Symposium CD
High and Ultra High Temperature Ceramics and Composites for Extreme Environments
ABSTRACTS
CD-1:IL01 Ceramic Matrix Composites for Application in Aeroengines
D. KOCH, Institute of Materials Resource Management MRM, University of Augsburg, Augsburg, Germany
Nonoxide fiber reinforced composites are promising candidates for high temperature applications under severe conditions. However, under oxidative atmosphere the long term stability may be limited due to corrosion and succeeding degradation of the mechanical properties. Nevertheless, SiC/SiC composites are on focus in the hot sections of aeroengines and some parts as shrouds are already in serial production. During manufacturing of high performance SiC/SiC composites the fibers are coated with several layers. The coating system protects the fibers against any attack during matrix processing and provides the desired fracture tough behavior of the composites during service. The matrices are then infiltrated into the fiber preforms and an outer environmental barrier coating system is applied for long term stability reasons. The matrix must show at least a reasonable oxidation resistance in case of crack formation. Furthermore, from mechanical point of view, the matrix should support a sufficient high proportional limit for engineering and design issues of the final components. The presentation focuses on these various manufacturing issues of nonoxide composites and discusses the challenges in material development for application in gas turbines.
CD-1:IL02 Processing of Sintered and Non-sintered UHTCMCs for Extreme Environments
D. SCITI, A. Vinci, P. Galizia, S. Failla, F. Servadei, L. Zoli, CNR-ISTEC, National Research Council of Italy - Institute of Science and Technology for Ceramics, Faenza, Italy
UHTCMCs represent a novel class of materials that can potentially couple the high oxidation resistance of UHTCs to the damage tolerance of CMCs, provided that a suitable matrix/fiber interface is tailored. Their specific application is in hypersonics and propulsion. Current processing methods for UHTCMC manufacturing originate from consolidated technologies of CMCs, such as chemical vapor infiltration (CVI), polymer infiltration and pyrolysis (PIP), reactive metal infiltration (RMI). In this talk, we explore the manufacturing of UHT-Composites via sintering or non-sintering techniques. So far, several kinds of composites have been produced using different preforms/architectures, matrix compositions, pan and pitch derived fibers. In the case of sintered UHTCMCs, water – based slurry infiltration is followed by hot pressing or spark plasma sintering. Ongoing studies on non-sintered UHTCMCs are instead focused on slurry infiltration coupled with PIP, using a commercial SiC precursor. We will compare sintered and non-sintered UHTCMCs, highlighting differences and advantages of these processing methods and resulting materials.
CD-1:L06 Colloidal Processing of Nano-nickel Doped WC Compacts for Improved Hot Press and Pressureless Sintering
E.M. Garcia Ayala, Z. Gonzalez, B. Ferrari, A.J. Sanchez-Herencia, ICV-CSIC, Madrid, Spain; J.Y. Pastor, Univ. Polytech. Madrid, Spain; L. Silvestroni, ISTEC-CNR, Faenza, Italy
Tungsten carbide has high melting point, hardness and good electrical and thermal conductivity. Under extreme conditions, tungsten carbide becomes a valid and safe alternative for nuclear applications such as the Gen-IV nuclear reactors or ITER. Traditional sintering processes use metal or ceramic additives to lower the sintering temperatures, nanosized powders or non-conventional methods (Hot Press or SPS). The addition of a metallic phase as binder to fabricate dense WC based materials brings associated problems such as low mechanical resistance at high temperature or higher corrosion. For this reason, efforts are made to lower the amount of metals as sintering aids to achieve complete densification in a pressureless sintering process. In this paper 3 wt% of nickel is colloidally dispersed in a matrix of WC powders to lower the sintering temperature while maintain the refractory properties of the materials. Nickel is added in form of powders of both nano and micrometric sizes as well as from directly precursors added to the slurries. A lowering in the sintering temperature to 1400 and 1500 for both Pressureless and Hot-Press Sintering is achieved while obtaining densities as high as 90 and 98% respectively. Sample are microstructural and mechanically characterized.
CD-1:IL07 C3HARME: Next Generation Ceramic Composites for Combustion Harsh Environments and Space
L. ZOLI, P. Galizia, L. Silvestroni, A. Vinci, S. Failla, F. Servadei, D. Sciti, CNR-ISTEC, National Research Council of Italy - Institute of Science and Technology for Ceramics, Faenza, Italy
There is an increasing demand for materials with superior temperature capability in harsh environments, for example enable space vehicles to resist several launches and re-entries at hypersonic speed.[1.2]. The H2020 project C3HARME, funded with 8 M€ aims at combining the best features of CMCs and UHTCs to design, develop, manufacture and qualify a new class of Ultra-High Temperature Ceramic Matrix Composite (UHTCMCs) with self-healing capabilities withstanding temperature above 2000°C without active cooling.[3,4]. Applications selected to implement the new materials are near-zero erosion nozzles and near-zero ablation thermal protection systems. In this talk we explore the challenges addressed by C3HARME project including manufacturing process, scale-up, production of prototypes, and relevent environments testing up to TRL 5-6.
