J.Am. Ceran.Soe.,892338-234002006 DOl:10.11.1551-29162006.01018x c The American Ceramic Society journal Fabrication of Ce/SiC Composites by Vapor Silicon Infiltration Qing Zhou, Shaoming Dong, Xiangyu Zhang, Yusheng Ding, and Dongliang Jiang Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China Carbon fiber reinforced on carbide matrix composites were s an interfacial layer. The layer was deposited by fabricated by the vapor silicon infiltration process. The density apor deposition(CVD) using methane as a recurse and the open porosity of the composite infiltrated at 1973 K were 250 nm Sic layer was deposited by Cvd, using MT 2.25 g/cm and -6%, respectively. The flexural strength of the cursor, to protect the fibers from reacting with th mposite at ambient conditions was 300 MPa. when the infil- vapors. The C-and Sic-coated fabrics were impregnated by mperature decreased, the density and flexural strength the slurry containing nano-SiC particles (about 60 nm in size, composite also decreased. However, the resulting com- Kiln Nanometer Technology Development Co. Ltd, Hefei, materials exhibited non-brittle fracture behavior China)and a phenolic resin, followed by pyrolysis at 2073 K to form a porous body. The volume fraction of nano-SiC in the slurry was about 15%. The pyrolyzed body contained a carbon L. Introduction matrix and a distribution of micropores. After pyrolyzation, the C RBON FIBER reinforced silicon carbide mple was reacted with gaseous silicon, which was obtained by nelting Si powder(99.9%, 75 um, Sinopharm Chemical Rea (CnSiC) have been proposed as advance gent Co Ltd, Shanghai, China)in a graphite crucible below the potential to exhibit damage tolerance, high sample inside a vacuum furnace(-l Pa)at high temperature for 3 h. The gaseous Si penetrated into the porous channel and In contrast to chemical vapor infiltration( CVi)and polymer oncurrently facilitated the reaction to form Sic. impregnation and pyrolysis(PIP), reaction sintering is a cost The density was measured by Archimedes method. The ethod for making ceramic-matrix composites samples were cut and ground into about 2.5 mm x 4 mm x 35 nm in size for three-point bending testing. The flexure tests were MC). Traditionally, the fabrication of continuous fiber rein- conducted using an INSTRON 5566(Canton, MA)test ma forced SiC-matrix composites by reaction sintering involves eactive melt infiltration (RMD or liquid silicon infiltration chine with a span of 24 mm and a crosshead speed of 0.5 mm/ LSD).2-However, vapor silicon infiltration has been most min. After the tests, the test specimen was immersed in a 70 wt% limited to the fabrication of biomorphic SiC ceramics. Chiang HF+30 wt% HNO3 solution at room temperature for 17h et al. found that two of the drawbacks of molten silicon infil Then. the silicon volume content was calculated according to the tration included reaction choking and flaw generations and that equation to achieve adequate infiltration and avoid flaw generation, it is ecessary to reduce the reaction rate with respect to the infiltra Isi= G1-G2 tion rate. Silicon vapor infiltration has the advantage of infil trating smaller pores compared with molten silicon infiltration. Furthermore, it can be controlled to avoid reaction choking be- where Psi and p are the density of the silicon powder and the sample before dissolution and G, and G? are the weight of the In this paper, dense C/siC composites were manufactured by sample before and after etching vapor silicon infiltration at high temperature and the mechanical The microstructures of the fracture surface were character behavior of the composites was investigated ized using an electron probe microanalyzer(EPMA; JXA-8100 JEOL, Tokyo, Japan) II. Experimental Procedure High modulus carbon fibers (M40JB, Toray, Tokyo, Japan) Il. Results and discussion with an average diameter of 6 um were used to fabricate Cd 'sic The bulk density and the open porosity of the CSic composites composites. The three-dimensional fabrics were braided by are shown in Fig. I as a function of infiltration temperature. I Nanjing Fiberglass Research and Design Institute(Nanjing was found that as the infiltration te ture increased from China). The preform architecture had a fiber distribution of 1873 to 1973 K the bulk density of the composites increased 8: 2: 1 in the x: y: z directions, respectively, and an -40% fiber from 1.68 to 2.25 g/cm whereas the open porosity decreased volume fraction. In the present work, a carbon layer(- 150 nm) from 28% to 6%. It is known& that the reaction between silicon was firstly deposited on the surface of the carbon fibers to serve vapor and carbon depends on the temperature of infiltration and the concentration of silicon vapors. In this case it was found that E. Lara-Curzo-contributing editor at 1873 k, the amount of reactive vapor silicon was not enoug to react with the carbon in the matrix, resulting in composite with the lowest density. At higher temperatures, a larger amount of vapor silicon reacted with the carbon and resulted in denser Manuscript No. 21231. Received December 8. 2005: approved February 14. 