Materials P rocessing Technology ELSEVIER of Materials Processing Technology 16 Processing and characterisation of model optomechanical composites in the system sapphire fibre/borosilicate glass matrix A.R. Boccaccini a,*. D. Acevedo a,A F. Dericioglu. C. Jana b National Institute for Materials Science, 1-2-1 Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan eSchott-Jenaer Glas GmbH. Otto Schott StraBe 13. D-07745 Jena germany Received 8 July 2004; accepted 11 March 2005 Abstract Optomechanical composites based on the system sapphire fibre/borosilicate glass matrix were fabricated and characterised. Different techniques of fabrication were used: composites with randomly orientated chopped sapphire fibres were produced by powder technology and pressureless sintering, whilst unidirectionally oriented fibre composites were fabricated by hot-pressing as well as by sandwiching glass slides and arrays of parallel fibres followed by heat-treatment. Pressureless sintered samples were poorly densified and were opaque. Hot-pressed and"sandwich structure"composites were dense and exhibited strong interfaces between fibres and matrix. Only the "sandwich structure composites were transparent and showed significant light transmittance in the visible wavelength range, only 20% lower than that of the unreinforced matrix. Due to the strong matrix/fibre interface limited fibre pull-out during composite fracture was observed. The fabricate B nsparent composites represent an improved version of the traditional material wired glass. They are candidate materials for applications in igh performance fire and impact resistant windows requiring high impact strength and avoidance of fragmentation upon fracture O 2005 Elsevier B. V. All rights reserved Keywords: Composite materials; Glass matrix; Hot-pressing; Sintering: Ceramic fibres; Mechanical properties; Optical properties 1. Introduction been carried out to understand the toughening mechanisms induced by the presence of the reinforcements and to inves- Silicate glasses have extremely low fracture toughness val- tigate the parameters that lead to satisfactory mechanical ues,which leads to the well known low reliability of these behaviour of glass and glass-ceramic matrix composites materials in load-bearing applications. Hence, strengthening [5-l1l and toughening of silicate glasses are required if these mate Limited previous research has been carried out focusing on rials are to find wider use in structural applications [1] improving simultaneously mechanical and functional prop- Forming composites by incorporation of reinforcing ele- erties of glass matrix composites. These include composites ments in glass and glass-ceramic matrices is a very effective for electric and electronic applications(e.g. induction heat approach to improve the mechanical properties of glasses, ing equipment, microwave components, electronic package including fracture strength, fracture toughness as well as substrates, connectors), high-temperature applications(e.g thermal shock and impact resistance Reinforcements thermal insulators, jet engine thermocouples), dimensional most commonly used are in the form of ceramic whiskers, stability applications(e.g. mirror supports for telescopes )and platelets, particulates or fibres [2-5]. Numerous studies have optical applications(e. g. impact resistant windows, struc ures for micro fluidics)[4, 12-20]. In particular, compos ding author. Tel 075946731;fax:+442075843194 ites exhibiting favourable optical and mechanical properties E-mail address: a boccaccini @imperial ac uk(A R. Boccaccini) are called <optomechanical composites>[ 18], which are the ss: GEMPPM de lyon,69621 Villeurbanne, France. focus of the present work 0924-0136/S- see front matter O 2005 Elsevier B V. All rights reserved doi: 10. 1016/j- imatprotec. 2005.03.011Journal of Materials Processing Technology 169 (2005) 270–280 Processing and characterisation of model optomechanical composites in the system sapphire fibre/borosilicate glass matrix A.R. Boccaccini a,∗, D. Acevedo a,1, A.F. Dericioglu b, C. Jana c a Department of Materials, Imperial College London, Prince Consort Road, London SW7 2BP, UK b National Institute for Materials Science, 1-2-1 Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan c Schott-Jenaer Glas GmbH, Otto Schott Straße 13, D-07745 Jena, Germany Received 8 July 2004; accepted 11 March 2005 Abstract Optomechanical composites based on the system sapphire fibre/borosilicate glass matrix were fabricated and characterised. Different techniques of fabrication were used: composites with randomly orientated chopped sapphire fibres were produced by powder technology and pressureless sintering, whilst unidirectionally oriented fibre composites were fabricated by hot-pressing as well as by sandwiching glass slides and arrays of parallel fibres followed by heat-treatment. Pressureless sintered samples were poorly densified and were opaque. Hot-pressed and “sandwich structure” composites were dense and exhibited strong interfaces between fibres and matrix. Only the “sandwich structure” composites were transparent and showed significant light transmittance in the visible wavelength range, only 20% lower than that of the unreinforced matrix. Due to the strong matrix/fibre interface limited fibre pull-out during composite fracture was observed. The fabricated transparent composites represent an improved version of the traditional material wired glass. They are candidate materials for applications in high performance fire and impact resistant windows requiring high impact strength and avoidance of fragmentation upon fracture. © 2005 Elsevier B.V. All rights reserved. Keywords: Composite materials; Glass matrix; Hot-pressing; Sintering; Ceramic fibres; Mechanical properties; Optical properties 1. Introduction Silicate glasses have extremely low fracture toughness val￾ues, which leads to the well known low reliability of these materials in load-bearing applications. Hence, strengthening and toughening of silicate glasses are required if these mate￾rials are to find wider use in structural applications [1]. Forming composites by incorporation of reinforcing ele￾ments in glass and glass-ceramic matrices is a very effective approach to improve the mechanical properties of glasses, including fracture strength, fracture toughness as well as thermal shock and impact resistance [2–5]. Reinforcements most commonly used are in the form of ceramic whiskers, platelets, particulates or fibres [2–5]. Numerous studies have ∗ Corresponding author. Tel.: +44 207 594 6731; fax: +44 207 584 3194. E-mail address: a.boccaccini@imperial.ac.uk (A.R. Boccaccini). 1 Present address: GEMPPM, INSA de Lyon, 69621 Villeurbanne, France. been carried out to understand the toughening mechanisms induced by the presence of the reinforcements and to inves￾tigate the parameters that lead to satisfactory mechanical behaviour of glass and glass-ceramic matrix composites [5–11]. Limited previous research has been carried out focusing on improving simultaneously mechanical and functional prop￾erties of glass matrix composites. These include composites for electric and electronic applications (e.g. induction heat￾ing equipment, microwave components, electronic package substrates, connectors), high-temperature applications (e.g. thermal insulators, jet engine thermocouples), dimensional stability applications (e.g. mirror supports for telescopes) and optical applications (e.g. impact resistant windows, struc￾tures for micro fluidics) [4,12–20]. In particular, compos￾ites exhibiting favourable optical and mechanical properties are called «optomechanical composites» [18], which are the focus of the present work. 0924-0136/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2005.03.011