Symposium CG
Ceramic Thin Films and Coatings for Protective, Tribological and Multifunctional Applications
ABSTRACTS
CG-1:IL01 Ionized and Hybrid Plasma Deposition Processes
H. BARANKOVA, L. Bardos, Angstrom Laboratory, Uppsala University, Sweden and BB Plasma Design AB, Uppsala, Sweden
Hollow Cathodes are high-density plasma sources characterized by high activation and ionization degrees. They can work in a broad range of parameters – pressures, powers and gas flows. They are scalable, versatile and cost effective. They enable both PVD (Physical Vapor Deposition) and PE-CVD (Plasma Enhanced Chemical Vapor Deposition) regimes and also both regimes in one hybrid mode. They can be used in various plasma-chemical processes. The paper shows different solutions of hollow cathode based plasma sources both for reduced and atmospheric pressures. The simple cylindrical hollow cathode can be used for local processing or for processing on inner surfaces and inside narrow tubes. The linear hollow cathodes in several arrangements for generation of plasma over large areas and suitable for further scale-up are presented, too. Combination with microwaves provides even more control of the discharge in a hybrid source. A new design with coupling of a magnetized hollow cathode with magnetron is presented. Examples of processes in PE-CVD, ionized PVD and hybrid regimes are given.
CG-1:L02 Deposition of Ge-Sb-Te Thin Films by Radio-frequency Magnetron Co-sputtering
M. Bouška1, T. Halenkovič1, V. Nazabal2, 1, M. Baillieul1, J. Gutwirth1, M. Kotrla1, P. NEMEC1, 1Department of Graphic Arts and Photophysics, Faculty of Chemical Technology, University of Pardubice, Pardubice, Czech Republic; 2Institut des Sciences Chimiques de Rennes, UMR CNRS 6226, Université de Rennes 1, Rennes, France
Radio-frequency (RF) sputtering is widely used for thin films fabrication. Specifically, rf co-sputtering technique brings advantage of adjustable electrical power applied on individual cathodes which enables to obtain thin films with various compositions making this method cost-effective for compositional dependencies’ studies of materials’ properties [1]. Generally, co-sputtering is less frequent for the growth of chalcogenide phase change thin films and mainly used for the doping of Ge-Sb-Te materials with other elements such as C, Al, Ti, Ni, Cu, Se, Zr, Sn or Bi. Contrary, RF co-sputtering is exploited in this work to fabricate thin Ge-Sb-Te films within broad region of chemical composition varying only the electrical power ratio applied to GeTe and Sb2Te3 sputtering targets. The characterization of thin films in amorphous as well as in crystalline state was performed exploiting AFM, SEM-EDX, XRD, electrical resistivity, and variable angle spectroscopic ellipsometry data. The results are discussed in relation with the chemical composition of the fabricated thin films.
The financial support of the Czech Science Foundation under the project No. 19- 24516S is greatly acknowledged.
References [1] T. Halenkovič et al. J. Am. Ceram. Soc. 101, 2877-2887, 2018
CG-1:IL03 New Surface Boriding Technologies
M. Mejauschek, H. Paschke, M. Weber, C. HERRMANN, Fraunhofer Institute for Surface Engineering an Thin Films IST, Braunschweig, Germany;
P. Kaestner, J. Vogtmann, Institute for Surface Technology, Braunschweig, Germany
Boriding of steel and other materials with powder or paste-like precursors has been studied for many years. The process involves boron diffusing into the material at temperatures above 750° C. Very hard and wear-resistant boride layers with a larger layer thickness are formed compared to conventional hard coatings. A disadvantage of this process are the resulting residues of the precursor on the material surface, which must be laboriously removed and disposed of. To get around this, gas boriding processes with BCL3 precursor and additional plasma support were developed. The problem here, however, was pore formation, and the technology was not suitable for the treatment of high-alloy steels and high-temperature materials. With a new gas boriding process, it is possible to produce almost non-porous boride layers on various high-alloyed steels. Coating thicknesses up to 20 μm with hardnesses above 2000 HV can be achieved. After post-hardening, according to the specifications of the steel manufacturers, a fine-grained edge zone with increased hardness can be observed. Actual studies with gas borided nickel and molybdenum based alloys showed also excellent results. Ball-on disk-tests against steel, aluminium and titanium demonstrate very good friction and wear properties.
