Availableonlineatwww.sciencedirect.com Science Direct E噩≈RS ELSEVIER Journal of the European Ceramic Society 29(2009)363-367 www.elsevier.comlocate/jeurceramsoc Unidirectional all-oxide mini-composites with crack-deflecting ndPOa interface E. G. Butler Yildiz Technical University, Faculry of Chemistry and Metallurgy. Department of Metallurgical and Materials Engineering, Davutpasa Campus, Esenler, Istanbul, Turkey b The University of Birmingham, IRC in Materials Processing and School of Metallurgy and Materials, Edgbaston, Birmingham B152TT,UK Received 6 February 2008: received in revised form 20 May 2008: accepted 6 June 2008 Available online 21 July 2008 Unidirectional Nextel 720M fibers were coated with crack-deflecting NdPOa interface using dip coating and int manufactur th silica-free alumina matrix using electrophoretic deposition followed by drying and pressureless sir at1200° In an attempt Ire oxide-based model 'mini-composites' which are less complex to produce in a short time and which therefore allow rapid results for cal and microstructural characterisation. This material is targeted for use at 1200C in an oxidising atmosphere and has shown an excellent tensile strength value of 1.2 GI and flexural strengths of 894 MPa at room temperature and 761 MPa at 1300 C in unidirectional form. o 2008 Elsevier Ltd. all rights reserved. Keywords: Composites: AlO3; Interface; Mini-composites: NdPO4 Introduction anisms that all contribute to increasing toughness. -79-15, 2To obtain ideal damage-tolerant behaviour, two concepts have been High strength continuous fiber-reinforced ceramic compos- developed so far+, 12, 13, 22; the first one is to create a relatively ites(CMCs) have emerged as leading candidates in gas-turbine weak bonding between fibers and the matrix by coating the fibers applications and power generation systems where future require- with suitable crack-deflecting interface materials, such as ZrO ments for increased operating temperature, reduction in weight or NdPO4 that do not react with the ceramic matrices/fibers or and in exhaust emissions are becoming difficult to meet using fugitive carbon that creates a gap at the fiber/matrix interface; the conventional metallic alloys. The physical and mechanical second one is to use highly porous matrices to isolate fibers from properties of new generation oxide/oxide CMcs enable innova- matrix cracks so that quasi-ductile deformation can be obtained tive solutions for problems with materials in thermal protection as the cracks do not have a continuous front since the matrix is systems and liners in gas-turbine engines, rocket engine, hot held together by grain pairs but the overall strength is quite low in gas filter technologies, fire prevention, catalytic converters, soot this case due to the presence of high porosity content up to 50% filters and medical applications. 7-9As a consequence, many In the present work, alumina ceramic matrix is reinforced gas-turbine manufactures are now placing greater emphasis with NdPO4-coated unidirectional ceramic fibers in an attempt on the evaluation of oxide/oxide components with enhanced to manufacture small damage-tolerant model composite sam- high temperature stability and long service life in oxidising ples called 'mini-composites'suitable for mechanical testin environments.-20 Although the reinforcement fibers and matri- and microstructural observations in a short processing time ces are brittle, the obtained composites display quasi-ductile deformation behaviour due to operation of crack deflection, 2. Experimental work fiber-matrix debonding, crack bridging and fiber pull-out mech- 2.. Materials Corresponding author. Tel. +90 2123834713: fax: +90 2123834665. Sinter-active high purity alumina powders (Tai-Micron E-mail address: cngzky(@ yahoo. co uk(C. Kaya) Japan)with an average particle size of 160 nm and surface area 0955-2219/S-see front matter o 2008 Elsevier Ltd. All rights reserved. doi: 10. 1016/j-jeurceramsoc. 2008.06.009Available online at www.sciencedirect.com Journal of the European Ceramic Society 29 (2009) 363–367 Unidirectional all-oxide mini-composites with crack-deflecting NdPO4 interface C. Kaya a,∗, E.G. Butler b a Yildiz Technical University, Faculty of Chemistry and Metallurgy, Department of Metallurgical and Materials Engineering, Davutpasa Campus, Esenler, Istanbul, Turkey b The University of Birmingham, IRC in Materials Processing and School of Metallurgy and Materials, Edgbaston, Birmingham B15 2TT, UK Received 6 February 2008; received in revised form 20 May 2008; accepted 6 June 2008 Available online 21 July 2008 Abstract Unidirectional Nextel 720TM fibers were coated with crack-deflecting NdPO4 interface using dip coating and infiltrated with silica-free alumina matrix using electrophoretic deposition followed by drying and pressureless sintering at 1200 ◦C in an attempt to manufacture oxide-based model ‘mini-composites’ which are less complex to produce in a short time and which therefore allow rapid results for mechanical and microstructural characterisation. This material is targeted for use at 1200 ◦C in an oxidising atmosphere and has shown an excellent tensile strength value of 1.2 GPa and flexural strengths of 894 MPa at room temperature and 761 MPa at 1300 ◦C in unidirectional form. © 2008 Elsevier Ltd. All rights reserved. Keywords: Composites; Al2O3; Interface; Mini-composites; NdPO4 1. Introduction High strength continuous fiber-reinforced ceramic compos￾ites (CMCs) have emerged as leading candidates in gas-turbine applications and power generation systems where future require￾ments for increased operating temperature, reduction in weight and in exhaust emissions are becoming difficult to meet using conventional metallic alloys.1–6 The physical and mechanical properties of new generation oxide/oxide CMCs enable innova￾tive solutions for problems with materials in thermal protection systems and liners in gas-turbine engines, rocket engine, hot gas filter technologies, fire prevention, catalytic converters, soot filters and medical applications.7–9 As a consequence, many gas-turbine manufactures are now placing greater emphasis on the evaluation of oxide/oxide components with enhanced high temperature stability and long service life in oxidising environments.10–20 Although the reinforcement fibers and matri￾ces are brittle, the obtained composites display quasi-ductile deformation behaviour due to operation of crack deflection, fiber–matrix debonding, crack bridging and fiber pull-out mech- ∗ Corresponding author. Tel.: +90 2123834713; fax: +90 2123834665. E-mail address: cngzky@yahoo.co.uk (C. Kaya). anisms that all contribute to increasing toughness.1–7,9–15,21 To obtain ideal damage-tolerant behaviour, two concepts have been developed so far4,12,13,22; the first one is to create a relatively weak bonding between fibers and the matrix by coating the fibers with suitable crack-deflecting interface materials, such as ZrO2 or NdPO4 that do not react with the ceramic matrices/fibers or fugitive carbon that creates a gap at the fiber/matrix interface; the second one is to use highly porous matrices to isolate fibers from matrix cracks so that quasi-ductile deformation can be obtained as the cracks do not have a continuous front since the matrix is held together by grain pairs but the overall strength is quite low in this case due to the presence of high porosity content up to 50%. In the present work, alumina ceramic matrix is reinforced with NdPO4-coated unidirectional ceramic fibers in an attempt to manufacture small damage-tolerant model composite sam￾ples called ‘mini-composites’ suitable for mechanical testing and microstructural observations in a short processing time. 2. Experimental work 2.1. Materials Sinter-active high purity alumina powders (Tai-Micron, Japan) with an average particle size of 160 nm and surface area 0955-2219/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2008.06.009