[1] B.D. Andrea, F. Lillo, A. Faure, C. Pet-m, New generation of solid propellants for space launchers, Acta Astronaut. 47 (2000) 103–112.
[2] H. Hald, Operational limits for reusable space transportation systems due to physical boundaries of C/SiC materials, Aerosp. Sci. Technol. 7 (2003) 551–559.
[3] D. Sciti, L. Silvestroni, F. Monteverde, A. Vinci, L. Zoli, Introduction to H2020 project C3HARME–next generation ceramic composites for combustion harsh environment and space, Adv. Appl. Ceram. (2018).
[4] L. Zoli, D. Sciti, Efficacy of a ZrB2-SiC matrix in protecting C fibres from oxidation in novel UHTCMC materials, Mater. Des. 113 (2017) 207–213.
CD-1:L08 Optimization of Processing Conditions for the Fabrication of Bulk High Entropy Borides
S. BARBAROSSA1, R. Orrù1, A. IACOMINI2, S. GARRONI2, G. Cao1, 1Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali, Università degli Studi di Cagliari, Cagliari, Italy; 2Dipartimento di Chimica e Farmacia, Università degli Studi di Sassari, Sassari, Italy
The fabrication of highly dense single-phase High Entropy Borides (HEBs), a recently discovered class of Ultra-High Temperature Ceramics (UHTCs), represents a challenging goal to achieve, due to their inherently chemical complexity as well as the related highly refractory nature. Indeed, the preparation routes proposed so far display several drawbacks, including the required long processing times and high temperatures, as well as the corresponding inadequate product characteristics (inhomogeneous materials, residual porosity, presence of oxides, etc.). In this work, various HEBs, such as (Hf0.2Mo0.2Nb0.2Ta0.2Ti0.2)B2, (Hf0.2Mo0.2Zr0.2Ta0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2, are successfully obtained in bulk form by Spark Plasma Sintering using combustion synthesized powders produced from suitable precursors. The effect of several operating parameters (reaction stoichiometry, initial particles size, ball milling treatment, graphite addition, sintering conditions, etc.) on product characteristics (density, composition, microstructure, etc.) is systematically investigated.
CD-1:L09 Near Net Shape Manufacturing of Complex Components of Thermal Protection System of a Re-entry Vehicle based on Liquid Silicon Infiltration (LSI) process
M. De Stefano Fumo, P. Spena, F. De Nicola, R. Gardi, R. Fauci, G. Rufolo. Centro Italiano Ricerche Aerospaziali (CIRA), Italy; L. Cavalli, F. Giacometti, M.Y. Akram, M. Boiocchi, M. Cantù, M. Valle. Petroceramics S.p.A., Stezzano, Italy
Ceramic matrix composites (CMCs) favorably combine the lightweight and the toughness of polymeric matrix composites with the high temperature resistance and the hardness of ceramics. These features are very attractive for several aerospace applications, such as reentry vehicles, where the lightweight requirements are very demanding and the materials face severe aerothermal loads and plasma oxygen exposure. The LSI process is a favorable technique for the manufacturing of Cf-SiC composites. This process offers several advantages over other CMCs manufacturing techniques. It is relatively cheap and fast and does not require the handling of gases that are hazardous to the healthy and to the environment. Recent enhancement in manufacturing technique demonstrated the process suitability for the production of parts with very large dimensions and complex shapes. Here is presented the development, the manufacturing and the testing of some components of the thermal protection system of the next European reusable re-entry vehicle Space Rider. The TPS parts were produced starting from a phenolic resin based pre-preg and were shaped by means of innovative ad hoc developed green manufacturing techniques and new approach to control macroscopic shrinkage during pyrolysis and infiltration phases.
CD-1:L10 Highly Electrically and Thermally Conductive Silicon Carbide - Graphene Composites
O. HANZEL, Z. Lenčéš, Y-W. Kim, J. Fedor, P. Šajgalík, Institute of Inorganic Chemistry, Slovak Academy of Sciences, Bratislava, Slovak Republic; Functional Ceramics Laboratory, Department of Materials Science and Engineering, University of Seoul, Seoul, South Korea; Institute of Electrical Engineering, Slovak Academy of Sciences, Bratislava, Slovak Republic
Almost fully dense silicon carbide composites with 1 vol.% Y2O3–Sc2O3 sintering additives and with different amount of graphene nanoplatelets (GNPs) from 1 to 10 wt. % or 1 wt. % of graphene oxide (GO) were sintered in rapid hot press (RHP) at 2000°C for 30 min with a pressure of 50 MPa under nitrogen atmosphere. Electrical conductivity and thermal conductivity were investigated as a function of amount of graphene, its orientation in SiC matrix and effect of annealing. The electrical conductivity of reference SiC sample (17 S/cm) gradually increased with increasing GO or GNP content, reaching the highest value of 67 S/cm for SiC with 10 wt.% GNPs. Remarkable improvement of electrical conductivity was achieved by annealing the samples in N2 atmosphere and the highest value of 118 S/cm was obtained for the sample with 10 wt.% GNPs. The highest thermal conductivities were obtained at room temperature in parallel direction to GNPs for annealed SiC samples with 1% GO (238 W/m.K) and 5% GNPs (233 W/m.K). The obtained results show that application of freeze granulation, rapid hot-pressing and annealing of samples at 1800°C for 6h in N2 atmosphere allows to obtain SiC ceramics with very high electrical and thermal conductivity.
