Symposium CC
Ceramics and Composites for Enhanced Tribologic and Corrosion Performance in High-demanding Applications
ABSTRACTS
Session CC-1 - Friction and Wear
CC-1:IL01 Strategies for Developing Hard Coatings for Demanding Application
P.H. MAYRHOFER, Materials Science and Technology, TU Wien, Vienna, Austria
Whenever mechanical attack is dominating the loading profile of materials in industrial applications, nitrides are highly preferred, whereas oxide materials provide best protection against high temperature corrosions. Thus, when mechanical and thermal loading is combined, the nitrides used should also provide an excellent stability against temperature as well as corrosive attack (such as oxidation). How nitride materials can be developed – implementing computational and experimental materials science – to withstand high mechanical as well as thermal loading, is the focus of this talk. We will use recent developments – where we applied alloying and architecture concepts (e.g., composition and/or phase modulated layers) to transition metal nitrides, for optimizing their properties – to derive important materials design guidelines for improved strength, ductility, but also stability. With the help of alloyed TiN coatings, we will discuss the potential of (supersaturated) solid solutions in increasing strength, ductility, as well as thermal stability. With multilayer and especially superlattice architectures, we will discuss the potential of various architectures to increase the performance of hard coatings.
CC-1:IL02 Structured and Layered Coatings for Reduction of Wear
DAE-EUN KIM, School of Mechanical Engineering, Yonsei University, Seoul, South Korea
In order to enhance the efficiency and durability of machines it is essential to minimize friction and wear. In this regard, coatings have been extensively utilized to lower friction and protect the surface of mechanical components. However, there are numerous variables that need to be considered to design and fabricate the coating for a given application, such as material, thickness, uniformity and process conditions. The general approach taken in this work to reduce wear was to exploit structured and layered coatings. The micro-scale structures on the surface were intended to deform elastically during sliding. By doing so, the structures were able to absorb the frictional energy during contact sliding. Also, the nano-layered coating was designed to deter crack propagation and optimize the stiffness of the coating. The ability of these types of coatings to reduce wear was demonstrated by using both soft and hard materials.
Acknowledgement: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2010-0018289).
CC-1:IL04 Ceramic/Carbon Nanofiller Composites: New Materials with Improved Tribological Performance
M. BELMONTE, P. MIRANZO, M. I. OSENDI, Institute of Ceramics and Glass (ICV-CSIC), Madrid, Spain
Nowadays, new materials with enhanced tribological properties are required to fulfil the increasing demanding working conditions needed to achieve higher efficiency and environmental protection in the manufacturing, power generation, and transportation industries. To accomplish this goal, we propose the development of carbon nanostructures, namely carbon nanotubes (CNTs) and graphene nanofillers, containing ceramic composites. Here we present the benefits and the role played by these carbon nanostructures on the friction and wear resistance of non-oxide ceramic materials; in particular, silicon nitride and silicon carbide, which have been tribological tested under dry and lubricated sliding conditions simulating those attained in gasoline direct injection systems. The results evidence that CNTs and graphene nanoplatelets are ideal nanofillers to extraordinarily enhance the tribological performance of ceramics due to both the formation of an adhered protective carbon-based lubricating tribofilm on the tested material, and the improvement on the macro/micro-mechanical response that promotes the stress field redistribution at the contact, especially at high loads.
CC-1:L05 Hollow Spherical and Nanosheet-base BN Nanoparticles as Perspective Additives for Friction and Wear Reduction. Correlation between Large-scale Friction Behavior and In situ TEM Compression Testing
D.V. SHTANSKY1, A.V. BONDAREV1, A.M. KOVALSKII1, K.L. FIRESTEIN1,2, P.A. LOGINOV1, D.A. SIDORENKO1, N.V. SHVINDINA1, I.V. SUKHORUKOVA1, 1National University of Science and Technology “MISIS”, Moscow, Russia; 2School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT), Brisbane, QLD, Australia
In the present study we utilized h-BN nanoparticles (NPs) with different morphologies (hollow NPs with smooth surface (H-BNNPs), solid NPs with petalled structure (P-BNNPs), and globular NPs formed by numerous thin h-BN nanosheets (N-BNNPs)) as additives to oil for friction and wear reduction. For BNNP characterization, SEM, TEM, EDS, and IR spectroscopy were used. Two sliding 100Cr6 surfaces were tested in the presence of PAO6+BNNP lubricants with 0.1 and 0.01 % of BNNPs. The positive effect of BNNP additives increased along the row: P-BNNPs, H-BNNPs, and N-BNNPs. Utilization of N-BNNPs permitted to decrease noticeably the friction coefficient from 0.1 to 0.06 and reduce significantly the wear rate. The superior lubricity of the N-BNNP was achieved due to their disintegration into individual nanosheets and alignment parallel to the friction direction. In addition, BN nanosheets formed small agglomerates uniformly distributed over the area of tribological contact thereby almost completely isolating two rubbing surfaces. In situ mechanical TEM tests were also performed to visualize and correlate the mechanical properties of individual NPs to their large-scale friction behavior. The results suggest that at low pressure, rolling of H-BNNPs was the most likely lubrication mechanism.
