Silicon carbide-based materials for joining silicon carbide composites for fusion energy applications Charles A. Lewinsohn a, * , Russell H. Jones a , Paolo Colombo b , Bruno Riccardi c a Pacific Northwest National Laboratory, Richland, WA 99352, USA b Department of Applied Chemistry and Materials Science, University of Bologna, 40136 Bologna, Italy c ENEA CR Frascati, EURATOM Association, I-00044 Frascati, Italy Abstract This paper describes issues related to using silicon carbide derived from inorganic polymer precursors for joining silicon carbide composites for fusion energy applications. Evolution of gases and shrinkage during processing are identified as critical processes that may control the presence of strength limiting flaws and residual stresses. Precursor composition and structure effect the amount of gaseous species evolved during processing, chemical compatibility with substrates, and processing environments. Results from the literature and from the authorsÕ investigations are used to illustrate the use of polymer derived material for joining. Ó 2002 Elsevier Science B.V. All rights reserved. 1. Introduction To enable the use of silicon carbide fiber reinforced silicon carbide matrix composites (SiC f /SiC m ) in fusion energy applications, a method of joining SiC f /SiC m components that satisfies the requirements of radiation resistance, mechanical integrity, desirable thermal properties, safety during operation and maintenance or accident, and acceptable waste management character- istics is required. Joints made from silicon carbide (SiC) satisfy the above criteria, but practical and reliable methods of their production must be developed. The use of pre-ceramic polymers for joining offers a number of attractive features, such as easy application and low processing temperatures (<1200 °C for obtaining a dense ceramic layer) that inhibit fiber damage during joining, but several issues remain to be addressed. The purpose of this paper is to illustrate the issues associated with using polymer pre-ceramic precursors to obtain silicon carbide-based joints. 2. Experimental methods To evaluate the effect of high-temperature heat treatments on joints derived from hydridopolycarbosi- lane (HPCS, Starfire Systems, Inc., Watervliet, NY), butt-joined, flexural specimens for four-point bend testing were fabricated from plates of chemically vapor deposited (CVD) SiC (Morton Advanced Materials, Woburn, MA). The HPCS contained 3 vol.% allyl groups attached to promote cross-linking and contained 42 wt% SiC powders (F800 powder from UK Abrasives. Lot No. SZ0802A7). Joining was performed by Starfire Systems, Inc. Two plates of CVD SiC, 4 mm thick, were cut into 25 mm long by 30 mm wide pieces. The 30  4 mm 2 faces were cleaned using hexane, polymer paste was applied by hand, and then the pieces were held together in a special fixture. The material was cured and pyrolysed at 850 °C for 1 h in inert gas, using a heating and cooling rate of 1 °C/min. After pyrolysis the joint was re-impregnated with polymer and pyrolysed again. The flexural strength of specimens was measured before Journal of Nuclear Materials 307–311 (2002) 1232–1236 www.elsevier.com/locate/jnucmat * Corresponding author. Current address: Ceramatec Inc., 2425 South 900 West, Salt Lake City, UT 84119, USA. Tel.: +1- 801 972 2455; fax: +1-801 972 1925. E-mail address: clewinsohn@ceramatec.com (C.A. Lewin- sohn). 0022-3115/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0022-3115(02)01063-2