Availableonlineatwww.sciencedirect.com Science Direct E噩≈RS ELSEVIER Journal of the European Ceramic Society 28(2008)229-233 www.elsevier.com/locate/jeurceramsoc Microstructure and material properties of double-network type fibrous(Al2O3-m-ZrO2)/t-zrO2 composites Byong-Taek Lee a Swapan Kumar Sarkar, Ho-Yeon Song Department of Biomedical Engineering and Materials, School of Medicine, Soonchunhyang University 366-I Ssangyoung-dong, Cheonan, Chungnam 330-090, South Korea b School of Advanced Materials Engineering, Kongju National University, 18 Depart Shinkwan-dong, Kongju, Chungnam 314-701, South Korea nt of Microbiology, School of Medicine, Soonchunhyang Universiry 366-1 Ssangyoung-dong, Cheonan, Chungnam 330-090, South Korea Received 20 February 2007: received in revised form 7 May 2007; accepted 13 May 2007 vailable online 2 August 2007 Al2O3-(m-zrO2)t-ZrO2 composites with a novel double-network microstructure were fabricated by multi-pass extrusion process using polymer bound ceramic green body. A simultaneous micro- and macro-level microstructure tailoring was made where unidirectionally aligned two-phase 2O3(m-ZrO2)fibers were enclosed in a t-Zro2 phase connected in a network formation and this network was further enclosed in a thicker t-ZrO2 phase. Composite green rods were hot extruded and reassembled in parallel for extrusion and after several passes of extrusion very fine microstructure with dimension of a few micrometers was obtained. Material properties such as hardness, bending strength and fracture toughnes were measured for the composites Microstructure characterization was carried out by SEM technique. In the 4th passed Al2O3-(m-zrO2)/t-ZrO2 composites, the outer network of t-ZrO2 was 15 er network 0.8 um and the inner Al2O3-m-ZrOz)core was 2.5 um. The highest hardness, fracture strength and toughness values were about 1452 Hv, 1006 MPa and 8.6MPam, respectively, in the sample sintered at 1500.C o 2007 Elsevier Ltd. all rights reserve Keywords: Extrusion; Composites; Microstructure-final; Al2O3; ZrO2 1. Introduction toughening due to phase transformation from tetragonal(t)to monoclinic(m). In case of the dispersion of m-ZrO2 particles in Alumina(Al2O3) is one of the high performance ceramics the Al2O3 matrix, the strong strain field and some microcrack used in high-temperature, structural, cutting and wear resis- were easily formed during the sintering process, due to the tance applications , The excellent chemical stability and difference in the co-efficient of thermal expansion.These bio-inertness extends its application for harsh environment strain fields and microcracks led to intergranular fracture and biomedical applications .However, there is a common with crack deflection and thus reduce the crack propagation drawback of Al2O3 like most other ceramics, i. e, it has poor energy. 'In addition when cracks propagate transgranularly fracture toughness(about 3.5 MPa m), which is a hindrance in m-ZrO2 the driving force of crack propagation is reduced for use in dynamic load-bearing applications. This is basically due to the plastic deformation of m-ZrO2. In conjunction to due to the absence of main toughening mechanisms such as this many other approaches have also been investigated for the microcracks, crack bridging, phase transformation, etc. Hence, improvement of fracture toughness like metal coating of raw many strategies have been proposed to improve the mechanical ceramic powder for metal-ceramic composites, whisker and properties of a monolithic Al2O3 body. Dispersion of ZrO2 in particle reinforcements. 9 Incorporation of metal as a fracture the Al2O3 matrix has been found to be effective for fracture toughening agent hinders high temperature applications, and dealing with whiskers poses the possibility of health hazards, 10 Microstructural modification of the composites systems is a way Corresponding author. Tel. +82 41 570 2427: fax: +82 41 577 2415 for improving the fracture toughness. The multi-pass extrusion E-mail address: Ibt @sch. ac kr(. -T. Lee) method has a remarkable potential in this regard, because 0955-2219/S-see front matter o 2007 Elsevier Ltd. All rights reserved. doi: 10.1016/j-jeurceramsoc. 