Symposium CF
High and Ultra High Temperature Ceramics and Composites for Extreme Environments

Session CF-1 - Synthesis and Processing

CF-1:IL01  Beyond YSZ For High Temperature Gas Turbines and Aerospace
D.R. CLARKE, Harvard University Cambridge, MA, USA

Thermal barrier coatings for gas turbine vanes and blades must satisfy several, and sometimes, conflicting requirements. Although their primary purpose is to provide thermal insulation between the expanding hot combustion gases, which drive the turbine, and the metallic turbine components, they must also remain adherent, withstand particle impact and resist corrosion, including from molten sand ingestion (CMAS attack). Up until now, these requirements have been largely met by yttria-stabilized zirconia (8YSZ), primarily in its metastable tetragonal crystal structure. For increased efficiency and power, the next and future generation turbines will likely operate at higher temperatures, above the capabilities of metastable tetragonal 8YSZ. Higher temperatures not only exacerbate the problems associated with CMAS attack but also demands a material with lower thermal conductivity all the while satisfying the thermo-mechanical demands associated with thermal expansion mismatch and impact. Many oxides have been identified to have lower thermal conductivity than 8YSZ but few have the potential for toughening as well as the ease of deposition. These multi-functional requirements will be described and will be used to narrow the selection of possible oxide coating materials.


CF-1:IL02  Ultra-high Temperature Ceramic Matrix Composites (UHTCMCs)
J. BINNER, V. RUBIO, M. PORTER, University of Birmingham, Edgbaston, Birmingham, UK

There is an increasing demand for advanced materials, for aerospace and other applications, with temperature capability ranging from 1500 °C to well over 2000 °C and able to survive highly corrosive environments whilst subject to intense heat fluxes and mechanical stresses. The interaction of environmental conditions together with the requirement that dimensional stability is maintained makes the selection of suitable materials extremely challenging. This paper discusses the design, development, manufacture and testing of a new class of ceramic matrix composites based on C fibre and SiC preforms enriched with ultra-high temperature ceramic (UHTC) powders and with a matrix infiltrated by either RF- or microwave-heated chemical vapour infiltration (CVI). These composites will form of suite of materials suitable for application in severe aerospace environments.


CF-1:IL03  Synthesis, Processing and Characterization of Thermal Barrier Ceramics Based on Gd2Hf2O7 Pyrochlore Structure
B. MATOVIC¹, J. MALETASKIC^{1, 2}, J. LUKIC¹, M. PREKAJSKI DJORDJEVIC¹, M. FAJAR², K. YOSHIDA², T. YANO², ¹Centre of Excellence-CextremeLab, Institute for Nuclear Sciences Vinca, University of Belgrade, Belgrade, Serbia; ²Lab.for Advanced Nuclear Energy, Institute of Innovative Research, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo, Japan

Dense ceramics based on Gd₂O₃–HfO₂ solid solution, xGdO_1.5–(1-x)HfO₂ with 0.0 ≥ x ≤ 1.0, were prepared from metal nitrates and NaOH using self-propagating room temperature synthesis (SPRT). The room temperature synthesis process initially yielded amorphous powders, which on further calcination, crystallized to yield crystalline ceramics. The evolution of the phase composition with thermal treatment was investigated by X-ray powder diffraction (XRPD). Powder properties such as crystallite size, lattice strain and lattice parameter were studied by X-ray diffraction (XRD) at room temperature. The crystallite size was estimated by means of the full width at half maxima (FWHM) of XRD peaks. Williamson–Hall plots were used to determine the lattice strain whereas the Ritveld analysis was employed for crystal structure refinement. Powder morphology and particle size distribution were analyzed by scanning electron microscopy (SEM) as well as densification and microstructure evolution was determined by means of density and scanning electron microscopy (SEM). Thermal conductivity of densified ceramics was measured up to 1000 °C. It was found that the powder properties are strongly affected by calcination temperature of thermal treatment. The results indicated that increasing x value (metal cations content) induce phase transition: pyrochlore (P)-orderd-disorderd –fluorite (F) type ceramic compound. Data obtained in this study are discussed in relation to the crystal chemistry of these solid solution.


CF-1:IL04  Fast Densification of UHT Ceramics and Composites by SPS
D. SCITI, L. SILVESTRONI, L. ZOLI, ISTEC-CNR, Faenza, Italy

The most diffused methods to densify UHT ceramic and composites are pressure-assisted techniques such as hot pressing (HP) or spark plasma sintering (SPS). In the case of monolithic materials, SPS is by far the best technique to achieve full densities and refined microstructure with minimum or no addition of secondary phases. In this talk we report examples of densification of bulk UHTCs, UHTC matrices with discontinuous SiC or C fibers and continuous C fibers by SPS. When adding reinforcing phases (such as fibers) to the UHTC matrix the sintering schedule must be carefully tailored to prevent excessive reaction at the matrix-fiber interface, or even collapse of the fibers. We will try to understand the principal densification mechanisms occurring during thermal cycle. Relevant mechanical properties such as room- and high-temperature flexural strength and fracture toughness will be shown for successfully densified materials. For the sake of comparison we will report microstructures and properties of similar materials densified by HP.


CF-1:L05  Synthesis of Ultra-fine Hafnium Carbide Powders Combining the Methods of Liquid Precursor Conversion and Plasma Activated Sintering
WEIMIN M. WANG, D.L. LU, H. WANG, F. ZHANG, J. WEI, Z.Y. FU, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China

Ultra-fine hafnium carbide (HfC) powders were synthesized using a novel method combining liquid precursor conversion and plasma activated sintering (PAS). Solution-based processing was used to achieve a fine-scale mixing of the reactants, and further treatment by PAS allowed fast formation of HfC. We investigated the effect of the type of acid used during the liquid precursor conversion on the synthesized powders, where mixtures were prepared using salicylic acid, citric acid, or a combination of these. The results show that pure HfC powders (with an average particle sizes of 350 nm) were obtained at a relatively low temperature (1550°C) using a HfOCl2•8H2O precursor with the mixed acids. The oxygen content of the synthesized powders was only 0.97 wt%. The type of acid had a significant effect on the synthesis product. When using only citric acid, the temperature required to produce pure hafnium carbide increased to 1700°C. In the case of a salicylic acid precursor, pure HfC was not obtained, even at a synthesis temperature of 1700°C.