CG-1:L04 Plasma Electrolytic Oxidation for the Formation of Thin Primer Coatings on Structural Aluminium Components for Automotive Applications
D. SHORE1, J.C. Avelar-Batista Wilson2, A. Matthews1, A. Yerokhin1, 1Department of Materials, The University of Manchester, Oxford Road, Manchester, UK; 2BCW Manufacturing Group Ltd, Burnley, Lancashire, UK
Plasma Electrolytic Oxidation (PEO) is an emerging technology for the formation of oxide coatings on valve metals that has been investigated for numerous applications including the promotion of corrosion resistant, wear resistant, biocompatible and catalytic surface properties. In this study, PEO was studied for the production of thin coatings on aluminium alloy AA6060-T6 for the provision of enhanced corrosion resistance and the promotion of sound bond durability in epoxy adhesive bonded automotive structures. For such applications, aluminium components have historically been treated via conventional anodizing processes which have logistical and environmental shortcomings. Producing thin (2-10um) coatings via PEO processing has proved difficult as uniformity in coating geometry and component coverage achieved in thicker PEO coatings (20-100 um) is harder to produce under these shorter processing conditions. In this work, we studied how changes to the process parameters of high frequency bipolar processing can improve coating formation for atypically thin PEO coatings and how this optimization can lead to the production of thin PEO coatings for adhesive bonded structural components.
CG-1:L05 Dynamic Voltammetry Diagnostics of Electrolytic Plasma Processes for Deposition of Ceramic Coatings of Valve Metal Substrates
A. Yerokhin, Department of Materials and Henry Royce Institute for Advanced Materials and Innovation, University of Manchester, UK
Real time process diagnostics is of interest for development of Industry 4.0 ready generation of surface engineering and coatings technologies. In Plasma Electrolytic Oxidation (PEO) of valve metals, the application of pulsed reverse polarisation can lead to synergetic effects in formation efficiency and characteristics of resulting oxide ceramic surface layers. Due to the transient nature of these effects, they are notoriously difficult to study and control. In this work, dynamic anodic and cathodic voltammograms were derived from specially designed polarisation signal combining working and diagnostic segments. The voltammograms were used to evaluate in real time the effects of pulsed reverse polarisation on the formation of PEO coatings leading to the decay of plasma discharge and transition to the soft sparking PEO regimes. This allows practical recommendations to be made for the design of efficient electrical regimes for intelligent electrolytic plasma processes, including controllable growth of PEO coatings on complex shape components and enabling PEO processing of metal substrates with large surface area.
CG-1:L06 Oxidation Resistance of SiAlOC Coated Chromium
N.C. PETRY1, M. Bik2, A.S. Ulrich1, M. Sitarz2, M. Lepple1, M.C. Galetz1, 1DECHEMA-Forschungsinstitut, Frankfurt am Main, Hesse, Germany; 2AGH University of Science and Technology, Krakow, Poland
Because of their excellent corrosion and oxidation resistance and their versatile processability, SiOC coatings are interesting materials to be used in high temperature environments. Due to their low CTE values they are especially interesting to be used on alloys also having low CTE values such as Cr-based alloys. In addition, their oxidation resistance can be further improved by cationic substitution of Si4+ by Al3+ (SiAlOC). In this work a SiAlOC sol-gel coating was deposited on pure Cr substrates using dip-coating. The oxidation kinetics of SiAlOC coated and pure Cr substrates were investigated at 950 °C and 1050 °C for 50 h and 100 h using thermogravimetric analysis. The drawbacks of Cr alloys, namely volatilisation of the protective scale beyond 1000°C and embrittlement due to Cr2N formation above 900 °C, were improved by the application of SiAlOC coating. Overall, nitridation at 1050 °C was significantly reduced and mass gain strongly decreased. The resulting oxide scale and microstructure were extensively studied using EPMA, XRD, Raman spectroscopy, and TEM. Additionally, the interaction of Cr and SiAlOC was assessed by oxidizing pellets consisting of Cr powder and SiAlOC precursor in the form of gel.
CG-1:L09 Advanced Iron Boride Coatings for Geothermal Power Generation
E. Medvedovski1, G. Leal Mendoza1, G. Ravier2, A. Genter2, 1Endurance Technologies Inc.; 2ES Geothermie, Mundolsheim, France
Iron boride coatings obtained by the CVD-based thermal diffusion process are proposed, tested and evaluated for high temperature corrosion and scaling conditions in geothermal power generation. The testing results in different corrosion environments, e.g., in modeling conditions and in actual Upper Rhine Graben (France) geothermal well, are presented. The influence of structure and surface composition on the materials’ performance is demonstrated. The dual-layer boride-based coatings on carbon steels successfully withstand strong acidic and high temperature/high pressure geothermal fluids and steam with a presence of H2S, CO+CO2 and brines environments. They demonstrated minimal scaling, corrosion and induced radioactivity compared to bare steels commonly used for tubing in geothermal wells. Large boronized steel spools successfully withstood the 3-month service campaign in the high temperature (over 150oC) field conditions where the geothermal fluid was circulated through the production system. The obtained advanced ceramic coatings and technology should promote significant extension of the steels’ service life in harsh geothermal corrosion-scaling environments.