2006. omposite with better mechanical behavior, as shown in Fig. 2. DI5 and the Key Project of Science an ology of Shang- When the temperature was 1973 K, the silicon vapor became respondence should be addressed. e-mail: zhouqing( a mail sicaccn abundant. Some reacted with carbon forming Sic matrix and nstitute of Graduate. Chinese Academy of Sciences, Beijing. China. the other remained in the matrix. It was found that the silicon 338Fabrication of Cf/SiC Composites by Vapor Silicon Infiltration Qing Zhou,z Shaoming Dong,w Xiangyu Zhang, Yusheng Ding,z and Dongliang Jiang Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China Carbon fiber reinforced silicon carbide matrix composites were fabricated by the vapor silicon infiltration process. The density and the open porosity of the composite infiltrated at 1973 K were 2.25 g/cm3 and B6%, respectively. The flexural strength of the composite at ambient conditions was 300 MPa. When the infil￾tration temperature decreased, the density and flexural strength of the composite also decreased. However, the resulting com￾posite materials exhibited non-brittle fracture behavior. I. Introduction CARBON FIBER reinforced silicon carbide matrix composites (Cf/SiC) have been proposed as advanced materials suitable for aerospace and gas turbine engine parts,1 because of their potential to exhibit damage tolerance, high strength, high stiff￾ness, and high oxidation resistance. In contrast to chemical vapor infiltration (CVI) and polymer impregnation and pyrolysis (PIP), reaction sintering is a cost￾effective method for making ceramic–matrix composites (CMC). Traditionally, the fabrication of continuous fiber rein￾forced SiC–matrix composites by reaction sintering involves reactive melt infiltration (RMI) or liquid silicon infiltration (LSI).2–4 However, vapor silicon infiltration has been mostly limited to the fabrication of biomorphic SiC ceramics.5,6 Chiang et al. 7 found that two of the drawbacks of molten silicon infil￾tration included reaction choking and flaw generations and that to achieve adequate infiltration and avoid flaw generation, it is necessary to reduce the reaction rate with respect to the infiltra￾tion rate. Silicon vapor infiltration has the advantage of infil￾trating smaller pores compared with molten silicon infiltration. Furthermore, it can be controlled to avoid reaction choking be￾cause the reaction between silicon vapors and carbon is slow. In this paper, dense Cf/SiC composites were manufactured by vapor silicon infiltration at high temperature and the mechanical behavior of the composites was investigated. II. Experimental Procedure High modulus carbon fibers (M40JB, Toray, Tokyo, Japan) with an average diameter of 6 mm were used to fabricate Cf/SiC composites. The three-dimensional fabrics were braided by Nanjing Fiberglass Research and Design Institute (Nanjing, China). The preform architecture had a fiber distribution of 8:2:1 in the x:y:z directions, respectively, and an B40% fiber volume fraction. In the present work, a carbon layer (B150 nm) was firstly deposited on the surface of the carbon fibers to serve as an interfacial layer. The layer was deposited by chemical vapor deposition (CVD) using methane as a precursor. Then, a 250 nm SiC layer was deposited by CVD, using MTS/H2 pre￾cursor, to protect the fibers from reacting with the silicon vapors. The C- and SiC-coated fabrics were impregnated by the slurry containing nano-SiC particles (about 60 nm in size, Kiln Nanometer Technology Development Co. Ltd., Hefei, China) and a phenolic resin, followed by pyrolysis at 2073 K to form a porous body. The volume fraction of nano-SiC in the slurry was about 15%. The pyrolyzed body contained a carbon matrix and a distribution of micropores. After pyrolyzation, the sample was reacted with gaseous silicon, which was obtained by melting Si powder (99.9%, 75 mm, Sinopharm Chemical Rea￾gent Co. Ltd., Shanghai, China) in a graphite crucible below the sample inside a vacuum furnace (B1 Pa) at high temperature for 3 h. The gaseous Si penetrated into the porous channel and concurrently facilitated the reaction to form SiC. The density was measured by Archimedes’ method. The samples were cut and ground into about 2.5 mm
4 mm
35 mm in size for three-point bending testing. The flexure tests were conducted using an INSTRON 5566 (Canton, MA) test ma￾chine with a span of 24 mm and a crosshead speed of 0.5 mm/ min. After the tests, the test specimen was immersed in a 70 wt% HF130 wt% HNO3 solution at room temperature for 17 h. Then, the silicon volume content was calculated according to the equation VSi ¼ G1 G2 G1 r rSi where rSi and r are the density of the silicon powder and the sample before dissolution and G1 and G2 are the weight of the sample before and after etching. The microstructures of the fracture surface were character￾ized using an electron probe microanalyzer (EPMA; JXA-8100, JEOL, Tokyo, Japan). III. Results and Discussion The bulk density and the open porosity of the Cf/SiC composites are shown in Fig. 1 as a function of infiltration temperature. It was found that as the infiltration temperature increased from 1873 to 1973 K the bulk density of the composites increased from 1.68 to 2.25 g/cm3 whereas the open porosity decreased from 28% to 6%. It is known8 that the reaction between silicon vapor and carbon depends on the temperature of infiltration and the concentration of silicon vapors. In this case it was found that at 1873 K, the amount of reactive vapor silicon was not enough to react with the carbon in the matrix, resulting in composites with the lowest density. At higher temperatures, a larger amount of vapor silicon reacted with the carbon and resulted in denser composite with better mechanical behavior, as shown in Fig. 2. When the temperature was 1973 K, the silicon vapor became abundant. Some reacted with carbon forming SiC matrix and the other remained in the matrix. It was found that the silicon Journal J. Am. Ceram. Soc., 89 [7] 2338–2340 (2006) DOI: 10.1111/j.1551-2916.2006.01018.x r 2006 The American Ceramic Society 2338 E. Lara-Curzio—contributing editor This work was supported by the National Natural Science Foundation Program of China under Grant no. 50472015 and the Key Project of Science and Technology of Shang￾hai, China, under Grant no. 04DZ14002. w Author to whom correspondence should be addressed. e-mail: zhouqing@mail.sic.ac.cn z Institute of Graduate, Chinese Academy of Sciences, Beijing, China. Manuscript No. 21231. Received December 8, 2005; approved February 14, 2006.