CC-1:L06 Frictional Behavior and Properties of Fabric Reinforced C/SiC Brake Pads on a Steel Brake Disk
S. FLAUDER, N. LANGHOF, W. KRENKEL, University of Bayreuth, Ceramic Materials Engineering, Bayreuth, Germany
Ceramic matrix composites like C/SiC combine the strength, thermal stability, wear resistant, and low density of ceramics with an additional damage tolerance due to the carbon fiber reinforcement. Hence, these materials can be used as high performance frictional material especially for emergency and service brakes at high power intensities. In this study the frictional behavior of fabric reinforced C/C-SiC brake pads with the same fiber architecture but different matrix composition and a frictional surface of 400 mm2 paired with a steel brake disk of 380 mm diameter were investigated with respect to the influence of brake pad pressure and the composition of the ceramic brake pads. Particular attention was given to the wear, the coefficient of friction (COF), and the peculiarity of the COF progression curves. The dynamometer tests were performed with a starting sliding velocity of up to 20 m/s. This leads to initial power intensities up to 800 W/mm2. Increasing the pad pressure from 20 to 40 MPa decreases the COF by up to 30 %. The progression curves of the COF show an initial rise and falling of the COF value at the beginning of braking, a constant plateau afterwards, and a steep increase of the COF value at the end of braking.
CC-1:IL07 Composite Solid Lubricants for Use in Extreme Environments
M.T. DUGGER, Sandia National Laboratories, Albuquerque, New Mexico, USA
Solid lubricants are used in high-consequence aerospace applications to insure predictable friction and wear behavior over a wide range of temperatures. These materials are frequently deposited and stored for years before they are placed in service, and may be dormant for years or decades longer prior to actual operation. Over long periods of storage, molybdenum disulfide-based solid lubricants are known to exhibit surface oxidation that results in elevated friction coefficient during initial sliding. Additionally, water vapor in the operating atmosphere influences steady-state friction behavior, through the modification of transfer film dynamics. Dopants have been added to MoS2-based solid lubricants for decades to create composite nanostructures that help reduce oxidative degradation, wear rate, and the sensitivity of frictional performance to operating environment. Recent capabilities in physical vapor deposition permit exquisite control of the composition and structure of solid lubricant composites. Insights into the desired structures for MoS2-based lubricants to resist environment and age-related performance impacts will be discussed, and efforts to create an environmentally robust thin film solid lubricant will be described.
CC-1:IL08 Diamond, cBN Reinforced Ceramic Materials: Potential Wear Resistant Components
M. HERRMANN, B. MATTHEY, S. KUNZE, A.-K. WOLFRUM, Fraunhofer-IKTS, Dresden, Germany
Materials with enhanced wear resistance are of great interest for modern industry. In many cases, advanced ceramics show high wear resistance at room and high temperatures. Nevertheless, there is a demand of a further improvement of the wear and tribological behaviour of these materials. One possibility could be the reinforcement of ceramic materials with super hard particles like cubic BN (cBN) or diamond. At normal sintering conditions of ceramic materials, diamond and cBN are metastable and transform into the soft modifications. Therefore, special approaches have to be applied to obtain dense materials with wear resistance. The most promising way for the production of diamond components was found to be the reaction bonding of diamond by silicon infiltration. The tribological properties of these materials under dry sliding conditions are analysed in details. Friction coefficients as low as 0.1 could be achieved for diamond containing ceramic composites. These values are similar to that of CVD diamond coatings. The data reveal, that for both types of materials- cBN- and diamond ceramic matrix composites - the friction is controlled by the super hard reinforcing particles. The results show the great potential of these materials for a wide range of applications.
CC-1:L09 On Silicon-based Ceramics for Utilization in High Pressure Pumps for Gasoline Direct Injection and the Effects of Laser Surface Texturing
P. SCHREIBER, J. SCHNEIDER, Karlsruhe Institute of Technology IAM-CMS, Karlsruhe, BW, Germany; P. ZIELONKA, K.G. SCHELL, E.C. BUCHARSKY, M.J. HOFFMANN, Karlsruhe Institute of Technology IAM-KWT, Karlsruhe, BW, Germany
To investigate the potential of ceramic materials for media lubricated high-pressure gasoline injection pumps in particular, different Si-ceramics have been characterized by means of self-paired, flat-on-flat tribological model experiments. Samples were tested under reciprocating sliding motion with stroke lengths of 5 and 10 mm respectively, while being submerged in an isooctane bath. In addition to two commercial ceramics (SSiC and Si3N4), newly developed ceramic composites, consisting of a Si3N4-matrix with varying amounts of embedded SiC- and BN-particles, were examined. Results show that self-paired SSiC can result in very low friction coefficients under certain circumstances, however the tribo-system might react very sensitive to changes in kinematics and surrounding conditions during testing in terms of sudden increase in friction. Further could be shown that the embedding of SiC-particles in a Si3N4 matrix has a friction reducing effect when compared to self-paired pure Si3N4. Additionally, the effects of micro-surface textures, applied via laser-ablation, were investigated. The tested textures seem to disable acting mechanisms, resulting in the observation of altered run-in processes and higher stability of friction courses during the experiments.
