CP - 7th International Conference
Advanced Inorganic Fibre Composites for Structural and Thermal Management Applications

Session CP-1 - Production and Properties of Reinforcements, Preforms, and Matrix Materials

CP-1:IL01  Heat-resistant Inorganic Fibers
T. ISHIKAWA, Ube Industries, Ltd., Ube, Yamaguchi, Japan

Up to now, many types of inorganic fibers have been developed. The main purpose is to develop composite materials with lightweight and high fracture toughness. Of these, carbon fiber has already established a very big market. By the way, representative oxide fibers (alumina/silica-based fibers) show heat-resistance's limitation at around 1200 degree C. In order to improve the heat-resistance, some types of eutectic oxide-fibers have been studied. On the other hand, SiC-based fibers with both heat-resistance and oxidation-resistance were developed over 30 years ago. After that, lots of improvements have been performed, and finally several types of excellent heat-resistant SiC-polycrystalline fibers, which can be used up to about 1800 degree C, were developed from polycarbosilane. Using these fibers, lots of applications have been considered in the fields of aerospace, nuclear system, and so on. Furthermore, making the best use of the aforementioned production process, several types of functional ceramic fibers with functional surface layers also have been developed. In this paper, historical view point on ceramic fibers will be also presented.


CP-1:IL02  New Developments in Carbon and Ceramic Fibers
E. FRANK, B. CLAUSS, Institute of Textile Chemistry and Chemical Fibers, Denkendorf, Germany; M.R. BUCHMEISER, Institute of Textile Chemistry and Chemical Fibers Denkendorf and University of Stuttgart, Institute of Polymer Chemistry, Stuttgart, Germany

High performance fibers are key components of fiber reinforced composite materials. Prominent examples are carbon fibers and ceramic fibers. Light weight construction is a very important future topic for aerospace, automotive and power engineering applications. In these areas the fibers of the composite materials have to meet specific requirements, which range from superior mechanical properties to low CO2-footprint of the production.
New approaches for the production of carbon fibers from renewable raw materials like lignin and cellulose offer new opportunities for the industry. Different research groups are involved in the development of new routes of carbon fiber production. Possible advantages and limitations shall be discussed.
Although there is some stagnation concerning commercially available ceramic fibers, there are also activities to improve fiber properties and to reduce production costs of such fibers. The current high fiber prices are still prohibitive for many applications.


CP-1:IL03  Porous Silicon Nitride and Sialon Prepared by Reaction Sintering Method
HAI-DOO KIM, Engineering Ceramics Group, Korea Institute of Materials Science, Changwon, Gyeongnam, Korea

The microstructure of porous SRBSN(sintered reaction bonded silicon nitride) has been controlled in order to modify the air permeability. The conditions to have porous microstructure with acicular grains was investigated. The different type, amount of sintering additives as well as the amount of fugitives are critical to control the porosity, the effective pore size and the air permeability of SRBSN. The nitridation conditions as well as post-sintering conditions are also critical in changing the microstructure, which gives rise to the different air permeability.
Porous sialon ceramics starting with silicon powder instead of silicon nitride powder can be prepared in a similar manner to SRBSN where silicon is nitrided and reacts with AlN, Al2O3 and/or Y2O3 at elevated temperature to give alpha-sialon, beta-sialon or alpha/beta mixture depending on the starting compositions. The conditions to give porous microstructure in sintered reaction-bonded sialon were investigated in order to modify the air permeability. The starting compositions and the sintering conditions are critical to control the porosity, the effective pore size and air permeability.
The efforts were made to enlarge the average pore size of porous SRBSN to reduce the pressure drop of the SRBSN filter. SRBSN DPF filter shows better trapping efficiency of PM compared to cordierite filter. Especially SRBSN filter shows better trapping efficiency for nanosized PM possibly due to the smaller pore size with minimum pressure drop compared to the conventional cordierite filter.


CP-1:L04  Polisiloxane Impregnation Pyrolysis for the cost-effective production of basalt fibers CFCCs
C. MINGAZZINI, M. SCAFÈ, ENEA - Faenza Technical Unit on Material Technologies (ENEA-UTTMATF), Faenza, Italy; A. BRENTARI, E. BURRESI, Certimac s.c.a.r.l.; D. CARETTI, D. NANNI, University of Bologna, Dipartimento di Chimica Industriale "Toso Montanari", Bologna, Italy

In this work, the optimisation of basalt fiber CFCCs (Continuous Fiber Ceramic Composites) production is presented, focusing on the development of a silicon-oxycarbide matrix by PIP (Polymer Impregnation Pyrolysis). The use of low cost polisiloxanes and basalt fibers is particularly promising for transports and constructions, where thermostructural CFCCs would be interesting for vehicle weight reduction and fire-resistant panels, but where it is even more important to contain production costs.
The pyrolysis was perfomed in a steel furnace, using steel moulds, under vacuum and nitrogen flow. The microstructure and the thermomechanical characteristics of the obtained composites were studied in both cases, being the vacuum procedure less expensive and so potentially more appealing for a large scale production. The basalt/SiCO composites are suitable for mechanical applications up to 600°C and stand up temperatures up to 1200°C, also in oxidative environments. Another key parameter in determining the production costs is the number of PIP steps, which has to be minimised. Two or three PIP steps could be a satisfactory compromise for many thermomechanical applications, on the condition that a suitable preform preparation and impregnation procedure were applied.


