In-situ production and microstructures of iron aluminide TiC composites

In this study we have tried to produce the titanium carbide reinforced iron aluminide composites by in-situ reaction between titanium and carbon in li quid iron-aluminum alloy doped with titanium and carbon. A homogeneous dist ribution of titanium carbide particles in the iron aluminide matrix up to a bout 16 vol% of titanium carbide was intended without agglomeration. The co mposition of TiC formed during in-situ reaction was investigated by ICP ana lysis and the Combustion-Infrared Absorption method after chemical dissolut ion of the iron aluminide matrix. It is found that the composition of titan ium carbide formed during melt processing is an average of Ti-48.4 mol% C. In addition, titanium carbide has very low solubility of Fe and Al. The mic rostructure of composites consists of three different regions; primary larg e TIC particles of 5-40 mu m, matrix with small dendritic TiC particles of about 1 mu m and particle-free regions around primary large TIC particles. The formation of this complex microstructure can be explained by assuming t he Fe3Al-TiC pseudo-binary system containing the eutectic reaction. Particl e-free regions are halos of iron aluminide phase and the formation of halos is explained by coupled zone concept. Subsequent heat treatment at 1373 K for 48 h induces spheroidization and/or coarsening of small TIC particles, while microstructure after heat treatment at 973 K for 48 h exhibits the ad ditional formation of small TiC precipitates. Though excess 1 mol% Ti addit ion over the Ti content for TiC formation is soluble to Fe-28 mol% Al, exce ss 1 mol% C addition forms the secondary Fe3AlC phase during melt processin g. (C) 1999 Elsevier Science Ltd. All rights reserved.