CG-2:IL01 Self-Lubricating PVD Coatings for Components and Tools
K. Bobzin, C. Kalscheuer, Surface Engineering Institute (IOT), RWTH Aachen University, Aachen, Germany
In many of today’s component and tool applications, physical vapor deposition (PVD) hard coatings are key to achieve the required efficiencies. Especially dry-running applications demand coatings that provide wear resistance and lubrication at the same time. Suitable approaches are diamond-like carbon (DLC) coatings and triboactive nitride or oxy-nitride hard coatings. DLC coatings can provide graphite under tribological load. Triboactive nitride and oxy-nitride coatings enable self-lubrication by metal disulfides, oxides or combinations thereof. For components, DLC and (Cr,Al)N+X:S (X = Mo, W) coatings show a high potential to reduce friction and wear under demanding dry-running conditions. Investigations under continuous sliding show significant friction and wear reduction compared to uncoated steel. Analyses with (Cr,Al)N:X:S coatings reveal friction and wear reduction by in situ formation of MoS2 and WS2 and oxides. This effect could also be proven for tool applications, where (Cr,Al)N:Mo:S coatings were applied in dry forming of steel. For the machining of steel and titanium, CrAlVN and CrAlMoN coatings enable the formation of lubricous V and Mo oxides. Overall, self-lubricating coatings offer high potential to meet the requirements of dry-running applications.
CG-2:L02 Direct Liquid Injection Chemical Vapor Deposited Zirconium Oxide-based Corrosion Barriers on Low-alloy Steels
A. JAUD, D. Samélor, D. Sadowski, C. Vahlas, CIRIMAT (Centre Inter-universitaire de Recherche et d’Ingénierie des Matériaux) - CNRS, Université de Toulouse, Toulouse Cedex, France; S. Ponton, H. Vergnes, B. Caussat, LGC (Laboratoire de Génie Chimique) - CNRS, Université de Toulouse, Toulouse Cedex, France; A. Abdel Aal, J. Etzkorn, Chemistry and Materials Engineering, Fachhochschule Dortmund, Dortmund, Germany
Low Cr containing alloy steels exhibit appealing mechanical properties. However they are prone to corrosion in wet environment. The objective of this work is to tackle this point by applying zirconium oxide ZrO2 thin films on their surface. Processing of this oxide by direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD) operating at 10 Torr allows its application on non-line-in-sight surfaces. Amorphous, conformal, 200 nm ZrO2 films are obtained from [Zr(OiPr)2(tbaoac)2] at 400-450 °C in the presence of O2. Although such low process temperatures ensure the microstructural integrity of the steel, the superficial oxidation of the substrate during the deposition results in the formation of oxides that may be deleterious for the adhesion of the coating on the steel and the durability of the proposed solution. For this reason, 50 nm thick protective layer (PL) are pre-deposited at 300 °C as oxidation barrier. Nanoscratch and electrochemical impedance spectroscopy tests are underway to evaluate the adhesion and the anticorrosion performance of three different coatings (ZrO2, PL and PL/ZrO2 stacks), respectively, thus yielding valuable insights into the correlations between growth parameters and anti-corrosion performance.
CG-2:IL08 Structure Effects on the Aging, Surface Chemistry and Friction Performance of Composite MoS2 Thin Films
M.T. DUGGER, J.F. Curry, N.S. Bobbitt, M.E. Chandross, Materials, Physical and Chemical Sciences Center, Sandia National Laboratories, Albuquerque, NM, USA
Physical vapor deposited MoS2 films are well known for the low friction and low wear rates that they exhibit in inert atmospheres, and for this reason have seen use in spacecraft and other aerospace mechanisms for several decades. Such mechanisms often see operation in terrestrial environments or storage for long periods of time before use. Composite MoS2 films containing metallic or oxide dopants have been developed to improve tribological performance during operation in these non-ideal conditions. These dopant species affect the long-term aging behavior of the coatings, their startup friction coefficient and run-in behavior. The aging and run-in behavior of several MoS2-based solid lubricant coatings have been examined and relationships between microstructure, oxidation and tribological behavior have been investigated. Results indicate that the near-surface microstructure of the coatings created during deposition, or by initial mechanical contact, impacts the subsequent aging behavior of the films. Results suggest that coating structure can be tailored to afford long service life, surface oxidation resistance and minimum startup friction coefficient to sputtered MoS2 lubricated surfaces.