CP-1:IL05  Processing of Nonoxide Fiber Reinforced Composites with Enhanced Oxidation Stability
D. KOCH, B. MAINZER, M. KOTANI, M. FRIEß, Department of Ceramic Composites and Structures, Institute of Structures and Design, German Aerospace Center, Stuttgart, Germany

The development of future gas turbines or aero engines demands new long term stable materials which are resistant against oxidation and corrosion under flowing atmosphere at high temperatures. Nonoxide fiber reinforced ceramics are promising candidates for these applications however the oxidation stability is generally limited. Therefore enhanced fiber matrix interphases and matrices and also environmental barrier coatings have to be developed. While the fiber coatings have to protect the fibers during processing and against oxidation during operation the matrix should reduce pronounced oxidation. Actual research focusses on the development of dense matrix systems with improved fiber matrix interphases for damage tolerant behavior. Furthermore the matrix is modified by additives or layered structures which form glassy phases when oxygen enters the matrix. Finally, outer coating systems need to be developed with adjusted thermal expansion properties for higher thermomechanical stability.
Optional matrix processing techniques like modified polymer infiltration and pyrolysis or liquid metal infiltration are compared and the effect of oxidation protection of fiber coating and matrix will be assessed. The potential to produce oxidation stable nonoxide composites will be discussed.


CP-1:IL06  Silicon Carbide Fibers Prepared with Polycarbosilane through the Halide Curing Process
DOHHYUNG RIU, JUNSUNG HONG, YOUNGJIN KO, KWANG-YEON CHO, DONG-GEUN SHIN, JEONG-IL KIM, Seoul National University of Science and Technology, Seoul, Korea

We present the recent research works regarding silicon carbide fibers prepared through the halide curing process. This type of curing method enabled us to make a fine polycarbosilane precursor fiber whose melting point is below 150 °C. For precursors of low temperature melting point, application of thermal curing has been failed due to thermoplastic behavior of the polycarbosilane. When the fiber was treated with the halide gas, we could cure the precursor fiber at much lower temperature and even at room temperature. The curing mechanism and the properties of the fiber is investigted. We also have tried the curing method without any oxygen presence, through which we can get fairly silicon carbide fibers of low oxygen content. The halide element remained inside the fiber at 1300 °C. However, the high temperature properties of the fiber was maintained as much as 2 GPa at 1100 °C and above. With higher temperature sintering the fiber yielded halide free and near stoichiometric SiC fiber.


Session CP-2 - Interfaces and Interphases

CP-2:IL01  Mechanics of Interfaces/Interphases in CMCs
J. LAMON, CNRS/LMT/ENS Cachan, Cachan, France

The fibre/matrix interfacial domain must have dual characteristics. It must be weak enough so that matrix cracks can be arrested by fibers, and it must be such that subsequent strong fibre/matrix interactions can take place after crack deflection, in order that a significant part of the load is still carried by the matrix. Experimental and modelling efforts have been directed towards optimization of interface properties in CMCs. SiC/SiCCVI composites with strengthened interfaces have been obtained using interphases and treated fibres. A sound model of crack deflection must take into account the features of the interphase and the characteristics of all the interfaces located ahead of matrix crack.
Two main approaches to crack deflection have been proposed in the literature: either the matrix crack is supposed to reach the interface and to be lying stationary, or a crack is nucleated at the interface ahead of the matrix crack (Cook and Gordon mechanism). A previous work has shown that an energy based approach is unable to account for the influence of interphase/fiber interface strength on crack deviation. It appeared that a criterion for initiation of a debond crack ahead of matrix crack is required. The paper discusses a model based on the Cook and Gordon mechanism of crack deflection. The model is applied to various fibre reinforced composites with or without an interphase. Finally, the post-deflection behaviour of composites is examined with respect to interface resistance.


CP-2:IL02  Studies on Wettability and Infiltration in Ceramic-Metal Joints for Structural and Thermal Management Applications
R. ASTHANA¹, N. SOBCZAK², M. SINGH³, ¹Department of Engineering and Technology, University of Wisconsin-Stout, Menomonie, WI, USA; ²Center for High-Temperature Studies, Foundry Research Institute, Krakow, Poland; ³Ohio Aerospace Institute, Cleveland, OH, USA