CF-1:IL07  Sintering of Ultra-high Temperature, High Entropy Ceramics based on Multi-component Metal Carbides
E.G. CASTLE, M.J. REECE, School of Engineering and Material Science, Queen Mary University of London, London, UK

High Entropy Ceramics (HECs) are a newly emerging class of ceramic materials that are attracting much attention, particularly in the Ultra High Temperature Ceramics (UHTCs) community. These single-phase crystalline materials typically consist of a chemically ordered anion sublattice (O, C, N or B) and a chemically disordered metal cation sublattice. The metal cation sublattice consists of several (>4) metallic elements in near-equiatomic proportions and is stabilized into the single phase by its enhanced configurational entropy. The discovery of HECs has therefore opened up a large new compositional space in which to explore new ceramic materials. Emerging research is showing that the lattice distortion and chemical disorder present in the materials is leading to interesting mechanical, thermal and oxidation behaviours, beyond what would be expected from a simple rule of mixtures approximation. The sluggish diffusion, low thermal conductivities and ultra-high melting temperatures of these materials therefore presents significant processing challenges. We present the results of our investigations into the optimization of appropriate current and/or pressure-assisted sintering processes in order to produce fully dense and chemically homogeneous high entropy carbide ceramics.


CF-1:IL08  Developing Cost-effective Manufacturing Methods and Processing Strategies for UHTCs
C. TALLON, Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA

Ultra-High Temperature Ceramics (UHTCs) are used in certain components for extreme applications. Their current state-of-the-art processing allow full densification and fine-grained microstructures, but the shaping capability remains a challenge. Especially since new designs require impregnation and infiltration of preforms, coatings, functionally graded porous and lightweight structures, joining, or intricate geometries. Near-Net-Shaping Colloidal Routes can help with those, while reducing amount of material needed, need for machining, overall temperature and need for pressure for densification (due to higher particle packing in green), translating into more cost-effective manufacturing approaches. This work will discuss, using zirconium diboride (ZrB2) as case study, particle packing in the green bodies (by the control of the interparticle forces in suspension), sintering profiles and incorporation of sintering aids for this route in comparison with hot-pressing. This route is further explored with other techniques (freeze casting and gelcasting), other materials (boron carbide (B4C) and titanium diboride (TiB2)), and multi-scale highly porous UHTCs. The promising results open new avenues for next generation of advanced and additive manufacturing technologies.


CF-1:L09  Target Materials for the Production of Radioisotopes at the SPES Facility
S. CORRADETTI, A. ANDRIGHETTO, M. BALLAN, F. BORGNA, M. MANZOLARO, INFN - Laboratori Nazionali di Legnaro, Legnaro, Italy; S. CARTURAN, Università di Padova, Dipartimento di Fisica e Astronomia, Padova, Italy; L. BIASETTO, Università di Padova, Dipartimento di Tecnica e Gestione dei Sistemi Industriali, Vicenza, Italy; G. FRANCHIN, P. COLOMBO, Università di Padova, Dipartimento di Ingegneria Industriale, Padova, Italy

The SPES project has the aim to develop an ISOL (Isotope Separation On-Line) facility at INFN-LNL (Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali di Legnaro) for the production of neutron-rich Radioactive Ion Beams (RIBs). The 70 MeV cyclotron, which will be used as the primary proton beam driver, has been installed and it is undergoing commissioning tests (alpha phase of SPES). The development of targets capable of producing and releasing radioactive isotopes is of extreme importance for the next two phases of the project: production of RIBs for nuclear physics (beta phase) and use of the facility for the production of medically relevant nuclides (gamma phase, in particular the ISOLPHARM project). In both cases, the design of a proper target is strictly related to the obtainment of porous refractory materials, which are capable to work under extreme conditions (temperatures up to 2000 °C in high vacuum) with a high release efficiency. Examples of developed materials are uranium carbide, lanthanum carbide, titanium carbide and zirconium germanide. Synthesis and characterization of a set of materials developed in this framework are presented.


CF-1:L11  Additive Manufacturing of Hard Transparent Ceramics
A.E.M. BROWAR, G. GUSS, J.D. KUNTZ, M.J. MATTHEWS, N. SHEN, R.M. PANAS, C.M. SPADACCINI, Lawrence Livermore National Laboratory, Livermore, CA, USA; J.D. ELLIS, University of Rochester, Rochester, NY, USA

Transparent ceramics can be used in multiple extreme environment applications such as laser windows and scratch-resistant optical elements. Due to conventional manufacturing difficulties, use of transparent ceramics is generally limited to high cost applications and mold-dependent shapes. Increased interest in Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) has produced advanced manufacturing techniques for metals and, more recently, ceramics. These techniques have allowed for denser green parts, unconventional designs utilizing complex geometries, and reduced cost for prototypes and manufacturing. However, research in this area has been limited due to a lack of suitable manufacturing parameters as well as non-ideal material properties. We propose using SLM for advanced manufacturing of transparent ceramics e.g. Aluminum Oxynitride (AlON). To our knowledge, this is the first comprehensive study of additively manufacturing hard transparent ceramics via direct SLS and SLM without a precursor. Through research into parameter optimization, we will be able to push the boundaries of both additive manufacturing and ceramics.
Prepared by LLNL under Contract DEAC52-07NA27344. LLNL-ABS-739969


Session CF-2 - Corrosion, Oxidation, and Testing

CF-2:IL02  Development of Environmental Barrier Coatings for Non-oxide Ceramic Matrix Composites
H. KLEMM, W. KUNZ, B. GRONDE, K. SCHÖNFELD, FhG IKTS Dresden, Dresden, Germany

In spite of the ambitious efforts to increase the portion of alternative and renewable resources, the energy production based on fossil fuels will still represent the main part of energy in the next years. Caused by the increasing energy price and the stronger requirements in environmental protection the main focus of future generations of gas turbines will be emphasized on an increased efficiency with a simultaneous reduction of the emissions. From technical point of view these goals can be obtained only by higher hot gas temperatures. Ceramic matrix composites (CMC) offer a high potential for applications as structural parts in advanced gas turbines. During recent years, significant progress in material development of oxide and non-oxide CMC has been achieved, however, there are still considerable deficits especially in the long-term behavior of the materials in hot gas conditions. The present study is focused on the environmental stability of the materials. Both oxidation and corrosion processes at the surface and inside the materials were observed resulting in significant material degradation. Hence, environmental barrier coatings (EBC) have been presented to be the solution to protect the surface of the ceramic materials. Systematic studies on oxidation and hot gas corrosion of non-oxide CMC have been performed with and without EBC. Based on a detailed understanding of the processes in the whole system, EBC and the ceramic base material during application in hot gas environments at elevated temperatures, general concepts for the development of environmental barrier coatings will be discussed.


