Availableonlineatwww.sciencedirect.com Part B: engineering ELSEVIER Composites: Part B 37(2006)499-508 www.elsevier.com/locate/composi Processing of Al,O3/Y-TZP laminates from water-based cast tapes A.J. Sanchez-Herencia s.J. Gurauskis C. Baudin Instituto de Ceramica y Vidrio, CSIC, C/Kelsen 5. 28049 Madrid, spain Received 11 March 2005; received in revised form 15 August 2005; accepted 24 August 2005 Available online 4 April 2006 Abstract Laminated structures have been investigated due to their capability for the reinforcement of ceramics. Crack deflexion and bifurcation, surface strengthening and threshold strength are the mechanisms associated to the fracture of laminated ceramic. In all the cases, a precise control of the thickness and composition of the layers is necessary. In this sense, colloidal processing techniques have proved their adequacy for the fabrication f designed layered structures. This paper This paper deals with the fabrication of layered ceramics by stacking water-based cast tapes at room temperature and using low pressures. In order to control the pressing procedure, the engineering strain-stress curves recorded during the stacking of the tapes were analyzed. Afterwards, the sintering conditions have been optimized by adjusting the green density of the tapes to avoid differential sintering and the associated cracks. Monolithic and layered materials free of cracks have been fabricated using optimized processing conditions C 2006 Elsevier Ltd. All rights reserved. Keywords: A. Layered Structures; Tape; E Joining: Sintering 1. Introduction much of the mechanical property benefit of fiber reinforcemen without the associated processing complexity Severe environments imposed by new technologies demand The use of laminar reinforcements is not however a the fabrication of materials with better properties and more completely original idea. For million of years, living creatures tolerance restrictions, in which reliability must be ensured. have designed protective laminar structures with optimized Consequently, ceramics have been proposed as either mechanical properties utilizing the rather limited resources substitutes for currently used materials (e.g. metals and provided by their surroundings [2]. Such is the case of the plastics) or as complements to existing materials (i. e in the mollusk shell, in which a laminar structure composed of form of composites), due to their favorable properties such as alternating brittle but strong aragonite layers and ductile but high temperature hardness and strength, and good thermal and weak organic polymer layers provides a protective shell with chemical stability. However, the intrinsic brittleness of ceramic toughness and strength roughly 10 times that of a correspond- materials has forced to look for new designs and processing ing aragonite single-crystal [3]. Mimicking this concept, Pizyk routes to improve their mechanical behavior while maintaining and Aksay fabricated several laminar metal-ceramic and the low cost and low environmental impact. ceramic-polymer composites that showed improved mechan- One such method for improving the mechanical behavior of ical properties compared to their corresponding monolithic ceramics has been the reduction of the defects in the ceramic materials [4 body through colloidal filtration and processing techniques [1] Layered ceramics were initially developed in the 1960s as a Another method has been the creation of multi-phase result of the necessity of these structures for the packaging of composite architectures composed of ceramic matrices microelectronics. As a consequence of this demand, different reinforced by the addition of particulate, fiber, and/or laminar methods to obtain ceramic multilayers with controlled secondary phases. The use of laminar reinforcement has been thicknesses, as well as handling and lamination possibilities, identified as a simple and inexpensive method of achieving were studied [5,6). These methods were based on the tape casting technique, in which multilayer structures were obtained by the stacking of green tapes followed by subsequent w Corresponding author. Tel: +34 91 735 5840: fax: +3491 735 5843. consolidation by either the application of pressure at a suitable E-lmail address: ajsanchez@icv temperature, or by roll-to-roll compaction 1359-8368/S- see front matter 2006 Elsevier Ltd. All rights reserved. The preparation of tape-cast layered ceramics for structural doi: 10. 1016/ applications was first reported by Mistler [7]. He described anProcessing of Al2O3/Y-TZP laminates from water-based cast tapes A.J. Sa´nchez-Herencia *, J. Gurauskis, C. Baudı´n Instituto de Cera´mica y Vidrio, CSIC, C/Kelsen 5, 28049 Madrid, Spain Received 11 March 2005; received in revised form 15 August 2005; accepted 24 August 2005 Available online 4 April 2006 Abstract Laminated structures have been investigated due to their capability for the reinforcement of ceramics. Crack deflexion and bifurcation, surface strengthening and threshold strength are the mechanisms associated to the fracture of laminated ceramic. In all the cases, a precise control of the thickness and composition of the layers is necessary. In this sense, colloidal processing techniques have proved their adequacy for the fabrication of designed layered structures. This paper deals with the fabrication of layered ceramics by stacking water-based cast tapes at room temperature and using low pressures. In order to control the pressing procedure, the engineering strain–stress curves recorded during the stacking of the tapes were analyzed. Afterwards, the sintering conditions have been optimized by adjusting the green density of the tapes to avoid differential sintering and the associated cracks. Monolithic and layered materials free of cracks have been fabricated using optimized processing conditions. q 2006 Elsevier Ltd. All rights reserved. Keywords: A. Layered Structures; Tape; E. Joining; Sintering 1. Introduction Severe environments imposed by new technologies demand the fabrication of materials with better properties and more tolerance restrictions, in which reliability must be ensured. Consequently, ceramics have been proposed as either substitutes for currently used materials (e.g. metals and plastics) or as complements to existing materials (i.e. in the form of composites), due to their favorable properties such as high temperature hardness and strength, and good thermal and chemical stability. However, the intrinsic brittleness of ceramic materials has forced to look for new designs and processing routes to improve their mechanical behavior while maintaining the low cost and low environmental impact. One such method for improving the mechanical behavior of ceramics has been the reduction of the defects in the ceramic body through colloidal filtration and processing techniques [1]. Another method has been the creation of multi-phase composite architectures composed of ceramic matrices reinforced by the addition of particulate, fiber, and/or laminar secondary phases. The use of laminar reinforcement has been identified as a simple and inexpensive method of achieving much of the mechanical property benefit of fiber reinforcement without the associated processing complexity. The use of laminar reinforcements is not, however, a completely original idea. For million of years, living creatures have designed protective laminar structures with optimized mechanical properties utilizing the rather limited resources provided by their surroundings [2]. Such is the case of the mollusk shell, in which a laminar structure composed of alternating brittle but strong aragonite layers and ductile but weak organic polymer layers provides a protective shell with toughness and strength roughly 10 times that of a correspond￾ing aragonite single-crystal [3]. Mimicking this concept, Pizyk and Aksay fabricated several laminar metal–ceramic and ceramic–polymer composites that showed improved mechan￾ical properties compared to their corresponding monolithic materials [4]. Layered ceramics were initially developed in the 1960s as a result of the necessity of these structures for the packaging of microelectronics. As a consequence of this demand, different methods to obtain ceramic multilayers with controlled thicknesses, as well as handling and lamination possibilities, were studied [5,6]. These methods were based on the tape casting technique, in which multilayer structures were obtained by the stacking of green tapes followed by subsequent consolidation by either the application of pressure at a suitable temperature, or by roll-to-roll compaction. The preparation of tape-cast layered ceramics for structural applications was first reported by Mistler [7]. He described an Composites: Part B 37 (2006) 499–508 www.elsevier.com/locate/compositesb 1359-8368/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesb.2006.02.002 * Corresponding author. Tel.: C34 91 735 5840; fax: C34 91 735 5843. E-mail address: ajsanchez@icv.csic.es (A.J. Sa´nchez-Herencia)