The paper focuses on wettability and infiltration phenomena in liquid-phase joining of select ceramic, metallic, and carbon-based systems that have been developed for use in niche structural and thermal management applications. Liquid-phase methods such as brazing rely on wettability, flow and infiltration characteristics of diverse material systems to create joints that integrate geometrically simple units into complex structures and assemblies. High-temperature wettability data in liquid-solid systems, therefore, serve as a useful index of brazeability of materials. Recent research developments in contact angle measurements, interface characterization, and joining response of oxides, carbides, nitrides, borides, and carbon (dense and porous) in contact with a variety of molten metals and alloys will be presented and discussed. Special emphasis will be placed on the role that processing parameters (temperature, time, atmosphere), and materials parameters (composition, morphology, coatings, roughness) play in wetting, infiltration and joining. In non-reactive wettable systems, molten metals could infiltrate interconnected pores and inter-fiber regions in composites and facilitate bonding via mechanical keying. In reactive systems, dissolution, reaction, segregation, and compound formation at the interface promote chemical bond formation. Specific examples shall include carbon with Al containing Si, Ti, Cr, and Zr; carbon foam and carbon-carbon with AgCuTi; monolithic SiC, SiC-SiC and C-SiC with AgCuTi with or without a reinforcement; ZrB₂-based ceramics with Pd-Co and Pd-Ni; single crystal and polycrystalline alumina with Al; and YSZ with various Ti-containing alloys. Challenges in addressing wettability and joining issues in ceramic composites displaying extensive compositional and structural inhomogeneity, and low inter-laminar shear strength shall be identified together with the ubiquitous challenges posed by residual stresses from thermal expansion mismatch and their resolution via established stress mitigation strategies. Generalizations concerning the wetting, infiltration and joining behaviors shall be attempted and certain anomalies and unresolved issues shall be highlighted together with suggestions for continued research.


CP-2:L03  Tailoring of the Fiber-Matrix Interface in Ceramic Matrix Composites by the Wet Chemical Deposition of Boron Nitride
A. NOETH, Fraunhofer Institute for Silicate Research, Center for High Temperature Materials and Design, Würzburg, Germany; L.D. TOMA, Fraunhofer Institute for Silicate Research, Center for High Temperature Materials and Design, Bayreuth, Germany

In order to achieve damage tolerant fracture behaviour of dense ceramic matrix composites (CMCs), a weak fiber-matrix interface is needed, which is typically realized by fiber coating with the chemical vapor deposition (CVD) process. In this paper the development of a viable fiber coating process by a wet chemical route is described, which is potentially cost-efficient and easy to upscale. High coating speeds of up to 1000 m/h can be accomplished. The weak fiber-matrix interface was realized by a boron nitride (BN) layer deposited both on carbon and silicon carbide fibers. The BN coating was approved by X-ray diffraction measurements. A top coating, e.g. silicon carbide, was applied to protect the fibers from their degradation when the liquid silicon infiltration (LSI) process is used. The coating quality was improved by the variation of the deposition parameters like the concentration of the solutions, the drawing speed, and the drying and curing temperatures. The deposited layers and the fiber matrix bonding were investigated by electron microscopy. The mechanical performance and the fracture behaviour of CMCs based on the coated fibers will be discussed.

 
Session CP-3 - Processing and Fabrication of MMCS, CMCS, and C/C Composites

CP-3:IL01  Advanced CMCs Design for Lightweight and High Temperature Applications
W. KRENKEL, Ceramic Materials Engineering, University of Bayreuth, Bayreuth, Germany

Reactive Melt Infiltration (RMI) processes offer advantageous properties like short processing times and near-net shape manufacture for the fabrication of CMCs. Dense preforms of fibers, temporary carbonaceous polymer binders and optional reactive particles are made in a first step. During the subsequent heat treatment in an inert atmosphere (pyrolysis) the binder is converted to amorphous carbon resulting in a micro-cracked matrix of high open porosity and high permeability. Within the third process step, metallic alloys of low viscosity and high reactivity are infiltrated into this connected system of pores and microcracks and high capillary forces allow a fast filling of the preform. The simultaneously conducted formation of the ceramic matrix is a diffusion-controlled process near the melting point of the metallic alloy. As a result, carbon fiber reinforced composites with matrices of silicon carbide, MAX-phases or UHTCs can be formed. This paper shows the development of short fiber as well as fabric-reinforced composites with matrices of SiC, Ti3SiC2 as well as HfC and describes the relationship between the fiber preform, the processing parameters and the resulting microstructures and properties of these RMI-derived CMC materials.


CP-3:IL03  Short-fiber Reinforced Oxide/Oxide Composites
T. WAMSER, S. SCHELER, B. MARTIN, W. KRENKEL, Ceramic Materials Engineering, University of Bayreuth, Bayreuth, Germany  

In recent years several manufacturing processes for endless fiber reinforced oxide fiber composites were presented. The focus regarding the fiber architecture lies on laminated composites based on fabrics and on rotation-symmetric components, which are produced with winding techniques. However, complex geometries are not possible because of the poor textile processability of the brittle rovings. That is why short-fiber reinforced oxide/oxide composites are an interesting alternative. The presented processing method for short-fiber reinforced composites can be divided in two steps. First, suitable fiber preforms are made of chopped fiber rovings. Secondly, the fiber preforms are infiltrated with slurries to design the matrix. It is shown, that the adapted processing leads to homogeneous microstructures and good mechanical properties can be achieved by adjusting high fiber volume contents.


CP-3:IL04  Ultra High Temperature Metal Matrix Composites
S.T. MILEIKO, Institute of Solid State Physics of RAS, Chernogolovka, Russia

Heat resistant metal matrix composites (MMCs) characterized by high fracture toughness at low temperatures are to occupy its own niche within the temperature range from 1100 to about 1600 °C. Composites based on nickel alloy matrices have the use temperature up to 1200 °C. A review of the corresponding research results is presented in the full text paper. The composites are reinforced with eutectic oxide fibres obtained by the internal crystallization method.
A further enhance in the use temperature is reached by using a refractory metal (either molybdenum or niobium) if low oxidation resistance of it is overcome. The first experiments with oxide-fibre/molybdenum-matrix composites have shown a possibility to design a creep resistant composite with high values of fracture toughness and high oxidation resistance, the use temperature of which is as high as 1300 °C. Prospects to develop MMCs with even higher use temperature are discussed.