CF-2:IL03  Creep of HfB2-based UHTCs up to 2000 °C: A Critical Assessment on Structural Stability for Hypersonic Applications
E. ZAPATA-SOLVAS¹, D. GÓMEZ-GARCIA², A. DOMÍNGUEZ-RODRÍGUEZ², W.E. LEE¹, ¹Centre for Nuclear Engineering (CNE), Dept. Materials, Imperial College London, UK; ²Dept. Condensed Matter Physics, University of Seville, Seville, Spain

Ultra-high temperature ceramics (UHTCs) are promising candidates for hypersonic applications as a consequence of their high melting points, in excess of 3000 ºC for ZrB2 and HfB2 UHTCs. The UHTCs community has traditionally focused on development of more oxidation-resistant UHTC composites as a consequence of poor oxidation resistance of monolithic UHTCs, which has led to the choice of SiC-reinforced MeB2 (where Me is Zr or Hf) as the baseline material for extreme environments. An overview of current understanding of high temperature creep of MeB2–based UHTCs will be described, discussing the following subjects; • Poor creep resistance of SiC-reinforced HfB2 and their structural instabilities. • Plastic behavior of HfB2 which deforms like an hcp-metal. • Plastic behavior of HfB2/2 wt.% La2O3 or how to maintain the creep resistance while improving the oxidation resistance. • New approaches to increase the creep resistance of HfB2


CF-2:IL04  Relation between Microstructure and Protection Efficiency of a Rare Earth Silicate-based Environmental Barrier Coating
F. REBILLAT¹, S. ARNAL¹, F. MAUVY², ¹Laboratoire des Composites Thermostructuraux, Pessac, France; ²Institut de Chimie de la Matière Condensée de Bordeaux, Pessac, France

Future generations of parts of turbines will be replaced by Ceramic Matrix Composites (CMCs). Generally these CMCs consist of ceramic matrices reinforced with fibers, both in silicon carbide. However, at elevated temperatures and under severe atmospheres, the silica protective scale over SiC volatilizes as hydroxides species and the resulting recession of SiC may cause the loss of the composite’s mechanical properties. To protect CMCs, EBCs are put in place. The most stable EBCs are often made of rare-earth silicates. This investigation is focused on yttrium silicates. To deposit EBCs, each process generates a different microstructure. These differences in microstructure will significantly impact on the diffusion limitation inside the coating as well as on its surface reactivity in various dry or wet environments. The challenge of this investigation is to measure the ionic conductivity of yttrium mono- and di-silicates by complex impedance spectroscopy, and to compare these values to O2- and/or OH- diffusion coefficients evaluated from oxidation/corrosion tests on original model samples. The surface reactivity is also evaluated in function of microstructures and compositions in terms of recession rates and CMAS degradations. Thus, concepts of optimized layered EBCs are proposed.


CF-2:IL05  Cyclic Oxidation of Ti3Al-based Materials
I. CVIJOVIC-ALAGIC, M.T. JOVANOVIC, D. ZAGORAC, B. MATOVIC, Institute of Nuclear Sciences “Vinča”, University of Belgrade, Belgrade, Serbia; Z. CVIJOVIC, Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia

The Ti3Al-based alloys are promising structural materials for high-temperature applications due to their better mechanical performance at elevated temperatures than conventional Ti alloys. However, a serious limitation of their industrial use can be attributed to their relatively poor oxidation resistance during exploitation in air at high temperatures. Considerable improvement of their high-temperature oxidation resistance can be achieved by diverse treatments, such as thermomechanical processing, additional alloying and protective coating deposition. Nevertheless, all of the mentioned procedures could be reflected in microstructural and mechanical properties variation. In the present study, cyclic oxidation behavior of the intermetallic alloy with the composition Ti-24Al-11Nb (at.%) in air at elevated temperature was studied. The cyclic annealing was performed for uncoated, as well as for hot-rolled sheets coated with a Ni-20Cr (at.%) layer. The oxidation products and alloy microstructure characteristics were modeled and analyzed. It was found that apart from the (α2+β) phases, the α2˝ and O phase appeared. The coating deposition affects the externally formed scale composition, causing the difference in the size and fraction of the phases present in the annealed microstructure.


CF-2:IL07  Corrosion Behavior of Slurry Coated RE Monosilicate EBCs on SiC/SiC
N. AL NASIRI, Imperial College London, London, UK

The need to increase the cycle efficiency and reduce noise and NOx emissions from engines has promoted the development of ceramic matrix composites (CMC) such as silicon carbide fiber reinforced (SiC-SiC). Use of CMCs will lead to a significant improvement in fuel consumption and weight savings of up to 30% compared to Ni-based super alloys. Si-based ceramics have excellent oxidation resistance due to formation of a protective silica layer in dry air. However, the same silica layer will react with water vapor to form gaseous silicon hydroxide, leading to high recession and component failure. To avoid this behavior, a prophylactic environmental barrier coating (EBC) is required. A variety of EBCs have been developed in the past consisting of a minimum of 4 layers requiring a costly application method such as plasma spraying. The main aim of this work is to develop a reliable single layer of EBC, develop a low cost applying method and studying the corrosion behavior. I have selected two rare earth monosilicates as promising EBCs: Yb2SiO5 and Lu2SiO5. I will discuss my patented coating application method and their performance in 90% steam at 1350˚C for 25-100 hours to determine which EBC candidate is most promising for protecting SiC-SiC CMCs in the jet engine environment.