CG-2:IL09 Characterisation of Plasma and Surface Modification of Multi-element Arc Cathodes for Coating Deposition
R. FRANZ, Department of Materials Science, Montanuniversität Leoben, Leoben, Austria
Cathodic arc deposition has been established as one of the standard techniques for the physical vapour deposition of thin films and coatings as it allows the synthesis of a wide variety of materials. With the advent of multifunctional thin films and coatings, the use of multi-element cathodes providing the non-gaseous elements during the synthesis has become an industrial standard. However, a detailed understanding of the discharge properties is vital for the further optimisation of the deposition processes to enable synthesising thin films or coatings with improved properties. In the present work, dedicated designs are employed to elucidate the erosion of multi-element cathode when exposed to arc discharges. In particular the intermixing of the elements and the formation of new phases on the cathode surface is of interest. Further, plasma properties like discharge voltage, ion energy and charge state are measured in order to relate them to the material properties of the cathode according to the so-called cohesive energy rule which was established for single-element cathodes. The calculation of the cohesive energy of the phases present on the eroded multi-element cathodes is supported by density functional theory calculations.
CG-2:IL10 Duplex PEO/TMD Composite Coatings for Aluminum Alloys
A. VOEVODIN1, A. Shirani1, D. Berman1, A. Yerokhin2, A. Korenyi-Both3, T.W. Liskiewicz4, S.M. Aouadi1, J.-E. Mogonye5, S. Berkebile5,
1University of North Texas, Denton, Texas, USA; 2University of Manchester, Manchester, UK; 3Colorado School of Mines, Golden, Colorado, USA; 4Manchester Metropolitan University, Manchester, UK; 5U.S. DEVCOM Army Research Laboratory, Aberdeen Proving Ground, Maryland, USA
Plasma electrolytic oxidation (PEO) of aluminum alloys generates 50-150 micrometer thick hard ceramic coatings with a dense region near the alloy interface and a porous outside region, which is an ideal substrate for transition metal dichalcogenide (TMD) solid lubricants to provide reservoirs for tribological contact lubrication. Tribological behavior of duplex PEO/TMD coatings during fretting and sliding wear is presented, where Al-Si-O PEO layer is combined with top chameleon MoS2-Sb2O3-graphite layer. Fretting and sliding wear tests in dry and moist atmospheres, at room and elevated temperatures, against steel and ceramic counterparts are summarized. Raman, post-test SEM and cross-sectional FIB/SEM/EDX analyses identify wear mechanisms and coating adaptation. The duplex coating provides friction and wear reduction in both sliding and fretting regimes, as well as a reduction of critical amplitude for stick-slip transition for surface fatigue mitigation. Tests with in-situ Raman spectroscopy reveal chemical stability up to 300 °C and coefficients of frictions as low as 0.02. The low friction and high endurance are attributed to the excellent adhesion of chameleon lubricant and shearing-assisted structural modifications inside wear tracks.
CG-2:IL12 Ceramic Thin Films for MEMS and Sensors Applications
J. PATSCHEIDER, C.V. Falub, M. Tschirky, B. Heinz, A. Mazzalai, H. Rohrmann, Evatec AG, Trübbach, Switzerland
Thin film materials for active elements as well as for sensors are essential for the coming “Internet of Things” (IoT) with its countless opportunities that will affect many areas of our daily life. They need to be precisely designed to achieve the requested electrical, mechanical and chemical properties. Digging underneath the surface of the shiny IoT reveals a fascinating new reality of various technology combinations. The ubiquitous combination of advanced functional thin film materials and layer stacks to form devices is the enabling technology for various sensors and actuators we find in every node connected to the IoT. This presentation illustrates these needs using examples from two different areas, where thin ceramic film systems enable the requested functions for MEMS and IoT. These include the piezoelectric materials AlN and AlScN for RF filter applications as well as microphones and speakers, multilayer stacks that form soft magnetic cores for on-chip inductors and transformers on 8’’ wafer level. These examples with their respective challenges necessitate corresponding equipment concepts for volume manufacturing. Advanced stress control, prevention of cross-contamination, parallel processing or dynamic sputtering in batches will be explained. Specific features and options complete this overview, but not without pointing out to still existing challenges, which both device manufacturers and equipment providers have to overcome. We will shed light on what is commonly known as the “More-than-Moore” paradigm from the perspective of an equipment supplier, and for potential device manufacturers we will highlight criteria and requirements before entering and investing in these fascinating technologies.
