Availableonlineatwww.sciencedirect.com Science Direct CERAMICS INTERNATIONAL ELSEVIER Ceramics International 35(2009)3073-3079 www.elsevier.com/locate/ceramint Sol-gel approach to near-net-shape oxide-oxide composites reinforced with short alumina fibres-The effect of crystallization Milan Kanti Naskar a,, Kunal Basu, Minati Chatterjee a Sol-Gel Division, Central Glass and Ceramic Research Institute(CSIR), Kolkata 700032, india Sagar Institute of Science and Technology, Gandhi Nagar, Bhopal 462034, India Received 24 July 2008: received in revised form 12 March 2009: accepted 14 April 2009 Available online 21 May 2009 Abstract Near-net-shape(NNS) high alumina(alumina: silica=96: 4, in equivalent weight ratio) fibre reinforced ceramic matrix composites(CMCs) were prepared with single and bicomponent sols following sol-gel vacuum infiltration technique. The CMCs were characterized by X-ray diffraction(XRD), three-point bend test and scanning electron microscopy(SEM) Crystallization of tetragonal zirconia(t-ZrO2)in the composite CZY having zirconia-yttria matrix and that of gamma alumina(y-Al2O3)in the composites, CAZ having alumina-zirconia matrix, CAs having alumina-silica matrix and CA having alumina matrix, enhanced the flexural strength values and pseudo-ductile character of CMCs C 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Sol-gel process; B. Fibres; B. Composites; C. Mechanical properties; E. Structural applications 1. Introduction 13, 8-14 Radsick et al. [8 fabricated oxide/oxide matrix composites by slurry infiltration-hot pressing sintering technique The use of monolithic ceramics has some restrictions in (SI-HP) Recently Ruggles-Wrenn et al. [14] have studied the structural applications because of their inherent catastrophic environmental effects on the creep behaviours of oxide/oxide nature. The development of ceramic fibre reinforced ceramic ceramic matrix composites prepared by sol-gel technique. Dey matrix composites(CMCs)has been proved to be promising et al. [ll] have fabricated near-net-shape fibre reinforced ceramic alternative to monolithic ceramics for structural materials matrix composites by sol infiltration technique. Sol-gel vacuum fabrication in engineering field [1, 2]. If CMCs could be made infiltration technique is a promising route for the fabrication of consistently and at reasonable cost, they could be ideal for high oxide-oxide ceramic matrix composite. In the vacuum infiltration temperature corrosive and abrasive environments. One of the technique, a solution containing metal compounds, e. g, metal processes of fabrication of CMCs is to infiltrate a liquid matrix alkoxides, acetates, nitrates or halides are treated chemically to into a reinforcement assemblage of required shape and size form a sol which is then infiltrated into the fibre preform. The sol which is called preform [2]. These preforms may be continuous in the preform is converted to gel form by physical and/or or discontinuous fibres or whiskers or particulates assemblages chemical means, which in turn is subjected to control heating to prepared to the desired volume fraction, shapes and sizes [2,3]. produce the desired products e.g. glass, glass-ceramic or ceramic Several techniques are currently used to fabricate CMCs with matrix. The main advantages of this technique are lower NNS capability which is used to produce NNS components that processing temperature and higher compositional homogeneity do not require machining or working with diamond tools. The with respect to slurry infiltration-hot pressing sintering technique conventional methods of producing CMCs are hot pressing [4], (SI-HP) In this process, preforms provide a uniform distribution melt infiltration [5], chemical vapour infiltration( CVI[6], slurry of fibres and a very high surface area to the matrix gel. However, nfiltration-high pressure sintering(SI-HPS)[3, 7, 8] and sol-gel during drying, shrinkage of matrix results in crack formation in the matrix. It can be minimized by repeated infiltrations with the Corresponding author. Tel. +91 33 2483 8086: fax: +91 33 2473 0957 The properties of CMCs an ellence d by th cteristics of the reinforcing fibres i.e., their strength, aspect ratio 2-8842/$3600C 2009 Elsevier Ltd and Techna Group S.r.L. All rights reserved 10.1016 1-ceramint.2009.04013Sol–gel