrSiN nanocomposite coatings are of consider interest due to their high hardness, oxidation resistance at high temperature, and their mechanical properties. To further improve the wear properties (friction coefficient, Specific wear rate), a method of solid lubrication is investigated. It has been found that combining hard and solid lubricant phases in thin nanocomposite coating provides new performance properties@footnote 1@. CrN/Ag and CrSiN/Ag nano scale multilayers were synthesized by reactive magnetron sputtering of Cr, Si and Ag targets in a reactive Ar/N₂ mixture. For all the experiments the thickness of the Ag layer will be fixed to 3-4nm in order to investigate the effect of the nitride layer thickness and the periodicity of the stack on the mechanical and tribological properties. Nanohardness, young’s modulus, residual stress and friction coefficient are described. XRD and TEM analysis will be also investigated to study the structural properties of the films. super 1@ A.A. Voevodin, J.S. Zabinski, Composites science and technology 65(2005) 741-748.
3:10 PM		B6-2-7 Microstructural Design of Ternary nc-TiC/a-C Based Nanocomposite Coatings Through Alloying With Second Metallic Element E Lewin, O. Wilhelmsson, M. Lindquist, B. André, M. Råsander, B. Sanyal, O. Eriksson, U. Wiklund, U. Jansson (Uppsala University, Sweden) Thin film nc-TiC/a-C nanocomposites are well known as tough low-friction coatings with inherent design possibilities. Using a concept of alloying we have expanded these design possibilities. By adding different amounts of a second transition metal, we have been able to control additional formation of the a-C matrix phase, as well as the formation of additional metallic phases. This is partly a process direct during the deposition, manifesting itself in the microstructure of the as-deposited samples. But it also, due to the metastable deposition conditions, provides a thermodynamic driving force for later phase segregation. This may by triggered by post deposition annealing or other process leading to local heating and used to design "intelligent" or self-adaptive coatings, e.g. self-lubricating or magnetic and wear-resistant coatings. We here present results from the Ti-Fe-C, Ti-Cu-C and Ti-Ni-C systems confirming and expanding the previously presented concept ¹ which was demonstrated in the Ti-Al-C system. Samples were produced using non-reactive magnetron sputtering and analyzed using (mainly) XRD and XPS. Experimental results are supported by ab initio calculations. ² Wilhelmsson et al, Advanced Functional Materials 17 (2007), 1611.
3:30 PM		B6-2-8 Structure and Properties of Nanocomposite and Multilayered TiCrBN/WSe_x Coatings Deposited by Ion Implantation Assisted Sputtering of TiCrB and WSe₂ Targets D.V. Shtansky, A.N. Sheveyko, D.I. Sorokin (State Technological University/Moscow Institute of Steel and Alloys, Russia); L.C. Lev (General Motors R&D and Planning); B.N. Mavrin (Institute of Spectroscopy of RAS, Russia); Ph.V. Kiryukhantsev-Korneev (State Technological University/Moscow Institute of Steel and Alloys, Russia) An effective route for decreasing friction coefficient of hard tribological coatings is a design of nanocomposite (NC) and multilayered (ML) coatings, which combine the advantages of hard and lubricant phases. Among various multicomponent coatings based on carbides, borides and nitrides of transaction metals, Ti-Cr-B-N coatings are characterized by high hardness and wear resistance, superior thermal stability up to 1000°C, improved oxidation resistance up to 900°C, and enhanced corrosion resistance in 1N H₂SO₄ solution. It has been previously shown that Ti ion implantation of growing films results in significant reduction in residual stress of the coatings and improves their adhesion to substrate. In the present study, NC and ML TiCrBN/WSe_x coatings were deposited by ion-implantation assisted sputtering of TiCrB and WSe₂ targets in the gaseous mixture of Ar+14%N₂. The coatings were characterized in terms of their structure, elemental and phase composition, adhesion, hardness, elastic modulus, elastic recovery, friction, and wear- and corrosion resistance. The structure of the coatings was studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron and Raman spectroscopy. All coatings showed a dense structure free of columnar grains. The NC TiCrBN/WSe_x coatings deposited at the magnetron current of 1 A (low growth rate) displayed completely amorphous structure. As the magnetron current was increased up to 2 A, the coatings consisted of TiCrBN crystallites of the NaCl type, 2 nm in size, embedded in an amorphous a-WSe_x matrix. The ML coatings demonstrated poor adhesion whereas NC coatings showed a critical load in the range of 90-100 N, which is two times higher than that of single-layer Ti-Cr-B-N coating. The incorporation of WSe_x in a TiCrBN coating was shown to significantly decrease the friction coefficient in ambient air with only little influence on the hardness, wear- and corrosion resistance. In the case of NC coatings the friction curves were typically flat with a very short running-in stage which did not exceed 50 m, whereas in the case of ML coatings, the fluctuations and spikes of friction coefficient were observed. The lowest friction coefficient of 0.2, recorded for NC gradient TiCrBN/WSe_x coatings with WSe_x content increased gradually toward the surface, was 2.5 times lower than the friction coefficient of 0.5, measured for the TiCrBN coating. The elemental and phase composition of the tribo layer inside the wear tracks was examined by SEM-EDS and Raman spectroscopy.