CF-2:IL09  High-temperature Stability of (Ti,Nb)-Al-C MAX Phases Composites in Oxidizing and Hydrogen Atmosphere
T. PRIKHNA, Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kiev, Ukraine

Hot pressure synthesized 211 and 312 MAX-phases-based materials of Ti,Nb – Al – C system are stable in hydrogen and oxidizing environments at high temperatures; they are more stable than Cr-containing steels (at 600 °C for 1000 h) and are about twice lighter. The Ti2AlC – based material was most resistant because some oxygen was present in its structure as Auger and SEM study showed. The high-temperature X-ray investigations showed that 211 and 312 phases were present in the materials after heating in air till 1200-1400 °C. The addition of Nb increases the 312-MAX phase-based material stability in oxide environment and leads to the formation of about 10 times thinner Nb-containing oxidized layer. All the studied MAX phases-based materials were stable in hydrogen and for Ti3AlC2-, and (Ti,Nb)3AlC2-based even the increase of bending strength after treatment at 600 °C in hydrogen for 40 h has been observed. The complex of characteristics of the developed materials make them promising for application in the extreme environments.


CF-2:IL10  Laser Melting of Ultra-high Temperature Ceramics
D. MANARA, K. BOBORIDIS, D. ROBBA, M. COLOGNA, R. KONINGS, European Commission, JRC Karlsruhe, Germany

A thorough assessment of ultra-refractory materials behaviour under extreme conditions (of temperature, pressure and chemical environment) is paramount in sensitive fields like the choice of coatings for aerospace applications and the safety of nuclear plants, particularly under hypothetical accidental conditions. Recent studies are presented on different types of refractory and nuclear materials under extreme conditions. In particular, the European Commission‘s Joint Research Centre of Karlsruhe (Germany) employs a laser-heating method to measure very high temperature (1500 K < T < 5000 K) properties based on quasi-containerless conditions under a controlled atmosphere with variable durations of the heating cycles (milliseconds to seconds). Example results are shown on the melting and vaporisation behaviour of pure and mixed ultra-refractory carbides (HfC, TaC, ZrC) and oxides (CaO, CeO2, ZrO2, ThO2, UO2 etc.) and on laboratory simulations of severe accidents in nuclear power plants. Materials characterisation campaigns and thermodynamic calculations supporting the interpretation of data obtained under extreme conditions are also shown and discussed.


CF-2:L11  UHTC Thermal Sprayed Coatings behavior under Plasma Wind Tunnel Tests
M. DE STEFANO FUMO, R. GARDI, CIRA, Capua, Italy; M. TULUI, F. ARCOBELLO VARLESE, S. LIONETTI, M. FORTUNATO, CSM, Rome, Italy

Systems for trans-atmospheric flight require sharp leading edges for wings, fins and intakes, asking for the development of materials and structures able to operate under extreme conditions. Metallic refractory alloys and CMC have good thermo-mechanical properties but poor oxidation resistance. Ultra-high temperature ceramics (UHTCs) have been identified as potential candidates for operating in harsh conditions. However, their poor fracture toughness and thermal shock resistance strongly limit their applicability. Combining metallic or CMC substrates with UHTC coating can couple the oxidation resistance of UHTC to the thermo-mechanical properties of substrates. Different substrate/coating systems were investigated; in particular, both metallic and CMC substrates were considered. A commercial alloy labeled WL10 was selected as a metallic substrate, whilst C/SiC was used as a CMC substrate. The ZrB2-SiC coatings were deposited by Plasma Spray under inert atmosphere. Different geometries simulating critical parts of hypersonic vehicles (e.g., sharp wing leading edges) were realized and tested in the 2 MW GHIBLI plasma wind tunnel facility available at CIRA. After the PWT tests, the specimens were observed by SEM to assess the modification induced by the high thermal flux exposure.


CF-2:L12  Oxidation Behavior of HfB2-SiC and ZrB2-SiC Ultra-high Temperature Ceramics in Different Air Atmospheres
C. PIRIOU, O. RAPAUD, S. FOUCAUD, SPCTS-CNRS UMR 7315, Limoges, France; L. CHARPENTIER, M. BALAT-PICHELIN, PROMES-CNRS UPR 8521, Font-Romeu Odeillo, France

Ultra-High Temperature Ceramics, in particular diborides of the IVb group, are promising materials for extreme environments, more specifically for thermal protection systems of hypersonic vehicles during their atmospheric reentry at temperatures higher than 1800 °C. The main objective of this work is to study the oxidation behavior in air of (Hf or Zr)B2-SiC composites under severe conditions. The first stage consists in elaborating fully-dense (Hf or Zr)B2-SiC ceramics, from 0 to 30 vol.% SiC, with similar and controlled microstructures using Spark Plasma Sintering to obtain materials with fine grains, high relative density (> 99 %) at lower temperatures and shorter dwell times. An optimization of sintering parameters has been carried out for every composition. The second step consists in understanding the oxidation mechanisms of both composites. To this end, these materials have been oxidized at several temperatures using concentrated solar energy, including the oxidation in atomic oxygen. The mechanisms have been highlighted through the study of the oxidized layers by combining XRD, SEM and Raman spectroscopy with imaging and by the monitoring of oxidation kinetics. This work was helped by a first thermodynamic approach of both systems through the modeling of ternary diagrams.


