Available online at www.sciencedirect.com ScienceDirect Journal of the European Ceramic Society 34 (2014) 903–913 Feature Article Joining of C/SiC composites by spark plasma sintering technique Stefano Rizzo a , Salvatore Grasso b , Milena Salvo a,∗ , Valentina Casalegno a , Michael J. Reece b , Monica Ferraris a a Department of Applied Science and Technology, Institute of Materials Physics and Engineering, Corso Duca degli Abruzzi 24, 10129 Torino, Italy b School of Engineering & Materials Science and Nanoforce Technology Ltd., Queen Mary University of London, Mile End Road, London E1 4NS, UK Received 24 July 2013; received in revised form 19 October 2013; accepted 21 October 2013 Available online 19 November 2013 Abstract CVD–SiC coated C/SiC composites (C/SiC) were joined by spark plasma sintering (SPS) by direct bonding with and without the aid of joining materials. A calcia-alumina based glass–ceramic (CA), a SiC + 5 wt% B 4 C mixture and pure Ti foils were used as joining materials in the non-direct bonding processes. Morphological and compositional analyses were performed on each joined sample. The shear strength of joined C/SiC was measured by a single lap test and found comparable to that of C/SiC. © 2013 Elsevier Ltd. All rights reserved. Keywords: Joining; C/SiC composites; Spark plasma sintering 1. Introduction Ceramic matrix composites (CMC), e.g. SiC/SiC, C/SiC and C/C, are being considered as the primary candidates for components and subsystems in the field of satellite (near- sun) missions, defence, aerospace missions (e.g. body flaps, nose cones, wings, leading edges, turbine components) and for terrestrial/industrial applications under extreme environmental conditions (e.g. valves, shaft sleeves for pump sliding bearings, heat exchangers, nuclear plant components, etc.). 1–3 A critical issue for a wider use of CMC is the development of inexpen- sive, reliable and user-friendly joining methods to assemble large components into more complex structures. 4 There are many possible techniques for joining CMC to themselves and to dissimilar materials: diffusion bonding; 5 transient eutectic phase methods such as nano-infiltration and transient eutectic-phase (NITE); 6 transient liquid-phase diffu- sion bonding; 7 pressure-less glass–ceramic joining; 8–10 solid state displacement reactions; 11 adhesive and preceramic poly- mer routes; 12,13 reaction forming; 14 brazing. 15 Brazing is the most commonly used joining and integration method for CMC ∗ Corresponding author. Tel.: +390110904706. E-mail address: milena.salvo@polito.it (M. Salvo). and extensive research on brazing of CMC for their joining and integration has been done by Singh and his group at NASA. 16–18 High temperature brazing alloys are based on gold, nickel and copper and are often used for joining CMC to cobalt, tita- nium alloys and nickel-based superalloys. 19 TiZrNiCu, Ni and Ag–Cu–Ti have been used as filler to join C/SiC to Ti–6Al–4V. 20 Whatever the joining process is, the joined interfaces need to be thermodynamically stable: reactions and diffusion of species from the joining material and the CMC can affect the quality of the joints and their performance in service. 21 Furthermore, the coefficient of thermal expansion (CTE) of CMC is lower than that of most metals and considerable residual stress is generated in the joint during the cooling process or when exposed to high temperature environments, thus leading to cracks or failure of the joints. In order to deal with the CTE mismatch between CMC and brazing alloys, several options have been proposed: different layers with a gradually changing CTE from CMC to the metal alloy; 22 compliant metallic layers (e.g. Cu); composite brazing alloys obtained by adding short fibres or particles to the brazing alloy. 22,23 Selecting the optimal braze filler metal for brazing CMC to metals is not easy because the application requires a high brazing temperature (high thermal load in operation predicted), while the prevention of high joining stresses should require a low brazing temperature. Moreover, the wetting of CMC often 0955-2219/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jeurceramsoc.2013.10.028