Availableonlineatwww.sciencedirect.com SCIENCE DIRECT● E噩≈S ELSEVIER Journal of the European Ceramic Society 25(2005)3639-364 www.elsevier.com/locate/jeurceramsoc Properties of reinforced boron carbide laminar composites S. Tariollea. F. Thevenota. T Chartier, * J L. Be a Departement Ceramiques Speciales, UMR CNRS 5146, Ecole Nationale Superieure des Mines de saint-Etienne, 158 Cours Fauriel, F.42023 Saint-Erienme Cedex 2. fra b SPCTS, UMR CNRS 6638, Ecole Nationale Superieure de Ceramique Industrielle, 47-73 avenue Albert Thomas, F-87065 Limoges Cedex, france Received 3 June 2004: received in revised form 15 September 2004; accepted 24 September 2004 Available online December 2004 Abstract The reinforcement by crack deflection in boron carbide laminar composites is obtained by both controlling macrostructure and microstruc- ture. This structure had never been studied before in boron carbide materials Composites were prepared using tape-casting technique. Different composites with either porous interlayers obtained by pore forming agent, or weak interlayers obtained without adding sintering aid, or weak interlayers obtained by a mixture of boron carbide and boron nitride or weak graphite or boron nitride interfaces have been elaborated and characterized. Reinforcement by crack deflection was observed in most of these composites. In comparison to the work of rupture of the dense material, i. e. 23.09kJm', the following values were obtained for the minar composites: 38 kJm-3for composites with interlayers with corn starch(55 vol %) 40kJ m-3for composites with B4 C-BN interlayers 30kJ m' for composites with weak interlayers in BN and 39 km for composites with weak interlayers in graphite C 2004 Elsevier Ltd. All rights reserved. Keywords: Tape casting; Composites, Porosity; Mechanical properties, B4 C, BN 1. Introduction energetic criterion. It is well known that the interface crack deflection is influenced by the fracture energy and by the A way to reinforce ceramics, often characterized by their Youngs modulus of materials constituting each side of the euwtoughness that induces catastrophic rupture of the mate- interface. These two properties are dependent on the porosity rials, is to use laminar materials. The use of weak interfaces In the case of a weak graphite interface in SiC material, He or interlayers in functionally graded materials could be effi- and Hutchinson established that the ratio between fracture cient to improve toughness in non-oxide ceramics. The weak energies of the weak interface Gi and of the strong layer Gs interface could be obtained by the incorporation of graphite, must fulfil the following criterion to allow the crack to deflect boron nitride2or oxide ceramics(LaPO4 or YPO4). Another at this interface way to reinforce ceramic materials was to introduce porous and alternate dense-porous SiC(solid phase sintering) have Gs 0.57 ceramic interlayers. Thus, alternate dense-porous alumina the interface between porous and dense layers leading to an For dense -porous laminates, Clegg and coworkers,5ex- increase of the fracture energy pressed this energetic criterion(Eq. (1)considering that the Clegg and coworkers4.5 analyzed crack deflection mech- interface energy G could be replaced by the ligament energy anism in alternate dense-porous ceramic materials using an Glig (ligament of ceramic material between pores in which Corresponding author. Tel. +33555 45 22 25; fax: +33 555 79 0998 Ge $0.57 0955-2219/S-see front matter c 2004 Elsevier Ltd. All rights reservedJournal of the European Ceramic Society 25 (2005) 3639–3647 Properties of reinforced boron carbide laminar composites S. Tariollea, F. Thevenot ´ a, T. Chartierb,∗, J.L. Bessonb a D´epartement C´eramiques Sp´eciales, UMR CNRS 5146, Ecole Nationale Sup´erieure des Mines de Saint-Etienne, 158 Cours Fauriel, F-42023 Saint-Etienne Cedex 2, France b SPCTS, UMR CNRS 6638, Ecole Nationale Sup´erieure de C´eramique Industrielle, 47-73 avenue Albert Thomas, F-87065 Limoges Cedex, France Received 3 June 2004; received in revised form 15 September 2004; accepted 24 September 2004 Available online 8 December 2004 Abstract The reinforcement by crack deflection in boron carbide laminar composites is obtained by both controlling macrostructure and microstruc￾ture. This structure had never been studied before in boron carbide materials. Composites were prepared using tape-casting technique. Different composites with either porous interlayers obtained by pore forming agent, or weak interlayers obtained without adding sintering aid, or weak interlayers obtained by a mixture of boron carbide and boron nitride, or weak graphite or boron nitride interfaces have been elaborated and characterized. Reinforcement by crack deflection was observed in most of these composites. In comparison to the work of rupture of the dense material, i.e. 23.09 kJ m−3, the following values were obtained for the laminar composites: 38 kJ m−3 for composites with interlayers with corn starch (55 vol.%), 40 kJ m−3 for composites with B4C-BN interlayers, 30 kJ m−3 for composites with weak interlayers in BN and 39 kJ m−3 for composites with weak interlayers in graphite. © 2004 Elsevier Ltd. All rights reserved. Keywords: Tape casting; Composites, Porosity; Mechanical properties; B4C; BN 1. Introduction A way to reinforce ceramics, often characterized by their low toughness that induces catastrophic rupture of the mate￾rials, is to use laminar materials. The use of weak interfaces or interlayers in functionally graded materials could be effi- cient to improve toughness in non-oxide ceramics. The weak interface could be obtained by the incorporation of graphite,1 boron nitride2 or oxide ceramics (LaPO4 or YPO4).3 Another way to reinforce ceramic materials was to introduce porous ceramic interlayers. Thus, alternate dense-porous alumina4 and alternate dense-porous SiC (solid phase sintering)5 have been studied. In these materials, crack deflection occurred at the interface between porous and dense layers leading to an increase of the fracture energy. Clegg and coworkers4,5 analyzed crack deflection mech￾anism in alternate dense-porous ceramic materials using an ∗ Corresponding author. Tel.: +33 555 45 22 25; fax: +33 555 79 09 98. E-mail address: t chartier@ensci.fr (T. Chartier). energetic criterion. It is well known that the interface crack deflection is influenced by the fracture energy and by the Young’s modulus of materials constituting each side of the interface. These two properties are dependent on the porosity. In the case of a weak graphite interface in SiC material, He and Hutchinson6 established that the ratio between fracture energies of the weak interface Gi and of the strong layer Gs must fulfil the following criterion to allow the crack to deflect at this interface: Gi Gs ≤ 0.57 (1) For dense-porous laminates, Clegg and coworkers4,5 ex￾pressed this energetic criterion (Eq. (1)) considering that the interface energy Gi could be replaced by the ligament energy Glig (ligament of ceramic material between pores in which the crack propagates): Glig Gs ≤ 0.57 (2) 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.09.014