Availableonlineatwww.sciencedirect.com Science Direct E噩≈RS ELSEVIER Joumal of the European Ceramic Society 29(2009)1625-1630 www.elsevier.com/locate/jeurceramsoc Creep mechanisms of laminated alumina/zirconia-toughened alumina composites A Morales-Rodriguez A Dominguez-Rodriguez G. de Portu, M. Jimenez-Melendo Departamento de Fisica de la Materia Condensada, Universidad de Sevilla, Aptdo. 1065, 41080 Sevilla, spain Institute of Science and Technology for Ceramics(ISTEC-CNR), Via granarolo 64, Faenza, Italy Received 12 August 2008; received in revised form 19 September 2008: accepted 24 September 2008 Available online 5 November 2008 High-temperature plastic deformation of laminar composites containing alternate layers of Al2O3 and a mixture of 60 vol. Al2O3+40 vol % 3 mol% Y2O3-stabilized tetragonal ZrO,(ZTA) produced by tape casting is investigated in isostrain compression testing at temperatures between 1400 and 1500C. The stress exponent n and the creep activation energy g are close to l and 700 kJ/mol, respectively. Microstructual observations reveal the lack of differential features in the ZTA layers and a general creep damage of the Al2O3 layers, with little microcracking by cavity coalescence even up to strains of 30%. The layer interfaces maintain their initial structural integrity after testing. An isostrain composite creep model predicts correctly the overall mechanical behavior of the laminates, which is dictated by the alumina phase via diffusional creep controlled by ygen grain boundary diffusion. C 2008 Elsevier Ltd. all rights reserved. Keywords: Creep: Al2O3; ZrO2: Composites; Laminates 1. Introduction The creep behavior of alumina/zirconia-toughened alumina ZTA)laminated composites with strong interfaces has bee In the last years, new strategies based on the development of previously evaluated in the isostress condition(stress axis pe ceramic/ceramic lamellar structures have emerged in order to pendicular to layer planes). It was found 0 that the overall improve the mechanical performance of ceramics for structural creep behavior of the laminates was controlled by the softer applications. -These structures provide a unique opportunity phase(ZTA), but with, superior creep resistance than its mono- for tailoring the mechanical properties and meeting apparently lithic counterpart because of the constraints imposed by the contradictory characteristics of structural ceramics. Al2O3-and harder phase through interface bonding In the present study, ZrO2-based ceramics have been preferentially used as starting Al2 O3/ZTA laminated composites were fabricated by warm materials to build up layered microarchitectures because of their pressing and sintering of layers produced by tape casting. The excellent mechanical rge improve- objective of this work is to characterize the high-temperature ments in strength and fracture toughness at room temperature mechanical behavior of these materials, when loaded axially in have been achieved in alumina/zirconia laminar composites compression(stress axis parallel to layer planes)and to generate because of various crack-shielding phenomena related to the the predictive rate equation for correlating microstructural and presence of the layers. It has also been shown that the laminar mechanical data. microarchitecture beneficially influences the high-temperature creep properties of layered ceramics, conjugating the ductility 2. Experimental procedure and creep resistance of the monolithic constituents. Sheets of pure-alumina and 60 vol. Al2O3+40 vol. mol% Y203-stabilized tetragonal Zro2(ztA) were prepare by tape casting; details of the fabrication process can be found Corresponding author. elsewhere Discs with a diameter of 40 mm were cut from E-mail address: melendo@ uses(M. Jimenez-Melendo) the green ceramic sheets and then stacked and warm-pressed 0955-2219 front matter@ 2008 Elsevier Ltd. All rights reserved. doi: 10. 1016/j-jeurceramsoc. 2008.09.01Available online at www.sciencedirect.com Journal of the European Ceramic Society 29 (2009) 1625–1630 Creep mechanisms of laminated alumina/zirconia-toughened alumina composites A. Morales-Rodríguez a, A. Domínguez-Rodríguez a, G. de Portu b, M. Jiménez-Melendo a,∗ a Departamento de Física de la Materia Condensada, Universidad de Sevilla, Aptdo. 1065, 41080 Sevilla, Spain b Institute of Science and Technology for Ceramics (ISTEC-CNR), Via Granarolo 64, Faenza, Italy Received 12 August 2008; received in revised form 19 September 2008; accepted 24 September 2008 Available online 5 November 2008 Abstract High-temperature plastic deformation of laminar composites containing alternate layers of Al2O3 and a mixture of 60 vol.% Al2O3 + 40 vol.% 3 mol% Y2O3-stabilized tetragonal ZrO2 (ZTA) produced by tape casting is investigated in isostrain compression testing at temperatures between 1400 and 1500 ◦C. The stress exponent n and the creep activation energy Q are close to 1 and 700 kJ/mol, respectively. Microstructual observations reveal the lack of differential features in the ZTA layers and a general creep damage of the Al2O3 layers, with little microcracking by cavity coalescence even up to strains of 30%. The layer interfaces maintain their initial structural integrity after testing. An isostrain composite creep model predicts correctly the overall mechanical behavior of the laminates, which is dictated by the alumina phase via diffusional creep controlled by oxygen grain boundary diffusion. © 2008 Elsevier Ltd. All rights reserved. Keywords: Creep; Al2O3; ZrO2; Composites; Laminates 1. Introduction In the last years, new strategies based on the development of ceramic/ceramic lamellar structures have emerged in order to improve the mechanical performance of ceramics for structural applications.1–3 These structures provide a unique opportunity for tailoring the mechanical properties and meeting apparently contradictory characteristics of structural ceramics. Al2O3- and ZrO2-based ceramics have been preferentially used as starting materials to build up layered microarchitectures because of their excellent mechanical properties. For example, large improve￾ments in strength and fracture toughness at room temperature have been achieved in alumina/zirconia laminar composites because of various crack-shielding phenomena related to the presence of the layers.4–7 It has also been shown that the laminar microarchitecture beneficially influences the high-temperature creep properties of layered ceramics, conjugating the ductility and creep resistance of the monolithic constituents.8,9 ∗ Corresponding author. E-mail address: melendo@us.es (M. Jiménez-Melendo). The creep behavior of alumina/zirconia-toughened alumina (ZTA) laminated composites with strong interfaces has been previously evaluated in the isostress condition (stress axis per￾pendicular to layer planes). It was found10 that the overall creep behavior of the laminates was controlled by the softer phase (ZTA), but with, superior creep resistance than its mono￾lithic counterpart because of the constraints imposed by the harder phase through interface bonding. In the present study, Al2O3/ZTA laminated composites were fabricated by warm pressing and sintering of layers produced by tape casting. The objective of this work is to characterize the high-temperature mechanical behavior of these materials, when loaded axially in compression (stress axis parallel to layer planes) and to generate the predictive rate equation for correlating microstructural and mechanical data. 2. Experimental procedure Sheets of pure-alumina and 60 vol.% Al2O3 + 40 vol.% 3 mol% Y2O3-stabilized tetragonal ZrO2 (ZTA) were prepared by tape casting; details of the fabrication process can be found elsewhere.9 Discs with a diameter of 40 mm were cut from the green ceramic sheets and then stacked and warm-pressed 0955-2219/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2008.09.017