CC-1:L11 Mechanical Properties and Wear Behaviour of Boron Carbide/Graphene Platelet Ceramics
R. SEDLAK1, A. KOVALCIKOVA1, J. BALKO1, P. RUTKOWSKI2, A. DUBIEL2, E. MUDRA1, V. GIRMAN3, 1, J. DUSZA1, 1Institute of Materials Research, Slovak Academy of Sciences, Division of Ceramic and Non-Metallic Systems, Kosice, Slovak Republic; 2AGH University of Science and Technology in Krakow, Faculty of Materials Science and Ceramics, Department of Ceramics and Refractories, Krakow, Poland; 3Pavol Jozef Safarik University in Kosice, Faculty of Science, Institute of Physics, Department of Condensed Matter Physics, Kosice, Slovak Republic
B4C/GPLs composites have been prepared with a different weight percent of GPLs as sintering additive and reinforcing phase, hot pressed at 2100 °C. The microstructure of composites consists of 4 µm B4C grains in all systems and of GPLs with length up to 15 µm, located as a single sheet between individual grains but also in overlapped form, connected with porosity. The hardness and fracture toughness varied from 18.21 to 30.35 GPa and from 3.81 to 4.48 MPa.m1/2, respectively. The highest value of fracture toughness, which was ~50 % higher than the KIC value of the reference material, was achieved at maximal GPLs content. The toughening mechanisms in all B4C/GPLs composites were similar, in the form of crack deflection, crack branching, crack bridging, and graphene sheet pull-out, only the frequency of their occurrence during crack propagation and their effectiveness in the toughening process is different. The electrical conductivity increased with GPLs addition and reached the maximum value at 8 wt.% of GPLs, 1526 S/m in the perpendicular and 872 S/m in the parallel direction to the hot press direction. The coefficient of friction for composites were similar (0.5-0.6), but the wear rate decreased ~77 % in the case of B4C+10 wt.% GPLs when compared to reference material.
CC-1:IL12 In Situ Generated Turbostratic 2D Graphite: A New Family of Self Lubricating Composites
J.D. BIASOLI DE MELLO1, C. BINDER1, R BINDER2, A.N. KLEIN1, 1Federal University of Santa Catarina, EMC, Florianópolis, SC, Brazil; 2Whirphool / Embraco, Joinville, SC, Brazil; 3Federal University of UberlAndia,UberlAndia, MG, Brazil
A new microstructural model/processing route able to produce a homogeneous dispersion of in situ generated, discrete, solid lubricant particles in the volume of sintered composites is presented. This new route was achieved by in situ formation of graphite nodules due to the dissociation of a precursor (SiC particles) mixed with metallic matrix powders during the feedstock preparation. Thermal debinding and sintering were performed in a single thermal cycle using a Plasma Assisted Debinding and Sintering (PADS) process. Nodules of graphite (size ≤ 20μm) presenting a nanostructured stacking of graphite foils with thickness of a few nanometres were obtained. Micro Raman spectroscopy indicated that the graphite nodules are composed of a so-called turbostratic 2D graphite which has highly misaligned graphene planes separated by large inter lamellae distance. The large inter planar distance and misalignment among the graphene foils has been confirmed by transmission electron microscopy and is, probably, the origin of the remarkably low dry friction coefficient (0.04). The effects of precursor content (0 to 5wt% SiC) and of sintering temperature (1100, 1150 and 1200 °C) and metallic matrix composition (Fe-C; Fe-C-Ni; Fe-C-Ni-Mo) on the tribological behaviour are presented and discussed.