CD-1:IL11 Effect of Sintering Technique on Properties of Nanocrystalline Composite B4C/SiC Ceramics
B. MATOVIC, University of Belgrade, Institute for Nuclear Sciences Vinca, Serbia
The effect of sintering technique on density, microstructure and mechanical properties of B4C/SiC composite was studied. Three different techniques for densification were applied. The main difference between these techniques was the mechanical pressure which was applied during sintering in order to fabricate dense composite samples. The first technique was pressureless sintering which was conducted without the help of mechanical pressure whereas the other two techniques were pressure assisted. One was Field Activated Sintering Technique (FAST), which provides relatively modest mechanical pressure of ~ 70 MPa and the other technique was pressure sintering assisted with very high mechanical pressure of ~ 4 GPa. It was found that the increase in applied mechanical pressure increases the density of sintered samples and improves mechanical properties. Microstructure development was examined by field emission scanning electron microscopy. The best results were measured in samples obtained by pressure sintering using high-pressure (4 GPa) "anvil-type with hollows" apparatus. Relatively dense samples (about 96%) were obtained after sintering at 1900°C for only 1 minute. Thermal conductivity has been found to increase with the increase of the B4C phase content.
CD-1:L12 Titanium Carbide Nanostructured Targets for Nuclear Medicine and Physics Applications
S. CORRADETTI, A. Andrighetto, INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy; S. Carturan, G. Maggioni, Università di Padova, Dipartimento di Fisica e Astronomia, Padova, Italy; G. Franchin, P. Colombo, Università di Padova, Dipartimento di Ingegneria Industriale, Padova, Italy
The SPES (Selective Production of Exotic Species) project has the aim to build an ISOL (Isotope Separation On-Line) facility at INFN-LNL (Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali di Legnaro) for the production of Radioactive Ion Beams (RIBs). The development of targets capable of producing and releasing radioactive isotopes is of extreme importance for two main applications: supply of RIBs to nuclear physics users and production of medical isotopes (ISOLPHARM project). Porous refractory materials able to work under extreme conditions (temperatures in many cases higher than 2000 °C in high vacuum for up to 15 days of continuous irradiation by a high power proton beam) are a common choice for this purpose. The need of carefully tailoring the material structure has been highlighted in several experimental works: aspects that positively affect the isotopic release like high open interconnected porosity and nanosyzed grains must be carefully balanced with properties related to heat dissipation, such as high thermal conductivity and emissivity. Titanium carbide has been recently proposed and used as a target to produce isotopes of different elements. Synthesis and characterization of nanostructured titanium carbide/carbon composites target materials are presented.
CD-1:L13 Novel Multicomponent Pyrochlore Oxides for Future Thermal Barrier Coatings
P. HUTTERER, M. Lepple, DECHEMA Research Institute, Frankfurt a.M., Germany
Multicomponent equiatomic oxides (MEOs), also named high entropy oxides (HEOs), have attracted great interest in recent years. Analogous to high entropy alloys (HEAs), they consist of five or more different cations on one or more cation sublattices in approximately same amount. The high configurational entropy results in improved phase stability at high temperatures and low thermal conductivity due to increased phonon scattering. Therefore, MEOs are proposed as promising materials for future thermal barrier coatings (TBCs). In this work, MEOs with the general formula A2Zr2O7 and 5 different cations on the A-site have been successfully synthesized by using reverse co-precipitation. The composition has been varied systematically to evaluate its influence on crystal structure and material properties. Chemical and structural characterization was performed using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction and electron microprobe. Dilatometry, differential scanning calorimetry, HT-XRD and long-term annealing experiments were conducted to assess the thermal stability as well as thermodynamic and thermophysical properties of the compounds. The results of this work underline the great potential of MEOs for future thermal barrier coatings.
CD-1:L14 Flash Spark Plasma Sintering of Pure TiB2 with Dieless Configuration
S. FAILLA1, SHUAI FU2, S. GRASSO2, D. Sciti1, 1ISTEC-CNR, Faenza, Italy; 2Key Laboratory of Advanced Technologies of Materials, Ministry of Education, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, China
A Spark Plasma Sintering (SPS) furnace was used to Flash-Sinter (FS) pure titanium diboride (TiB2) powder. A pre-sintering green body (Ø= 20 mm, relative density 60%) was used for the Flash-SPS using a dieless configuration with current passing entirely across the sample. The results show that the samples were densified in very short time (< 60 seconds) up to 90-95% of theoretical density. The rapid heating (≈6000 °C/min ) prevented the complete evaporation of B2O3, leading to the formation of rarely seen segregation of boron at the grain boundaries. Compared to SPS or hot press, the rapid Flash-SPS processing promoted the formation boron rich grain boundaries during sintering, thus enhancing consolidation. TiB2 obtained by Flash-SPS was characterized using XRD and SEM analysis in order to quantify texturization induced by the FSPS hot forging effect. The Flash-SPS approach might be suitable to consolidate other refractory borides.