CG-2:IL13 Multifunctional Nitride and Oxide Thin Film for Thermo-electrics and Energy Harvesting
a. le febvrier, P. EKLUND, Energy Materials Unit, Thin Film Physics Division, Dept. of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, Sweden
Thermoelectric devices have the potential to contribute to energy harvesting in society by directly converting heat into electricity or vice versa. However, the conversion efficiency of thermoelectric devices of today is limited. In this invited lecture, I present an overview of our work on CrN-, ScN-, and Ca3Co4O9-based thin films. We have introduced a two-step sputtering/annealing method for the formation of highly textured virtually phase-pure Ca3Co4O9 thin films. These can further be deposited on flexible mica substrates, enabling flexible inorganic thermoelectric thin films that withstand repeated bending. They can also be made as free-standing films and as nanoporous materials for reduced thermal conductivity. ScN thin films exhibit an anomalously high power factor (S2/rho) for transition metal nitrides, but has high thermal conductivity, thus its ZT is low (~0.2). To reduce lattice thermal conductivity, potential strategies are nanostructuring, alloying or nanoinclusion formation. Pure CrN exhibits n-type conduction with a high power-factor enabled by a high electron concentration thermally activated from N vacancies, and alloys can be made of rocksalt-Cr1-xScxN. We have demonstrated that it can be rendered p-type by Al alloying in combination with N superstoichiometry.
CG-3:IL01 Ceramic Superhydrophobic Coatings by Solution Precursor Plasma Spray
T.W. COYLE, P. Xu, J. Mostaghimi, Centre for Advanced Coating Technologies, University of Toronto, Toronto, ON, Canada
Surface topography and surface chemistry both have significant effects on wettability. In this work, hydrophobic Yb2O3 coatings were deposited via solution precursor plasma spray by a radial injection of Yb(NO3)3 solution into the plasma jet. Coatings with different microstructures and surface topographies were fabricated by manipulating process parameters such as the torch transverse speed and solution concentration, and by post-deposition plasma exposure of the coating. Hierarchical columnar-structured coatings, columnar-structured coatings with smooth surfaces, and dense coatings with relatively flat topography were fabricated and exhibited different wetting behaviors. The coating microstructures were characterized and compared, and the wettability of coatings was characterized by measuring the static water contact angle and roll-off angle. The wetting behaviors of various coatings were correlated with the different coating structures, surface topographies, and surface chemical compositions.
CG-3:IL04 Thermal Spraying with Suspensions for Tribological Applications
S. Björklund, S. Mahade, S. Joshi, University West Trollhättan, Trollhättan, Sweden
Utilizing suspensions in thermal spraying provides a unique opportunity to obtain coatings with vastly different characteristics compared to those derived using conventional spray-grade powders. Although an overwhelming proportion of prior studies on suspension thermal spraying have focused on thermal barrier coatings (TBCs), the growing understanding related to use of suspensions for both plasma and high velocity oxy-fuel (HVOF) spraying has also spurred wide-ranging research efforts aimed at exploring their utility for tribological applications. While there have been no concerted efforts targeting deposition of wear-resistant coatings yet, use of suspensions for depositing materials such as chromia, alumina, titania etc., as well as titanium and chromium carbides, has been demonstrated. The talk will outline prospects of depositing high-performance tribological coatings by suspension thermal spraying based on results from the authors’ laboratory. Use of mixed suspensions, such as alumina-zirconia and chromia-titania, is also a convenient pathway to expand the spectrum of possibilities. Deploying hybrid powder-liquid feedstock combinations for thermal spraying represents a further extension enabling deposition of a wide array of composite coatings with unusual microstructures. Illustrative examples of these approaches will also be presented.
CG-3:IL07 Developments in Cold Spray Coatings and 3D Material Architecture
G.C. SAHA, Nanocomposites and Mechanics Laboratory, University of New Brunswick, Fredericton, New Brunswick, Canada
Revolutionary materials design and their atomic scale manufacturing is within the reach with the availability of supersonic/hypersonic technologies in this Industry 4.0 manufacturing era. The focus away from traditional metal/alloy materials based component design and mass manufacturing is a result of enabling technologies supporting the handling of high modulus ceramics and composite materials for ultra-high-strength high-rewarding applications, namely nuclear, aerospace, petrochemical, defence, etc. The goal of this presentation is to showcase the recent ceramic-metallic (cermet) composites design and their additive manufacturing in a high-pressure cold spray process (HPCS). In particular, the design and nanoscale synthesis of particulate feedstock comprising of a hard ceramic oxide nanograin embedded in a NiCr binder matrix will be divulged, followed by the feedstock deposition and thin coatings development and microstructure evolution in the HPCS method. The pertinent results will connect the mechanical (Young’s modulus, residual stress, nanohardness) properties with the high-impact erosion characteristics of the novel coatings.
