Preparation of a titanium carbide coating on carbon fibre using a molten salt method Xuanke Li a,b, * , Zhijun Dong a , Aidan Westwood b , Andy Brown b , Shaowei Zhang a,c , Rik Brydson b , Nan Li a , Brian Rand b a The Hubei Province Key Laboratory of Ceramics and Refractories, Wuhan University of Science and Technology, Wuhan, Hubei 430081, PR China b Institute for Materials Research, The University of Leeds, Leeds LS2 9JT, United Kingdom c Engineering Materials, The University of Sheffield, Western Bank, Sheffield S10 2TN, United Kingdom ARTICLE INFO Article history: Received 14 August 2007 Accepted 20 November 2007 Available online 2 January 2008 ABSTRACT A method for preparing protective titanium carbide (TiC) coatings on carbon fibres has been developed using a molten salt synthesis method. The TiC coatings were formed on the sur- face of carbon fibres in a reaction medium consisting of Ti powder in a mixture of molten LiCl–KCl–KF salts under an argon atmosphere at 900 and 950 °C. The structure and morphol- ogy of the TiC coatings were characterized by XRD, SEM and energy dispersive X-ray (EDX) analyses. The coatings consisted of homogeneous single phase cubic TiC with thicknesses in the range of 60–800 nm. Variation of the synthesis time and reaction mixture was found to significantly affect the thickness and integrity of the TiC coating although variation of the reaction temperature had little effect. The coating thickness was closely related to the com- position of the molten salts and to the molar ratio between the carbon fibre and titanium. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction Despite their uniquely superior properties, the interface compatibility problems between carbon fibre and most matri- ces have limited the industrial application of carbon fibre reinforced metallic and ceramic matrix composites. More- over, the applications of carbon fibres for composite rein- forcement are also limited since carbon reacts with many metallic and ceramic matrix materials. Much effort is there- fore being expended in attempts to provide a refractory coat- ing on the surface of the carbon to shield carbon materials from reactive environments at elevated temperatures and to improve the carbon fibre–matrix interfacial properties [1–5]. This approach is only partially successful since the thickness, homogeneity and integrity of coating on the carbon fibre sur- face is difficult to control. Titanium carbide (TiC) is one of the most important refractory metal carbides used as advanced ceramics for wear resistance and aerospace applications. This is primarily due to its high melting temperature (3067 °C), high Young’s modu- lus (410–450 GPa), high chemical stability and high Vickers hardness (28–35 GPa) [6,7], which allow its use in cemented carbides, such as cermets, and oxidation resistant materials. Thin protective titanium nitride and carbide layers have been formed on the surface of carbon fibres [3,5] using a chemical vapour deposition method. However, Kerridge and Polyakov reported [8] that Li–LiCl and Ca–CaCl 2 ionic–electronic melts could be used as a medium for the reaction of a mixture of carbon black and transition metals to synthesis the carbides of titanium, zirconium, niobium and tantalum at 800–1000 °C over 5–10 h under an argon atmosphere. The mol- ten salt synthesis (MSS) method offers a route for synthesis of 0008-6223/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2007.11.020 * Corresponding author: Address: The Hubei Province Key Laboratory of Ceramics and Refractories, Wuhan University of Science and Technology, Wuhan, Hubei 430081, PR China. Fax: +86 27 86551274. E-mail address: xkli8524@sina.com (X. Li). CARBON 46 (2008) 305 – 309 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon