Availableonlineatwww.sciencedirect.com Science Direct CERAMICS INTERNATIONAL ELSEVIER Ceramics International 35(2009)2277-2282 www.elsevier.com/locate/ceramint Oxidation analysis of 2D C/zrc-sic composites with different coating structures in CHa combustion gas environment Houbu Li", Litong Zhang, Laifei Cheng, Yiguang Wang National Key Laboratory of Themostructure Composite Materials, Nort/westem Polytechnical University, Xi'an 710072, China Received 13 October 2008 28 mber 2008; accepted 29 December 2008 Available online 22 January 2009 Abstract 2D C/Zrc-SiC composites were fabricated by chemical vapor infiltration combined with polymer slurry infiltration and pyrolysis. Liquid highly branched polycarbosilane was used as the pre-ceramic precursor. In order to improve the oxidation resistance, three kinds of coating structures were prepared on C/Zrc-SiC composites: pure zirconium carbide coating, SiC-ZrC coating, and ZrB2-SiC coating. Structural evolutions of the as-produced composites after oxidation in CHa combustion gas atmosphere at about 1800C were investigated and compared Based on a model of the oxidation process, the mixture ZrB2-CVD SiC showed the best oxidation resistance. C 2009 Elsevier Ltd and Techna Group S.r. I. All rights reserved. Keywords: A Precursors: organic: B Composites; B Surfaces: Oxidation mechanism 1. Introduction barrier to oxygen diffusion because of the high evaporation rates of silicon oxide and the deterioration of the oxide film Carbon fiber reinforced silicon carbide composites(C/SiC) Researchers have been looking for new solutions to provide are one of the most promising structural materials for high oxidation/ablation protection for C/Sic composites at ultra temperature applications [1, 2]. C/SiC composites have a high high temperatures [9]. Zirconium and its composites have thermal stability and are usually considered useful up to exceptional properties. Especially, zirconium carbide(ZrC)and 1650C. However, they have a low durability except in inert zirconium boride (zrB2) have attracted much attention. They atmospheres. At higher temperatures(>1700C), the oxidation have melting points over 3000C, relatively low densities, and of the fiber, interphase and matrix cooperatively influence the the abilities to form refractory oxide zirconia scales(melting oxidation behavior of C/SiC composites in oxygen atmosphere point 2770C)[10]. However, these oxide coating are porou 3, 4]. Thus, reducing oxidation at high temperature in oxygen and do not provide oxidation protection. Thus, the poor environment is the challenge to extend application of C/Sic oxidation resistance of Zr B2 and Zrc makes them seldom to be composites. As a rule this problem is usually resolved by used alone. The addition of Sic has been shown to effectively applying oxidation-resistant coatings. improve the oxidation resistance of ZrB2 [11, 12 Because the oxidation of SiC is passive up to 1650C and the n the present paper, 2D C/ZrC-Sic composites were formed Sio2 film has a low oxygen diffusion coefficient, SiC is prepared by chemical vapor infiltration and polymer slurry the fundamental coating material for high temperature oxidation infiltration with a high-branched polycarbosilane(HBPCS)as protection of structural composites [5]. SiC coating prepared by the pre-ceramic precursor. Three kinds of coating structures chemical vapor deposition(CVD)shows different oxidation have been applied on the composites surface, i.e. (i)mixtu behavior in various environments, such as air and combustion Sic with CVd Zrc, (ii) mixture of ZrB, with CVD SiC, and atmosphere [6-8. But at T>1800C, the oxide film is a poor (iii) pure ZrC coating for comparison. Microstructure changes after oxidation in CHa combustion gas environment at about 1800C were investigated and compared. The erosion 86 29 88486068x834: fax: +8629 88494620. mechanism of different coating structures was discussed based nail. com(H. Li) on the oxidation results 2-884234.00 09 Elsevier Ltd and Techna Group S.r.L. All rights reserved 10.1016/j-cera 008.12002Oxidation analysis of 2D C/ZrC–SiC composites with different coating structures in CH4 combustion gas environment Houbu Li *, Litong Zhang, Laifei Cheng, Yiguang Wang National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi’an 710072, China Received 13 October 2008; received in revised form 28 November 2008; accepted 29 December 2008 Available online 22 January 2009 Abstract 2D C/ZrC–SiC composites were fabricated by chemical vapor infiltration combined with polymer slurry infiltration and pyrolysis. Liquid highly branched polycarbosilane was used as the pre-ceramic precursor. In order to improve the oxidation resistance, three kinds of coating structures were prepared on C/ZrC–SiC composites: pure zirconium carbide coating, SiC–ZrC coating, and ZrB2–SiC coating. Structural evolutions of the as-produced composites after oxidation in CH4 combustion gas atmosphere at about 1800 8C were investigated and compared. Based on a model of the oxidation process, the mixture ZrB2–CVD SiC showed the best oxidation resistance. # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Precursors: organic; B. Composites; B. Surfaces; Oxidation mechanism 1. Introduction Carbon fiber reinforced silicon carbide composites (C/SiC) are one of the most promising structural materials for high temperature applications [1,2]. C/SiC composites have a high thermal stability and are usually considered useful up to 1650 8C. However, they have a low durability except in inert atmospheres. At higher temperatures (>1700 8C), the oxidation of the fiber, interphase and matrix cooperatively influence the oxidation behavior of C/SiC composites in oxygen atmosphere [3,4]. Thus, reducing oxidation at high temperature in oxygen environment is the challenge to extend application of C/SiC composites. As a rule this problem is usually resolved by applying oxidation-resistant coatings. Because the oxidation of SiC is passive up to 1650 8C and the formed SiO2 film has a low oxygen diffusion coefficient, SiC is the fundamental coating material for high temperature oxidation protection of structural composites [5]. SiC coating prepared by chemical vapor deposition (CVD) shows different oxidation behavior in various environments, such as air and combustion atmosphere [6–8]. But at T > 1800 8C, the oxide film is a poor barrier to oxygen diffusion because of the high evaporation rates of silicon oxide and the deterioration of the oxide film. Researchers have been looking for new solutions to provide oxidation/ablation protection for C/SiC composites at ultra￾high temperatures [9]. Zirconium and its composites have exceptional properties. Especially, zirconium carbide (ZrC) and zirconium boride (ZrB2) have attracted much attention. They have melting points over 3000 8C, relatively low densities, and the abilities to form refractory oxide zirconia scales (melting point 2770 8C) [10]. However, these oxide coating are porous and do not provide oxidation protection. Thus, the poor oxidation resistance of ZrB2 and ZrC makes them seldom to be used alone. The addition of SiC has been shown to effectively improve the oxidation resistance of ZrB2 [11,12]. In the present paper, 2D C/ZrC–SiC composites were prepared by chemical vapor infiltration and polymer slurry infiltration with a high-branched polycarbosilane (HBPCS) as the pre-ceramic precursor. Three kinds of coating structures have been applied on the composites surface, i.e. (i) mixture of SiC with CVD ZrC, (ii) mixture of ZrB2 with CVD SiC, and (iii) pure ZrC coating for comparison. Microstructure changes after oxidation in CH4 combustion gas environment at about 1800 8C were investigated and compared. The erosion mechanism of different coating structures was discussed based on the oxidation results. www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 35 (2009) 2277–2282 * Corresponding author. Tel.: +86 29 88486068x834; fax: +86 29 88494620. E-mail address: houbuli@gmail.com (H. Li). 0272-8842/$34.00 # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2008.12.002