C MATERIALIA Pergamon cta mater.4902001)1189-1197 www.elsevier.com/locate/actamat FABRICATION AND CHARACTERISATION OF NI-COATED CARBON FIBRE-REINFORCED ALUMINA CERAMIC MATRIX COMPOSITES USING ELECTROPHORETIC DEPOSITION C KAYA,21, F. KAYA A R BOCCACCINI and K. K CHAWLA and tratesrials. The Universit of birmingham. Edgbaston. Baminghpapm. B15 2 n. sK. M et lurgacar ay Material Engineering Department, Yildiz Technical University, Besiktas, Istanbul, 80750 Turkey, Department of Materials, Imperial College of Science, Technology and Medicine, Prince Consort Road, London, SW7 2BP UK and"Department of Materials and Mechanical Engineering, University of Alabama at Birmingham, Birmingham. AL 35294 USA Received 26 May 2000: received in revised form 21 December 2000: accepted 27 December 2000) Abstract-The present study explores the feasibility of fabricating Ni-coated carbon fibre-reinforced alu mina ceramic matrix composites via a single-infiltration electrophoretic deposition(EPD) process perfo ned in vacuum. The nano-size boehmite sol was seeded using nano-size 8-alumina powder in order to ntrol the final sintered microstructure and then characterised using transmission electron microscopy differential thermal and thermogravimetric analysis (DTA/TG) and X-ray disc centrifuge system(Bl- DC) in order to determine the sol microstructure, phase transformation temperatures and particle siz (also degree of agglomeration), respectively. An EPD manufacturing cell for fabrication of Ni-coated oon fibre reinforced alumina matrix cor tes was designed and experiments were conducted under acuum (first time to date), resulting in full deposition of the sol material throughout the voids ithin/between the fibre tows. Composites with high green density (67%0 theoretical density) were pro duced using an applied voltage of 15v d. c. and deposition time of 400 s. The sintered dens pressureless sintering at 1250C for 2 h was 91% theoretical density Crack path propagation tes that the metallic Ni coating was able to provide a weak interface, as an indenter induced cr he alumina matrix was deflected and arrested at the Ni interface. c 200/ Acta Materialia Ine by Elsevier Science Ltd. All rights reserved. Keywords: Electrophoretic deposition: Composites: Nickel: Interface: Microstructure 1 INTRODUCTION ered by several hundred degrees. A commercial sol can be seeded with isostructural seeds in order to A sol is generally defined as a colloidal dispersi ower crystallisation temperature and enhance of sol (or colloidal) processing route has many modifiers/seeds in terms of grain size, pore size and advantages, such as greater purity, higher homogen- pore size distribution. Boehmite(y-AlOOH)sol ity and ultrafine (5-100 nm)particle size distri- one of the ideal candidate materials to manufacture bution, in comparison to conventional ceramic pow- high quality alumina base ceramic components with der manufacturing processes. The main goal of this controlled tinal sintered microstructure, as it con technique is to achieve an ultra homogeneous or tains highly sinter-active ceramic particles on a atomic scale mixing of different chemical compo- ometer scale. Without seeding, however, a commer nents. The high surface area to volume ratio of a cial or hydrothermally produced boehmite sol ceramic sol makes the material usually highly sin- requires very high sintering temperatures(1600C) ter-active, thus sintering temperatures can be low- for complete densification. This is due to the large and extensive pore network that develops during the reconstructive transformation to the final stable t To whom all correspondence should be addressed. Fax: phase a-Al2O3, according to the dehydration and +44-121-4143441. high temperature phase transformation of boehm- E-mail address: c kaya@bhamac uk(C. Kaya) te[3]: 1359-6454/01/$20.00@ 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved PI:S1359-6454(01)00018-0Acta mater. 49 (2001) 1189–1197 www.elsevier.com/locate/actamat FABRICATION AND CHARACTERISATION OF Ni-COATED CARBON FIBRE-REINFORCED ALUMINA CERAMIC MATRIX COMPOSITES USING ELECTROPHORETIC DEPOSITION C. KAYA1, 2†, F. KAYA1 , A. R. BOCCACCINI3 and K. K. CHAWLA4 1 Interdisciplinary Research Centre (IRC) For High Performance Applications and School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK, 2 Metallurgical and Material Engineering Department, Yildiz Technical University, Besiktas, Istanbul, 80750 Turkey, 3 Department of Materials, Imperial College of Science, Technology and Medicine, Prince Consort Road, London, SW7 2BP UK and 4 Department of Materials and Mechanical Engineering, University of Alabama at Birmingham, Birmingham, AL 35294, USA ( Received 26 May 2000; received in revised form 21 December 2000; accepted 27 December 2000 ) Abstract—The present study explores the feasibility of fabricating Ni-coated carbon fibre-reinforced alu￾mina ceramic matrix composites via a single-infiltration electrophoretic deposition (EPD) process perfor￾med in vacuum. The nano-size boehmite sol was seeded using nano-size δ-alumina powder in order to control the final sintered microstructure and then characterised using transmission electron microscopy, differential thermal and thermogravimetric analysis (DTA/TG) and X-ray disc centrifuge system (BI￾XDC) in order to determine the sol microstructure, phase transformation temperatures and particle size (also degree of agglomeration), respectively. An EPD manufacturing cell for fabrication of Ni-coated carbon fibre reinforced alumina matrix composites was designed and experiments were conducted under vacuum (first time to date), resulting in full deposition of the sol material throughout the voids within/between the fibre tows. Composites with high green density (67% theoretical density) were pro￾duced using an applied voltage of 15 V d.c. and deposition time of 400 s. The sintered density after pressureless sintering at 1250°C for 2 h was 91% theoretical density. Crack path propagation test showed that the metallic Ni coating was able to provide a weak interface, as an indenter induced crack within the alumina matrix was deflected and arrested at the Ni interface.  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. Keywords: Electrophoretic deposition; Composites; Nickel; Interface; Microstructure 1. INTRODUCTION A sol is generally defined as a colloidal dispersion of very fine solid particles in the range of 10 nm to 2 µm in a liquid medium, where the suspension is sustained indefinitely by Brownian motion. The use of sol (or colloidal) processing route has many advantages, such as greater purity, higher homogen￾eity and ultrafine (5–100 nm) particle size distri￾bution, in comparison to conventional ceramic pow￾der manufacturing processes. The main goal of this technique is to achieve an ultra homogeneous or atomic scale mixing of different chemical compo￾nents. The high surface area to volume ratio of a ceramic sol makes the material usually highly sin￾ter-active, thus sintering temperatures can be low- † To whom all correspondence should be addressed. Fax:
44-121-4143441. E-mail address: c.kaya@bham.ac.uk (C. Kaya) 1359-6454/01/$20.00  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved. PII: S13 59-6454(01)00018-0 ered by several hundred degrees. A commercial sol can be seeded with isostructural seeds in order to lower crystallisation temperature and enhance densification with refined microstructure through solid-state epitaxy [1, 2]. The final sintered micro￾structure can be controlled using these modifiers/seeds in terms of grain size, pore size and pore size distribution. Boehmite (γ-AlOOH) sol is one of the ideal candidate materials to manufacture high quality alumina base ceramic components with controlled final sintered microstructure, as it con￾tains highly sinter-active ceramic particles on a nan￾ometer scale. Without seeding, however, a commer￾cial or hydrothermally produced boehmite sol requires very high sintering temperatures (>1600°C) for complete densification. This is due to the large and extensive pore network that develops during the reconstructive transformation to the final stable phase α-Al2O3, according to the dehydration and high temperature phase transformation of boehm￾ite [3]: