CERAMICS INTERNATIONAL ELSEVIER Ceramics International 30(2004)257-265 www.elsevier.com/locate/ceramint Effects of processing parameters on the fabrication of near-net-shape fibre reinforced oxide ceramic matrix composites via sol-gel route M.K. Naskar, M. Chatterjee, * A. Deya, K. Basub Sok-Gel d Central Glass Ceramic Research Institute, Kolkata 700 032. India Regional Research laboratory, Bhopal 462026, India Received 5 March 2003: received in revised form 12 March 2003: accepted 2 May 2003 Abstract sol infiltration technique was found to be very effective for the fabrication of near-net-shape mullite fibre reinforced ceramic composites(CMCs). The infiltrated sol. in single- and bi-component oxide systems with equivalent molar compositions of (A), 60 Al,O3: 40 SiO,(AS), 87 Al2O3: 13 ZrO,(AZ), and 94 Zro2: 06Y2O3(ZY), after drying and calcination, formed the matrix. The discontinuous mullite fibres (as preforms with 15 vol. fibre content) acted as the reinforcement agents. The charac- teristics of the CMCs were found to be strongly dependent on the type of the sols (infiltrates)and their viscosity, presence of non- reactive fillers in the sol, number of infiltrations, intermediate and final sintering temperatures and in-situ deposition of carbon in the fabricated materials. The CMCs were characterised by X-ray diffraction(XRD), scanning electron microscopy (SEM) and the three point bend test. SEM indicated fibre pull-out in the fracture surface of the CMCs. The pseudo-ductile character, developed in the CMCs, was evident from the load-elongation curve of the three-point bend test. The carbon-containing CMCs exhibited a modulus value of almost 51 gpa C 2003 Elsevier Ltd and Techna S r.L. All rights reserved Keywords: A: Soh-gel process; B: Composites; C: Mechanical properties; D: Mullite: E: Structural applications 1. Introduction ceramic matrix and the physicochemical nature of the interface between the fibres and the matrix. The inter- Ceramic fibre reinforced ceramic matrix composites action between the fibre and the matrix is expected to (CMCs) are considered as promising candidates for use take place and judicious control of processing para in high temperature structural application due to their meters is necessary to establish the optimum degree of high strength, high modulus and toughness. The fibre interfacial bonding [1, 71 reinforced ceramic materials have been successful in Although numerous processing methods are already eliminating the catastrophic behaviour of monolithic known for producing CMCs, e.g. polymer impregnation ceramics [1, 2]. Incorporation of reinforcing inorganic and pyrolysis, melt infiltration, chemical vapour infil- fibres into the ceramic matrix develops CMCs which tration(CvI), hot pressing and sol-gel [4, 5, 8, 9], the sol- exhibit pseudo ductility, preventing catastrophic crack gel infiltration has proved to be a viable technique for growth by such mechanisms as crack bridging, fibre fabrication of CMCs using fibrous preforms as the pre- debonding, fibre pull-out [1-7. The characteristics of cursor materials, as the method involves several advan- the CMCs will depend upon the shape, size and disper- tages, such as better homogeneity, low processing sion of the reinforcement, the microstructure of the temperatures, near-net-shape fabrication [9]. However, the technique requires multiple infiltration with inter Corresponding author. Tel. +91-33-2483-8086: fax: +91-33- mediate heat-treatment to overcome matrix cracking 2473-0957. due to excessive shrinkage of matrix during drying and E-mailaddress:minati33(@hotmail.com(M.Chatterjee) sintering [1, 4, 8, 9]. Further, well dispersed fillers, i 0272-8842/03/$30.00@ 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.1016/S0272-8842(03)007XEffects of processing parameters on the fabrication of near-net-shape fibre reinforced oxide ceramic matrix composites via sol–gel route M.K. Naskara , M. Chatterjeea,*, A. Deya , K. Basub a Sol–Gel Division, Central Glass & Ceramic Research Institute, Kolkata 700 032, India bRegional Research Laboratory, Bhopal 462 026, India Received 5 March 2003; received in revised form 12 March 2003; accepted 2 May 2003 Abstract The sol infiltration technique was found to be very effective for the fabrication of near-net-shape mullite fibre reinforced ceramic matrix composites (CMCs). The infiltrated sol, in single- and bi-component oxide systems with equivalent molar compositions of Al2O3 (A), 60 Al2O3:40 SiO2 (AS), 87 Al2O3: 13 ZrO2 (AZ), and 94 ZrO2:06 Y2O3 (ZY), after drying and calcination, formed the matrix. The discontinuous mullite fibres (as preforms with 15 vol.% fibre content) acted as the reinforcement agents. The charac￾teristics of the CMCs were found to be strongly dependent on the type of the sols (infiltrates) and their viscosity, presence of non￾reactive fillers in the sol, number of infiltrations, intermediate and final sintering temperatures and in-situ deposition of carbon in the fabricated materials. The CMCs were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the three point bend test. SEM indicated fibre pull-out in the fracture surface of the CMCs. The pseudo-ductile character, developed in the CMCs, was evident from the load–elongation curve of the three-point bend test. The carbon-containing CMCs exhibited a modulus value of almost 51 GPa. # 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. Keywords: A: Sol–gel process; B: Composites; C: Mechanical properties; D: Mullite; E: Structural applications 1. Introduction Ceramic fibre reinforced ceramic matrix composites (CMCs) are considered as promising candidates for use in high temperature structural application due to their high strength, high modulus and toughness. The fibre reinforced ceramic materials have been successful in eliminating the catastrophic behaviour of monolithic ceramics [1,2]. Incorporation of reinforcing inorganic fibres into the ceramic matrix develops CMCs which exhibit pseudo ductility, preventing catastrophic crack growth by such mechanisms as crack bridging, fibre debonding, fibre pull-out [1–7]. The characteristics of the CMCs will depend upon the shape, size and disper￾sion of the reinforcement, the microstructure of the ceramic matrix and the physicochemical nature of the interface between the fibres and the matrix. The inter￾action between the fibre and the matrix is expected to take place and judicious control of processing para￾meters is necessary to establish the optimum degree of interfacial bonding [1,7]. Although numerous processing methods are already known for producing CMCs, e.g. polymer impregnation and pyrolysis, melt infiltration, chemical vapour infil￾tration (CVI), hot pressing and sol–gel [4,5,8,9], the sol– gel infiltration has proved to be a viable technique for fabrication of CMCs using fibrous preforms as the pre￾cursor materials, as the method involves several advan￾tages, such as better homogeneity, low processing temperatures, near-net-shape fabrication [9]. However, the technique requires multiple infiltration with inter￾mediate heat-treatment to overcome matrix cracking due to excessive shrinkage of matrix during drying and sintering [1,4,8,9], Further, well dispersed fillers, i.e. 0272-8842/03/$30.00 # 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.1016/S0272-8842(03)00097-X Ceramics International 30 (2004) 257–265 www.elsevier.com/locate/ceramint * Corresponding author. Tel.: +91-33-2483-8086; fax: +91-33- 2473-0957. E-mail address: minati33@hotmail.com (M. Chatterjee)