MATERIALS HIENGE& ENGIEERING ELSEVIER Materials Science and Engineering A 465 (2007)290-294 www.elsevier.com/locate/msea Short communication Fabrication and characterization of C/Sic composites with large thickness, high density and near-stoichiometric matrix by heaterless chemical vapor infiltration Sufang Tang, Jingyi Deng, Shijun Wang, Wenchuan Liu Instinte of Metal Research, Chinese Academy of Sciences, Shenyang 110016, PR China Received 14 December 2006: received in revised form I February 2007; accepted 6 February 2007 The C/SiC composites with a 7-8 mm thickness, a 2.3-2.4 g/em'density, and a Si/C ratio 1.08-1.09 matrix have been fabricated by heaterless chemical vapor infiltration(CVi) in a 25-h deposition time. The C/siC composites exhibited a damage-tolerant fracture behavior, and its average flexural strength, longitudinal/transverse compressive strength and fracture toughness were 163 MPa, 304/276 MPa and 6.5 MPam, respectively The composites presented a thermal expansion of (1.09-1.93)10C- and a thermal conductivity (tC) of 8.34-6.56 W/m"C in the range 200-1000°C 2007 Elsevier B. v. All rights reserved. Keywords: C/SiC composites: CVI; Mechanical properties; Thermal conductivity 1. Introduction the densification process, and also because large numbers of arying preforms are easily accommodated in a reactor [3-5] As material requirements become more and more sophis- However, the process has several disadvantages for fabricating ticated, there seems to be a substantially greater emphasis on the composites: low deposition rate, time-consuming treatment, development of advanced thermo-structural composites such as severe corrosion of vacuum pump, and consequent high cost C/C, C/SiC and SiC/SiC, because of their low density, high- The liquid silicon infiltration(LsD) is an attractive method for temperature strength, thermal shock resistance, low coefficient preparation SiC composites due to an effective cost of thermal expansion(CTE), good thermal conductivity (TC), [6-8. The method is infiltration of molten Si into low den- abrasion resistance and high fracture toughness. The excellent sity C/C and transformation by a reactive sintering process into mechanical and thermo-physical properties provide many poten- the dense materials. Nevertheless, the residual Si metal and the tial applications for these materials, including re-entry shields, etched fibers will result in poor high-temperature strength of the rocket nozzles, disc brakes, etc. [1, 2]. However, the major obsta- composites. Another interesting method is the liquid polymer cle to a much broader application in the civil sector, such as disc impregnation(LPD)method based on organometallic precur- brakes, heat exchangers, gas turbines and chemical reactors, is sors such as polycarbosilane [9-11]. However, high numbers till their quite high price of impregnation/pyrolysis steps employed for manufacturing a Several main processes, including chemical vapor infiltra- relatively dense material are required because of the high poros- tion(CVi), liquid and solid infiltration and polymer conversion, ity of the initial fiber preform and the low ceramic yield of the have been employed for fabrication of this new class of the precursor materials 3-11]. The isothermal CVi method is considered as Therefore, it is required to develop a low-cost process for one of the most promising techniques because its major advan- fabricating the high-performance thermo-structural composites tage is the lower thermal and mechanical stress achieved during Such an attempt has been made and a novel low-cost manufac- turing method has been developed, primarily for of the C/C, C/SiC and SiC/SiC composites [12, 13]. In this Corresponding author. Tel. +86 2483978056 paper, large thickness, high density and near-stoichiometric E-mail address: jydeng @imr ac cn ( Deng) matrix C/SiC composites were fabricated by a simple heaterless 0921-5093/S-see front matter O 2007 Elsevier B v. All rights reserved doi:10.1016/msea.2007.02037Materials Science and Engineering A 465 (2007) 290–294 Short communication Fabrication and characterization of C/SiC composites with large thickness, high density and near-stoichiometric matrix by heaterless chemical vapor infiltration Sufang Tang, Jingyi Deng ∗, Shijun Wang, Wenchuan Liu Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, PR China Received 14 December 2006; received in revised form 1 February 2007; accepted 6 February 2007 Abstract The C/SiC composites with a 7–8 mm thickness, a 2.3–2.4 g/cm3 density, and a Si/C ratio 1.08–1.09 matrix have been fabricated by heaterless chemical vapor infiltration (CVI) in a 25-h deposition time. The C/SiC composites exhibited a damage-tolerant fracture behavior, and its average flexural strength, longitudinal/transverse compressive strength and fracture toughness were 163 MPa, 304/276 MPa and 6.5 MPa m1/2, respectively. The composites presented a thermal expansion of (1.09–1.93) × 10−6 ◦C−1 and a thermal conductivity (TC) of 8.34–6.56 W/m ◦C in the range 200–1000 ◦C. © 2007 Elsevier B.V. All rights reserved. Keywords: C/SiC composites; CVI; Mechanical properties; Thermal conductivity 1. Introduction As material requirements become more and more sophis￾ticated, there seems to be a substantially greater emphasis on development of advanced thermo-structural composites such as C/C, C/SiC and SiC/SiC, because of their low density, high￾temperature strength, thermal shock resistance, low coefficient of thermal expansion (CTE), good thermal conductivity (TC), abrasion resistance and high fracture toughness. The excellent mechanical and thermo-physical properties provide many poten￾tial applications for these materials, including re-entry shields, rocket nozzles, disc brakes, etc. [1,2]. However, the major obsta￾cle to a much broader application in the civil sector, such as disc brakes, heat exchangers, gas turbines and chemical reactors, is still their quite high price. Several main processes, including chemical vapor infiltra￾tion (CVI), liquid and solid infiltration and polymer conversion, have been employed for fabrication of this new class of the materials [3–11]. The isothermal CVI method is considered as one of the most promising techniques because its major advan￾tage is the lower thermal and mechanical stress achieved during ∗ Corresponding author. Tel.: +86 24 83978056. E-mail address: jydeng@imr.ac.cn (J. Deng). the densification process, and also because large numbers of varying preforms are easily accommodated in a reactor [3–5]. However, the process has several disadvantages for fabricating the composites: low deposition rate, time-consuming treatment, severe corrosion of vacuum pump, and consequent high cost. The liquid silicon infiltration (LSI) is an attractive method for preparation of the C/SiC composites due to an effective cost [6–8]. The method is infiltration of molten Si into low den￾sity C/C and transformation by a reactive sintering process into the dense materials. Nevertheless, the residual Si metal and the etched fibers will result in poor high-temperature strength of the composites. Another interesting method is the liquid polymer impregnation (LPI) method based on organometallic precur￾sors such as polycarbosilane [9–11]. However, high numbers of impregnation/pyrolysis steps employed for manufacturing a relatively dense material are required because of the high poros￾ity of the initial fiber preform and the low ceramic yield of the precursor. Therefore, it is required to develop a low-cost process for fabricating the high-performance thermo-structural composites. Such an attempt has been made and a novel low-cost manufac￾turing method has been developed, primarily for manufacturing of the C/C, C/SiC and SiC/SiC composites [12,13]. In this paper, large thickness, high density and near-stoichiometric matrix C/SiC composites were fabricated by a simple heaterless 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.02.037