CF-2:L13  Oxidation Performance of BN-coated SiC Sylramic Fibers under Relevant Conditions for High-temperature Applications
V. ANGELICI AVINCOLA, E.J. OPILA, University of Virginia, Charlottesville, VA, USA

Ceramic matrix composites (CMCs) were introduced into aircraft engines as high-pressure turbine shroud in 2016, and are currently considered for the high-temperature section of gas turbines due to their light weight and resistance to higher temperature compared to the currently used superalloys. A BN interphase between SiC fibers and matrix is used to increase toughness, allowing fiber pull-out and graceful failure. When matrix cracking occurs, oxidant species can enter in contact with the BN interface and the SiC fibers, forming a borosilicate glass. The presence of a borosilicate glass increases the SiC fiber degradation. In this work the influence of a Si-doped BN layer of around 1 um thickness on the oxidation of 1 ply of Sylramic fibers was studied. Results obtained under dry and wet conditions, at temperatures between 800 and 1200 °C, were compared in order to isolate the role of H2O, which is formed in combustion environments. Oxidation kinetics and microstructures were investigated by means of thermogravimetric devices, scanning electron microscopy, and inductively coupled plasma optical emission spectroscopy. Considerations on the use of SiC/BN fibers under these conditions and the influence of BN are discussed.


CF-2:L14  Anti-oxidation Performance of a Cf/UHTC Composite with a BN Interface
P. MAKURUNJE, I. SIGALAS, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa and DST-NRF Centre of Excellence in Strong Materials, South Africa

This study presents an ultra-high temperature useful Cf/C composite with a BN fibre to matrix interface prepared by the liquid urea-boron infiltration and nitridation route. Cf/C composite skeletons were upgraded for anti-oxidation by introducing a (Hf,Ti)C-SiC matrix through reactive melt processing. The resultant Cf/UHTC composites were exposed to an oxyacetylene flame around 3000°C, and the oxidation products in the scale studied by X-Ray diffraction. The microstructures were examined by scanning electron microscopy and transmission electron microscopy. The performance of the Cf/UHTC composite with the BN interface was compared to the composite without the interface The BN interface is capable of improving the anti-oxidation and structural integrity of Cf/C composites.


Session CF-3 - Mechanical and Thermal Properties

CF-3:IL01  Modeling of Damage Evolution and Life Prediction in Fiber-reinforced Ceramic Matrix Composites under Tensile and Cyclic Loading at Elevated Temperatures in Oxidative Environments
LONGBIAO LI, Nanjing University of Aeronautics and Astronautics, Nanjing, P.R. China

The damage evolution and lifetime prediction of fiber-reinforced ceramic matrix composites (CMCs) subjected to tensile and cyclic fatigue, dwell-fatigue and thermal fatigue have been investigated using the micromechanical approach. The multiple damage mechanisms of matrix multicracking, fiber/matrix interface debonding, interface wear and interface oxidation under tensile and mechanical and thermal fatigue loading have been considered. The relationships between the damage developement, micromechanical damage parameters and fatigue lifetime have been established. The experimental tensile stress-strain curves, fatigue hysteresis loops, fatigue hysteresis-based damage development and fatigue lifetime curves have been predicted for different loading conditions.


CF-3:IL02  Deformation Mechanisms in Transitional Metal Carbides
G.B. THOMPSON, C. SMITH, M. ROSS, XIAO-XIANG YU, N. DELEON, University of Alabama, Tuscaloosa, AL, USA; C.R. WEINBERGER, Colorado State University, Fort Collins, CO, USA

Depending on temperature and phase type, transition metal carbides exhibit an array of thermo-mechanical responses. This talk will address how stacking fault energy governs those responses for TaC and HfC. Room temperature indentation revealed <110>{111} slip in TaC and <110>{110} in HfC, though each phase is rocksalt with similar melting temperatures (bonding beahvior). Using DFT calculations, this slip difference has been linked to an intrinsic stacking fault (ISF) on the {111} planes in TaC that is absent in HfC. Upon adding Ta to HfC, the transition from {110} to {111} slip was noted with the stabilization of the ISF. Interestingly, the increase in available slip is insufficient to increase the plasticity response demonstrating the importance of lattice friction. Using a novel non-contact means of thermos-mechanical testing via a Lorentz force, the deformation deflection and associated mechanisms up to 2900 deg. C has been characterized in the carbides. Upon increasing temperature, TaC exhibited a propensity of {110} slip identification while still exhibiting classical plastic behavior with temperature. In contrast, HfC showed non-uniform plastic flow. At that highest temperature, both carbides revealed the onset of abnormal grain growth during the mechanical testing.


CF-3:L03  Finite Element Constitutive Modeling of High-temperature Ceramics
J.Y.R. RASHID, ANATECH-SI, San Diego, CA, USA

A class of high-temperature ceramics, namely, uranium oxide nuclear fuel pellets, are subjected to large thermal gradients, greater than 2000°C/cm, under normal operations. Such high gradient creates, within less than half a centimeter distance, a state of high compressive plasticity at the centerline and tensile fracture at the outer surface of the pellet. Accurate description of the constitutive behavior of the material under the time-dependent stress-strain state created by large thermal gradient is critical to high fidelity predictive analysis using finite element simulation. In developing a constitutive model for such material behavior, two major elements make the ceramic material different from metals, and more difficult to deal with, which are: porosity induced non-volume-preserving hydrostatic compression and tensile fracture and fragmentation as a normal mode of operation. This paper describes a constitutive model for such material. The model’s formulation differs from metals by allowing for porosity accommodating volume change under hydrostatic plasticity. In the tensile regime, the model employs a multi-axial smeared cracking formulation. The model is applicable to finite element simulations of ceramic materials in general subjected to severe thermal environments.


CF-3:IL04  Making Porous UHTC’s for Transpiration Cooling of Components
L.J. VANDEPERRE, D. GLYMOND, L. LARRIMBE, W.E. LEE, Centre for Advanced Structural Ceramics & Department of Materials, Imperial College London, South Kensington Campus, London, UK

The basis of transpiration cooling is the introduction of a cool layer of gas between the component and the hot freestream flow in order to reduce the heat flux to the material. This work addresses the manufacturing of innovative porous Ultra High Temperature Ceramics (UHTCs) to be used as porous walls in these systems. ZrB2 samples with different porosities that can deliver a fluid to the surface were manufactured with a range of techniques : by partial sintering, by addition of fugitive inclusions, using starch as a pore former, by uni-axial pressing with a tool introducing cylindrical pores and gelcasting. Furthermore, systematic experiments were carried out in order to measure the relationship between pore structure, porosity and some properties such as permeability of the cooling gas, strength and conductivity. All this information enabled to select the most relevant candidate for the application that can maintain excellent thermal and structural properties while moving to a high porosity.