CG-3:IL08 The New Frontier in Liquid Feedstock HVOF Thermal Spray: Porosity with Neutron Scattering and Performance of TBCs
T. HUSSAIN, D. Tejero-Martin, A. Rincon Romero, A. Lynam, Coatings and Surface Engineering, Faculty of Engineering, University of Nottingham, Nottingham, UK
Suspension thermal spray is the new fronting that has opened up the processing of submicron particles not suitable using conventional thermal spray and allowed us to tailor the composition and microstructure like never before. This talk will focus on the latest work on suspension high-velocity oxy-fuel (SHVOF) thermal spray in relation to developing next generation of thermal barrier coatings. We will show the effect of suspension medium on the coating microstructure in SHVOF thermal spray, which has a much higher deposition efficiency than other liquid feedback-based techniques. The phases present in the coatings will be critically examined, and their evolution with temperature will be assessed. Porosity in suspension sprayed coatings is of great interest. Neutron scattering can measure porosity with radii between 1 nm and 10 μm, thanks to the combination of small-angle and ultra-small-angle neutron scattering. For the first time in SHVOF 8YSZ, pore size distribution, total porosity and pore morphology were studied to determine the effects of heat treatment. The results show an abundant presence of nano-pores in the as-sprayed coatings, which are eliminated after heat treatment at 1100 °C. The second part of the talk will cover gadolinium zirconate (GDZ) developed from a precursor solution in an HVOF thermal spray. The multi-layered architecture, along with its performance, will be critically evaluated with regards to the YSZ coatings.
CG-3:IL09 Superlubricity and Superior Wear Resistance of 2D Materials: Recent Developments and Future Prospects
A. ERDEMIR, Texas A&M University, Mechanical Engineering Department, College Station, TX, USA
In recent years, great strides have been made in the design, synthesis and tribological characterization of 2D materials and their coatings affording friction and wear coefficients that are among the lowest ever reported. In this presentation, a comprehensive overview of what makes and breaks such a nearly-frictionless and -wearless sliding performance will be outlined. In light of the recent analytical, experimental, and computational findings, an attempt will also be made to underscore those mechanisms that are most responsible for their unusual friction and wear behaviors. Overall, these and other breakthrough developments in our tribology field are leading the way for further diminishing adverse impacts of friction and wear on energy efficiency of future mechanical systems and hence potentially contributing to the goals of a green and sustainable future.
CG-3:IL10 Status of Thermally Sprayed Hardmetal Coatings
L.-M. BERGER, Fraunhofer IKTS, Dresden, Germany
The current most important hardmetal compositions can be described as a series starting with plain WC-Co(Ni), with a stepwise replacement by Cr3C2, and ending with Cr3C2-NiCr. This series is characterised by complex interactions between both carbides during feedstock powder production, leading to the formation of new phases depending on the WC/Cr3C2 ratio. A common feature has been the apparent empirical approach to hardmetal composition development, rather than the systematic consideration of the interaction between the constituents during feedstock powder production and the changes in chemical and phase composition during spraying. Cr3C2-based compositions are very promising for future applications. Highly wear resistant HVOF- and HVAF-sprayed hardmetal coating solutions are now an industrial standard. >From the range of alternative carbides, TiC is the most promising alternative in many applications, where the unique properties of WC are not irreplaceable. Need of cobalt replacement is another driving force. For many wear applications it has already been shown that TiC-based compositions are competitive when properly alloyed. In any case, it must always be considered that a sudden substitution is practically impossible and will always require long-term development efforts.
CG-3:IL11 Tribological Behavior of Hard Metal Thermal Spray Coatings
G. BOLELLI, L. Lusvarghi, P. Puddu, L. Lusvarghi, V. Testa, Dipartimento di Ingegneria "Enzo Ferrari", Università di Modena e Reggio Emilia, Modena, Italy; P. Sassatelli, Il Sentiero International Campus S.r.l., Schio (VI), Italy
Hard metal thermal spray coatings represents the state of the art in many demanding applications, where components must be protected from wear and, in many cases, from wear and corrosion combined. Since they contain both hard phases and a more ductile metallic binder, their performance is more reliable than pure ceramic layers, in particular when loads become significant. The most used compositions at temperatures from room to 400°C are WC-based, with cobalt usually as metallic matrix. At higher temperatures, chromium carbides compositions are selected for their much lower oxidation rates. This presentation wants to review the main tribological processes where hard metals thermal spray coatings are used, pointing out their advantages and their limits. At the same time, this work wants to provide a complete overview of the most promising compositions, which can act as alternatives to the most common hard metals systems and be free from the Critical Raw Materials recently enlisted by the EU Commission or from hazardous elements and compounds.