CD-2:IL01 Effects of Coating and Substrate Chemistry on the Steam Oxidation Kinetics of Environmental Barrier Coatings for Ceramic Matrix Composites
kang lee, NASA Glenn Research Center, Cleveland, OH, USA; A. GARG, NASA Glenn Research Center / University of Toledo, Toledo, OH, USA; W.D. Jennings, Vantage Partners, Cleveland, OH, USA
Environmental Barrier Coatings (EBCs) have enabled the implementation of ceramic matrix composites (CMCs) in gas turbines by protecting CMCs from H2O-induced volatilization. One critical EBC failure mode is spallation due to a build-up of elastic strains caused by the formation of SiO2 scale, known as TGO (thermally grown oxide). H2O, a byproduct of combustion reactions, accelerates the TGO-induced EBC failure by increasing TGO growth rates by orders of magnitude. NASA's approach to improve the EBC life, therefore, is to reduce TGO growth rates. To this end, one needs to understand the variables that influence TGO growth rates. NASA has developed modified Gen 2 EBCs, Si/Yb2Si2O7 doped by Al2O3 or Al2O3-containing compounds, which reduce the TGO thickness by up to 80% compared to the baseline EBC (Si/Yb2Si2O7) at 1316C in steam. Another NASA study has shown that the CMC chemistry also has a significant influence on EBC oxidation kinetics. These studies have demonstrated that the chemistry of EBC and CMC substrate is a key variable for EBC oxidation. This paper will discuss the effects of EBC and CMC chemistry on EBC oxidation and propose the mechanisms on how the chemistry influences EBC oxidation kinetics.
CD-2:IL02 High-temperature Oxidation/Corrosion of Silicon Carbide for Nuclear Applications
M. Steinbrück, Karlsruhe Institute of Technology, Institute for Applied Materials (IAM-AWP), Germany
This paper presents a brief overview on high-temperature (HT) oxidation of silicon carbide in various atmospheres as well as results of high-temperature oxidation experiments with SiCf-SiC composite materials in steam and impure helium atmospheres for application in water and gas cooled nuclear reactors. The experiments were conducted in the frameworks of KIT’s nuclear safety research program NUSAFE and the European MatISSE and IL TROVATORE programs. Experiments in steam up to 2000°C were conducted in the inductively heated QUENCH-SR (single rod) facility coupled with a mass spectrometer for off-gas analyses. Very limited oxidation of the SiCf-SiC cladding was observed up to 1700°C due to the formation of a protective silica scale on the SiC protective CVD layer. Failure of cladding tubes with strong gas release and volatilization occurred beyond 1700°C when the SiCf-SiC CMC was attacked. The maximum “survival” temperature was dependent on the design of the SiC CMC cladding. The oxidation kinetics of SiCf-SiC cladding tube segments in impure helium atmosphere, prototypical for GFRs, was investigated at ambient pressure in the temperature range between 900°C and 1600°C using a thermo-gravimetric device. The transition from passive oxidation (formation of a protective silica scale) to active oxidation (volatilization of silica due to the formation of SiO and other volatile species) occurred between 1200°C and 1300°C. In summary, SiC composite materials offer very promising oxidation/corrosion properties up to very high temperatures for nuclear applications for various types of nuclear reactors.
CD-2:IL03 Corrosion Behavior of RE-doped Silicate for Environmental Barrier Coatings
Byung-Koog Jang, Interdisciplinary Graduate School of Engineering Science (IGSES), Kyushu University, Fukuoka, Japan
Environmental barrier coatings (EBCs) require important resistance to degradation from silica-based particles (desert sand and volcanic ash) entering the engine in a combustion environment at high temperature for gas turbine application. Chemical attack on EBCs by molten silicate precipitates, commonly known as CMAS( CaO–MgO–Al2O3–SiO2), is an important issue. In the present work, sintered Gd2SiO5 was prepared by the spark plasma sintering (SPS) method at 1400°C for 20 min. The purpose of this study is to evaluate the high-temperature corrosion behavior by the thickness of the reaction layer formed as the reaction time of sintered Gd2SiO5 exposed to CMAS (0.73) and volcanic ash (0.11) with different Ca:Si ratios for 2, 12, and 48 h at 1400°C by isothermal heat treatment. It is considered that CMAS and volcanic ash with different Ca:Si ratios react with Gd2SiO5 to form Ca2Gd8(SiO4)6O2 with increasing time. As a result, Ca2Gd8(SiO4)6O2 is formed in the reaction layer, which grows vertically in the form of needles. It is confirmed that Ca2Gd8(SiO4)6O2 is better formed by CMAS with higher Ca concentration.