CF-3:IL05  Defect Engineering in Development of Low Thermal Conductivity Materials
WEI PAN, MENG ZHAO, XIAORUI REN, JUN YANG, CHUNLEI WAN, ZHIXUE QU, JING FENG, State Key Lab of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing, China  

Increasing thermal efficiency and lower emissions require gas turbine designers to further increase the combustion temperature that leads to the high temperature components such as combustion chambers, blade and vanes surfaces face more rigorous conditions. Therefore, there is urgent demand to develop new ceramic coatings with even lower thermal conductivity, higher stability and durability than currently used thermal barrier coatings coating on the surface of high temperature alloy components. Defect engineering has attracted much attention in seeking low thermal conductivity materials since lattice defects play a crucial role in phonon scattering and thermal conductivity reduction. Oxygen vacancies and substitutions are proven to be the most effective, while the accompanying lattice distortion is also of great importance. In this talk, recent advances of reducing the thermal conductivity of potential materials for thermal barrier coating by defect engineering are comprehensively reviewed. Effects of the mass and size mismatch between the defects and the host lattice are quantitatively estimated and unconventional thermal conductivity reduction caused by the lattice distortions is also introduced. Finally, challenges and potential opportunities are briefly assessed.


CF-3:L06  On the Non-linear Young’s Modulus Behavior of Carbon-bonded Materials at High Temperatures
B. LUCHINI, J. GRABENHORST, J. FRUHSTORFER, C.G. ANEZIRIS, IKGB, TU-Bergakedemie Freiberg, Freiberg, Sachsen, Germany; V.C. PANDOLFELLI, GEMM, UFSCar, São Carlos, SP, Brazil

The origin of the non-linear behavior of the Young’s modulus of carbon-bonded alumina (Al2O3-C) at high temperatures was studied. The research was based on the microstructural changes during thermal processing and the thermo-mechanical behavior. Impulse excitation technique, thermogravimetric analysis, porosity test and scanning electron microscopy were carried out. The results pointed out that the decreasing Young’s modulus behavior of a cured sample in a temperature range from room temperature up to 500°C was governed by the release of volatiles. Above this temperature (500°C - 1000°C), the thermal expansion mismatch among alumina, graphite and the carbon matrix ruled the behavior, leading to an increase of the effective Young’s modulus. During cooling, crack networks as well as gaps among alumina and the carbon matrix were developed. The former were related to volatile release and the graphite’s highly anisotropic thermal expansion. The latter originated by the thermal expansion mismatch between alumina and the carbon matrix. During re-heating, the closure of the gaps and cracks ruled the expansion behavior and a non-linear increase of the effective Young’s modulus as function of temperature was found out.


CF-3:L07  Effect of Microstructural Features of SPSed Boron Carbide Ceramics on their Mechanical Properties
L. ROUMIGUIER, A. JANKOWIAK, DEN-Service de Recherches Metallurgiques Appliquees, CEA, Universite Paris-Saclay, Gif-sur-Yvette, France; N. PRADEILLES, G. ANTOU, A. MAITRE, Science of Ceramic Processing and Surface Treatments Lab.- SPCTS, UMR CNRS 7315, Limoges, France

Within the French project ASTRID, aiming at the development of an Advanced Sodium Technological Reactor for Industrial Demonstration, boron carbide (B4C) phase has been retained as neutron absorber for control rods. In working conditions, this material would undergo high temperatures and a thermal gradient up to 1000 °C.cm-1. In order to improve thermo-mechanical properties, a better control of the microstructure is needed. This objective involves the choice of finer raw powders (from sub-micro to nano particle sizes) and the use of Spark Plasma Sintering method to promote densification kinetic. Firstly, the sintering behavior of two powders and the mechanical properties of fully-dense SPSed specimens are discussed, at the grain scale (by nano-indentation) and at the macroscopic scale (by ultrasonic measurements and Knoop micro-indentation). Secondly, the effect of the sample height on its microstructure and mechanical properties is studied and compared to thermo-physical numerical simulations performed using COMSOL Multiphysics software.


CF-3:L08  Aluminum-dodecaboride- and Boroncarbide-based Lightweight Ceramics
T.A. PRIKHNA¹, P.P. BARVITSKIY¹, V.B. MURATOV², S.N. DUB¹, V. DOMNICH³, M.V. KARPETS¹, R. HABER³, ¹Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kiev, Ukraine; ²Institute for Problems in Material Science, NAS Ukraine, Kiev, Ukraine; ³Department of Materials Science and Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ, USA

The results of the complex study of AlB12–based ceramics sintered from submicron a-AlB12 powder at varying pressures and temperatures will be discussed. The effect of C and TiC additions on the structure and mechanical properties of the resultant products is also investigated. The results were compared with the characteristics of B4C and B4C-SiC ceramics prepared by the authors (for B4C hardness HV(49 N)=26.6 GPa, fracture toughness K1c(49 N)=3.3 MPa•m0.5, bending strength Rbs =392 MPa and compressive strength Rcs =1551 MPa, density p=2.52 g/cm3, and for B4C-20%SiC HV(49 N)=29.6–23.0 GPa, K1c=4.2-5.9 MPa, Rbs=474 MPa, Rcs=943 MPa, p=2.56 g/cm3). Usually for the materials at 1000-1200oC some increase of Rbs were observed due to the plasticity increase. Materials sintered from a-AlB12 powder at 30 MPa, 2080-1950oC were contained 94-98% of a-AlB12 (p=2.53-2.58 g/cm3) and have the following mechanical properties: HV(49 N)=24.1 GPa, K1c(49 N)=4.9 MPa•m0.5, Rbs=336 MPa, Rcs=378 MPa. The material sintered at 30 MPa, 1950 °C from a-AlB12-17% C contained 86% AlB12C2 had p=2.67 g/cm3, K1c(49 N) = 5.9 MPa•m0,5 and Rcs=423 MPa and that from a-AlB12-20% TiC contained 74% AlB12C2, 22% TiB2, 4% Al2O3 and its HV(49N)=28.9 GPa, K1c(49 N)=5.2 MPa•m0.5, Rbs=633 MPa, Rcs=640 MPa, p=3.2 g/cm3.


