Tribology of Coatings for Automotive and Aerospace Applications

Thursday, May 1, 2014 2:10 PM in Room California

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2:10 PM E3-2-3 Solid Particle Erosion Resistant Nanolayered CrAlTiN and Multilayered CrAlTiN-AlTiN Coatings
Qi Yang, Rob McKellar (National Research Council, Canada)

Airborne particles ingested by gas turbine engines may cause severe erosion damage to compressor gas-path components, leading to structural and aerodynamic engine performance deterioration and, in extreme cases, causing engine failure. Applying hard coatings on airfoil surfaces is proven to be an effective approach to mitigating erosion damage to engine components. Nanolayered or multilayered coatings, because of their capability of tailoring the properties through modifications in the chemistry and architecture of layer constituents, have been explored as potential candidates for this specific application. In this study, nanolayered CrAlTiN coatings with different modulation periods, along with multilayered CrAlTiN-AlTiN coatings having different number of layers and different thickness of individual layers, were fabricated, characterized and evaluated. All the coatings significantly outperformed the CrN baseline coating in erosion resistance, and their performance was strongly affected by the modulation period of the nanolayered coatings or the layer architectural characteristics of multilayered coatings.

2:30 PM E3-2-4 Microstructure and Properties of WC-Co(-Cr) HVOF Coatings Obtained from Standard, Superfine and Modified by Sub-microcrystalline Carbide Powders
Krzysztof Szymański (Silsian University of Technology, Poland); Grzegorz Moskal, Hanna Myalska (Silesian University of Technology, Poland)

In this paper microstructure and basic mechanical properties of WC-Co coatings obtained by HVOF technique were shown. Two different feedstock powders of WC-Co 83-17 type were used for coatings deposition on a steel substrate. First of them was a standard powder of Amperit 625.074, second one was Inframat from category InfralloyTM S7400 superfine powder. Four different powders were used to modify coating deposited from Amperit 625.074. Sub-microcrystalline powders applied in order to modify standard WC-Co coating were as follow: WC, Cr3C2, B4C, TiC. The aim of investigations was to compare microstructure and some mechanical properties of coatings deposited from different types of carbides. An influence of sub-microcrystalline additions on basic mechanical properties of coatings was analyzed. the range of investigations included short characterization of feedstock powders by SEM, EDS, EBSD and XRD methods and theirs technological properties as well. Then deposited coatings were characterized. Overall quality, porosity, adhesion of coatings to substrate and theirs tendency to making cracks were analyzed.

Financial support of Structural Funds in the Operational Program - Innovative Economy (IE OP) financed from the European Regional Development Fund - Project No POIG.0101.02-00-015/09 is gratefully acknowledge.

2:50 PM E3-2-5 Corrosion and Tribological Properties of Thick Diamond-like Carbon (DLC) Coatings Deposited using a Meshed-PIID Process
Ronghua Wei, Jianliang Lin, Leonardo Caseres, Vasiliki Poenitzsch (Southwest Research Institute, US)
In this paper, preliminary results of thick (up to 20 micrometer) diamond-like carbon (DLC) coatings are presented. These coatings were prepared using a meshed plasma immersion ion deposition (PIID) process. Carbon steel and 304 stainless steel, as well as Si wafer coupons, were used as the substrates. They were installed in a meshed metal cage and then processed using the PIID process. The meshed-PIID process is similar to that of a hollow cathode process in which a much higher current density can be achieved, and hence, a higher deposition rate and thickness can be achieved than the conventional PIID process. Four different DLC coatings were prepared, including: (1) a thin single-layered DLC (10 micrometer), (2) a thick single-layered DLC (20 micrometer), both derived from C2H2, (3) a multilayered DLC (SiC/DLC, 7.5 micrometer) derived from TMS/C2H2, and (4) a single-layered DLC variant (7.5 micrometer) derived from hexamethylsiloxane (HMDSO). The microstructure and morphology of the applied DLC coatings were analyzed using Raman spectroscopy, atomic force microscopy, and scanning electron microscopy. The hardness and modulus of elasticity were measured using nanoindentation technique. The coefficient of friction and sliding wear rate were evaluated using a pin-on-disc tester. The corrosion resistance of the coatings was studied using electrochemical impedance spectroscopy (EIS) and anodic-cathodic polarization tests. It has been observed that the thick DLC coating exhibited highest wear resistance, while the multi-layered coating exhibited the highest corrosion resistance. The principles for the increased wear and corrosion resistance and the potential applications of these DLC coatings will be discussed.
3:10 PM E3-2-6 MoSx/WC PVD Coatings for Harmonic Drive Gears in Space Applications Characterized by Vacuum Pin on Disc Tests and XPS
Christoph Gabler (AC²T research GmbH, Austria); Andreas Merstallinger (Aerospace & Advanced Composites GmbH, Austria); Markus Jansson (Harmonic Drive AG, Germany); Jose-Luis Viviente (Tecnalia, Spain)

One of the major issues for the use of devices in spacecrafts is the reduction of their mass and lowering power consumption. Harmonic drive gears provide these requirements since the high gear ratio possible, enables the use of small actuator motors (low mass and power). State of the art in harmonic drive technology is the grease lubricated gear. The drawback of these gears in space application is that the used lubricant tends to outgas which causes a reduction of the lubrication ability plus the resulting vapours can contaminate sensible surfaces e.g mirrors, which is even more defacing for the functionality of the respective devices.