CG-4:IL01 Coatings for Protection of Aero Engine Components
U. SCHULZ, German Aerospace Center, Institute of Materials Research Linder Hoehe, Cologne, Germany
Advanced aero engines require new materials at increasing temperatures that need to be protected by coatings to prolong lifetime of components and to increase operating temperatures. The presentation highlights the interplay between processing, microstructure, and lifetime of thermal barrier coatings (TBCs) that are produced by EB-PVD. New topcoat chemistries have been developed that offer low thermal conductivity, higher phase stability, and especially enhanced resistance against degradation by volcanic ash and CMAS deposits. The presentation provides results on several new single and double-layer TBCs, especially their behaviour under the influence of deposits and under thermo-cyclic loading. CMCs are new materials already introduced in the latest generation of aero-engines. Environmental barrier coatings (EBCs) are mandatory to protect the underlying CMC. In this presentation, multilayer EBCs manufactured by PVD methods are introduced. The multilayer coating architecture was designed to protect the CMC, to minimize chemical interactions between different layers, and to have a strain tolerant microstructure. Samples were tested up to 1250°C in air in a furnace cycle test and under flowing water vapor at isothermal conditions.
CG-4:IL03 Environmental Barrier Coatings made by Atmospheric Plasma Spraying (APS)
R. Vaßen, D. Zhou, E. Bakan, Forschungszentrum Jülich GmbH, IEK-1, Jülich, Germany
Environmental barrier coatings (EBCs) are essential to protect ceramic matrix composites (CMCs) against water vapor recession in typical gas turbine environments. In the present paper results on thermally sprayed coatings made of Yb2Si2O7, a frequently used EBC material, with a Si bond coat on SiC/SiC CMCs or SiC based ceramics are presented. The most often used thermal spray techniques for the deposition of EBCs is atmospheric plasma spraying (APS). This technique with its major problems as limited crystallinity, crack formation or loss of constituents will be addressed. In comparison to rather conventional spray conditions high velocity APS process parameters with a small nozzle diameter and high process gas flows showed improved properties giving high crystallinity and rather low porosity levels. These conditions were combined with a single passage deposition which gave further improvement of the coating microstructure. Promising thermal cycling results of different coatings for 100h at 1300°C will be shown. In addition, also results from suspension plasma spraying experiments will be presented. Adopted spray conditions using high substrate temperature allow the deposition of dense and crystalline coatings.
CG-4:IL04 Advanced Suspension Plasma Sprayed Thermal Barrier Coatings
M. GUPTA, University West, Trollhättan, Sweden; X.-H. LI, Siemens Energy, Finspång, Sweden; B. Kjellman, GKN Aerospace, Trollhättan, Sweden
Thermal barrier coatings (TBCs) are a vital component of gas turbine engines in power generation and aerospace applications. Increased functional, environmental and economic demands on today’s gas turbines require improved TBCs that are capable of withstanding higher operating temperatures, show increased durability, and at the same time, are cheaper to produce. By using suspension plasma spraying (SPS), a porous columnar TBC microstructure can be produced that can combine the advantages of conventionally used electron beam – physical vapour deposition (EB-PVD) and atmospheric plasma sprayed (APS) coatings, that is high cyclic durability and low thermal conductivity along with relatively lower cost. Improvements in lifetime of SPS TBCs that enables their widespread commercialisation is thus of high interest. The scientific aim of this work is to achieve fundamental understanding of relationships between spray parameters, interface characteristics, coating microstructure and its properties, with focus on SPS TBCs. Before spraying the topcoat, the bondcoats were subjected to combination of grit blasting, shot peening, and vacuum heat treatment. The influence of these treatments on oxide growth and coating lifetime will be discussed.
CG-4:IL05 Failure of Thermally Sprayed 7YSZ Coatings during Cyclic Loading of Microcantilevers
D. Lal1, P. Kumar1, S. Sampath2, V. Jayaram1, 1Department of Materials Engineering, Indian Institute of Science, Bangalore, India; 2Centre for Thermal Spray Research, University of Stony Brook, NY, USA
A variety of techniques now exist to probe the mechanical behaviour of small systems, such as coatings, with the resolution to measure small loads and displacements and with the convenience of compressive loading. In this talk we describe damage evolution and failure of free-standing microcantilevers of plasma-sprayed 7YSZ coatings during cyclic bending in a nanoindentation system in both, the as-sprayed condition as well as after low temperature thermal cycling to 700 C while attached to the substrate. This low temperature thermal exposure is designed to simulate operating conditions during which crack healing and sintering, which are known to lead to stiffening, are minimal. The load-displacement curves typically display hysteretic behaviour with an increasing permanent residual displacement (ratchetting) after each cycle, accompanied by a reduction in stiffness that is characteristic of damage accumulation. Failure appears to result from the formation of macrocracks after a critical amount of ratchetting. The number of mechanical cycles to failure reduces with the number of prior thermal cycles and also with increasing maximum stress. Thus, mechanical cycling can act as a proxy for thermal cycling in evaluating progressive damage accumulation in TBCs.