CD-2:IL05 Tungsten Carbides and Borides for Shielding of Compact Tokamak Fusion Reactors
S.A. Humphry-Baker, Department of Materials, Imperial College London, London, UK
Spherical tokamaks present a relatively low-cost path to the development of fusion power. However, their small size necessitates new high-performance shielding materials to be developed. The carbides and borides of tungsten are highly effective for this application, due to the efficient gamma-ray attenuation of W, and neutron moderation and absorption from C and B. We present work on candidate WC and WBx-based materials in demanding thermal, mechanical, and oxidation environments. In particular, good oxidation resistance is critical to ensure safe operation in an accident combining loss of coolant and vacuum. WC-based composites oxidise with linear kinetics as the WO3-based scale is unprotective. Work on Si-based coatings is shown to alleviate this issue. WBx materials, on the other hand, show a distinct advantage, due to the formation of a continuous and protective boria film, with correspondingly parabolic oxidation kinetics. The limits of such protection are mapped out as a function of boron composition (16-50 at.%) and temperature (600-1200°C). Ongoing efforts to develop W2B5-based composites (i.e. with increased boron content) will be presented, as these materials could simultaneously improve both oxidation and neutron attenuation performance.
CD-2:L06 Oxidation Behaviour and Thermal Shock Resistance of Ceramic Composites based on Carbides and Borides
a. Kovalčíková1, M. Ivor1, P. Tatarko2, H. Ünsal2, R. Sedlák1, D. Medved1, A. Naughton-Duszová1, 3, E. Baczek3, M. Podsiadło3, J. Dusza1, 1Institute of Materials Research, Slovak Academy of Sciences, Košice, Slovak Republic; 2Institute of Inorganic Chemistry, Slovak Academy of Sciences, Bratislava, Slovak Republic; 3Institute of Advanced Manufacturing Technology, Krakow, Poland
The influence of different carbides addition on the thermal shock resistance and oxidation behaviour of spark plasma sintered ZrB2 + B4C, ZrB2 + SiC and ZrB2 + ZrC composites was investigated under different temperature (1000-1450°C). The effect of chemical composition on mechanical properties was also studied. For comparison, TiB2 composites with 15-25 wt. % of SiC were sintered. Microstructure - property relationships were analysed. The best thermal shock resistance and oxidation behaviour showed ZrB2 ceramics with 10 wt. % SiC addition.
The authors gratefully acknowledge the financial support from the following projects: VEGA 2/0118/20 and APVV-17-0328. This work was realised within the framework of the Research Centre of Advanced Materials and Technologies for Recent and Future Applications “PROMATECH” Project, ITMS 26220220186, supported by the “Research and Development” Operational Programme financed through European Regional Development Fund.
CD-2:IL08 C/C/UHTC Composites, towards Reusable Materials
F. Rebillat1, C. Liégaut1, 3, P. Bertrand2, L. Maillé1, 1Université de Bordeaux, CNRS, Safran Ceramics, CEA, Laboratoire des Composites ThermoStructuraux (LCTS), UMR-5801, Pessac, France; 2Université de Bourgogne Franche Comté, Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), Site de Sévenans, Sévenans, France; 3Safran Ceramics, Le Haillan, France
Space propulsion applications require the development of new ceramic matrix composites with a chemical and structural stability at ultra high temperature. Instead to limit the protection of a C/C composite to an outside coating made in UHTC (ultra high temperature ceramic), it is proposed to introduce UHTC materials as a matrix inside poorly densified C/C composites. Both powder impregnation (ZrB2, SiB4, SiC in various proportions) and liquid silicon-zirconium mixture infiltration enable manufacturing these UHTC based matrices in Cf/C preforms. The matrix is made of various proportions of ZrB2, SiC and ZrC. It is strongly bonded to the C/C matrix without degradation of this latter, due to the development of a limited reaction zone between the constituents. The oxidation behaviour is evaluated on composites structures at temperatures higher than 2000°C up to 6 minutes, using an oxyacetylene torch. Chemical analyses and microstructural observations before and after oxidation testing are done. A multi-oxides scale ensures the protection of the C/C composite, underneath, and oxidation progresses on a single and stable front in time. Thermal-cycling tests in such severe environmental conditions are finally carried out to evaluate the possibility to reuse these materials.
CD-2:IL09 Oxidation of Zirconium and Uranium Carbides
C. GASPARRINI1*, R. Podor2, R.J. Chater3, D. Horlait4, O. Fiquet5, S. May6, M.J.D. Rushton7,1, W.E. Lee1,7, 1Centre for Nuclear Engineering (CNE) & Department of Materials, Imperial College London, South Kensington Campus, London, UK; 2Institut de Chimie Séparative de Marcoule, UMR 5257 CEA/CNRS/UM/ENSCM, Site de Marcoule, Bagnols-Sur-Cèze, France; 3Department of Materials, Imperial College London, South Kensington Campus, London, UK: 4CNRS, Centre D’Etudes Nucléaires de Bordeaux-Gradignan, UMR 5797, Chemin Du Solarium, Gradignan, France; 5DEN/DEC/SA3E/LCU Building 315, Atomic Energy Commission (CEA), Saint Paul lez Durance Cadarache, France; 6National Nuclear Laboratory, Preston Laboratory (A709), Springfields, Preston, Lancashire, UK; 7Nuclear Futures Institute, Bangor University, Bangor, Gwynedd, UK; *Consorzio RFX, Padova, Italy
Zirconium carbide (ZrC) and uranium carbide (UC) are receiving attention as alternative materials to silicon carbide and uranium dioxide thanks to their attractive high thermal conductivity at high temperature. However, their purity is difficult to achieve and when in contact with oxygen at relatively low partial pressure and low temperature they show poor oxidation resistance. In situ techniques coupled with macro to nano characterisation techniques were used to reveal the oxidation mechanism of ZrC and UC. A key result was the improved understanding of the role of cracking in the oxidation mechanism of both carbides. ZrC oxidation was governed by oxygen diffusion through a layer of constant thickness formed by the cyclic debonding of the interface after the oxide layer reached approximately 20μm at 1073K. The interface between ZrC and m-ZrO2 was an approximately 2μm thick layer comprising of ZrC and t/c-ZrO2 nanocrystals (≤5nm) in an amorphous carbon matrix. Experiments on UC in air showed that oxidation proceeded quicker at lower temperatures, 873K, as oxide sintering at higher temperatures, 1173K, limited oxidation only on cracked surfaces. UC ignition was triggered by an exponential increase of crack length and network due to a fragmentation process.