CF-3:L09  Thermo-mechanical Behaviour of Carbon-carbon Composite
T. VOIRIN, P. REYNAUD, G. FANTOZZI, University of Lyon, INSA Lyon, MATEIS, Villeurbanne, France

Carbon-carbon composites are very interesting materials, considering their low weight, good mechanical properties and stability at high temperature.
The main objective of this work is to improve the understanding of the carbon-carbon composite materials, used under original loading modes (under compressive stress, inter-laminar shear stress, flexural stress etc.) and their evolution with the increase of temperature. In this paper, the compressive behaviour in Z direction and the inter-plies shear behaviour at room temperature and high temperature are studied, in order to point out the effects of plies crunching and delamination on the composite mechanical behavior. Damaged materials are also observed post-mortem using optical microscopy and Scanning Electron Microscopy in order to understand the mechanisms that are induced under these loadings. In-situ compressive tests have been also performed under an X-ray tomograph to better show up and analyze these mechanisms.


CF-3:L11  On the Thermal Properties of Celsian Ba/SrAl2Si2O8 Ceramics: Theoretical and Experimental Study
LUCHAO SUN, J.Y. WANG, Shenyang National Laboratory for Materials Science; Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China

BaAl2Si2O8 and SrAl2Si2O8 are materials of great technological interests due to their high melting temperature, low thermal expansion coefficient, low dielectric constant, and chemical inertness. Thus, they are used as matrix of fiber-reinforced ceramic composites, protective coatings, electro-ceramics and refractories for a long time. In the present work, an in-depth research on the thermal properties such as thermal conductivity and thermal expansion coefficients of celsian BAS and SAS was carried out utilizing both theoretical and experimental methods. Temperature dependent lattice thermal conductivities of BAS and SAS were predicted by the combination of first-principles calculation method and lattice dynamics theory. Then, we further fabricated phase-pure and dense BAS and SAS samples via multi-step processing method and measured their lattice thermal conductivity and thermal expansion coefficients. The experimental results agreed well with our theoretical predictions. Furthermore, comparative analyses of structural stability, bonding characteristics, group velocities, and mode Grüneisen parameters were done to recognize the predominant factors affecting their thermal behavior. The results provided the solid supports to tailor optimal thermal properties of BAS and SAS.


CF-3:L12  XFEM Investigations of Double Torsion Fracture Test
K.P. MARIMUTHU, K. LEE, H. LEE, Sogang University, Seoul, South Korea

The double torsion (DT) fracture test is a powerful, versatile and relatively simple technique for fracture mechanics characterization (i.e. fracture toughness and subcritical crack growth) of ceramic materials at room and elevated temperatures. However, the DT testing technique is not yet standardized (test procedure and specimen geometry) and therefore the results from this method should be interpreted with appropriate assumptions and clarifications. In this present work, extended finite element method (XFEM) is extensively used to investigate the DT fracture test for the application of fracture toughness evaluation and an attempt is made to tackle some unresolved questions such as crack length independent stress intensity factor, specimen dimensions and corresponding correction factors. The crack propagation in DT test is numerically simulated for a wide range of material properties and specimen dimensions. Based on the XFE results, new correction factors are proposed to improve the previous analytical methods for fracture toughness evaluations. Finally, XFE results are compared with experimental data obtained from sodalime glass, silicon carbide and alumina specimens. Suggestions are provided to standardize the DT testing technique for fracture toughness evaluation.


CF-3:IL14  Boride Ceramics with High Strength at Ultra-high Temperatures
L. SILVESTRONI¹, D. SCITI¹, J. WATTS², W. FAHRENHOLTZ², G. HILMAS², ¹CNR-ISTEC, Faenza, Italy; ²Dept. of Materials Science and Engineering, Missouri University of Science and Technology, Rolla, MO, USA  

Boride-based ceramics have strengths of 500-600 MPa up to 1500°C when doped with suitable secondary phases and densified using the proper sintering technique. However, in order for these materials to be employed in the ultra-high temperature regime, exploration of their performance at higher temperatures is necessary. Here, we present the strength behavior at temperatures up to 2100°C and show the effects of microstructure tailoring in terms of secondary phases, grain morphology and grain size. Strengths exceeding 1 GPa have been achieved at 1800°C and analysis showed this behavior was due to sub-grain refinement which occurred as a consequence of intragranular plasticity under load.


CF-3:L15  Grahene-reinforced Alumina and Zirconia Composites: On their Potential Applications
R. CANO-CRESPO, B.M. MOSHTAGHIOUN, D. GOMEZ-GARCIA, R. MORENO, A. DOMINGUEZ RODRIGUEZ, Department of Condensed Matter Physics, University of Seville, Spain Institute of Ceramics and Glass, CSIC, Spain

Graphene-reinforced alumina composites and grahene-reinforced zirconia composites have been sintered by spark plasma sintering up to full density and homogeneous distribution of graphene layers. The composites have been tested at room temperature as well as high-temperatures to go insight into their mechanical properties and plasticity. The results show a moderate improvement on the mechanical properties, which are compared to those of pure monolithic ceramics and nanotube-reinforced ones. Analysis on the advantage of graphene as a reinforced phase is carefully discussed.


Session CF-4 - Characterization and Analysis

CF-4:IL01  Nano-mechanical Testing of ZrB2 Ceramics
J. DUSZA, Institute of Materials Research, SAS, Kosice, Slovakia

The deformation and damage characteristics of differently oriented ZrB2 grains/crystals in ZrB2 polycrystal were investigated. Depth-sensing nano-indentation and scratch tests of grains and micro-compression tests of micropillars prepared by focused ion beam from oriented facets of grains were studied. Electron backscatter diffraction (EBSD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) investigations were performed to determine the grain orientation and to study the surface morphology and the resulting deformation and damage mechanisms around the indents and in micropillars. The hardness and scratch resistance of the differently orientated grains showed significant angle dependence from the basal towards the prismatic directions. A strong influence of the grains orientation on compressive yield stress and rupture stress values was found during the micropillar test, too. The active slip systems have been recognized. The different properties of the basal and prismatic planes was found to be connected with the different deformation mechanisms – slip and dislocation activities.