The aim of the presented research work here was to apply solid lubrication in the field of harmonic drive gears for vacuum application. The main problem of coatings providing this lubrication is their durability under the high contact stress occurring in theses gears.

After discussing the specifications needed, a multilayer coating of nanoperiod of MoSx/WC PVD coating with a WC interlayer between substrate and coating was selected. This coating was already tested in space on the ISS in the TriboLAB tribometer and is known for its good tribological properties under space conditions.

The coating was characterized in vacuum pin on disc tests with varying substrate material for pin and discs. This was important since also the condition of the substrate material is important for a successful coating and the components engaged in a harmonic gear, are manufactured out of materials with different properties (e.g. stiffness).

The main focus of this paper will be the surface analysis of the resulting wear tracks of the pin on disc tests and the characterization of reference samples of the MoSx/WC coating by XPS and the deduction of wear mechanisms of the MoSx/WC under space conditions.
3:30 PM E3-2-7 Tribological Behaviour of the Non-Hydrogenated Diamond-like Carbon (DLC) Coatings Against Ti-6Al-4V: Effect of Surface Passivation by Alcohol
Sukanta Bhowmick, Anindya Banerji, Ahmet Alpas (University of Windsor, Canada)
The role of alcohol in the tribological behaviour of non-hydrogenated DLC (NH-DLC) coated M2 steel disks sliding against Ti-6Al-4V have been investigated. Pin-on-disk tests were performed in argon (0% RH) and ambient (40% RH) atmosphere and while the samples were submerged in water and ethanol. The running-in friction behaviour of the NH-DLC coatings under each condition was studied. The highest coefficient of friction (COF) of 0.55 was observed for tests conducted under an argon atmosphere. A slightly lower running-in COF of 0.43 was observed for ambient air while the running-in COF reduced by 50% (0.21) in water due to OH passivation. Alcohol was more effective in providing OH passivation, as evident from the lowest running-in COF of 0.14. Based on the COF results, the NH-DLC coated drills were used in machining tests for Ti-6Al-4V; a 45% reduction in drilling torque and 75% reduction in thrust force were obtained when 10% alcohol was added to metal removal fluid (MRF) compared to an alcohol free MRF consisting of oil-water mixture.
3:50 PM E3-2-8 Diamond-like Carbon Nanocomposite Coatings to Mitigate Friction and Wear in Harsh Environments
Somuri Prasad, Jon-Erik Mogonye (Sandia National Laboratories, US)

Diamond-like carbon (DLC) coatings exhibit an unusual combination of tribological and mechanical properties: low coefficients of friction and high hardness/high elastic modulus. However, synthesizing a single DLC material to achieve low friction and low wear in all environments (e.g., from ultra-high vacuum to humid air and from ambient to elevated temperatures) is a challenging task. Most commercial DLCs are either doped with metals, hydrogen or synthesized as nanocomposites. This talk will first provide a brief overview of the roles of chemistry and composition of multi-phase DLCs and nanolaminates in imparting environmental robustness. The role of substrate-coating interface reliability, specifically the onset of plastic deformation in the underlying substrate, on the tribological performance of DLCs will be discussed. In this context, finite element modeling was used to predict the contact stresses at which the transition from elastic to plastic deformation in a metallic substrate underneath a hard DLC coating occurs. Experimental data confirmed that accumulated plastic strains at the coating-substrate interface can lead to fracture and subsequent removal of the coating, highlighting the need for incorporating a load bearing nanolaminate underneath the DLC.

The second part of the talk will address the high temperature tribology of DLCs. A tetragonally bonded amorphous DLC and a silica doped diamond like nancomposite (DLN) coating were selected for this study. Friction and wear measurements were made at 300°C in lab air with a RH of 40-50% against a 440C steel ball in reciprocating sliding motion. Results indicate that the silica doped nanocomposite showed low friction (0.05-0.1) and low wear (2E-9 mm3/Nm) both at ambient temperature and at 300°C. Time of flight SIMS and Raman spectroscopy analyses of the interfaces, i.e., wear tracks and transfer films, were used to gain a fundamental understanding of the role of interfacial chemistry on friction and wear mechanisms, and to elucidate the “chameleon” nature of the nanocomposite.

* Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.