and manufacturing ELSEVIER Composites: Part A 30(1999)537-547 Micro/minicomposites: a useful approach to the design and development of non-oxide cmcs Roger Naslain", Jacques Lamon, Rene Pailler, Xavier Bourrat, Alain Guette, Francis Langlais aboratory for Thermostructural Composites, UMR-47(CNRS-SEP-UB1), University of bordeaux. 3 Allee de la boetie, 33600 Pessac, france Micro(one single filament)and mini (one single fiber tow) non-oxide composites(C/C; C/SiC and SiC/SiC)with simple(Pyc or BN)or complex interphases [C (B)or(Pyc-SiC) multilayers] are fabricated in a short time by CVD/CVI. The fiber/matrix interfacial zone is characterized by aEs and TEM. Tensile tests are used to assess the mechanical properties and the weibull statistical parameters of both the fiber and matrix, as well as the fiber-matrix interfacial parameters(Ti Id, Gis). The tensile stress-strain behaviour has been modelled. The tensile curves exhibit the same features as those previously reported for real nD-composites. Lifetime at high temperatures in air is characterized through static/cyclic fatigue tests and modelled. It is improved by replacing conventional pyrocarbon by highly engineered interphases. The micro/mini composite approach is used in the optimization of processing conditions and to derive parameters necessary fo the modelling of the thermomechanical and chemical behaviour of composites with more complex fiber architectures. o 1999 Elsevier Science ltd. All rights reserved Keywords: A Ceramic matrix composites(CMCs); Model composites; B. Interface/interphase 1. Introduction CMC, which requires several processing/characterization be tir Non-oxide ceramic matrix composites(CMCs), such as fabrication technique. Moreover, the complexity of real C/C, C/SiC or SiC/SiC composites, usually exhibit a fiber architectures often precludes the derivation of simple complex fiber architecture(2D, 2.5D or 3D). They are correlations between composite properties and processing produced according to liquid or gas phase routes requiring conditions relatively long processing times. In the liquid phase routes, within the scope of the design and development of new the starting fibrous material is impregnated with a liquid materials it can be more appropriate to use ID model precursor of the matrix, e.g. a slurry or an organic/organo- composites, such as the microcomposites or the minicom metallic polymer, and pyrolysed at high temperature. The posites(comprising one single fiber or one single tow, impregnation/pyrolysis sequence is repeated several times respectively), in order to conduct several processing/char- in order to achieve a high densification level. In the ga acterization iterative loops in a relatively short time phase routes, such as the isothermal/isobaric chemical Furthermore, for such very simple fiber architectures vapor infiltration process(I-CVI), a porous fiber preform micromechanics-based models exist which can be used to is infiltrated with the matrix deposited from a gaseous derive useful material parameters, such as load transfer precursor(a hydrocarbon for carbon and a chlorosilane for parameters, from simple mechanical tests [5,6]. Examples SiC). The deposition process should be conducted at low of studies conducted via the use of the micro/mini compo- temperature and low pressure, in order to avoid an early site approach, have been already reported in the field of non- sealing of the pore entrances. The densification duration oxide materials, however it is not by far a generalised way can be relatively long, depending on the size of the preform for designing CMCs and for optimising their processing and the residual porosity [1]. Although accelerated CVI- conditions [7-191 processes have been proposed, the densification duration Micro/mini model composites have been used during is still of several tens of hours [2-4]. Thus, the optimizatio almost one decade at LCts to optimize the fiber-matrix of the composition and the processing conditions for a given ( FM)interfacial zone in SiC/SiC composites and to generate micromechanical data necessary for modelling the mechan- en四+3006 ical behaviour. More recently, the approach has been tended to cc co 1359-835X/99/S- see front matter @1999 Elsevier Science Ltd. All rights reserved P:S1359-835X(98)00147-XMicro/minicomposites: a useful approach to the design and development of non-oxide CMCs Roger Naslain*, Jacques Lamon, Rene´ Pailler, Xavier Bourrat, Alain Guette, Francis Langlais Laboratory for Thermostructural Composites, UMR-47 (CNRS-SEP-UB1), University of Bordeaux, 3 Alle´e de La Boe¨tie, 33600 Pessac, France Abstract Micro (one single filament) and mini (one single fiber tow) non-oxide composites (C/C; C/SiC and SiC/SiC) with simple (PyC or BN) or complex interphases [C (B) or (PyC-SiC)n multilayers] are fabricated in a short time by CVD/CVI. The fiber/matrix interfacial zone is characterized by AES and TEM. Tensile tests are used to assess the mechanical properties and the Weibull statistical parameters of both the fiber and matrix, as well as the fiber–matrix interfacial parameters (ti; ld; Gic). The tensile stress–strain behaviour has been modelled. The tensile curves exhibit the same features as those previously reported for real nD-composites. Lifetime at high temperatures in air is characterized through static/cyclic fatigue tests and modelled. It is improved by replacing conventional pyrocarbon by highly engineered interphases. The micro/mini composite approach is used in the optimization of processing conditions and to derive parameters necessary for the modelling of the thermomechanical and chemical behaviour of composites with more complex fiber architectures. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: A. Ceramic matrix composites (CMCs); Model composites; B. Interface/interphase 1. Introduction Non-oxide ceramic matrix composites (CMCs), such as C/C, C/SiC or SiC/SiC composites, usually exhibit a complex fiber architecture (2D, 2.5D or 3D). They are produced according to liquid or gas phase routes requiring relatively long processing times. In the liquid phase routes, the starting fibrous material is impregnated with a liquid precursor of the matrix, e.g. a slurry or an organic/organo￾metallic polymer, and pyrolysed at high temperature. The impregnation/pyrolysis sequence is repeated several times in order to achieve a high densification level. In the gas phase routes, such as the isothermal/isobaric chemical vapor infiltration process (I-CVI), a porous fiber preform is infiltrated with the matrix deposited from a gaseous precursor (a hydrocarbon for carbon and a chlorosilane for SiC). The deposition process should be conducted at low temperature and low pressure, in order to avoid an early sealing of the pore entrances. The densification duration can be relatively long, depending on the size of the preform and the residual porosity [1]. Although accelerated CVI￾processes have been proposed, the densification duration is still of several tens of hours [2–4]. Thus, the optimization of the composition and the processing conditions for a given CMC, which requires several processing/characterization loops, can be time consuming whatever the nature of the fabrication technique. Moreover, the complexity of real fiber architectures often precludes the derivation of simple correlations between composite properties and processing conditions. Within the scope of the design and development of new materials it can be more appropriate to use 1D model composites, such as the microcomposites or the minicom￾posites (comprising one single fiber or one single tow, respectively), in order to conduct several processing/char￾acterization iterative loops in a relatively short time. Furthermore, for such very simple fiber architectures, micromechanics-based models exist which can be used to derive useful material parameters, such as load transfer parameters, from simple mechanical tests [5,6]. Examples of studies conducted via the use of the micro/mini compo￾site approach, have been already reported in the field of non￾oxide materials, however it is not by far a generalised way for designing CMCs and for optimising their processing conditions [7–19]. Micro/mini model composites have been used during almost one decade at LCTS to optimize the fiber–matrix (FM) interfacial zone in SiC/SiC composites and to generate micromechanical data necessary for modelling the mechan￾ical behaviour. More recently, the approach has been extended to C/C composites [20]. The aim of the present Composites: Part A 30 (1999) 537–547 1359-835X/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-835X(98)00147-X * Corresponding author. Tel.: 133-5-56844706; fax: 133-5-56841225; e-mail: admin@lcts.u-bordeaux.fr