CD-2:IL10 Wear Resistance, High Temperature Stability and Electrical Conductivity in Air of Ti,Nb-Al-C MAX Phases-based Hot-pressed Bulks and Vacuum-arc Deposited Films
T.A. PRIKHNA1, T.B. Serbenyuk1, O.P. Ostash2, A.S. Kuprin3, V.Ya. Podhurska2, V.B. Sverdun1, 1Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kiev, Ukraine; 2Karpenko Physical-Mechanical Institute of the National Academy of Sciences of Ukraine, Lviv, Ukraine; 3National Science Center Kharkov Institute of Physics and Technology, Kharkov, Ukraine
Ti,Nb-Al-C MAX materials synthesized in vacuumed and/or by hot pressing (at 15-30 MPa) and vacuum-arc deposited films are stable in air and hydrogen at high temperatures. The high temperature X-rays showed that dense Ti2AlC was oxidized more intensive than Ti3AlC2: the notable increase of surface oxide film thickness in the case of Ti2AlC starts at 700- 750 ° C and for Ti3AlC2 at 1050-1100 °C. Addition of Nb leads to essential decrease of oxide film thickness. The (Ti,Nb)3AlC2 was stable in oxidizing (1000 h) and hydrogen (40 h) atmospheres at 600 oC. The more stable at thermal cycling up to 1200 °C was dense Ti3AlC2. The bending strength of Ti3AlC2-based material in air at 20 °С was 535 MPa, after been keeping at 600 °С in air and hydrogen it decreased to 490 and 500 MPa, respectively. While for (Ti,Nb)3AlC2 materials the bending strength at 20 °C in air was 480 MPa and even increased for 10% after heating at 600°С both in air and in hydrogen. The surface electrical conductivity of 6 mm thick Ti-Al-C film after heating for 1000 h at 600 °C in air stayed practically unchanged: 1.3´106 S⋅m-1. Wear of porous Ti3AlC2-based material in contact with Cu occurred in 40 times lower than that of silumin and wear of Cu was 13 and 50 times lower without and with lubricant, respectively.
CD-2:IL11 Hot Gas Corrosion of Ceramic Matrix Composites
W. KUNZ, H. Klemm, A. Michaelis, Fraunhofer Institute for Ceramic Technologies and Systems IKTS, Dresden, Germany
Ceramic matrix composites are of growing interest for gas turbine applications such as turbines for aircrafts. A higher temperature capability and lower weight are the main reasons to substitute metallic superalloys in order to achieve higher turbine efficiency. Depending on the addressed turbine component different CMCs are required. Oxide CMCs are mainly used in lower temperature sections. They help to reduce the weight of the turbine and can be manufactured for reasonable costs. In the high temperature section of the turbine (combustion chamber, blades, vanes) non-oxide CMCs are one option to reduce cooling efforts due to their high temperature capability. Unfortunately, the incorporation with water vapor leads to significant recession mechanisms (hot gas corrosion) in both types of CMC. At Fraunhofer IKTS extensive testing of different CMC materials has been carried out in a high temperature burner rig. The surface recession of different oxide and non-oxide CMCs will be presented as well as the influence of the testing conditions (combustion chamber material) on the recession behavior of some actual EBC materials.
CD-3:IL01 Ultra-high Temperature Mechanical and Thermal Properties of UHTCs
W.G. FAHRENHOLTZ, G.E. Hilmas, Missouri University of Science and Technology, Materials Research Center, Rolla, MO, USA
The carbides, nitrides, and borides of early transition metals belong to a family of materials known as ultra-high temperature ceramics (UHTCs). Because of melting points in excess of 3000°C, these ceramics have been proposed for use in the extreme environments such as those associated with hypersonic flight, nuclear fusion, and concentrated solar power. Research at Missouri S&T has examined processing, densification, properties, and oxidation of a broad variety of UHTCs. This presentation will focus on recent progress on the understanding of elevated temperature mechanical and thermal properties of UHTCs up to at least 2000°C. Some specific areas of discussion include the effect of Ta additions on the elevated temperature mechanical behavior of ZrB2 ceramics, the elevated temperature mechanical behavior of entropy-stabilized carbide ceramics, vacancy ordering in zirconium carbide, and the elevated temperature properties of zeta phase tantalum carbide ceramics. The elevated temperature mechanical and thermal properties of these materials will be discussed in the context of the fundamental mechanisms that control behavior as identified in previous studies.