CP-3:L05  Multilayered Fiber-reinforced Oxide Composites Produced by Lamination of Thermoplastic Prepregs 
R. JANSSEN, D. PAULA GUGLIELMI, Technische Universität Hamburg-Harburg, Germany; D. BLAESE, M. HABLITZEL, G. NUNES, V. LAUTH, D. GARCIA, H.A. AL-QURESHI, D. HOTZA, Universidade de Santa Catarina at Florianoplois, Brazil

For advanced ceramics composites, affordable manufacturing is still the most essential shortcoming with respect to successful commercial use. This holds particularly for components made out of composites with complex hierarchical structure and high demands of mechanical performance and reliability at the same time, e.g. fibre-reinforced ceramic composites (FRCMCs). Therefore, we developed a new processing route based on the lamination of thermoplastic prepregs which allows not only affordable manufacturing but also advanced mechanical reliability. Basically, the route integrates processing techniques well known in the ceramic community: (a) manufacturing of 2 D prepregs using commercial fiber fabrics which will be infiltrated with compounds of ceramic particles embedded in an organic matrix, (b) followed by respective stacking, (c) burn out of the organic matrix, (d) subsequently sintering to consolidate the matrix and (e) final treatment to stabilize the porosity needed to obtain the desired interface behaviour.
In the presentation, the focus is on porous  Al₂O₃/ZrO₂ matrix reinforced  by NEXTEL 6190 textile. Composites of 8 layers exhibit a bending strength of 440 MPa with graceful failure behavior, e.g. a stepwise stress reduction after peak nominal stress. The fracture of these composites is controlled by a series of interfacial delamination events, which enhance energy dissipation during failure. The results are reasoned considering theoretical predictions from the well-known He and Hutchinson model as well as features from the fracture surfaces of the composites. Lastly, emphasis will be given in the presentation to the joining and tailoring options given by the new processing route.

 
Session CP-4 - Ultrahigh Temperature Ceramic Composites (UHTCCs) and Laminated Composite Structures

CP-4:IL01  Coating and Matrix Modification with Ultrahigh Temperature Ceramics for Carbon Fiber Reinforced SiC Matrix Composites
SHAOMING DONG, L.R. ZHANG, X.Y. ZHANG, L. GAO, State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China

Carbon fiber reinforced SiC ceramic matrix composites (Cf/SiC) show low density, high strength at room and high temperature, good oxidation and ablation resistance, which make them important materials suitable for aerospace applications. However, the applying temperature of Cf/SiC composites is limited at 1650 DC, because of the active oxidation of silicon carbide at temperature above that. To improve the high-temperature performance of Cf/SiC composites, ultra high temperature ceramic (UHTC) component are often introduced in the matrix and coatings. These composites combine advantages of UHTCs and Cf/SiC composites, showing superior ablation/oxidation resistance at temperature over 1800 DC. In present study, UHTC matrix is produced by polymer infiltration and pyrolysis process and in situ reaction sintering method. UHTC coatings are prepared by chemical vapor infiltration technique. The microstructures, phase assemblages and ablative properties of the materials are studied. Both microstructure and phase evolution during the oxidation and ablation process are investigated. The result indicated that the oblation property of UHTC based composites are much better than that of Cf/SiC composites, mainly due to the formation of UHTC oxides on the material surface during testing.


CP-4:IL02  Fibres Reinforced SiC Matrix Composites Modified by Ti3SiC2
XIAOWEI YIN, LITONG ZHANG, LAIFEI CHENG, Science and Technology on Thermostructural Composite Materials Laboratory, Northwestern Polytechnical University, Xi'an, China

Owing to the unique nanolaminate crystal structure, the MAX phases with A = Al and Si offer superior mechanical properties, which make them a potential reinforcement for brittle ceramic matrix materials. Capillary driven infiltration of a reactive melt allows near-net shape manufacturing of MAX phase reinforced composites with high flexibility in component geometry at low production costs. Formation of MAX phase in fiber reinforced ceramic matrix composites could improve not only the mechanical properties but also the wear resistance and oxidation resistance, extending the application fields of advanced ceramic composite materials. This review work will focus on the microstructure and properties of fibers reinforced SiC matrix composites modified by Ti3SiC2.
References:
[1] Xiaowei Yin*, Shanshan He, Litong Zhang, et al, Mater Sci and Eng A 527, 3, 835-841, (2010).
[2] Beiya Nan, Xiaowei Yin*, J Am. Ceram. Soc., 94, 4, 969-972(2011).
[3] Xiaomeng Fan, Xiaowei Yin*, Shanshan He, Litong Zhang, Laifei Cheng, Wear, 274-275, 188-195(2012).
[4] Xiaomeng Fan, Xiaowei Yin*, Lei Wang, Laifei Cheng, Litong Zhang, Corrosion Science 74, 98-105(2013).