CC-1:IL13 Tribochemistry and Environmental Effects in Friction of Amorphous Carbon Films
F. MANGOLINI, Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, USA; K.D. KOSHIGAN, J. FONTAINE, Laboratoire de Tribologie et Dynamique des Systèmes, Ecole Centrale de Lyon, Ecully cedex, France; M.H. VAN BENTHEM, J.A. OHLHAUSEN, Sandia National Laboratories, Albuquerque, New Mexico, USA; J.B. McCLIMON, Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA; J. HILBERT, R.W. CARPICK, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA, USA
Among the variants of diamond-like carbon films developed for meeting the performance requirements of advanced tribo-mechanical applications, silicon- and oxygen-containing hydrogenated amorphous carbon (a-C:H:Si:O) is of interest as it exhibits good tribological performance across a broader range of environments compared to hydrogenated amorphous carbon, and higher thermal stability. However, the scientific basis for this behavior is not established. In this work, we aim to develop fundamental understanding of the environmental impact on the tribology of a-C:H:Si:O. Upon sliding a-C:H:Si:O against steel, a minimum pressure was necessary to obtain a low friction and wear behavior, i.e., 1 mbar in H2O, 10 mbar in O2, and 50 mbar in H2. Below these pressures, the friction coefficient quickly reached values above 1, with a transfer of material from the steel pin to a-C:H:Si:O. Above the pressure thresholds, the friction coefficient decreased to values below 0.1, and a tribofilm formed on steel pins. A simple phenomenological model based on the investigation of the tribologically-induced structural transformations and chemical reactions occurring on a-C:H:Si:O will be proposed to account for the observed tribological behavior.
CC-1:L14 Machining of Ceramic Matrix Composites
R. GOLLER, A. ROESIGER, Augsburg University of Applied Sciences, Augsburg, Germany
CMCs gained high attention in the last year, when GE announced the first flight of components in its leap gas turbine engine. The potential of CMCs for further application in the future is high nonetheless to further improve fuel efficiency. The special anisotropic structure however provides many challenges in process technology. One important step on the way to the finished part is the machining (grinding) operation of the parts surface to reach the required tolerances and roughness. In this research work the effect of machining on material surface roughness is presented. Hereby process parameters, tools and CMC-materials are varied. Roughness as a function of feed rate, cutting speed and tool type will be presented.
CC-1:IL15 Friction and Wear of Diamond: Atomic-scale Insights from Computer Simulations
G. MORAS, Fraunhofer IWM, MicroTribology Centre, Freiburg, Germany
The chemical and topographic structures of a surface, as well as the nano- and microstructure of the underlying material, evolve under tribological load. This structure evolution determines the tribological properties of a material but takes place at buried interfaces which are usually not accessible by in situ experiments. As a result, atomic-scale simulations are increasingly used as a complementary tool to gain insights into the mechanisms that govern the formation of the “tribomaterial” and its effects on friction and wear. In this lecture, I will present the results of atomistic simulations of tribological processes that occur on diamond surfaces. In particular, I will discuss the importance of tribologically induced material transformations, such as phase transitions, aromatic surface reconstructions and surface chemical terminations for technological processes like the mechanical and chemical-mechanical polishing of diamond surfaces and the water-lubrication of diamond films.
CC-1:L17 Development of Si3N4 – SiC Composites for Tribological Applications
P. ZIELONKA, P. SCHREIBER, E.C. BUCHARSKY, K.G. SCHELL, J. SCHNEIDER, M.J. HOFFMANN, Institute for Applied Materials, Karlsruhe Institute of Technology, Karlsruhe, Germany
For gasoline direct injection (GDI) engines, the increase of injection pressure can be one approach to improve internal combustion processes, resulting in higher efficiencies and significantly lowered amount of harmful particles in the exhaust gases. However, the pressure increase results in critical tribological conditions in the gasoline lubricated metal on metal contacts inside the pump. Therefore ceramic materials based on silicon nitride (Si3N4) and silicon carbide (SiC) are proposed. They should have the potential to fulfill the requirements of this contact. To investigate the tribological behavior, different silicon nitride and silicon carbide based materials were investigated. In addition to commercially available SiC and Si3N4, ceramics, fully dense silicon nitride- /silicon carbide composites up to 50 Vol.-% SiC were developed. The influence of SiC content on microstructure and mechanical properties of the Si3N4/SiC composites are discussed and correlated to the tribological behavior. Results show interesting effects for the newly developed composites as well as distinct frictional behavior for the different commercially available ceramics.
CC-1:L19 Surface Properties of Sulfnitrided Layer formed on AISI4140 Steel by Plasma Nitriding
HYUN JUN PARK1, 2, SANG-SUP KIM2, KYOUNG IL MOON1, 1Korea Institute of Industrial Technology, Heat Treatment R&D Group, Siheung-si, South Korea; 2School of Materials Science and Engineering, Inha University, Incheon, South Korea
To improve the service life of the shaft-bushing tribo system, the bushing was treated by plasma sulfur nitrocarburizing process. Before a plasma sulfur nitrocarburizing, the specimens were treated by plasma nitriding. As a result, a compound layer was formed with thickness about 10 ㎛. After then, by introducing a plasma sulfur nitrocarburizing process with C-source gas such as CH4, C2H2, a very fine and porous FeS layer with the grain size less than 100 nm was formed on the top of the compound layer. This fine and porous FeS layer formed on the samples led to improved friction coefficient and resulted in better wear resistance during the ball on disk test in dry conditions. So, it is considered that this fine and porous FeS layer could replace the PTFE (Polytetrafluorethylene) and MoS2 coating that have been commercially used in busing parts. Corrosion tests were also performed in 3.5% NaCl solution using potentiodynamic polarization test.