CD-3:IL03 The Effect of Rare-earth based Additives on the Mechanical Properties of ZrB2-SiC Composites prepared by Reactive and Non-Reactive Sintering Route
P. TATARKO1, H. Ünsal1, B. Matović2, Z. Chlup3, M. Tatarková1, A. Kovalčíková4, M. Hičák1, I. Dlouhý3, P. Šajgalík1; 1Institute of Inorganic Chemistry, Slovak Academy of Sciences, Bratislava, Slovakia; 2Centre of Excellence "CEXTREME LAB", Vinča Institute of Nuclear Sciences - National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia; 3Institute of Physics of Materials, Czech Academy of Sciences, Brno, Czech Republic; 4Institute of Materials Research, Slovak Academy of Sciences, Košice, Slovak Republic
Near fully dense ZrB2-25vol.%SiC composites were prepared by Field Assisted Sintering Technology (FAST) using both non-reactive and reactive routes. While in the case of non-reactive sintering, the final materials were obtained by sintering of the mixture of ZrB2 and SiC powders, in situ reactions between ZrSi2, B4C and carbon black during reactive sintering led to the formation of the final composition. The use of in-situ reactive sintering significantly reduced the sintering temperature from 2000°C (non-reactive sintering) to 1600°C. The effect of rare-earth (RE) oxides and RE zirconates (2 – 10 wt.%) on the densification, microstructure development, and mechanical properties of ZrB2-25vol.%SiC composites was investigated. While no significant effect of the RE-based additives on the room temperature mechanical properties of the composites was observed (hardness, elastic modulus, fracture toughness, strength), the ablation resistance of the composites linearly increased with the addition of RE-based additives. The composites with 10 wt.% RE additives showed ~ 80% improvement in the ablation resistance when compared to the reference ZrB2-25vol.%SiC. Moreover, The materials prepared by reactive sintering showed superior properties to the materials prepared by non-reactive route.
CD-3:IL06 Thermal and Mechanical Properties of Zeta Phase Tantalum Carbide
G.E. HILMAS, W.G. Fahrenholtz, Missouri University of Science and Technology Rolla, MO, USA
This presentation will focus on the thermal and mechanical properties of zeta phase tantalum carbide (ζ-Ta4C3-x), an ultrahigh temperature ceramic of interest to the ceramic engineering community due to its unique mechanical behavior, especially its high fracture toughness. High purity zeta phase tantalum carbide was synthesized and densified using reaction hot pressing with elemental sources of tantalum and carbon. Tantalum hydride powder and carbon black were used as the tantalum source and the carbon source, respectively. X-ray diffraction and Rietveld refinement were used to ensure high phase purity, while scanning electron microscopy was used to perform microstructural analysis. Thermal diffusivity and heat capacity were measured at room and elevated temperatures and the thermal conductivity was calculated. Electrical resistivity was also measured at room and elevated temperatures. Fracture toughness and flexure strength were measured at room and elevated temperatures (up to 2000°C). This study is the first to report the thermal and mechanical properties of zeta phase tantalum carbides at elevated temperatures. Time permitting, the presentation will also discuss the unique cyclic fatigue behavior and machinability of zeta phase tantalum carbide ceramics.
CD-3:L08 Structure and Mechanical Characteristics of High Pressure Sintered ZrB2, HfB2 and ZrB2- TiB2, ZrB2-SiC Composite Materials
T. Prikhna, A. Lokatkina, V. Moshchil, M. Karpets, P. Barvitskyi, O. Borymskyi, V. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine, Kiev, Ukraine
The ZrB2 and HfB2 materials are promising for application in hypersonic aerospace, cutting tools, metallurgy, microelectronics and refractory industries. The structure and properties of sintered under high pressure (4 GPa) - high temperature (1800 °C) or HP-HT conditions ZrB2, HfB2, ZrB2+30%TiB2 and ZrB2-20% SiC refractory materials are under consideration. HP-HT sintered HfB2 (a=0.3141, c=0.3473 nm γ=10.42 g/cm3) demonstrated hardness HV(9.8 N)=21.27±0.84 GPa, HV(49 N)=19.29±1.34 GPa, and HV(98 N)=19.17±0.5 GPa and fracture toughness K1C(9.8 N)=6.47 MN×m0.5. High pressure sintered ZrB2 (a=0.3167 , c=0.3528 nm, γ=6.1 g/cm3) demonstrated HV(9.8N)= 17.66±0.60 GPa, HV(49 N)= 15.25±1.22 GPa, and HV(98 N)= 15.32±0.36 GPa and K1C(9.8 N)=3.64 MN×m0.5. Addition of 30 wt.% of TiB2 to ZrB2 did not allow to increase hardness of the material essentially (HV(9.8 N)=17.75±2.36 GPa, γ=5.29 g/cm3 ). Addition of 20 wt.% of SiC to ZrB2 and sintering under high pressure allowed essential increase of hardness to HV(9.8 N)=24.18±0.7 GPa, HV(49 N)=16.68±0.5 GPa, and HV(98 N)=17.59±0.4 GPa and fracture toughness (K1C(9.8 N)=6.49 ± 0.25 MN×m0.5, K1C(49 N)=7.06± 1.55 MN×m0.5 , K1C(98 N)=6.18± 1.24 MN×m0.5) of composite ZrB2- SiC material (γ=5.03 g/cm3).
