Availableonlineatwww.sciencedirect.com . Science Direct E≈RS ELSEVIER Joumal of the European Ceramic Society 26(2006)3539-3546 www.elsevier.comlocate/jeurceramsoc Effect of the volume ratio of zirconia and alumina on the mechanical properties of fibrous zirconia/alumina bi-phase composites prepared by co-extrusion Hiroyuki Miyazaki", Yu-ichi Yoshizawa, Kiyoshi hira Advanced Manufacturing Research institute, National Institute of Advanced Industrial Science and Technology (AIST 2266-98, Shimo-shidami, Moriyama- ku, Nagoya 463-8560, Japan Received 30 October 2005: received in revised form 16 December 2005 ted 28 December 2005 Available online 20 Febr Fibrous zirconia/alumina composites with different composition were fabricated by piston co-extrusion. After a 3rd extrusion step and sintering at 1600C, crack-free composites with a fibre width of -50 um were obtained for all compositions. The effect of the volume ratio of secondary phase on the mechanical properties was investigated. The Youngs modulus of the composites decreased linearly with increasing the zirconia content. The fracture toughness of the composites was improved by introducing fine second phase filaments into the matrix. The maximum fracture toughness of 6.2 MPa m 2 was attained in the 3rd co-extruded 47/53 vol% zirconia/alumina composite. The improvement in toughness was attributed to bothstress-induced"transformation of zirconia and a crack deflection mechanism due to thermal expansion mismatch between the two phase Bending strength of the composites was almost the same as that of the monolithic alumina regardless of the composition o 2006 Elsevier ltd. all rights reserved. Keywords: Co-extrusion; ZrO2/Al2O3 composite; Mechanical properties 1. Introduction reports on the microstructure of the fibrous composites with a rigid interface,8-14 but the evaluation of their mechanical prop- Continuous fibre-reinforced ceramics have promising poten- erties is limited. 8-11 tial for high-temperature application because of the remarkable In our previous reports, the feasibility of forming fine-scale fracture toughening through the crack bridging mechanism. fibrous microstructures was demonstrated for alumina/zirconia However, they are very expensive, and many problems appear in composites with a rigid interface, by using a repeated co- the fabrication process. Different geometric configurations that extrusion process through a reduction die. 10, I It was revealed incorporate crack deflecting systems, such as ceramic/ceramic that fracture toughness of these composites was increased over lamellar compositesand fibrous monolithic ceramics, are pro- the constituent monoliths. Leeet al clarified the effect of number posed for low-cost alternatives to conventional continuous-fiber of extrusion steps on the mechanical properties of the 50/50 vol% ceramic composites. In the case of such composites, increased alumina-(m-zirconia)/t-zirconia fibrous composite. However, toughness is usually associated with the presence of a weak the examination of the mechanical properties of the fibrous com- interface, which enables crack deflection into the interface. The posites has been limited to a few compositions. It seems possibl weak interface, however, results in a reduction in strength. In to improve the mechanical properties further by optimizing the order to maintain strength and yet obtain high toughness, lamel- composition. The aim of this study is to clarify the effect of the composites with a strong interface were proposed, in which volume fraction of zirconia phase on the mechanical properties crack deflection was generated by thermal residual stress at the of the fibrous zirconia/alumina composites interface. -In the case of fibrous composites, there are some 2. Experimental Corresponding author. Tel: 7367486:fax:+81527367405 Commercial alumina powder(AL-160SG-4, Showa De E-mail address: h-miyazaki ( aist go. jP(H Miyazaki) KK, Japan) and yttria-stabilized zirconia powder (TZ-3Y 0955-2219/S-see front matter o 2006 Elsevier Ltd. All rights reserved. doi: 10. 1016/j-jeurceramsoc 2005.12 019Journal of the European Ceramic Society 26 (2006) 3539–3546 Effect of the volume ratio of zirconia and alumina on the mechanical properties of fibrous zirconia/alumina bi-phase composites prepared by co-extrusion Hiroyuki Miyazaki ∗, Yu-ichi Yoshizawa, Kiyoshi Hirao Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2266-98, Shimo-shidami, Moriyama-ku, Nagoya 463-8560, Japan Received 30 October 2005; received in revised form 16 December 2005; accepted 28 December 2005 Available online 20 February 2006 Abstract Fibrous zirconia/alumina composites with different composition were fabricated by piston co-extrusion. After a 3rd extrusion step and sintering at 1600 ◦C, crack-free composites with a fibre width of ∼50
m were obtained for all compositions. The effect of the volume ratio of secondary phase on the mechanical properties was investigated. The Young’s modulus of the composites decreased linearly with increasing the zirconia content. The fracture toughness of the composites was improved by introducing fine second phase filaments into the matrix. The maximum fracture toughness of 6.2 MPa m1/2 was attained in the 3rd co-extruded 47/53 vol% zirconia/alumina composite. The improvement in toughness was attributed to both “stress-induced” transformation of zirconia and a crack deflection mechanism due to thermal expansion mismatch between the two phases. Bending strength of the composites was almost the same as that of the monolithic alumina regardless of the composition. © 2006 Elsevier Ltd. All rights reserved. Keywords: Co-extrusion; ZrO2/Al2O3 composite; Mechanical properties 1. Introduction Continuous fibre-reinforced ceramics have promising poten￾tial for high-temperature application because of the remarkable fracture toughening through the crack bridging mechanism. However, they are very expensive, and many problems appear in the fabrication process. Different geometric configurations that incorporate crack deflecting systems, such as ceramic/ceramic lamellar composites1 and fibrous monolithic ceramics,2 are pro￾posed for low-cost alternatives to conventional continuous-fiber ceramic composites. In the case of such composites, increased toughness is usually associated with the presence of a weak interface, which enables crack deflection into the interface. The weak interface, however, results in a reduction in strength. In order to maintain strength and yet obtain high toughness, lamel￾lar composites with a strong interface were proposed, in which crack deflection was generated by thermal residual stress at the interface.3–7 In the case of fibrous composites, there are some ∗ Corresponding author. Tel.: +81 52 736 7486; fax: +81 52 736 7405. E-mail address: h-miyazaki@aist.go.jp (H. Miyazaki). reports on the microstructure of the fibrous composites with a rigid interface,8–14 but the evaluation of their mechanical prop￾erties is limited.8–11 In our previous reports, the feasibility of forming fine-scale fibrous microstructures was demonstrated for alumina/zirconia composites with a rigid interface, by using a repeated co￾extrusion process through a reduction die.10,11 It was revealed that fracture toughness of these composites was increased over the constituent monoliths. Lee et al. clarified the effect of number of extrusion steps on the mechanical properties of the 50/50 vol% alumina-(m-zirconia)/t-zirconia fibrous composite.9 However, the examination of the mechanical properties of the fibrous com￾posites has been limited to a few compositions. It seems possible to improve the mechanical properties further by optimizing the composition. The aim of this study is to clarify the effect of the volume fraction of zirconia phase on the mechanical properties of the fibrous zirconia/alumina composites. 2. Experimental Commercial alumina powder (AL-160SG-4, Showa Denko K.K., Japan) and yttria-stabilized zirconia powder (TZ-3Y, 0955-2219/$ – see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2005.12.019