Availableonlineatwww.sciencedirect.com DIRECT E噩≈3S SEVIER Journal of the European Ceramic Society 25(2005)847-856 www.elsevier.com/locate/jeurceramsoc Design and processing of Al2O3-Al2TiO5 layered structures Salvador Bueno Rodrigo moreno Carmen Baudin* Instituto de Ceramica y Vidrio, CS/C, Campus de Cantoblanco, 28049 Madrid, Spain Received 5 February 2004; received in revised form 22 April 2004; accepted 1 May 2004 Available online 10 July 2004 Abstract Al2O3-Al2 TiOs layered composites were manufactured by a colloidal route from aqueous Al2O and TiO2 suspensions with 50 vol % solids The mechanical behaviours of individual monolithic composite materials were combined and taken as basis for the design of the layered tructures. Residual stresses which are likely to occur due to processing and thermally introduced misfits were calculated and considered for the manufacture of the laminates Monoliths with 10, 30 and 40 vol. of second phase showed that increasing proportions of aluminium titanate decrease strength and increase the non-inear behaviour In order to obtain the desired combination of mechanical behaviours of the layers, two laminate designs with external and central layer of one composition and the alternating internal layer of the other composition were chosen taking into account chemical compatibility and development of residual stresses. In the system AAlO, external and central layers of monophase Al2O3 with high strength were combined with intermediate layers of Al2 O3 with 10 vol %of Al2TiOs. The system A10A40 was selected to combine low strength and energy absorbing intermediate layers of Al2O with 40 vol % of Al]TiOs and sufficient strength provided by external layers of Al2O3 with 10 vol %of Al2TiOs The stress-strain behaviour of the laminates was linear up to their failure stresses, with apparent strain for zero load after fracture larger than that corresponding to the monoliths of the same composition as that of the external layers. Moreover, the stress drop of the laminate samples occurred in step-like form thus suggesting the occurrence of additional energy consuming processes during fracture C 2004 Elsevier Ltd. All rights reserved Keywords: Ceramic laminates; Slip casting, Sintering; Al2O3; Al2TiOs: Laminates 1. Introduction the alumina-aluminium titanate system. These authors fab- ricated trilaminates with surface layers consisting of a ho. Improved flaw tolerance and toughness with alumina mogeneous mixture of alumina-20 vol aluminium titanate (Al2O3/aluminium titanate (Al2TiOs) composites have and a flaw tolerant inner layer of the same composition with been reported previously. -6 The toughening mechanisms heterogeneous microstructure. As opposite to laminate de acting in these composites are crack bridging and microc sign in which the high strength is due to residual compressive racking and, therefore, toughening is often associated with stresses acting in the outer layers, 9. 0 such a design would rather low strength. Both mechanisms are originated by assure also high strength for increasing temperature. The the residual stresses that develop during cooling from the limit of this approach is the difficulty to obtain co-sinterec sintering temperature due to thermal expansion mismatch layers of the same composition with large microstructural between alumina and aluminium titanate differences and therefore with significant differences in the In composite materials in which ceramic layers of differ- mechanical behaviour ent composition and, or microstructure are combined, the In a previous work, the processing conditions to achieve properties can be tailored to be superior to those of the con- crack free and completely reacted alumina-aluminium ti- stituent layers. In particular, it is possible to achieve high tanate monolithic composites were established. Uniform flaw tolerance, without sacrificing strength, by using a lami- distribution of the second phase was obtained by a strict nate design in which an R-curve material is located between control of the colloid chemistry of the mixture and grain hig igh strength layers, as demonstrated by Russo et al.in growth was controlled by using a thermal treatment at relatively low temperature. Increased sintering tempera- Corresponding author. Tel. +34 91 735 5840; fax: +34 91 735 5843. ture and aluminium titanate content led to microstructures E-mail address: cbaudin @icv csic es(C. Baudin) with larger grains that presented non-linear stress-strain 0955-2219/s-see front matter O 2004 Elsevier Ltd. All rights reserved doi: 10.1016/j jeurceramsoc 2004.05.001Journal of the European Ceramic Society 25 (2005) 847–856 Design and processing of Al2O3–Al2TiO5 layered structures Salvador Bueno, Rodrigo Moreno, Carmen Baud´ın∗ Instituto de Cerámica y Vidrio, CSIC, Campus de Cantoblanco, 28049 Madrid, Spain Received 5 February 2004; received in revised form 22 April 2004; accepted 1 May 2004 Available online 10 July 2004 Abstract Al2O3–Al2TiO5 layered composites were manufactured by a colloidal route from aqueous Al2O3 and TiO2 suspensions with 50 vol.