Composites: Part A 40(2009)137-143 Contents lists available at ScienceDirect Composites: Part A ELSEVIER journalhomepagewww.elsevier.com/locate/compositesa Design and processing of a ceramic laminate with high toughness and strong interfaces S Bueno, C Baudin Instituto de Ceramica y Vidrio(CSIC. Campus de Cantoblanco, Kelsen 5, 28049 Madrid, Spain ARTICLE IN F O ABSTRACT Article history: An alumina-aluminium titanate laminate designed to Received 7 July 2008 trong interfaces is proposed. It is constituted by relative l stine ng b ite exsternct av eraspwith y c Received in revised form 13 October 2008 Accepted 28 October 2008 cracked internal layers to produce multiple crack deflection at the microstructural scale. The mo tant difference of the laminated structure proposed here and that of other laminates with high for crack deflection is that the crack deflection process occurs at local level, thus, delamination lengths are imited and delamination does not lead to the lost of structural integrity B Mechanical properties A symmetric structure formed by five layers has been design to minimise residual stresses taking into D Mechanical testing account the strain on cooling and the Youngs modulus of monolithic materials of the same compositio E Slip casting as those of the layers and fabricated using the same processing procedure as that of the laminate pecial care was given to adjust the processing variables that permitted the fabrication of the designed minated by sequential slip casting and sintering. ms of strength(4 modulus, work of fracture and apparent toughness. The two latter parameters have been determined by 3-points bending of Single-Edge-V-Notch-Beams (SEVNB) and fractographic analysis has been per- formed on the tested samples. The apparent toughness value at the point of failure(12 MPa m"/2)wa omparable to values reported for the stationary state of transformation-toughened ceramics. Work of fracture(62+3Jm-)was significantly higher(26%)than that obtained by calculation from the values corresponding to monolithic materials of the same composition as that of the layers, revealing the syn- ergic effect of the laminated structure on the mechanical behaviour of the material e 2008 Elsevier Ltd. All rights reserved. 1 Introduction and brittle aragonite platelets held together by a easily to deform and tough proteinaceous matrix make nacre a rigid material in for metals in structural applications that involve high temperature those of aragonite, which constitutes the 95 vol% of nacre. Several in severe erosive and corrosive environments and or compressive mechanisms leading to energy dissipation have been identified to loads. The major problem for the structural use of ceramics is re- occur during the fracture of nacre [2, 3 ] sliding of the aragonite lated with their brittle fracture mode, which implies the variation layers, stretching of the filaments in the proteinaceous matrix f strength of different components within the same batch as a and crack deflection around the aragonite plates. function of the distribution of strength limiting flaws. Although On the basis of the toughening mechanisms proposed for nad particularly weak components can be removed from the batch by two groups of materials have been developed. One of them com- proof testing, once a component enters service, subcritical growth bines relatively thick rigid external layers with thin internal layers of pre-existing flaws or the formation of new cracks, for instance capable of deformation and energy absorption during fracture a lead to unpredicted failure of the components [1. number of ceramic-metal and ceramic-polymer laminates have One of the most promising new approaches to avoid the lack of been developed on this basis [ 4-8 which main drawback is the mechanical reliability of ceramics is that of layered materials. Nat- lack of stability at high temperature due to the characteristics of ure offers a number of simple layered structures, such as shells or the metal and polymeric layers On the other hand, since the sem- teeth, which present improved failure behaviour as compared to inal work by Clegg et al. [9 ceramic-ceramic layered composites that of the individual components. For example, layers of stiff, hard have been designed and processed on the basis of weak interfaces between layers to originate crack deflection [1, 10-11 An alterna- Corresponding author. Tel. +34 91 7355840: fax: +34 91 7355843 tive way to produce crack deflection is to incorporate porous layers of the same composition between dense ceramic layers [12-14: natter 2008 Elsevier Ltd. All rights reservedDesign and processing of a ceramic laminate with high toughness and strong interfaces S. Bueno, C. Baudín * Instituto de Cerámica y Vidrio (CSIC), Campus de Cantoblanco, Kelsen 5, 28049 Madrid, Spain article info Article history: Received 7 July 2008 Received in revised form 13 October 2008 Accepted 28 October 2008 Keywords: A. Layered structures B. Mechanical properties D Mechanical testing E. Slip casting abstract An alumina–aluminium titanate laminate designed to combine high crack deflection capability with strong interfaces is proposed. It is constituted by relatively stiff and brittle external layers with micro￾cracked internal layers to produce multiple crack deflection at the microstructural scale. The most impor￾tant difference of the laminated structure proposed here and that of other laminates with high capability for crack deflection is that the crack deflection process occurs at local level, thus, delamination lengths are limited and delamination does not lead to the lost of structural integrity. A symmetric structure formed by five layers has been design to minimise residual stresses taking into account the strain on cooling and the Young’s modulus of monolithic materials of the same compositions as those of the layers and fabricated using the same processing procedure as that of the laminate. Special care was given to adjust the processing variables that permitted the fabrication of the designed laminated by sequential slip casting and sintering. Mechanical characterisation has been done in terms of strength (4-points bending), dynamic Young’s modulus, work of fracture and apparent toughness. The two latter parameters have been determined by 3-points bending of Single-Edge-V-Notch-Beams (SEVNB) and fractographic analysis has been per￾formed on the tested samples. The apparent toughness value at the point of failure (12 MPa m1/2) was comparable to values reported for the stationary state of transformation-toughened ceramics. Work of fracture (62 ± 3 Jm2 ) was significantly higher (26%) than that obtained by calculation from the values corresponding to monolithic materials of the same composition as that of the layers, revealing the syn￾ergic effect of the laminated structure on the mechanical behaviour of the material. 2008 Elsevier Ltd. All rights reserved. 1. Introduction Ceramic materials are being proposed and used as substitutes for metals in structural applications that involve high temperature in severe erosive and corrosive environments and/or compressive loads. The major problem for the structural use of ceramics is re￾lated with their brittle fracture mode, which implies the variation of strength of different components within the same batch as a function of the distribution of strength limiting flaws. Although particularly weak components can be removed from the batch by proof testing, once a component enters service, subcritical growth of pre-existing flaws or the formation of new cracks, for instance by erosion, can lead to unpredicted failure of the components [1]. One of the most promising new approaches to avoid the lack of mechanical reliability of ceramics is that of layered materials. Nat￾ure offers a number of simple layered structures, such as shells or teeth, which present improved failure behaviour as compared to that of the individual components. For example, layers of stiff, hard and brittle aragonite platelets held together by a easily to deform and tough proteinaceous matrix make nacre a rigid material in which both toughness and strength are significantly higher than those of aragonite, which constitutes the 95 vol.% of nacre. Several mechanisms leading to energy dissipation have been identified to occur during the fracture of nacre [2,3]: sliding of the aragonite layers, stretching of the filaments in the proteinaceous matrix and crack deflection around the aragonite plates. On the basis of the toughening mechanisms proposed for nacre, two groups of materials have been developed. One of them com￾bines relatively thick rigid external layers with thin internal layers capable of deformation and energy absorption during fracture. A number of ceramic-metal and ceramic-polymer laminates have been developed on this basis [4–8] which main drawback is the lack of stability at high temperature due to the characteristics of the metal and polymeric layers. On the other hand, since the sem￾inal work by Clegg et al. [9] ceramic-ceramic layered composites have been designed and processed on the basis of weak interfaces between layers to originate crack deflection [1,10–11]. An alterna￾tive way to produce crack deflection is to incorporate porous layers of the same composition between dense ceramic layers [12–14]; 1359-835X/$ - see front matter 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesa.2008.10.012 * Corresponding author. Tel.: +34 91 7355840; fax:+34 91 7355843. E-mail address: cbaudin@icv.csic.es (C. Baudín). Composites: Part A 40 (2009) 137–143 Contents lists available at ScienceDirect Composites: Part A journal homepage: www.elsevier.com/locate/compositesa