CP-4:IL05  Mechanistic Aspects of the Strength and the Fracture Toughness of Laminated Polymer-ceramic Composites 
K. TUSHTEV, University of Bremen, Bremen, Germany

For several decades, many efforts have been focused on the enhancement of the ability of advanced ceramics for both structural and functional applications to resist crack propagation. Biological structures like shells of nacre, teeth or glass sponges, which comprise both strength and flexibility by joining hard and brittle minerals with minor organic phase, are one source of inspiration for designing multilayer ceramic composites with improved fracture resistance. The feasibility of fabrication of bioinspired multilayered ceramic composites with very high crack resistance is demonstrated by bounding of zirconium oxide sheets of 70 micrometers thickness with only a few micrometers thin adhesive layers. The small amount of organic adhesive of approx. 6 vol% provides the composites with a crack resistance which is about four times as high as that of the basic ceramic material. For several material variants, the fracture behaviour is correlated to the individual performance of the used adhesive and to the overall composite structure. In the case of composites with strong interfaces, the mechanisms of stress redistribution and the ability of the composites to prevent catastrophic failure are explained by numerical simulation.

 
Session CP-5 - Property, Modeling and Characterization

CP-5:IL01  Microstructure and Properties of C/SiC/GH783 Joint Brazed with Cu-Ti + Mo
SHANGWU FAN, XING WANG, LAIFEI CHENG, LITONG ZHANG, Science and Technology on Thermostructural Composite Materials Laboratory, Northwestern Polytechnical University, Xi'an, Shaanxi, China

Using Cu-Ti + Mo composite filler, C/SiC composites were brazed to GH783 under vacuum condition. The microstructure and properties of the joints were investigated. The results showed that the joints were composed of four regions: a reaction layer, a stress relief layer, a residual Cu layer and a diffusion layer. The maximum flexural strength of the joints with 10 vol.% Mo particles reached 198 MPa. The additional Mo released the joint residual stress, inhibited Ti and C/SiC excessive reaction, and thus effectively improved the strength of joints. The flexural strength of the joint with Cu-Ti + 10 vol.% Mo composite filler decreased dramatically with the increase of thermal shock times in air at 800 °C. The flexural strength of the joint after 5, 10 and 15 times thermal shock was about 42.9%, 22.7% and 9.7% of the initialize strength, respectively. The flexural strength of the joint with Cu-Ti + 10 vol.% Mo decreased dramatically with the increase of environment temperature. The flexural strength of the joint at 600 °C, 800 °C and 900 °C was about 60%, 39% and 29% of that at room temperature, respectively.


CP-5:L02  Effect of Loading Rate on the Behaviour of Partially Pyrolyzed Basalt Fibre Reinforced Composite
M. HALASOVA¹, Z. CHLUP¹, M. CERNY², A. STRACHOTA³, Z. SUCHARDA², I. DLOUHY¹, ¹Institute of Physics of Materials, Academy of Sciences of the Czech Republic, v.v.i., Brno, Czech Republic; ²Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, v.v.i., Prague, Czech Republic; ³Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Prague, Czech Republic

Several basalt fibre reinforced composites based on SiOC glass derived from the polysiloxane resins were prepared at different pyrolysing temperature regimes. Very high fracture resistance was measured for unidirectional fibres, in the range of 20 MPa.m1/2 at room temperature. When the woven fabric was used as reinforcement, the good properties remained on the satisfactory level. The fracture toughness and flexural strength were observed at quasi-static loading. The effect of higher loading rates was investigated using an instrumented impact pendulum accompanied by a high speed camera. Significant change in the fracture behaviour was observed and higher consumption of energy was obtained for higher loading rates. All results were supported by fractographic observation of fracture surfaces.


CP-5:L03  Lifetime Prediction with Acoustic Emission during Static Fatigue Tests on Ceramic Matrix Composite at Intermediate Temperature under Air
E. MAILLET, N. GODIN, M. R'MILI, P.L REYNAUD, G. FANTOZZI, J. LAMON, INSA-Lyon, Laboratoire MATEIS, Villeurbanne, France

A main purpose of this paper is to consider the possibility of predicting rupture time of SiCf/[Si-B-C] composites, under static fatigue at 450 °C under air, from damage evolution recorded by acoustic emission technique. A new method has been developed in order to evaluate attenuation coefficient, with AE monitoring, in real-time due to damage. During the static fatigue test, attenuation coefficient B increases significantly during the first half of tests and reaches a plateau value at approximately 50% of the rupture time. The increase of attenuation coefficient B may be related to matrix crack opening. In static fatigue under air, matrix crack opening controls the oxygen flux that reaches interphases and fibers. The plateau observed on the evolution of B indicates that matrix crack opening gets to an equilibrium state around 50% of the rupture time. Beyond that point, the imposed oxygen flux controls the speed at which fibers break by subcritical crack growth. This critical aspect corresponds to a second damage phase where subcritical crack growth in fibers is predominant, leading to ultimate failure of the composite. The monitoring of B constitutes a new indicator for damage monitoring of CMC and the detection of the plateau is an indicator for lifetime prediction.


