Availableonlineatwww.sciencedirect.com SCIENCE IRECTI SOLID STATE CHEMISTRY ELSEVIER Journal of Solid State Chemistry 177(2004)487-492 http://elsevier.com/locate/jssc Preparation, microstructure and mechanical properties of SiC-Sic and B4c-B4c laminates S. Tariolle, C. Reynaud, F. Thevenot, T. Chartier, and J. L. Besson Laboratoire Ceramiques Speciales, Ecole Nationale Superieure des Mines de saint-Etienne, 158 Cours Fauriel, F-42023 Saint-Etienne Cedex 2, france b SPCTS. Ecole Nationale Superieure de Ceramique Industrielle, 47-73 avenue Albert Thomas, F-87065 Limoges Cedex, france mber 2002: accepted 27 February 2003 Abstract Silicon carbide and boron carbide are high hardness materials with a low density but, like most ceramics, with a low toughness, that limits their use in various applications. One approach to reinforce ceramic materials consists in using crack deflection by weakening the interfaces in laminar materials In our study, ceramic layers of different compositions were prepared by tape castin spray for B.C. After debinding, SIC(Al2O3, Y2O3 additions) and BC(C addition) were pressureless sintered. For evaluation of the sintered parts, firstly the macrostructure and microstructure were characterized. Then, mechanical properties of multi-layered materials, obtained by stacking dense and porous layers that should contain enough porosity to initiate crack deflection, according to the models. were evaluated C 2003 Elsevier Inc. All rights reserved Keywords: Boron carbide; Silicon carbide: Laminar materials; Tape casting: Rupture: Crack deflection 1. Introduction porous ceramic materials. It is well-known that the interface crack deflection is influenced by the fracture a way to reinforce ceramics, often characterized by energy and by Youngs modulus of materials constitut- their low toughness that induces catastrophic rupture of ing each side of the interface [6,7]. These two properties the materials, is to use laminar materials. Thus, are dependent on the porosity functionally graded materials were chosen to improve He and Hutchinson [8] established, in the case of a fracture toughness in non-oxide ceramics. The use of weak graphite interface in SiC material, that the ratio mechanical properties of ceramic materials Improve between fracture energies of the weak interface G and of weak interfaces or interlayers allows he strong layer Gs must fulfil the following criterion to interface can be made by the incorporation of graphite allow the crack to deflect at this interface [1], boron nitride [2] or oxide ceramics(LaPO4 or YPO4) [3]. Another way to reinforce ceramic materials is to G/G≤0.57 introduce porous ceramic interlayers. Thus, alternate For dense-porous laminates, Clegg et al. [4,5 dense-porous alumina 14] and alternate dense-porous expressed this criterion considering that the interfac SiC (solid phase sintering) were made [5]. In these energy G is replaced by the ligament energy Glig materials, crack deflection occurred at the interface (ligament of ceramic material between pores in which was in porous and dense layers and the fracture energy the crack propagates) ased Clegg et al. [4, 5] proposed an energetic criterion to Glig/Gs$0.57 explain crack deflection mechanism in alternate dense- Therefore, Eq (2)can be expressed in relation with porosity Corresponding author. Fax: + 33-4-77-42-00-00 E-mail address. tariolle(@ emse. fr(S. Tariolle) Gp/Ga(1-p)≤0.57 0022-4596/Ssee front matter C 2003 Elsevier Inc. All rights reserved. doi:10.1016/jc.2003.02007Journal of Solid State Chemistry 177 (2004) 487–492 Preparation, microstructure and mechanical properties of SiC–SiC and B4C–B4C laminates S. Tariolle,a,
C. Reynaud,a F. The´venot,a T. Chartier,b and J.L. Bessonb a Laboratoire Ce´ramiques Spe´ciales, Ecole Nationale Supe´rieure des Mines de Saint-Etienne, 158 Cours Fauriel, F-42023 Saint-Etienne Cedex 2, France bSPCTS, Ecole Nationale Supe´rieure de Ce´ramique Industrielle, 47-73 avenue Albert Thomas, F-87065 Limoges Cedex, France Received 24 September 2002; accepted 27 February 2003 Abstract Silicon carbide and boron carbide are high hardness materials with a low density but, like most ceramics, with a low toughness, that limits their use in various applications. One approach to reinforce ceramic materials consists in using crack deflection by weakening the interfaces in laminar materials. In our study, ceramic layers of different compositions were prepared by tape casting and stacked in predefined sequences. Different weak layers were tested: porous layers made with different pore forming agents for SiC; porous layers made with pore forming agent or by varying the quantity of sintering aid and weak interfaces made with graphite spray for B4C. After debinding, SiC (Al2O3, Y2O3 additions) and B4C (C addition) were pressureless sintered. For evaluation of the sintered parts, firstly the macrostructure and microstructure were characterized. Then, mechanical properties of multi-layered materials, obtained by stacking dense and porous layers that should contain enough porosity to initiate crack deflection, according to the models, were evaluated. r 2003 Elsevier Inc. All rights reserved. Keywords: Boron carbide; Silicon carbide; Laminar materials; Tape casting; Rupture; Crack deflection 1. Introduction A way to reinforce ceramics, often characterized by their low toughness that induces catastrophic rupture of the materials, is to use laminar materials. Thus, functionally graded materials were chosen to improve fracture toughness in non-oxide ceramics. The use of weak interfaces or interlayers allows to improve mechanical properties of ceramic materials. The weak interface can be made by the incorporation of graphite [1], boron nitride [2] or oxide ceramics (LaPO4 or YPO4) [3]. Another way to reinforce ceramic materials is to introduce porous ceramic interlayers. Thus, alternate dense–porous alumina [4] and alternate dense–porous SiC (solid phase sintering) were made [5]. In these materials, crack deflection occurred at the interface between porous and dense layers and the fracture energy was increased. Clegg et al. [4,5] proposed an energeticcriterion to explain crack deflection mechanism in alternate dense– porous ceramic materials. It is well-known that the interface crack deflection is influenced by the fracture energy and by Young’s modulus of materials constitut￾ing each side of the interface [6,7]. These two properties are dependent on the porosity. He and Hutchinson [8] established, in the case of a weak graphite interface in SiC material, 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=Gsp0:57: ð1Þ For dense–porous laminates, Clegg et al. [4,5] expressed this criterion considering that the interface energy Gi is replaced by the ligament energy Glig (ligament of ceramic material between pores in which the crack propagates): Glig=Gsp0:57: ð2Þ Therefore, Eq. (2) can be expressed in relation with porosity p: Gp=ðGdð1  pÞÞp0:57; ð3Þ ARTICLE IN PRESS
Corresponding author. Fax: +33-4-77-42-00-00. E-mail address: tariolle@emse.fr (S. Tariolle). 0022-4596/$ - see front matter r 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jssc.2003.02.007