% solids. The mechanical behaviours of individual monolithic composite materials were combined and taken as basis for the design of the layered structures. Residual stresses which are likely to occur due to processing and thermally introduced misfits were calculated and considered for the manufacture of the laminates. Monoliths with 10, 30 and 40 vol.% of second phase showed that increasing proportions of aluminium titanate decrease strength and increase the non-linear behaviour. In order to obtain the desired combination of mechanical behaviours of the layers, two laminate designs with external and central layers of one composition and the alternating internal layer of the other composition were chosen taking into account chemical compatibility and development of residual stresses. In the system AA10, external and central layers of monophase Al2O3 with high strength were combined with intermediate layers of Al2O3 with 10 vol.% of Al2TiO5. The system A10A40 was selected to combine low strength and energy absorbing intermediate layers of Al2O3 with 40 vol.% of Al2TiO5 and sufficient strength provided by external layers of Al2O3 with 10 vol.% of Al2TiO5. The stress–strain behaviour of the laminates was linear up to their failure stresses, with apparent strain for zero load after fracture larger than that corresponding to the monoliths of the same composition as that of the external layers. Moreover, the stress drop of the laminate samples occurred in step-like form thus suggesting the occurrence of additional energy consuming processes during fracture. © 2004 Elsevier Ltd. All rights reserved. Keywords: Ceramic laminates; Slip casting; Sintering; Al2O3; Al2TiO5; Laminates 1. Introduction Improved flaw tolerance and toughness with alumina (Al2O3)–aluminium titanate (Al2TiO5) composites have been reported previously.1–6 The toughening mechanisms acting in these composites are crack bridging and microc￾racking and, therefore, toughening is often associated with rather low strength. Both mechanisms are originated by the residual stresses that develop during cooling from the sintering temperature due to thermal expansion mismatch between alumina and aluminium titanate. In composite materials in which ceramic layers of differ￾ent composition and, or microstructure are combined, the properties can be tailored to be superior to those of the con￾stituent layers.7 In particular, it is possible to achieve high flaw tolerance, without sacrificing strength, by using a lami￾nate design in which an R-curve material is located between high strength layers, as demonstrated by Russo et al.8 in ∗ Corresponding author. Tel.: +34 91 735 5840; fax: +34 91 735 5843. E-mail address: cbaudin@icv.csic.es (C. Baud´ın). the alumina–aluminium titanate system. These authors fab￾ricated trilaminates with surface layers consisting of a ho￾mogeneous mixture of alumina–20 vol.% aluminium titanate and a flaw tolerant inner layer of the same composition with heterogeneous microstructure. As opposite to laminate de￾sign in which the high strength is due to residual compressive stresses acting in the outer layers,9,10 such a design would assure also high strength for increasing temperature. The limit of this approach is the difficulty to obtain co-sintered layers of the same composition with large microstructural differences and, therefore, with significant differences in the mechanical behaviour. In a previous work,11 the processing conditions to achieve crack free and completely reacted alumina–aluminium ti￾tanate monolithic composites were established. Uniform distribution of the second phase was obtained by a strict control of the colloid chemistry of the mixture and grain growth was controlled by using a thermal treatment at relatively low temperature. Increased sintering tempera￾ture and aluminium titanate content led to microstructures with larger grains that presented non-linear stress–strain 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.05.001