CP-5:L04  Water Vapour Corrosion of Oxide Ceramic Matrix Composites (O-CMC) in Hot Gas Environments
A. RÜDINGER, C. ECKARDT, F. RAETHER, Fraunhofer Institute for Silicate Research ISC / Centre for High Temperature Materials and Design, Bayreuth, Germany

Oxide Ceramic Matrix Composite (O-CMC) parts can substitute metallic components very successfully in a number of applications where a long-term stability at high temperatures is required. O-CMC offer much higher thermal stability in hot gas atmospheres containing water vapour and show better performance under thermal cycling conditions.
The O-CMC samples for the determination of mechanical properties were made of 3MT NextelT fibers 610 and 720 along with different matrices in the system of alumina / zirconia and mullite.
The mechanical properties of the O-CMC after exposure at 1000 °C and 1150 °C for 10, 100 and 500 hours dwell in different atmospheres, dry and 4 % water vapor content respectivly, were investigated. In this regard interlaminar shear strength, three-point bending strength, Young´s modulus and elongation at fracture were determined. In order to detect corrosion and aging mechanisms concerning the influence of the hot gas exposure to the mechanical properties, microstructural analyses were carried out. In this context the characterization focussed on SEM and XRD as well as the investigation of density, porosity and mass loss of the specimen.
For comparison purposes the experimental and the testing program was also conducted with a commercial available O-CMC-material.


CP-5:IL05  From Images to Property Computations in Carbon-carbon Composites at Various Scales 
G.L. VIGNOLES, J.-M. LEYSSALE, B. FARBOS, P. WEISBECKER, O. CATY, G. COUÉGNAT, M. CHARRON, P. ENGERAND, Lab. For ThermoStructural Composites (LCTS), University Bordeaux/CNRS, Pessac, France; J.-P. DA COSTA, Institute from Materials to Systems (IMS), University Bordeaux, Talence, France

Carbon-carbon composites are outstanding materials in extreme aerospace & energy applications. Their design rests on the knowledge of the properties of their constituents and of their relative arrangement in space; however, as opposed to other ceramic-matrix composites, this task is particularly difficult, because: (i) at the nanometer scale, the carbon phases have a versatile non-ideal nanotexture; (ii) at the fiber and fabric scales, the variety of fiber shapes and packing as well of the woven/stitched reinforcement architectures may be poorly captured by virtual weaving approaches.
We will focus on the use of image analysis and synthesis in the prediction of Carbon-Carbon composites properties, at 3 scales.
First, the nanotexture of pyrocarbon matrices is captured by the Image-Guided Atomistic Reconstruction method, giving a better insight into their structure-property relationship.
At the fiber scale, effective mechanical and thermomechanical properties from the direct imaging of a transverse bundle have been obtained and correlated to image properties.
At the fabric scale, the thermal expansion of composites reinforced by stitched fiber plies has been computed from X-ray CMT scans. The results give a consistent view of the role of every structural component.


CP-5:IL06  SiC/SiC Composites for Nuclear Applications 
T. HINOKI, Kyoto University, Uji, Kyoto, Japan

SiC/SiC composites are considered as promising materials for nuclear applications due to its enhanced toughness by fiber reinforcement and intrinsic properties of SiC such as low activation, chemical and environmental inertness, irradiation stability, and high temperature performance. Excellent stability to high temperature steam makes SiC/SiC composites attractive as cladding materials for light water reactor.
The mechanical properties of ceramic matrix composites depend on the properties of their constituents (e.g. fiber, matrix and interphase), geometry and concentration of constituents and residual stress between fiber and matrix. It is important to evaluate irradiation effect on the constituents and the residual stress to understand irradiation effect on mechanical properties of SiC/SiC composites. The residual stress is attributed to coefficient of thermal expansion mismatch of constituents during fabrication process. The residual stress is affected by the differential swelling of the constituents and irradiation induced creep following irradiation.
This paper reviews the current status of SiC composites for the nuclear application including material development, irradiation effect and environmental effect such as high temperature steam and discusses issues.

 
Session CP-6 - Composites for Thermal Management. Applications of Inorganic Fiber Composites

CP-6:IL01  Mechanical Reliabilities of High-Thermal-Conductivity Silicon Nitride In-Situ Composites
T. OHJI, Y. ZHOU, H. HYUGA, K. HIRAO, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Japan

For substrate materials for next generation power devices, silicon nitride in situ composites with high thermal conductivities and high fracture toughness were developed via nitridation of Si powder compacts followed by post-sintering. The thermal conductivities and fracture toughnesses of SRBSN composites were increased with increasing sintering time. The conductivities of the samples fabricated under reducing nitridation atmosphere followed by post-sintering of 3, 6, 12 and 24 hrs were 109, 125, 146, and 154 W/(mK), respectively. The toughness values, determined by the single-edge-precracked-beam (SEPB) method, were 8.4, 8.6, 9.7, and 10.7 MPa m1/2 for the materials sintered for 3, 6, 12, and 24 h, respectively. The high fracture toughness is attributable to the weak beta-Si3N4/oxynitride-glass interfacial bonding strength and large residual tensile stresses at the grain boundary that enhanced the crack-bridging toughening effects. In addition, their fracture resistance behaviors with crack extension were evaluated by chevron-notched beam methods; the materials sintered for longer times (12 and 24 h) showed stronger R-curve behaviors over longer range of crack extension, in comparison with the materials sintered for shorter times (3 and 6 h).