CG-4:IL06 Characterisation of Thermal and Environmental Barrier Coatings for Lifetime Extension
PING XIAO, University of Manchester and Henry Royce Institute, Manchester, UK
With exposure to high temperature environments, thermal and environmental barrier coatings (TBCs and EBCs) degrade with evolution of microstructure and mechanical properties, particularly with CMAS attack. This talk will cover study of both TBCs and EBCs with focus on microstructural, chemical and mechanical characterisation with research goal to understand the failure mechanisms of TBCs and EBCs after heat treatments in certain environments. Here various modern characterisation techniques will be applied to understand degradation mechanisms of TBCs and EBCs. The talk will present a few example cases to demonstrate the importance of characterisation study to extend lifetime of TBCs and EBCs.
CG-4:IL09 Compositional and Structural Stability of Compositionally Complex Rare-Earth Oxides Under Thermal and Corrosion Exposures
N. MOTLEY, D.R. MUMM, University of California at Irvine, Irvine, CA, USA
Under service conditions, ceramic coatings utilized in the hot section of propulsion and power generation systems are subject to high temperature environments that generally include corrosive species (water vapor, salts, silicates, etc.). Previous and ongoing research has illustrated that the performance and service lifetime of such materials is highly dependent upon the exposure temperatures, thermal cycling history, mechanical stress inherent in the engine operation, and the unique, oxidative/corrosive exposure environment. This talk will discuss ongoing efforts to explore the compositional and phase stability of compositionally complex rare-earth oxide systems considered as candidate materials for application as thermal or environmental barrier coatings. The phase stability and evolution of select oxide systems under extended thermal exposures, and subject to elevated water vapor and corrosive species (including oxides and sulfate/silicate mixtures) is explored, with a focus on the synergistic role of mixed-mode thermal exposures and complex corrosive deposit chemistries. The implications of the observations on the design and development of new materials capable of being utilized in increasingly hostile turbine operational scenarios, particularly the marine environment, will be discussed.
CG-4:L10 Corrosion of EBCs by CMAS: Reactivity of Rare-earth Silicates
J. BONNAL, C. Petitjean, P.J. Panteix, Université de Lorraine, CNRS, IJL, Nancy, France; S. Arnal, E. Bouillon, Safran Ceramics, Mérignac, France; M. Vilasi, Université de Lorraine, CNRS, IJL, Nancy, France
Environmental Barrier Coatings (EBCs) are required for the protection of CMC used in turbine gas engines against degradation by combustion products. In this application, rare-earth (RE) silicates are considered as good candidates. However, the development of EBCs is hindered by the high-temperature corrosion due to interactions with calcium-magnesium-aluminosilicates (CMAS). Indeed, the infiltration of these silicate melts into the coating causes thermomechanical and thermochemical degradations. The thermochemical degradation consists in the dissolution of the RE-silicate in the melt and the precipitation of new phases. The aim of this work is to determine the thermodynamic equilibrium of the system: (i) solubility limits of the species, and (ii) nature of the phases. Many parameters, as the basicity of the melt, the temperature or the nature of the EBC, can modify the equilibrium between rare-earth silicate and CMAS. Here, an original device has been used to set the parameters independently and study their influence on reactivity. It provides optimal reproducibility and allows to rapidly reach the thermodynamic equilibrium. The physico-chemistry of several RE mono- and disilicates has thus been studied in simplified melt compositions, on the base of acido-basic considerations.
CG-4:IL12 Multilayerered, Multifunctional Thermo-structural coatings Enabled by Layered Manufacturing
S. SAMPATH, Center for Thermal Spray Research Stony Brook University, Stony Brook, NY, USA
Majority of contemporary TBCs applied either via plasma spray or EB-PVD can typically be described as monolithic single layers, principally based on yttria stabilized zirconia (YSZ). Advent of new ceramic compositions has necessitated to some extent the need for double layers where the interfacial ceramic layer on the bond coat is often made of YSZ to prevent reaction of advanced compositions with TGO. Even in these situation the coating architecture is generally of a single variant. Since TBCs experience location specific performance needs (example interfacial oxidation, sintering resistance in the volume and need for distinct surface characteristics to mitigate against CMAS and erosion) there is an opportunity to engender unique microstructural and material characteristics. In this presentation, we will discuss the coupling of multilayer coating design to meet the disparate coating needs along with advanced layered manufacturing concepts. Plasma spray is uniquely capable of taking advantage of such layered design concepts as the coating itself is built in discrete layers of particle based assembly. Several variants of such multilayer, multifunctional coatings will be presented incorporating guidance from mechanics model, manufacturing advances and performance attributes.