Availableonlineatwww.sciencedirectcom Science Direct Acta materialia ELSEVIER Acta Materialia 54(2006)4929-4937 www.actamat-journals.com Design and production of ceramic laminates with high mechanical resistance and reliability Vincenzo m. sglavo. Massimo bertoldi Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Unitersita degli Studi di Trento, Via Mesiano 77, Trento 38050, Italy Received 27 December 2005: received in revised form 31 May 2006: accepted 14 June 2006 Available online Il September 2006 This paper is dedicated to the memory of Luigi Sglavo, father of vi M. Sglavo, a great person. Abstract a design and processing approach for high failure resistance and increased damage tolerance in laminated ceramic structures is pre- sented. Layers of different compositions are stacked in order to develop a specific residual stress profile by the sintering process. The fracture toughness of the laminate is related to the residual stress. The fracture toughness behaviour can be tailored so that surface efects are forced to grow in a stable way before becoming critical. In this way a ceramic with a unique value of fracture strength is obtained. Laminates composed of alumina/ mullite and alumina/zirconia layers have been designed and fabricated. These materials pos- ss a strength of 700 MPa with a standard deviation of <4%. The strength is insensitive to surface damage and in good agreement with the design value o 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved Keywords: Ceramics: Toughness: Layered structures; Fracture: Ceramic composite 1. Introduction la laminates [3, 4] these strategies promote delamina tion and crack deflection [5, 6]. These approaches, however, The application of brittle materials, like ceramics and provide only a limited relief from the variability in fracture glasses, is often limited by the reliability of their mechanical strength and place high demands on process control for esistance. The variability in strength arises from flaws gen- achieving desired microstructures erated either during processing or arising from damage and In a different approach [7-9] the strength of laminated degradation when in service. The variability is usually too structures is controlled by introducing residual stresses large to allow safe design. In addition, fracture can occur For example, laminates of high strength have been pro- in a catastrophic manner without warning [1]. duced by Lange and co-workers [9] using alternating thin Efforts have been made to reduce the severity of defects compressive layers and thicker tensile layers. An important or to increase fracture toughness by microstructural con- limitation of such laminates is that they can be used only trol. Higher fracture toughness has been achieved via with specific orientations to the applied load; they are not grain-shape anisotropy, by introducing suitable for producing plates, shells or tubes as required and by promoting crack shielding by phase transformation in typical applications or microcracking [1]. As an alternative, fracture behaviour More recently, Orlovskaya and co-worke produced has been improved by introducing low-energy paths for high-toughness Si3 N4 laminates by alternating layers of dif- crack propagation in using porous [2] or within weak inter- ferent composition that resulted in alternating compressive and tensile residual stresses after sintering [10-12]. Fracture Corresponding author. Fax: +39 0461881945 toughness values of up to 17 E-mail address However, the high residual compressive stresses in these 1359-6454/$30.00 O 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. do: 10. 1016/j.actamat. 2006.06.019Design and production of ceramic laminates with high mechanical resistance and reliability Vincenzo M. Sglavo *, Massimo Bertoldi Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Universita` degli Studi di Trento, Via Mesiano 77, Trento 38050, Italy Received 27 December 2005; received in revised form 31 May 2006; accepted 14 June 2006 Available online 11 September 2006 This paper is dedicated to the memory of Luigi Sglavo, father of Vincenzo M. Sglavo, a great person. Abstract A design and processing approach for high failure resistance and increased damage tolerance in laminated ceramic structures is pre￾sented. Layers of different compositions are stacked in order to develop a specific residual stress profile by the sintering process. The fracture toughness of the laminate is related to the residual stress. The fracture toughness behaviour can be tailored so that surface defects are forced to grow in a stable way before becoming critical. In this way a ceramic with a unique value of fracture strength is obtained. Laminates composed of alumina/mullite and alumina/zirconia layers have been designed and fabricated. These materials pos￾sess a strength of 700 MPa with a standard deviation of <4%. The strength is insensitive to surface damage and in good agreement with the design value. 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Ceramics; Toughness; Layered structures; Fracture; Ceramic composite 1. Introduction The application of brittle materials, like ceramics and glasses, is often limited by the reliability of their mechanical resistance. The variability in strength arises from flaws gen￾erated either during processing or arising from damage and degradation when in service. The variability is usually too large to allow safe design. In addition, fracture can occur in a catastrophic manner without warning [1]. Efforts have been made to reduce the severity of defects or to increase fracture toughness by microstructural con￾trol. Higher fracture toughness has been achieved via grain-shape anisotropy, by introducing second phases and by promoting crack shielding by phase transformation or microcracking [1]. As an alternative, fracture behaviour has been improved by introducing low-energy paths for crack propagation in using porous [2] or within weak inter￾layers in laminates [3,4]; these strategies promote delamina￾tion and crack deflection [5,6]. These approaches, however, provide only a limited relief from the variability in fracture strength and place high demands on process control for achieving desired microstructures. In a different approach [7–9] the strength of laminated structures is controlled by introducing residual stresses. For example, laminates of high strength have been pro￾duced by Lange and co-workers [9] using alternating thin compressive layers and thicker tensile layers. An important limitation of such laminates is that they can be used only with specific orientations to the applied load; they are not suitable for producing plates, shells or tubes as required in typical applications. More recently, Orlovskaya and co-workers produced high-toughness Si3N4 laminates by alternating layers of dif￾ferent composition that resulted in alternating compressive and tensile residual stresses after sintering [10–12]. Fracture toughness values of up to 17 MPa m1/2 were measured. However, the high residual compressive stresses in these 1359-6454/$30.00 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2006.06.019 * Corresponding author. Fax: +39 0461881945. E-mail address: vincenzo.sglavo@unitn.it (V.M. Sglavo). www.actamat-journals.com Acta Materialia 54 (2006) 4929–4937