CP-6:IL03  Metastable Phases and Microstructures in Alumina-silica Glasses and Mullite Ceramics
S. RISBUD, University of California, Davis, CA, USA

Understanding metastability, liquid-liquid immiscibility, and precipitation of mullite crystalline phase solid solutions are important issues in the alumina-silica system. Ceramic literature dating back to the classic study of Bowen and Grieg in the 1920s showing mullite as the only stable phase has been followed by several phase diagram studies which will be reviewed in the first part of my talk. Metastability in the silica-alumina system is equally interesting both from a fundamental standpoint and practical applications of refractory mullite ceramics and composites. Success of new ceramic processing technologies has made it possible to make materials by rapid melt-quenching, sol-gel techniques, or other non-equilibrium methods. I will revisit previous work in the ceramics literature on mapping metastable phase boundaries of different phase systems (e.g. silica-alumina without mullite, or silica-mullite without alumina) and immiscibility domes applicable to glass-ceramic technologies. Recent efforts in my group to characterize samples by high resolution imaging in the electron microscope will be discussed. Examples of the usefulness of metastable diagrams in the refractory industry to engineer products for high temperature service will be given.


CP-6:L04  The Thermal-physical Property of C/SiC Composites
HAIJUN ZHOU, SHAOMING DONG, PING HE, LIANGRUN ZHANG, LIN LIN, Structural Ceramics and Composites Engineering Research Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China

Carbon fibers reinforced silicon carbide matrix (C/SiC) composites are one of the most promising materials for high temperature structural applications, due to their high specific strength, high specific modulus and excellent mechanical properties at high temperature. The thermal physical property of materials is the key factor for these thermal protection system components design. In order to get clear guideline for design of the SiC matrix of C/SiC composites, chemical vapor infiltration (CVI) followed by polymer infiltration and pyrolysis (PIP) or liquid silicon infiltration (LSI) process are developed to fabricate C/SiC composites in this work. Effects of these two combinations of SiC matrix on the microstructure of C/SiC composites are examined. The thermal physical property with various proportions SiC matrix of C/SiC composites are also studied in present work.


CP-6:IL05  C/C and CMC-composites for Industrial Applications
R. WEISS, Schunk Kohlenstofftechnik GmbH, Heuchelheim, Germany 

Industrial applications of CMC-composites are mainly cost-driven. The technical requirements depend on the field of application and have to be cost efficient. Therefore, all high temperature composites for industrial applications have to be tailored in order to fulfil mechanical, thermal and corrosion requirements with respect to costs and life time.
All these requirements can only be fulfilled by a variety of CMC-materials. Improved cost efficiency of carbon/carbon for photovoltaic industry can be realized by reduction of material and processing costs or by improved C/C-properties which will be demonstrated in more detail.
For applications in semi conductor industry reliability improved purity and best corrosion resistance are an absolute need. State of the art and future improvements will be demonstrated.
Various applications of C/C-SiC materials will be shown with respect to the requirements of the final components.


CP-6:IL06  Joining of SiC-based Materials for Nuclear Applications
M. FERRARIS, Politecnico di Torino, Department of Applied Science and Technology - DISAT - Institute of Materials Physics and Engineering, Torino, Italy 

SiC-based materials are being considered the primary candidates for components in the field of advanced nuclear reactor technology. A critical issue for a wider use of these materials is the development of sound joining materials and technologies to assemble large components into more complex structures.
An overview on the most promising joining techniques and materials for SiC-based components to be used in a nuclear environment will be given, in particular on pressure-less joining methods.
Issues related to the mechanical characterization of the joints will be also discussed.
The use of glass-ceramics as joining materials in a neutron environment will be briefly reported.


CP-6:IL07  SiTE-SiCf/SiC Composite for Application in Future Fusion Reactors
S. NOVAK^{1, 2, 3}, A. IVEKOVIC^{1, 2, 3}, ¹Department for Nanostructured Materials, Jozef Stefan Institute, Ljubljana, Slovenia; ²Jozef Stefan International Postgraduate School, Ljubljana, Slovenia; ³Slovenian Fusion Association (SFA) Euratom MESCS 

Fusion energy has a potential to comply the anticipated worldwide energy needs in the future. In order to fulfil the promise to provide safe, economical, and environmentally acceptable energy, carefully selected structural materials capable to resist extreme conditions are needed.
Silicon carbide (SiC) is due to its high thermal, mechanical and chemical stability regarded as one of the most promising candidates for structural material in future fusion power plants. It has low neutron activation and it is stable at temperatures above 1000 °C, which would enable higher energy efficiency of the power plant in comparison to other candidate materials. Due to its inherent brittleness, reinforcement with continuous SiC-fibers is proposed. However, densification of the SiCf/SiC composites is quite a challenging task. The recently developed SiTE process involves two steps: fine SiC powder in aqueous suspension is electrophoretically infiltrated into the 3D-fiber preform to fill the large voids and then the remaining pores are impregnated with a pre-ceramic polymer, which after thermal treatment transforms to pure polycrystalline SiC. The processes will be described and the properties of the resulting composite discussed in terms of the proposed application.


