CERAMICS INTERNATIONAL ELSEⅤIER Ceramics International 28(2002)899-905 www.elsevier.com/locate/ceramint Microstructural evolution and mechanical performances of SiC/SiC composites by polymer impregnation/ microwave pyrolysis (PIMP) process S M. Donga,*, Y. Katoh, A. Kohyama, S.T. Schwab, LL. Snead CREST-ACE, JST and Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan Thor Technologies, Inc. 7600 Jefferson NE, Suite 9-115. Albuquerque, NM Metals and Ceramic Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831-6087, US.A Received 8 January 2002: received in revised form 9 February 2002: accepted 26 March 2002 SiC/SiC composites were prepared by polymer impregnation /microwave pyrolysis(PIMP) process, and their microstructural evolution and the mechanical performances were characterized Using non-coated Tyranno Sa fiber preforms as reinforcement and impregnation with only allylperhydropolycarbosilane(AHPCS) into the preforms, Tyranno SA/SiC composite (TSA/ SiC)with higher density was obtained. While using carbon-coated Tyranno SA fiber preforms, Tyranno SA/C/SiC composite(TSA/C/SiC) h lower density were also fabricated In this composite, Sic particulate was loaded with polymer precursor(AHPCS)in the first cycle impregnation. Microstructural observation revealed that pore and crack formation was affected by processing conditions Bending strength was also dependent on the microstructural evolution of the samples. In TSA/SiC composite, relatively strong interfaces contribute to effective load transfer so that higher bending strength could be reached. In the tsa/C/SiC composite, weak interfaces provide a relatively lower strength. Meanwhile, different microstructural evolution and interfacial properties of the composites lead to the variation of the fracture behaviors. C 2002 Published by elsevier Science Ltd and Techna s.r.I Keywords: B Composites; B. Microstructure-final; C Mechanical properties; D SiC: PIMP 1. Introduction [1-5]. However, because of the lengthy pyrolysis cycles, much time is required in conventional PIP process to Sic/Sic composite is a well-known material promis- produce a dense component, resulting in high-cost for ng for high temperature structural applications because even simple shapes. of its intrinsic thermal stability and excellent mechanical Fast heating, techniques such as microwave or laser properties. Polymer impregnation and pyrolysis(PIP) heating are now being applied for ceramic fabrication or processing is considered to be an effective manufactur- polymer pyrolysis process [6-8]. These novel processing ing technique for preparing high performance SiC/Sic techniques provide a time and energy saving way for composite. Since the shapes of the impregnated parts ceramic preparation. Although those works are still on can be varied intentionally, it will be widely applied to the fundamental stage, promising features have been the complex-shaped components [l] For matrix forma- demonstrated for ceramics development such as short tion, many kinds of polymer precursors have been processing time, uniformity of the products as well as investigated and the details of polymer to ceramic con- tailoring particular design requirements of the materi- version, microstructural development as well as some als. Meanwhile, high frequency microwave radiation physical and mechanical properties have been studied can also be applied to induce the polymer-to-ceramic conversion process, and can induce very high tempera- re in irradiated parts in just minutes [9] The aim of the present study is to characterize the microstructural evolution of SiC/SiC composites 0272-8842/02/$22.00@ 2002 Published by Elsevier Science Ltd and Techna S.r.I PII:S0272-8842(02)00071-8Microstructural evolution and mechanical performances of SiC/SiC composites by polymer impregnation/microwave pyrolysis (PIMP) process S.M. Donga,*,Y. Katoha ,A. Kohyamaa ,S.T. Schwabb,L.L. Sneadc a CREST-ACE, JST and Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan bThor Technologies, Inc. 7600 Jefferson NE, Suite 9-115, Albuquerque, NM 87109, USA c Metals and Ceramic Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831-6087, USA Received 8 January 2002; received in revised form 9 February 2002; accepted 26 March 2002 Abstract SiC/SiC composites were prepared by polymer impregnation/microwave pyrolysis (PIMP) process,and their microstructural evolution and the mechanical performances were characterized. Using non-coated Tyranno SA fiber preforms as reinforcement and impregnation with only allylperhydropolycarbosilane (AHPCS) into the preforms,Tyranno SA/SiC composite (TSA/SiC) with higher density was obtained. While using carbon-coated Tyranno SA fiber preforms,Tyranno SA/C/SiC composite (TSA/C/SiC) with lower density were also fabricated. In this composite,SiC particulate was loaded with polymer precursor (AHPCS) in the first cycle impregnation. Microstructural observation revealed that pore and crack formation was affected by processing conditions. Bending strength was also dependent on the microstructural evolution of the samples. In TSA/SiC composite,relatively strong interfaces contribute to effective load transfer so that higher bending strength could be reached. In the TSA/C/SiC composite,weak interfaces provide a relatively lower strength. Meanwhile,different microstructural evolution and interfacial properties of the composites lead to the variation of the fracture behaviors. # 2002 Published by Elsevier Science Ltd and Techna S.r.l. Keywords: B. Composites; B. Microstructure-final; C. Mechanical properties; D. SiC; PIMP 1. Introduction SiC/SiC composite is a well-known material promis￾ing for high temperature structural applications because of its intrinsic thermal stability and excellent mechanical properties. Polymer impregnation and pyrolysis (PIP) processing is considered to be an effective manufactur￾ing technique for preparing high performance SiC/SiC composite. Since the shapes of the impregnated parts can be varied intentionally,it will be widely applied to the complex-shaped components [1]. For matrix forma￾tion,many kinds of polymer precursors have been investigated and the details of polymer to ceramic con￾version,microstructural development as well as some physical and mechanical properties have been studied [1–5]. However,because of the lengthy pyrolysis cycles, much time is required in conventional PIP process to produce a dense component,resulting in high-cost for even simple shapes. Fast heating,techniques such as microwave or laser heating are now being applied for ceramic fabrication or polymer pyrolysis process [6–8]. These novel processing techniques provide a time and energy saving way for ceramic preparation. Although those works are still on the fundamental stage,promising features have been demonstrated for ceramics development such as short processing time,uniformity of the products as well as tailoring particular design requirements of the materi￾als. Meanwhile,high frequency microwave radiation can also be applied to induce the polymer-to-ceramic conversion process,and can induce very high tempera￾ture in irradiated parts in just minutes [9]. The aim of the present study is to characterize the microstructural evolution of SiC/SiC composites 0272-8842/02/$22.00 # 2002 Published by Elsevier Science Ltd and Techna S.r.l. PII: S0272-8842(02)00071-8 Ceramics International 28 (2002) 899–905 www.elsevier.com/locate/ceramint * Corresponding author. Tel.: +81-774-38-3465; fax: +81-774-38- 3467. E-mail address: sm-dong@iae.kyoto-u.ac.jp (S.M. Dong)