3:50 PM		B6-2-9 Nanocomposite and Nanolayerd PVD Hard Coatings in Industrial Research and Application J. Vetter, G. Erkens, J. Mueller (Sulzer Metaplas GmbH, Germany) The improvement of the overall coating performance of wear protecting PVD coatings concentrates to achieve lower friction values, better thermal stability , optimization of hardness and toughness and higher oxidation stability. The aim of these improvements is to get a higher performance of tools and parts of components. Nowadays composite materials having structures in the nanometre dimensions are in the scope of industrial applications. Different coating architectures were developed in industrial scale: isotropic composites coatings, gradient nanocomposite coatings and nanomultilayer coatings. Modern industrial PVD systems are designed to deposit these types of sophisticated coating architectures. Both arc evaporation and magnetron sputtering and its combinations are suitable to create nanostructures. The coating processes to deposit nanostructured coatings will be discussed in more detail and it will be shown that the analytical methods for coating development and production control have to be shifted toward a nanostructure compatible level.
4:10 PM		B6-2-10 Effect of Alloying Element (Si, Y) on Properties of Arc-Deposited (TiCrAl)N Coating K. Yamamoto, S. Kujime (Kobe Steel Ltd., Japan); G. Fox-Rabinovich (McMaster University, Canada) High temperature stability of a coating used for high-speed dry cutting is a big issue when the system temperature is extremely high, possibly more than 1000°C. Hardness and oxidation resistance is both critical factor for improving high temperature wear resistance. (TiCrAl)N coating is characterized by the combination of high hardness and fairly good oxidation resistance according to cubic structure maintained up to high Al content (60 to 70 at%). Experiment on systematic alloying of Si and Y to (TiCrAl)N coating was conducted and effect of Si, Y addition is investigated. (TiCrAl₅₅Si₃Y₂)N coatings were deposited by cathodic arc ion plating (AIP), and crystal structure was mixture of cubic and hexagonal when substrate bias is lower than 100 V, then transformed to cubic single phase when bias is increased. From TEM observation, grain size is siginificantly smaller than (TiCrAl)N. Max. hardness of 33GPa is obtained when coatings is cubic single phase. For conventional (TiAl)N, rapid oxidation weight gain started at 850 C and 1000°C for (TiCrAl)N, whereas up to 1200 C, significant weight change was not observed in case of Si+Y added (TiCrAl)N. The oxide layer, measured by AES, thickness is nearly 1/4 and 1/2 compared to (TiAl)N and (TiCrAl)N. Cutting tests were conducted against hardened alloy steel and titanium alloys. In case of high speed cutting of hardened die steel (H13, HRC 57 up to 500m/min) showed that the tool life of (TiCrAlSiY)N is nearly 5 times longer than (TiCrAl)N. Cutting test against Ti-6Al-4V showed that the tool life is again nearly 5 times longer compared to (TiCrAl)N.