CC-1:L20 Numerical Modelling of Nano / Micro Scratch Test Considering Scratch Tip Size Effect
KWANGMIN LEE, K.P. MARIMUTHU, H. LEE, Sogang University, Seoul, South Korea
To make numerical models of scratch test with considering scratch-tip size effect, experimental and extended finite element (XFE) studies are performed with soda-lime glass. Scratch-tips of different sizes cause various failure modes such as tensile cracking and chipping; each failure mode has a distinct effect on the coefficient of friction (COF) change. An occurrence of chipping in the nano scratch test increases the interfacial COF, whereas, in the micro scratch test, the occurrence of tensile cracks does not change the COF. As yield models for amorphous materials are limited in the literature, linear Drucker-Prager (DP) yield model is calibrated by considering indentation size effect through numerical nano / micro indentation analyses. With DP yield model in FE models for nano / micro scratch test, numerical results are validated by comparing with experimental results. XFE studies are then conducted to analyze the effect of crack propagation on COF and each component of COF in nano / micro scratch tests. The proposed numerical model can be used to comprehend the effect of scratch-tip size on friction mechanism of brittle materials during the scratch tests.
Session CC-2 - Corrosion
CC-2:IL01 Silicate Deposit Induced Degradation of Thermal and Environmental Barrier Coatings: Toward Integrated Models for Accelerated Coating Design
D.L. POERSCHKE, University of Minnesota, Minneapolis, MN, USA
As the operating temperatures of gas turbine engines have risen, the thermal and environmental barrier coatings (TBCs and EBCs) used to protect the structural components in are increasingly exposed to molten silicate (CMAS) deposits that originate when sand or volcanic ash are ingested into the engine. The development of coatings offering improved resistance to the accelerated degradation caused these deposits is critical to enable future improvements in engine performance. However, the process of identifying suitable coating architectures is complicated by both the multiple competing coating design requirements (e.g., toughness, thermal conductivity, corrosion resistance) and the variability in the nature of the deposits arising in service. Therefore, the development of improved coatings requires an integrated approach with models capturing the influence of service conditions, and the coating material and microstructure on the severity of degradation. The present work describes progress toward developing and validating a design framework integrating the phase equilibrium and reaction dynamics models to provide insight into the relative efficacy of various prospective coating materials in mitigating the deposit-induced degradation.
CC-2:IL02 Corrosion and Oxidation of SiC Composites under High Temperature Water and Steam
TATSUYA HINOKI, S. KONDO, K. KAWASAKI, F. SHINODA, Kyoto University, Gokasho, Uji, Kyoto, Japan
Silicon carbide (SiC) is one of very attractive engineering ceramics in particular for high temperature use and nuclear application. Fundamental mechanical properties of highly crystalline nuclear grade SiC composites are stable following neutron irradiation. Silicon carbide composites are promising materials for accident tolerant fuel. However the highly crystalline nuclear grade SiC composites have carbon (C) interphase between fiber and matrix to retain ductile fracture behavior. Liquid phase sintered (LPS) SiC has remained sintering additives as impurities. Remained Al2O3 and Y2O3 phase in grain boundaries are the weakest link for corrosion behavior under high temperature water and high temperature steam. The grain boundary of LPS SiC was modified. High temperature water corrosion resistance of the LPS SiC was significantly improved. The SiC composites were developed with the particle dispersion in matrix instead of C interphase by LPS to improve high temperature oxidation resistance. The surface of SiC was damaged by ion-irradiation. The corrosion of the ion-irradiated SiC was accelerated under high temperature water with very high dissolved oxygen. The effect of irradiation induced defect on corrosion behavior is discussed.
CC-2:IL03 Electrochemical Corrosion and Electrochemical Machining of Ceramics
M. SCHNEIDER, Fraunhofer IKTS Dresden, Dresden, Germany
Ceramics are usually not susceptible for electrochemical corrosion due to the negligible electron conductivity but of course there are obvious exceptions. Silicon carbide, for example, is an intrinsic semi-conductor. Depending on the production procedure the conductivity can be enhanced by orders of magnitude and electron transfer reactions across the interface ceramic/electrolyte are reasonable. From the thermodynamic point of view silicon carbide forms a silicon oxide layer under acidic and weakly alkaline conditions. Under acidic conditions, e.g. in sulfuric acid, silicon carbide passivated spontaneously. The passive oxide is formed according the high field mechanism and can be artificially grown by anodic polarization. Otherwise, electron transfer reaction are still possible and leads to anodic gas evolution. For that reason SiC-ceramics can also play a key role as local cathode in the galvanic corrosion of mixed material constructions consisting of SiC-ceramics and metals. At least, the author show the utilization of the electrochemical behavior of a silicon carbide to machine such ceramics electrochemically. Electrochemical machining is a useful technique to shape very hard and brittle materials without mechanical tensile impact and negligible tool wear.