2007.05.010Available online at www.sciencedirect.com Journal of the European Ceramic Society 28 (2008) 229–233 Microstructure and material properties of double-network type fibrous (Al2O3–m-ZrO2)/t-ZrO2 composites Byong-Taek Lee a,∗, Swapan Kumar Sarkar b, Ho-Yeon Song c a Department of Biomedical Engineering and Materials, School of Medicine, Soonchunhyang University 366-1, Ssangyoung-dong, Cheonan, Chungnam 330-090, South Korea b School of Advanced Materials Engineering, Kongju National University, 182, Shinkwan-dong, Kongju, Chungnam 314-701, South Korea c Department of Microbiology, School of Medicine, Soonchunhyang University 366-1, Ssangyoung-dong, Cheonan, Chungnam 330-090, South Korea Received 20 February 2007; received in revised form 7 May 2007; accepted 13 May 2007 Available online 2 August 2007 Abstract Al2O3–(m-ZrO2)/t-ZrO2 composites with a novel double-network microstructure were fabricated by multi-pass extrusion process using polymer bound ceramic green body. A simultaneous micro- and macro-level microstructure tailoring was made where unidirectionally aligned two-phase Al2O3–(m-ZrO2) fibers were enclosed in a t-ZrO2 phase connected in a network formation and this network was further enclosed in a thicker t-ZrO2 phase. Composite green rods were hot extruded and reassembled in parallel for extrusion and after several passes of extrusion very fine microstructure with dimension of a few micrometers was obtained. Material properties such as hardness, bending strength and fracture toughness were measured for the composites. Microstructure characterization was carried out by SEM technique. In the 4th passed Al2O3–(m-ZrO2)/t-ZrO2 composites, the outer network of t-ZrO2 was 15m, inner network 0.8 m and the inner Al2O3–(m-ZrO2) core was 2.5m. The highest hardness, fracture strength and toughness values were about 1452 Hv, 1006 MPa and 8.6 MPa m1/2, respectively, in the sample sintered at 1500 ◦C. © 2007 Elsevier Ltd. All rights reserved. Keywords: Extrusion; Composites; Microstructure-final; Al2O3; ZrO2 1. Introduction Alumina (Al2O3) is one of the high performance ceramics used in high-temperature, structural, cutting and wear resis￾tance applications.1,2 The excellent chemical stability and bio-inertness extends its application for harsh environment and biomedical applications.3,4 However, there is a common drawback of Al2O3 like most other ceramics, i.e., it has poor fracture toughness (about 3.5 MPa m1/2), which is a hindrance for use in dynamic load-bearing applications.5 This is basically due to the absence of main toughening mechanisms such as microcracks, crack bridging, phase transformation, etc. Hence, many strategies have been proposed to improve the mechanical properties of a monolithic Al2O3 body. Dispersion of ZrO2 in the Al2O3 matrix has been found to be effective for fracture ∗ Corresponding author. Tel.: +82 41 570 2427; fax: +82 41 577 2415. E-mail address: lbt@sch.ac.kr (B.-T. Lee). toughening due to phase transformation from tetragonal (t) to monoclinic (m). In case of the dispersion of m-ZrO2 particles in the Al2O3 matrix, the strong strain field and some microcracks were easily formed during the sintering process, due to the difference in the co-efficient of thermal expansion.6 These strain fields and microcracks led to intergranular fracture with crack deflection and thus reduce the crack propagation energy.3 In addition when cracks propagate transgranularly in m-ZrO2 the driving force of crack propagation is reduced due to the plastic deformation of m-ZrO2. 6,7 In conjunction to this many other approaches have also been investigated for the improvement of fracture toughness like metal coating of raw ceramic powder for metal–ceramic composites, whisker and particle reinforcements.8,9 Incorporation of metal as a fracture toughening agent hinders high temperature applications, and dealing with whiskers poses the possibility of health hazards.10 Microstructural modification of the composites systems is a way for improving the fracture toughness. The multi-pass extrusion method has a remarkable potential in this regard, because 0955-2219/$ – see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2007.05.010