Materials Science and Engineering, A168 (1993) 183-187 183 Microstructure of chemically vapour codeposited SiC-TiC-C nanocomposites R. Hillel and M. Maline IMP-CNRS, UniversitOde Perpignan, 66860, Perpignan Cedex (France) F. Gourbilleau and G. Nouet LE RMA T, URA-CNRS 1317, ISMRA, 14050 Caen (France) R. Carles and A. Mlayah URA-CNRS 74, Universit~ Toulouse III, 31062 Toulouse Cedex (France) Abstract SiC-TiC-C nanocomposites were chemically vapour codeposited onto a graphite substrate under atmospheric pressure, in the temperature range 950-1150 °C, using the TiCI4-C4H 10-SiH2CI2-H2 gas system. SiC, TiC and excess carbon molar compositions were calculated using determination by electron probe microanalysis-wavelength-dispersive spectroscopy of the atomic percentages of Si, Ti and C after having identified SiC and TiC by Auger electron spectroscopy. The (220) preferential orientation corresponding to r-SiC + cubic TiC, revealed by X-ray diffraction, decreased with deposition temperature and almost no texture remained at 1050 °C. The apparent crystallite size along the (220) direction was about 10-20 nm. Micro-Raman spectra showed that the Raman size of the excess carbon did not exceed a few nanometres and that TiC and SiC were structurally disordered. Using transmission and high resolution electron microscopies, codeposits were found to consist of needles of SiC + TiC embedded in a poorly crystallized SiC matrix. They were stacking faulted and 10-15 nm broad. The needles were predominantly (220) oriented perpendicular to the substrate, whereas secondary needles were growing in { 111 }planes with (112) average direction. 1. Introduction Combining two or more different ceramics through dispersed composites offers the promise of tailoring properties. Combinations such as SiC-TiC are examples providing enhancement of mechanical properties or protection against oxidation. However, most of these mixtures, fabricated by high-temperature and high-pressure sintering, are found to consist of grains of several micrometres which limits their appli- cations under extreme conditions (stress and tempera- ture). So recently, increasing interest has focused on structures with nano-sized particles, because these materials are expected to provide improved properties compared with composites presenting coarser struc- tures [1, 2]. Among the available techniques for the preparation of nanocomposites [3] chemical vapour deposition (CVD) is a very attractive method for codepositing ceramics which are very intimately dispersed under near equilibrium conditions [4]. Taking into account previous works concerning CVD codeposition in the ternary system Ti-Si-C [5-8], we have prepared SiC-TiC-C nanocomposites. Owing to the drastic reduction in grain size and the strong imbrication of the phases, characterization of these materials required cross-checking of different data from complementary microanalytical techniques. 2. Experimental procedure Deposits were prepared by conventional thermal CVD, under atmospheric pressure [9]. The reactor chamber consisted of a vertical silica tube (~b= 5.0 or 6.2 cm, L=20 cm). The codeposition was onto mechanically polished polycrystalline graphite sub- strate (thickness 1 mm) heated in the range 950-1150°C by an electric current, the substrate shape being designed to obtain a uniformly heated zone of 25 × 5 mm 2. Vaporized liquid TiCI4, gaseous C4H10 and SiHzC1 z in H 2 gas were used as reactant sources at different concentrations. The H 2 gas flow rate was 30 1h- l or 40 1h- t. Samples of different com- positions were prepared by varying both the codeposi- tion temperature and concentrations of the input gas species. The codeposition time was 0.5 h. Coating thicknesses ranged from 100 to 600/~m, depending on the experimental conditions. 0921-5093/93/$6.00 © 1993 - Elsevier Sequoia. All rights reserved