approach to near-net-shape oxide–oxide composites reinforced with short alumina fibres—The effect of crystallization Milan Kanti Naskar a, *, Kunal Basu b , Minati Chatterjee a a Sol-Gel Division, Central Glass and Ceramic Research Institute (CSIR), Kolkata 700032, India b Sagar Institute of Science and Technology, Gandhi Nagar, Bhopal 462034, India Received 24 July 2008; received in revised form 12 March 2009; accepted 14 April 2009 Available online 21 May 2009 Abstract Near-net-shape (NNS) high alumina (alumina:silica = 96:4, in equivalent weight ratio) fibre reinforced ceramic matrix composites (CMCs) were prepared with single and bicomponent sols following sol–gel vacuum infiltration technique. The CMCs were characterized by X-ray diffraction (XRD), three-point bend test and scanning electron microscopy (SEM). Crystallization of tetragonal zirconia (t-ZrO2) in the composite, CZY having zirconia–yttria matrix and that of gamma alumina (g-Al2O3) in the composites, CAZ having alumina–zirconia matrix, CAS having alumina–silica matrix and CA having alumina matrix, enhanced the flexural strength values and pseudo-ductile character of CMCs. # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Sol–gel process; B. Fibres; B. Composites; C. Mechanical properties; E. Structural applications 1. Introduction The use of monolithic ceramics has some restrictions in structural applications because of their inherent catastrophic nature. The development of ceramic fibre reinforced ceramic matrix composites (CMCs) has been proved to be promising alternative to monolithic ceramics for structural materials fabrication in engineering field [1,2]. If CMCs could be made consistently and at reasonable cost, they could be ideal for high temperature corrosive and abrasive environments. One of the processes of fabrication of CMCs is to infiltrate a liquid matrix into a reinforcement assemblage of required shape and size which is called preform [2]. These preforms may be continuous or discontinuous fibres or whiskers or particulates assemblages prepared to the desired volume fraction, shapes and sizes [2,3]. Several techniques are currently used to fabricate CMCs with NNS capability which is used to produce NNS components that do not require machining or working with diamond tools. The conventional methods of producing CMCs are hot pressing [4], melt infiltration [5], chemical vapour infiltration (CVI) [6], slurry infiltration-high pressure sintering (SI-HPS) [3,7,8] and sol–gel [3,8–14]. Radsick et al. [8] fabricated oxide/oxide matrix composites by slurry infiltration-hot pressing sintering technique (SI-HP). Recently Ruggles-Wrenn et al. [14] have studied the environmental effects on the creep behaviours of oxide/oxide ceramic matrix composites prepared by sol–gel technique. Dey et al.[11] have fabricated near-net-shape fibre reinforced ceramic matrix composites by sol infiltration technique. Sol–gel vacuum infiltration technique is a promising route for the fabrication of oxide–oxide ceramic matrix composite. In thevacuum infiltration technique, a solution containing metal compounds, e.g., metal alkoxides, acetates, nitrates or halides are treated chemically to form a sol which is then infiltrated into the fibre preform. The sol in the preform is converted to gel form by physical and/or chemical means, which in turn is subjected to control heating to produce the desired products e.g., glass, glass–ceramic or ceramic matrix. The main advantages of this technique are lower processing temperature and higher compositional homogeneity with respect to slurry infiltration-hot pressing sintering technique (SI-HP). In this process, preforms provide a uniform distribution of fibres and a very high surface area to the matrix gel. However, during drying, shrinkage of matrix results in crack formation in the matrix. It can be minimized by repeated infiltrations with the sol matrix and subsequent drying. The properties of CMCs are influenced by the characteristics of the reinforcing fibres i.e., their strength, aspect ratio, www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 35 (2009) 3073–3079 * Corresponding author. Tel.: +91 33 2483 8086; fax: +91 33 2473 0957. E-mail address: milan@cgcri.res.in (M.K. Naskar). 0272-8842/$36.00 # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2009.04.013