CC-2:IL05 Progress in Gas-solid Reaction Kinetics for Non-oxide Ceramic Materials at High Temperature
ENHUI WANG, XINMEI HOU, KUOCHIH CHOU, State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, China; Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing, China
Non-oxide ceramic materials (NOCMs), as the kind of structure and function materials, are usually applied in metallurgical industry as refractories, gas turbine as blades and linings and aerospace field as seal components and heat insulations due to their a series of excellent properties. Under these severe conditions, NOCMs tend to be confronted with the oxidation issue. Generally, the oxidation proceeds in passive way where the protective oxide layer can be formed to hinder the further diffusion of oxidant sources. In specific temperature and partial pressure of oxidant gas, however, active oxidation can take place, which can aggravate the consuming rate of NOCMs. What’s worse, simultaneous oxidation and volatilization can occur under oxidizing-reducing gas and/or water vapor at high temperatures. In the later ways of active oxidation and coexistence of oxidation and volatilization, the formation of votatile sub-oxides can generate steadily and lead to rapid material consumption. This review will consider and discuss the gas-solid oxidation kinetics of NOCMs from the perspective of models and microstructure evolution and simulation. The review will be a good reference for researchers to further study the gas-solid oxidation kinetics of NOCMs in the future.
CC-2:IL06 Hot Gas Corrosion of Ceramic Materials
W. KUNZ, H. KLEMM, A. MICHAELIS, Fraunhofer Institute for Ceramic Technologies and Systems IKTS, Dresden, Germany
The need for higher efficiency of gas turbines leads to a growing demand on higher operating temperatures or lower cooling efforts. Therefore, the interest of gas turbine industry has focused on high temperature ceramics, e.g. silicon nitride and silicon carbide as well as ceramic matrix composites, again. Due to great improvements regarding mechanical properties and sophisticated simulation possibilities, ceramics seem to meet the ambitious thermomechanical requirements. However, at high temperatures hot gas corrosion causes strong surface degradation, impeding long term application in hot gas atmospheres of all structural ceramics. Environmental barrier coatings can reduce the surface degradation considerably. Nevertheless, current coatings show distinct influences on the short term and long term mechanical integrity of ceramic components, limiting the applicability of ceramics in gas turbines. To overcome these limitations a global consideration of corrosive and mechanical properties of the ceramic components and a realistic assessment of attainable loads is necessary.
CC-2:L07 Development of Advanced Environmental Barrier Coatings at NASA
KANG N. LEE, B.J. HARDER, B.J. PULEO, NASA Glenn Research Center, Cleveland, OH, USA; G. COSTA, Vantage Partners, Cleveland, OH, USA
Increased fuel efficiency is a game changer for gas turbines as fuel is the single most important cost, accounting for up to about 40% of the overall operation cost of commercial aircrafts. Increased fuel efficiency is obtained through increasing thermal efficiency of engine by increasing the overall pressure ratio (OPR). Increased OPR requires increased turbine inlet temperature, which is paced by advances in turbine hot section materials temperature capability. SiC/SiC Ceramic Matrix Composites (CMCs) are the most promising materials to enable a quantum leap in materials temperature capability. Environmental Barrier Coatings (EBCs) is an enabling technology for CMCs by protecting them from water vapor-induced recession. A long-life EBC, reliable EBC lifing, and engine-relevant EBC life validation methods are on a critical path to successful introduction of CMCs in gas turbines. Environmental degradation, such as oxidation by water vapor and degradation by CMAS, are key life-limiting EBC failure modes. Current EBC research at NASA focuses on developing advanced EBCs with enhanced resistance to such corrosive species. This paper will discuss the current status of advanced EBC development at NASA.
CC-2:IL08 High Temperature Ceramic Materials for Space Applications
M. BALAT-PICHELIN, PROMES-CNRS Laboratory, Font-Romeu Odeillo, France
Solar probe missions of NASA and ESA are designed to make measurements in the never-observed region of the heliosphere. They will plunge directly into the solar corona in order to understand its heating and the acceleration of the solar winds. For both missions, a main thermal protection system will protect the payload within its umbra. In this way, pyrolytic boron nitride thin films deposited by CVD on C/C composites was studied as a potential candidate for the PHOIBOS mission (ESA). Experimental results of the degradation of the pBN films in such severe environment will be presented together with the evolution of its thermal radiative properties at high temperature. In the aim of mastering the atmospheric re-entry in Europe, ESA has launched the IXV vehicle that has also needed a thermal protection system based on ceramic materials. Experimental study of the behavior of two C/SiC-based materials from Herakles-Safran for the nose and MT Aerospace for the flaps was performed. The transition between active and passive oxidation was determined for both materials using two different plasma facilities and the sudden temperature increase occurring at conditions beyond active oxidation was attributed to the carbon fiber ablation rendering the material unusable in such conditions.