CP-6:IL08  Development of a High-temperature High-efficiency Thermal Energy Storage System for Concentrated Solar Power
D. SINGH¹, T. KIM¹, W. ZHAO¹, D. FRANCE¹, W. YU¹, A. GYEKENYESI², M. SINGH², ¹Argonne National Laboratory, Argonne, IL, USA; ²Ohio Aerospace Institute, Cleveland, OH, USA

This presentation will focus on the development of a high efficiency thermal energy storage (TES) system. Proposed high thermal conductivity, low-density graphite foams infiltrated with a phase change material (PCM) salt offers a combined system with significantly greater thermal conductivities than the salt alone. A detailed thermal analysis was conducted of the proposed latent heat thermal energy storage to quantify the benefits of the proposed system. It was determined that the solidification thickness/front increased by an order of magnitude as the effective PCM thermal conductivity increased from 0.3 W/mK (no foam) to 85 W/mK by the addition of the graphite foam. As part of the materials development effort, graphite foam samples were received from a commercial vendor and characterized. Results on the detailed characterizations of the foam samples will be presented, including porosity measurements, coefficient of thermal expansion, mechanical properties and oxidation behavior.  Further, it was demonstrated that use of protective ceramic coatings  prevent oxidation of the graphite under the expected operating conditions.
Acknowledgements
This work was supported by the US Department of Energy’s EERE Solar Energy Technology Program (Sunshot Initiative) at Argonne National Laboratory, a US Department of Energy’s Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC.
 
 
Poster Presentations

CP:P02  Evaluation of Properties of Glass Wool Reinforced Plastic Composite
M. TSUKAMOTO^{1, 2}, Y. YOSHIMURA^{2, 3}, Y. KUROKI², T. OKAMOTO², M. TAKATA^{2, 4}, ¹MAG-ISOVER K.K., Kasumigaura, Ibaraki, Japan; ²Nagaoka University of Technology, Nagaoka, Niigata, Japan; ³Yoshimura Co., Ltd., Kuki, Saitama, Japan; ⁴Japan Fine Ceramics Center, Atsuta-ku, Nagoya, Japan

Glass wool is discontinuous glass fiber with the average diameters of 3-4 μm produced by means of centrifugal process. Glass wool is mainly applied to heat and acoustic insulation. But, there are few reports on glass wool applied to reinforcement of plastic materials in which chopped strand made by chopping continuous glass fiber is used primarily. In this study, the polypropylene-based composite material samples containing of glass wool were synthesized and some properties such as tensile strengths were evaluated. The treatment of glass wool with 3-amino propyl triethoxy silane coupling agent together with epoxy resin emulsion enhanced the tensile strength of the composite samples including the glass wool. The tensile strength reached to the same level of the conventional composite samples including chopping continuous glass fiber. This result suggested that glass wool has a good potential as a reinforcing material in thermoplastic composites.


CP:P03  Microstructural Characterization of Stone Wool Materials
L. CHAPELLE¹, P. BROENDSTED², Y. KUSANO², M. ROSENDAHL FOLDSCHACK¹, D. LYBYE¹, ¹ROCKWOOL International A/S, Frederiskberg, Denmark; ²DTU Wind Energy

Stone wool consists of a network of amorphous alumina silicate fibres kept together by a polymer phase. Stone wool materials are broadly encountered in everyday life as thermal and acoustic insulation and damping materials. The mechanics of these materials are defined by the structure of their fibre network and by the mechanical behaviour of individual fibres. To evaluate the relationship between the microstructure and the fibre network properties, knowledge of the microstructure is needed and thus methodologies for the microtructural characterisation of fibre networks should be developed. The structure is characterized by a number of parameters, such as the density, the fibre orientation, length and diameter as well as the number of cross-links between fibres. In the present study, 2D and 3D methods to determine those parameters and quantify the microstructure of stone wool materials are presented. Samples preparation, image acquisition, algorithms for image analysis and statistical analysis of the data will be outlined.


CP:P04  Fracture Toughness Evaluation of Ceramic Substrates Using Precracked Specimens
H. MIYAZAKI,  Y. YOSHIZAWA, K. HIRAO, T. OHJI, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Japan

The heat dissipating board for the power modules usually consists of a ceramic substrate such as aluminum nitrides or silicon nitrides sandwiched by copper plates. The mechanical sustainability of the substrate after sever heat cycles is significant issue because thermal stress due to thermal expansion mismatch between Cu and ceramic plates damages the substrate. The fracture toughness, KIC, of thin ceramic plate is a main factor which controls the thermal fatigue of the heat dissipating board. However, a test method of KIC for such a thin ceramic plate with a thickness of ~0.32 mm has not been studied systematically. In this study, KIC of both thin AlN and Si3N4 plates was measured using a single-edge precracked beam. A small, thin single-edge notched beam was bonded on one side of a metallic beam and the assembly was deformed in three-point bending to introduce the precrack. The single edge-precracked specimen was then removed from the beam and KIC was measured using standard single edge-precracked beam (SEPB) method. KIC obtained using this method was compared with that obtained for the standard specimens by SEPB method.
Part of the research work was supported by NEDO, Japan.