Availableonlineatwww.sciencedirect.com DIRECT Part B: ELSEVIER Composites: Part B 37(2006)556-567 Laminated ceramic structures from oxide systems G. de portu c,L. micele G. pe b. c Research institute of Science and Technology for Ceramics, ISTEC-CNR, via Granarolo 64. 48018 Faenza Ceramic Physics Laboratory, Kyoto Institute of Technology, KIT, Sakyo ku, Matsugasaki, 606-8585 Kyoto, Research institute for Nano-S.science, RIN, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8585 Ky Received 11 March 2005: received in revised form 5 August 2005; accepted 24 August 2005 Available online 19 April 2006 Abstract In this paper we present the results recently obtained in the study of laminated ceramic composites. The motivation for studying and producing laminated ceramic composites have been illustrated. Theoretical model useful to guide the design of laminated structures have been discussed and a route to prepare layered structures in the system Al2O3-ZrO2 have been suggested. The residual stresses developed in the ceramic layers have been quantified by indentation technique and piezo-spectroscopic analysis. With the latter technique also the stress distribution in the different layers has been assessed. Higher wear resistance under sliding and abrasive conditions of layered ceramics have been demonstrated. The improvement of fatigue contact damage resistance and an increase of Weibull modulus underlined. C 2006 Elsevier Ltd. All rights reserved Keywords: A. Layered structures: B. Mechanical properties; C. Residual internal stress; B. Wear 1. Introduction The interest in structural properties of such materials is not The main limit for an extensive application of ceramics as concerns the phenomena related to contact damage resistance, structural materials is their inhert brittleness and, as a tribological behaviour and machinability consequence, their poor reliability. In order to overcome this The motivation for the use of graded materials and problem three principal routes have been explored in the last laminated composites(considered as a special case of FGM) can be traced back to the observation of biological One consists in increasing the knowledges of macro-micro In those structures, the most performing parts of the materia mechanical behaviour of brittle materials. the second one deals are located in regions that experience the highest stresses. with the improvement of the preparation process of these Similarly, considering the tribological aspect, for example materials and the third one regards the design and development it has been recognized that the performances of wear-resistant of new materials and structures with improved flaw tolerance. materials are mainly related to the properties of thin surface The development of ceramic composites [1, 2], in general and functional graded materials(FGM)[3, 4] or laminated The development of laminated structures is based on the structures[5-7], in particular, incorporates the latter two tasks assumption that it is possible to design a material containing and stimulates, also, the interset in the first one, promoting the controlled residual stresses that can be used to increase refinement and progress of theoretical models able to describe the mechanical [16-23] and tribological performances of the the structural behaviour of such complex multiphase micro- system [24,25]. This goal can be achieved exploiting the structures [8-13 differences in thermal-physical properties (i.e. different sintering rates or coefficients of thermal expansion-CTE) among the laminae of dissimilar materials utilized in the process. w Corresponding author. Address. Research Institute of Science and These laminar ceramics containing large compressive Technology for Ceramics, ISTEC-CNR, via Granarolo 64. 48018 Faenza, stresses were shown to exhibit crack bifurcation [26,27 and Italy.Tel:+390546699752;fax:+39054646381 increasing strain to failure during fexural failure and a threshold strength when loaded in tension [28]. In the latter 1359-8368/- see front matter o 2006 Elsevier Ltd. All rights reserved. case, large cracks that initiate in the 'tensile layers'are stopped doi: 10.1016/j- composites. 2006.02.018 by the compressive layers at low stresses. Because the crackLaminated ceramic structures from oxide systems G. de Portu a,c,*, L. Micele a,c, G. Pezzotti b,c a Research Institute of Science and Technology for Ceramics, ISTEC-CNR, via Granarolo 64, 48018 Faenza, Italy b Ceramic Physics Laboratory, Kyoto Institute of Technology, KIT, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan c Research Institute for Nano-Sscience, RIN, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan Received 11 March 2005; received in revised form 5 August 2005; accepted 24 August 2005 Available online 19 April 2006 Abstract In this paper we present the results recently obtained in the study of laminated ceramic composites. The motivation for studying and producing laminated ceramic composites have been illustrated. Theoretical model useful to guide the design of laminated structures have been discussed and a route to prepare layered structures in the system Al2O3-ZrO2 have been suggested. The residual stresses developed in the ceramic layers have been quantified by indentation technique and piezo-spectroscopic analysis. With the latter technique also the stress distribution in the different layers has been assessed. Higher wear resistance under sliding and abrasive conditions of layered ceramics have been demonstrated. The improvement of fatigue contact damage resistance and an increase of Weibull modulus underlined. q 2006 Elsevier Ltd. All rights reserved. Keywords: A. Layered structures; B. Mechanical properties; C. Residual internal stress; B. Wear 1. Introduction The main limit for an extensive application of ceramics as structural materials is their inhert brittleness and, as a consequence, their poor reliability. In order to overcome this problem three principal routes have been explored in the last decades. One consists in increasing the knowledges of macro–micro mechanical behaviour of brittle materials, the second one deals with the improvement of the preparation process of these materials and the third one regards the design and development of new materials and structures with improved flaw tolerance. The development of ceramic composites [1,2], in general, and functional graded materials (FGM) [3,4] or laminated structures [5–7], in particular, incorporates the latter two tasks and stimulates, also, the interset in the first one, promoting the refinement and progress of theoretical models able to describe the structural behaviour of such complex multiphase micro￾structures [8–13]. The interest in structural properties of such materials is not limited to the enhancement of strength and toughness but also concerns the phenomena related to contact damage resistance, tribological behaviour and machinability. The motivation for the use of graded materials and laminated composites (considered as a special case of FGM) can be traced back to the observation of biological structures. In those structures, the most performing parts of the material are located in regions that experience the highest stresses. Similarly, considering the tribological aspect, for example, it has been recognized that the performances of wear-resistant materials are mainly related to the properties of thin surface layers [14,15]. The development of laminated structures is based on the assumption that it is possible to design a material containing controlled residual stresses that can be used to increase the mechanical [16–23] and tribological performances of the system [24,25]. This goal can be achieved exploiting the differences in thermal–physical properties (i.e. different sintering rates or coefficients of thermal expansion-CTE) among the laminae of dissimilar materials utilized in the process. These laminar ceramics containing large compressive stresses were shown to exhibit crack bifurcation [26,27] and increasing strain to failure during flexural failure and a threshold strength when loaded in tension [28]. In the latter case, large cracks that initiate in the ‘tensile layers’ are stopped by the compressive layers at low stresses. Because the crack is Composites: Part B 37 (2006) 556–567 www.elsevier.com/locate/compositesb 1359-8368/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2006.02.018 * Corresponding author. Address. Research Institute of Science and Technology for Ceramics, ISTEC-CNR, via Granarolo 64, 48018 Faenza, Italy. Tel.: C39 0546 699752; fax: C39 0546 46381. E-mail address: deportu@istec.cnr.it (G. de Portu)