CC-2:IL09 Preparation and Oxidation Resistance of ZrB2-SiC Composite Powders by Molten-salt-mediated Magnesiothermic Reduction Synthesis
HAIJUN ZHANG, The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan, China
ZrB2-SiC are the most promising materials in ultra-high temperature field. In this paper, a novel molten-salt-mediated magnesiothermic reduction method was used to prepare ZrB2-SiC powders by using magnesium powders as reducing reagent. The influences of firing temperatures, soaking time and the dosage of raw materials on the synthesis of ZrB2-SiC powders were investigated. The phase composition and microstructure of as-prepared powders were characterized by using XRD, FE-SEM, EDS and TEM. The oxidation kinetics of prepared ZrB2-SiC powders was also studied via non-isothermal oxidation method. The results indicate that: 1) The grain size of the prepared ZrB2-SiC composite powders was about several microns, and SiC was well distributed around the ZrB2 particles. 2) The apparent activation energy of ZrB2 in the composite powders were 380.96 kJ·mol-1, which was much higher than that of phase pure ZrB2 of 325.25 kJ·mol-1, indicating that the addition of SiC could improve the oxidation resistance of ZrB2.
CC-2:L10 Elastomer Seal Corrosion Protection using DLC-Ag Film
T. BAESSO1, A.C. SENE1, L.A. MANFROI, A.A. VIEIRA1, P.A. RADI1, 2, M.A. RAMIREZ1,T.C.A.SANTOS1, L. VIEIRA1, 2, 1University of Paraiba Valley- UNIVAP/ IP&D, Sao José dos Campos, SP-Brazil; 2Aeronautics Institute of Technology, ITA / LPP, Sao José dos Campos, SP-Brazil
Elastomeric gas pressure seals has been using to confine corrosive liquids, vapous, and breathing air inside space vehicles, however destinations such as low-Earth orbit, asteroids, lunar and the Martian surfaces are harsh for materials. The leakage of elastomer gas pressure seals is dominated by permeation of gas through the body of the seal. The flow through the interface between the seal and its counter face is neglected. A short time under gas permeation the seals become more sticky and the pressure inside the cabin needs to be improved to compensate the air leak to the environment outside the cabin. Resistant materials are required to survive long life withstand atomic oxygen. In this work DLC-Ag as a protective coating was deposited by plasma enhanced chemical vapor deposition (PECVD) in silicone elastomer S0383-70 O-ring. The O-ring with DLC-Ag film were used to run out tribological studies as a protective coating on silicone elastomer S0383-70 O-ring. The silicone elastomer S0383-70 O-ring with and whithout DLC-Ag film were tested under atomic oxygen bombardment. The oxygen bombardment were run out in oxygen discharge using a RIE (Reative Ion Etching) reactor. The chemical structure and morphology of the DLC-Ag film was analised before and after atomic oxygen exposition.
CC-2:IL11 High Temperature Corrosion in Molten Salts & Molten Salts Technology: Past, Present and Future Through Coatings Technology
F.J. PEREZ, Universidad Complutense de Madrid, Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica, Madrid, Spain
In the past molten salts where associated to the high temperature corrosion processes that appeared in the combustion of fossil fuels or that appears in gas turbines. From years ago renewal energies appears in the molten salts scenario, for example with the development of biomass and waste incineration plants, where the production of energy where associate also with the undesirable molten salts that corrodes the plant and decreasing at the same time their lifetime. On the other hand appears technologies, that far away that dealing with undesirable salts, they want to use the properties of molten salt systems to use them in the power plants: this is the case of molten carbonate fuel cells and solar power concentration plants (CSP). The possibility to increase their efficiency and to be more competitive energy resources, in comparison with fossil and nuclear, deals with molten salt technology. A review of the corrosion mechanism of those different applications will be done, with the possibilities in the use of coatings for corrosion protection and the possibility to use their capabilities to monitor the corrosion “in situ” for the electrochemical corrosion mechanism associated with this corrosion phenomena. Moreover, the role of the coatings technology will be stated, taking into account their role in the new CSP plants design.
