Availableonlineatwww.sciencedirect.com .e Science Direct Scripta materialia ELSEVIER cripta Materialia 61(2009)686-689 www.elsevier.com/locate/scriptam Fabrication of super-high-strength microchanneled Al2O3-ZrO2 ceramic composites with fibrous microstructure Byong Taek Lee"and Swapan Kumar Sarkar Biomedical Engineering and Materials Department, School of Medicine, Soonchunhyang University 366-1, Sangyoung-dong, Cheonan City 330-090, South Korea Received 11 May 2009: accepted 30 May 2009 Available online 9 june 2009 Continuously porous Al,Oxmonolinic-ZrO,)/tetragonal-zrO2 ceramic composites with tailored fine-scale fibrous microstruc- ture was fabricated by a multipass extrusion process. Precise control of the microstructure was achieved, giving AlO(m-zrO2) fibrous phase (3.5 um)in the t-ZrO2 phase(1. 5 um thickness ). The pore size and porosity was 175 um and 36%. The rounded micro- channels and fine geometric control of the fibrous microstructure result in composites with a remarkably high bending strength value of 588 MPa which is 2- to 6-fold higher than their monolithic counterparts o 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved Keywords: Extrusion; Ceramics: Ceramic matrix composites; Microstructure Due to their excellent mechanical, thermal and mesoscale. Template and replica methods with fugitive chemical properties, Al2O3-ZrO2 composites are utilized pore-forming agents have been reported for different as advanced materials in many industrial applications ceramics [9, 10]. However, the size and distribution of such as high-temperature structural materials, refractory pores was not homogeneous and the mechanical proper materials, cutting and grinding tools, high-temperature ties were also very poor. Another problem with this type corrosion-resistant materials, various electric and elec- of porous body is that the tronic applications, supportive biomaterials for human on a higher extent of porosity, which significantly de- hard tissue, high-performance filters and membranes, grades the mechanical property of the ceramics due to var- and supports for catalysts, etc. [1, 2]. However, like other ious internal flaws in the dense zone of the composites. ceramics, they have an intrinsic drawback of low fracture Porous Al2O3 with hierarchical micromorphologies and toughness. Many approaches to improve the fracture a well-oriented biomorphic structure has been fabricated toughness as well as other mechanical properties of the with a pyrolyzed carbon template and subsequent al va AlO3-ZrO, systems, including significant strengthening, por infiltration and oxidation [ll]. The porosity was high have been reported. Microporous Al2O3-ZrO2 ceramics but the material lacked significant structural strength have been studied for various applications including hot Moreover, as it depends on the pyrolysis of a natura gas and molten metal filtration, membrane support, cata- plant, the flexibility of realizing tailored micromorphol- lyst support, refractory applications and biomaterials ogy and porosity is restricted applications [3-7]. The functional behavior and use of A relatively new kind of highly ordered porous mem- these porous materials largely depends on the pore size brane of Al_, was fabricated by an anodizing method and extent of porosity. Various methods have been used [12]. However, this process is only applicable to thin to date to make monolithic or composite porous struc monolithic membranes and is not suitable for bulk tures from AlO3 and ZrO2 ceramics. Mesoporous materials or composites. Furthermore, the pore size is Al2O3 or Zro, membrane has been produced by the restricted to a very narrow range, mainly in the sub sol-gel method [8] but the bulk property of the material micrometer level. The strength considerations for these was poor and porosity was restricted to only a nano-or nanoporous ceramics have rarely been discussed. In both the microporous and mesoporous materials, the usability and performance of the porous composites largely Corresponding author. Tel. +82 41 570 2427: fax: +82 41 577 depend on their mechanical strength. Fabrication of 2415: e-mail: Ibt(@sch. ac kr porous ceramics with significant mechanical strength 1359-6462/S.see front matter 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. do: 10. 1016/j.scriptamat. 2009.05.047Fabrication of super-high-strength microchanneled Al2O3–ZrO2 ceramic composites with fibrous microstructure Byong Taek Lee* and Swapan Kumar Sarkar Biomedical Engineering and Materials Department, School of Medicine, Soonchunhyang University, 366-1, Sangyoung-dong, Cheonan City 330-090, South Korea Received 11 May 2009; accepted 30 May 2009 Available online 9 June 2009 Continuously porous Al2O3–(monolinic-ZrO2)/tetragonal-ZrO2 ceramic composites with tailored fine-scale fibrous microstruc￾ture was fabricated by a multipass extrusion process. Precise control of the microstructure was achieved, giving Al2O3–(m-ZrO2) fibrous phase (3.5 lm) in the t-ZrO2 phase (1.5 lm thickness). The pore size and porosity was 175 lm and 36%. The rounded micro￾channels and fine geometric control of the fibrous microstructure result in composites with a remarkably high bending strength value of 588 MPa which is 2- to 6-fold higher than their monolithic counterparts. 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Extrusion; Ceramics; Ceramic matrix composites; Microstructure Due to their excellent mechanical, thermal and chemical properties, Al2O3–ZrO2 composites are utilized as advanced materials in many industrial applications such as high-temperature structural materials, refractory materials, cutting and grinding tools, high-temperature corrosion-resistant materials, various electric and elec￾tronic applications, supportive biomaterials for human hard tissue, high-performance filters and membranes, and supports for catalysts, etc. [1,2]. However, like other ceramics, they have an intrinsic drawback of low fracture toughness. Many approaches to improve the fracture toughness as well as other mechanical properties of the Al2O3–ZrO2 systems, including significant strengthening, have been reported. Microporous Al2O3–ZrO2 ceramics have been studied for various applications including hot gas and molten metal filtration, membrane support, cata￾lyst support, refractory applications and biomaterials applications [3–7]. The functional behavior and use of these porous materials largely depends on the pore size and extent of porosity. Various methods have been used to date to make monolithic or composite porous struc￾tures from Al2O3 and ZrO2 ceramics. Mesoporous Al2O3 or ZrO2 membrane has been produced by the sol–gel method [8], but the bulk property of the material was poor and porosity was restricted to only a nano- or mesoscale. Template and replica methods with fugitive pore-forming agents have been reported for different ceramics [9,10]. However, the size and distribution of pores was not homogeneous and the mechanical proper￾ties were also very poor. Another problem with this type of porous body is that the interconnectivity of pores relies on a higher extent of porosity, which significantly de￾grades the mechanical property of the ceramics due to var￾ious internal flaws in the dense zone of the composites. Porous Al2O3 with hierarchical micromorphologies and a well-oriented biomorphic structure has been fabricated with a pyrolyzed carbon template and subsequent Al va￾por infiltration and oxidation [11]. The porosity was high but the material lacked significant structural strength. Moreover, as it depends on the pyrolysis of a natural plant, the flexibility of realizing tailored micromorphol￾ogy and porosity is restricted. A relatively new kind of highly ordered porous mem￾brane of Al2O3 was fabricated by an anodizing method [12]. However, this process is only applicable to thin monolithic membranes and is not suitable for bulk materials or composites. Furthermore, the pore size is restricted to a very narrow range, mainly in the sub￾micrometer level. The strength considerations for these nanoporous ceramics have rarely been discussed. In both the microporous and mesoporous materials, the usability and performance of the porous composites largely depend on their mechanical strength. Fabrication of porous ceramics with significant mechanical strength 1359-6462/$ - see front matter 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2009.05.047 * Corresponding author. Tel.: +82 41 570 2427; fax: +82 41 577 2415; e-mail: lbt@sch.ac.kr Available online at www.sciencedirect.com Scripta Materialia 61 (2009) 686–689 www.elsevier.com/locate/scriptamat