Availableonlineatwww.sciencedirect.com Science Direct CERAMICS INTERNATIONAL ELSEVIER Ceramics International 36(2010)1463-1466 www.elsevier.com/locate/ceramint Short communication A hot-pressing reaction technique for SiC coating of carbon/carbon composites Fu Qian-Gang", Xue Hui, Wu Heng, Li He-Jun, Li Ke-Zhi, Tao Jun C/C Composites Research Center, State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, PR China Received 16 September 2009: received in revised form 31 October 2009; accepted 12 December 2009 Available online 28 January 2010 Abstract A hot-pressing reactive sintering(HPRS)technique was explored to prepare SiC coating for protecting carbon/carbon(C/C)composites against oxidation. The microstructures of the coatings were analyzed by X-ray diffraction and scanning electron microscopy. The results show that, SiC ating obtained by HPRs has a dense and crack-free structure, and the coated C/C lost mass by only 1.84 wt %o after thermal cycles between 1773 K and room temperature for 15 times. The flexural strength of the HPRS-SiC coated C/C is up to 140 MPa, higher than those of the bare C/C and the C/C with a Sic coating by pressure-less reactive sintering. The fracture mode of the C/C composites changes from a pseudo-plastic behavior to a brittle one after being coated with a HPRS-Sic coating C 2010 Elsevier Ltd and Techna Group s.r. l. All rights reserved. Keywords: A. Hot pressing: A Sintering: D SiC 1. Introduction densification occur in single step. This technique can be economical due to low cost starting powders and relatively low Oxidation resistance is a key requirement for carbon/carbon sintering temperature, and it also leads to the possibility of / C)composites for applications in an oxygen-containing densifying the materials without additives [10, 11]. As far as the environment at high temperature [1-3]. To prevent C/C authors know, no literature has been published about using composites from oxidation, SiC coating was widely used HPRS technique to prepare ceramic coatings for C/C due to its excellent oxidation resistance and good compatibility composites. Though HPRS technique is not practical to with C/C composites [4, 5]. Presently, Sic can be coated on the prepare coatings for complex shaped C/C composites, it can surface of C/C composites by several methods, such as pack be applicable to regular shaped ones by designing suitable cementation [6], chemical vapor deposition(CVD)[7] and moulds. In the present work, HPRS technique was proposed to laser-induced chemical decomposition (LICD)[8]. Among prepare SiC coating for C/C composites. The microstructures these methods, pack cementation was usually used for and oxidation protective ability of the coatings were providing a strong interface bonding between SiC coating investigated, and the effect of Sic coating on the flexural and C/C composites [9]. However, cracks will be formed property of the coated C/C composites was also studied inevitably in this coating during the cooling process from high temperature to room temperature due to the mismatch of 2. Experimental thermal expansion between SiC and C/C composites, which offer entrance channels for oxygen and result in the failure of The substrates were cut from bulk 2D C/C composites with a the coating [5,7] density of 1.75 g/cm. Powder compositions for the HPRS Hot-pressing reactive sintering(HPRS)is a technique in which both the chemical reactions of the starting materials and process were 65-80 wt% Si and 20-35 wt. graphite. These powders were mixed by a blender for 2 h C/C specimens were packed by these mixtures in a graphite crucible, and were pre aphite pressing head. The pressi Eomoil address f +862988494197;fax:+862988495764 controlled by 250 kPa. Then the graphite crucible was heated g@nwpu.edu.cn(F.Qian-Gang) to 1873-2073 K and held at that temperature for 2 h under 2-8842/$36.00 2010 Elsevier Ltd and Techna Group S.r.L. All rights reserved 10.1016 1-ceramint.2010.01002Short communication A hot-pressing reaction technique for SiC coating of carbon/carbon composites Fu Qian-Gang *, Xue Hui, Wu Heng, Li He-Jun, Li Ke-Zhi, Tao Jun C/C Composites Research Center, State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, PR China Received 16 September 2009; received in revised form 31 October 2009; accepted 12 December 2009 Available online 28 January 2010 Abstract A hot-pressing reactive sintering (HPRS) technique was explored to prepare SiC coating for protecting carbon/carbon (C/C) composites against oxidation. The microstructures of the coatings were analyzed by X-ray diffraction and scanning electron microscopy. The results show that, SiC coating obtained by HPRS has a dense and crack-free structure, and the coated C/C lost mass by only 1.84 wt.% after thermal cycles between 1773 K and room temperature for 15 times. The flexural strength of the HPRS-SiC coated C/C is up to 140 MPa, higher than those of the bare C/C and the C/C with a SiC coating by pressure-less reactive sintering. The fracture mode of the C/C composites changes from a pseudo-plastic behavior to a brittle one after being coated with a HPRS-SiC coating. # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Hot pressing; A. Sintering; D. SiC 1. Introduction Oxidation resistance is a key requirement for carbon/carbon (C/C) composites for applications in an oxygen-containing environment at high temperature [1–3]. To prevent C/C composites from oxidation, SiC coating was widely used due to its excellent oxidation resistance and good compatibility with C/C composites [4,5]. Presently, SiC can be coated on the surface of C/C composites by several methods, such as pack cementation [6], chemical vapor deposition (CVD) [7] and laser-induced chemical decomposition (LICD) [8]. Among these methods, pack cementation was usually used for providing a strong interface bonding between SiC coating and C/C composites [9]. However, cracks will be formed inevitably in this coating during the cooling process from high temperature to room temperature due to the mismatch of thermal expansion between SiC and C/C composites, which offer entrance channels for oxygen and result in the failure of the coating [5,7]. Hot-pressing reactive sintering (HPRS) is a technique in which both the chemical reactions of the starting materials and densification occur in single step. This technique can be economical due to low cost starting powders and relatively low sintering temperature, and it also leads to the possibility of densifying the materials without additives [10,11]. As far as the authors know, no literature has been published about using HPRS technique to prepare ceramic coatings for C/C composites. Though HPRS technique is not practical to prepare coatings for complex shaped C/C composites, it can be applicable to regular shaped ones by designing suitable moulds. In the present work, HPRS technique was proposed to prepare SiC coating for C/C composites. The microstructures and oxidation protective ability of the coatings were investigated, and the effect of SiC coating on the flexural property of the coated C/C composites was also studied. 2. Experimental The substrates were cut from bulk 2D C/C composites with a density of 1.75 g/cm3 . Powder compositions for the HPRS process were 65–80 wt.% Si and 20–35 wt.% graphite. These powders were mixed by a blender for 2 h. C/C specimens were packed by these mixtures in a graphite crucible, and were pressed by a graphite pressing head. The pressure was controlled by 250 kPa. Then the graphite crucible was heated to 1873–2073 K and held at that temperature for 2 h under www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 36 (2010) 1463–1466 * Corresponding author. Tel.: +86 29 88494197; fax: +86 29 88495764. E-mail address: fuqiangang@nwpu.edu.cn (F. Qian-Gang). 0272-8842/$36.00 # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2010.01.002