CC-2:L12 High-temperature Ageing of Si/SiC Ceramics
L. CHARPENTIER, C. CALIOT, PROMES-CNRS, Font-Romeu Odeillo, France
The receivers used in the concentrated solar power plants are expected to support high solar fluxes and high temperatures in ambient air for twenty years or more. One of the sources of damaging is the growth of an oxide layer on the irradiated surfaces, which will affect their radiative properties. One perspective scientific challenge for new technical solutions is to identify, on shorter times and at a laboratory scale, if a material would last several years of use as a solar receiver while maintaining its performance. An ageing procedure on commercial Si/SiC (less than 10 v.% Si and below 0.2 v.% contaminant such as Al) from EngiCer SA was performed inside a solar reactor in open air at 1600, 1630 and 1670 K, with 4 cycles of heating of either 20 min or 1h. The hemispherical directional emissivities were measured on reference and aged materials in the solar spectrum (250 – 2500 nm) and infra-red (2.5 – 25 µm) ranges, showing an increase of the absorptivity of the solar spectrum and a drop of the infra-red emissivity in the 8-9 µm on the aged materials. Surface analyses (SEM/EDS, 3D profilometry, µ-Raman spectroscopy) identified that these changes were due to the growth of silica, with a noticeable content of aluminum that increases with temperature and exposure time.
CC-2:L13 Tribocorrosion and Corrosion Studies on Stainless Steel Substrates Covered with DCL Films in Ethanol with Different Concentrations of Water
P.A. RADI1, 2, A.C. SENE2, M.A. RAMIREZ2, P. LEITE2, L.VIEIRA1, 2,1Instituto Tecnologico de Aeronautica (ITA), Sao José dos Campos, SP, Brazil; 2Universidade do Vale do Paraíba (UniVap), Urbanova, Sao José dos Campos - SP, Brazil
Ethanol can be produced from various renewable materials like corn, cellulose and can also be obtained from Sugarcane bagasse and are called as 2nd generation ethanol. Ethanol is the dominant biofuel in many countries and has been used as a blend component in gasoline or as pure fuel. One disadvantage of the use of ethanol is its hygroscopic properties. Xiaoyuan Lou and Preet Singh showed that the increase in the water concentration in ethanol induces pitting and metal loss. Diamond-Like Carbon (DLC) films can protect the engine components against corrosion and reduces the friction coefficient and wear. This paper shows the tribocorrosion and corrosion studies of DLC films deposited on stainless steel substrates. The friction coefficient, wear rate, scratching resistance, and surface morphology were analyzed before and after 7 days of long-term exposure test. The tribocorrosion was studied in ethanol as a function of water concentration.
CC-2:IL14 Environmental Barrier Coating Stability in High Temperature Water
R.A. GOLDEN, C.G. PARKER, M.J. RIDLEY, E.J. OPILA, Dept. of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, USA
Environmental Barrier Coatings (EBCs) are required for use of SiC-based ceramic composites in combustion environments. Rare earth (RE) disilicates are currently state-of-the art EBCs due to their chemical and thermal expansion match with the underlying SiC as well as their increased stability in the combustion environment relative to thermally grown silica. Nevertheless, silica is selectively depleted from the RE disilicates in high-temperature high-velocity steam, forming RE monosilicates plus porosity due to volumetric reduction accompanying the phase change. Transport of water vapor through the pore network allows continued reaction, but at a rate that slows with time. In addition, the microstructure of the resulting porous surface layer evolves with time. Methods to mitigate the continued reaction of the EBC with water vapor, including incorporation of water-vapor resistant phases in the coating, alternative choices of EBC materials, and self-healing by sintering will be discussed.
CC-2:IL15 Effects of Oxygen Potential Gradient and Electrical Characteristics on Mass Transfer in Environmental Barrier Coatings at High Temperature
SATOSHI KITAOKA, T. MATSUDAIRA, M. TANAKA, Japan Fine Ceramics Center, Nagoya, Japan; T. Sato, O. Sakurada, Gifu University, Gifu, Japan; Y. KAGAWA, Tokyo University of Technology, Hachioji, Japan
Mass transfer mechanisms in aluminum based oxides were investigated by evaluating oxygen permeability through oxide wafers at high temperature using an oxygen tracer (18O2). These wafers served as models for environmental barrier coatings. When an alumina wafer was subjected to a large oxygen potential gradient (dµO), the GB diffusion coefficient for oxygen ions near the high oxygen partial pressure (PO2(hi)) surface was significantly smaller than that (self-diffusion) in the absence of a dµO. The electronic transference number for the wafer increased in the presence of a dµO, resulting in the development of a negative charge on the PO2(hi) surface, and a positive charge on the opposing low oxygen partial pressure surface. On the other hand, a mullite wafer, of which is a chemical formula of Al4+2xSi2-2xO10-x with x=0.278, exhibited ionic conductivity, and its oxygen GB diffusion coefficient was independent of the presence or absence of a dµO. This resulted in the polarity of the surface charges being opposite to that for alumina. The oxygen shielding properties and structural stability of a bilayer structure consisting of alumina and mullite, which have markedly different electrical characteristics, were strongly affected by the dµO direction and magnitude.