CD-3:L09 The Behavior of UHTC Carbides and Nitrides in Various Environments up to 4500 K
M. SHEINDLIN, T. BGASHEVA, M. BRYKIN, A. FROLOV, S. PETUKHOV, A. VASIN, P. VERVIKISHKO, JIHT RAS, Moscow, Russia
The latest experimental results are presented on the thermal conductivity, thermal expansion and spectral emissivity of ZrCx, HfCx and TaCx prepared by SHS synthesis followed by either HP or SPS sintering. The dynamics of oxide scale formation on ZrCx during its heating in the air flow with power laser irradiation using high speed spectro-pyrometry, multiwave laser probing and high-speed video recording has been studied. Laser melting of group IV nitrides was carried out at various nitrogen pressures of up to 1 kbar in order to determine the parameters of their congruent melting. It turned out that the congruent melting temperature of some group IV metal nitrides is by far higher than the melting point of the corresponding carbides. Comprehensive characterization of both prepared samples and after high temperature treatment was provided by SEM-EDX, XRD, Raman microscopy and chemical analysis.
CD-4:IL01 First Principles Simulations of Entropy Stabilized UHTCs
M. Lim, S. Daigle, Z. Rak, D.W. Brenner, Department of Materials Science and Engineering North Carolina State University Raleigh, NC, USA
High entropy ceramics (HECs), in particular di-borides and carbides, have recently emerged as potential new materials for ultra-high temperature applications. Unlike their more traditional cousins, these ceramics are composed of five or more cations in roughly equi-molar concentrations. Unlike high entropy metal alloys, these materials are composed of interpenetrating ordered and high entropy sublattices. We have been using first principles methods to understand and predict how the structure, stability, and thermo-mechanical properties of HECs can be related to the properties of their respective binaries. Lattice constants, bulk moduli and cohesive energies are all found to be well represented by averages of their respective binaries. Vacancy formation energies, however, are not well-represented by binary averages, and may have values that are outside of those for the respective binaries. Similarly, the density of electronic states of the HECs are much more similar to each other than the binaries, and the density of states at the Fermi level are well represented by averages of the respective binaries. However, an expression that gives the electrical conductivity of HECs based on the binaries has not (yet) been determined.
CD-4:IL03 Strong Boride Hierarchical Composites for Ultra-high Temperature Applications
L. SILVESTRONI1, N. Gilli1,2, A. Migliori2, D. Sciti1, J. Watts3, G.E. Hilmas3, W.G. Fahrenholtz3, 1CNR-ISTEC, Institute of Science and Technology for Ceramics, Faenza, Italy; 2CNR-IMM, Institute for Microelectronics and Microsystems, Bologna, Italy; 3Department of Materials Science and Engineering, Missouri University of Science and Technology, MO, Rolla, USA
A simple method to obtain highly refractory boride-based ceramic nano-composites is presented. Fundamental requirement for the development of a hierarchical boride composite is the formation of a solid solution around the native MB2 boride grain during the densification step. This can be obtained upon addition of soluble transition metal compounds. In the present case, introduction of WC enabled to form (M,W)B2 shells around the original MB2 cores. Subsequent annealing treatment at high temperature further developed a nano-texturing in the shell, which constituted a nano-composite where metallic W nano-particles were embedded within MB2 grains and displayed unprecedented refractoriness. Here we show the microstructural evolution from the as-sintered to the annealed state of different diboride composite and show how these microstructural change impact on local properties measured by nanoindentation and on the ultra-high temperature strength. The unique microstructural findings reported open vast opportunities for nano-composite ceramic development, manufacturing and applications.
CD-4:IL04 Computational Studies of the Phase Stability of UHTC Transition Metal Carbides and Nitrides
C.R. WEINBERGER, Colorado State University, Fort Collins, CO, USA; Xiao-Xiang Yu, North Western University, Evanston, IL, USA; G. Thhompson, The University of Alabama, Tuscaloos, AL, USA
The group IVB and VB transition metal carbides and nitrides represent one of the major classes of ultrahigh temperature ceramics (UHTCs). Here, we investigate the stability of these compound at low temperature for a wide range of stoichiometries using electronic structure density functional theory (DFT). This, combined with intelligent search algorithms, have been able to suggest potential stable phases in these materials. The results of which have highlight a competition between vacancy ordering in the carbon/nitrogen depleted rocksalt matrix with other stacking fault derived structures, such as the nanolamellar zeta phase (M4X3-x or M3X3-2). These results are able to, for the first time, identify the stability and crystal structure of the zeta and eta phases in these materials. Using these computational tools and models, we are also able to elucidate the underlying physics that gives rise to phase and microstructure stability for this particular class of UHTCs.