CF-4:L02  Characterization of the Microstructure of 3C-SiC Coatings Grown by Chemical Vapor Infiltration (CVI)
I. BERDOYES^{1, 2}, Y. LE PETITCORPS², H. PLAISANTIN^{1, 2}, J. ROGER², ¹Safran CERAMICS; ²University of Bordeaux, LCTS, UMR 5801, Pessac, France

SiC-SiC composites are interesting materials for Aeronautic applications, especially jet engines, since they offer lightness, stiffness, refractoriness and oxidation resistance properties. A process for elaborating SiC-SiC composites is the infiltration of liquid silicon in a fibrous SiC preform, previously filled with SiC powders. Besides the filling of the remaining pores of the powder-densified preform, the liquid silicon may react with the fiber SiC coating grown by CVI. Understanding the mechanism of the corrosion by liquid silicon requires beforehand a precise characterization of the SiC coatings. The microstructures of the SiC coatings have been characterized from the atomic scale up to the morphologic scale. Coherent domains and polytypism are discussed on the basis of X-ray Diffraction (XRD), Raman spectroscopy and High-Resolution Transmission Microscopy (HRTEM/TEM) results. Preferential orientations as well as orientation maps are assessed by Electron Back-Scattered Diffraction (EBSD) and XRD. EBSD and TEM are used to study the morphology of the crystallites and their disorientations within the coatings. The characterization of five coatings provides enough elements to determine criteria for a rational classification of the microstructure of a CVI-grown SiC coating.


CF-4:L03  Pitfalls of Determining the Elastic Properties of Stabilized Zirconia with Indentation Methods
K. WERBACH¹, S. HUMMEL¹, C. EBNER¹, U. LOHBAUER², H. PETERLIK¹, ¹University of Vienna, Vienna, Austria; ²University Erlangen-Nürnberg, Erlangen, Germany

The properties of stabilized zirconia, as one of today’s standard materials for many purposes, have been investigated with various methods in the past. Especially when used for thin films, e.g.in thermal barrier coatings, measurement of its elastic properties with indentation methods may be used as a check for the quality of the coating. The work presented here aims at giving a deeper understanding of the influence the methods -in particular the resulting extremely high pressure- has on the material itself; this will be demonstrated by investigating the results of indentation tests on various members of the stabilized-zirconia family with different proneness to transformation toughening in comparison to non-invasive methods. Furthermore, spectroscopy methods -chiefly Raman spectroscopy- will by employed to qualitatively and quantitatively characterize the structural changes in the specimens.


CF-4:IL04  Nanometer-scale Computer Simulation of Structure and Mechanical Properties of UHT Ceramics
D. BRENNER, S. DAIGLE, M. LIM, M. DELOWER HOSSAIN, J.-P. MARIA, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, USA; C. TOHER, P. SARKER, S. CURTAROLO, Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC, USA

The number of materials that can be used for ultra-high temperature (UHT) applications is limited, even when just considering melting point. When considering other performance factors the list of viable materials becomes even smaller. With this in mind, we have been working within a Multi-University Research Initiative (MURI) to develop a new material class, high entropy ceramics, to expand the palette of possible UHT candidates. These materials are unique within the broader classification of high entropy alloys in that they have an ordered crystal sublattice together with a second crystal sublattice containing four or more elements in roughly equi-molar concentrations. The entropic carbides, nitrides and oxides, for example, are in a rock salt structure containing an fcc sublattice of C, N or O atoms, respectively, with a second fcc sublattice containing a random population of cations. After a brief introduction to our MURI team, this talk will focus on first principles and molecular modeling studies we are using to characterize the atomic and electronic structure of these materials, their point defect energies, and their thermal transport properties.
This work is supported by the U.S. Office of Naval Research.


CF-4:IL05  Non-destructive Methods for Ceramic Materials - Characterization of SiC and SiC composite materials by HF Eddy Current Techniques
S. HILLMANN, M. SCHULZE, H. HEUER, Fraunhofer IKTS Dresden, Germany

High and Ultra High Temperature Ceramics and Composites for extreme environments require a nondestructive inspection (NDI) in case they are used in safety relevant structures e.g. aero engines or power plants. Methods of nondestructive inspection provides an opportunity to detect defects in materials and material properties inside the component and on the components surface without preparation of the samples. For metals, polymers and a variety of carbon composite materials extensive expertise on the application of NDI method and the material fatigue behavior already exists. Due to individual properties of ceramic composite materials, industrial proved NDI methods cannot be applied to ceramic composites without (larger) adaption. This paper presents various established and new developed methods of nondestructive inspection of Ceramic fiber composites and exemplifies their potential and the current state of development for the application. These include acoustic methods such as ultrasonics and electromagnetic methods such high-frequency eddy current Technique.


CF-4:L07  The Characterization of Highly Porous Reaction-bonded Silicon Nitride Ceramics in the Presence of Oxide Additives
R. NIKONAM M., M.D. PUGH, R.A.L. DREW, Concordia University, Department of Mechanical, Industrial and Aerospace Engineering, Montreal, Quebec, Canada

Porous silicon nitride (Si₃N₄) ceramics can be used at elevated temperatures as a medium to reduce diesel particulate matter, which is a part of a complex mixture of diesel exhaust that impacts human health. With direct nitridation of porous Si structure under pure nitrogen atmosphere, Si₃N₄ with high porosity has been obtained. However, in addition to the silicon nitride grains, silicon oxinitride and silica might form when oxide additives increased oxygen in the system. Based on the dominant reactions, the morphology and crystalline microstructure of the products will be different which could affect the foam properties. Using XRD and SEM-EDX analysis, this research tries to investigare and differentiate the various products in terms of the phases present and their morphology. While silicon nitride formed with a structure which was a mixture of fine matte, hexagonal grains and whiskers (α- or β-), silicon oxinitride grains and silica whiskers formed when the dominant reactions have changed due the presence of MgO and CaO.