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 liquid iron–aluminum alloy doped with titanium and carbon. A homogeneous distribution of titanium carbide particles in the iron aluminide matrix up to about 16 vol% of titanium carbide was intended without agglomeration. The composition of TiC formed during in-situ reaction was investigated by ICP analysis and the Combustion-Infrared Absorption method after chemical dissolution of the iron aluminide matrix. It is found that the composition of titanium 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 microstructure of composites consists of three different regions; primary large TiC particles of 5–40 μm, matrix with small dendritic TiC particles of about 1 μm and particle-free regions around primary large TiC particles. The formation of this complex microstructure can be explained by assuming the Fe₃Al–TiC pseudo-binary system containing the eutectic reaction. Particle-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 additional formation of small TiC precipitates. Though excess 1 mol% Ti addition over the Ti content for TiC formation is soluble to Fe–28 mol% Al, excess 1 mol% C addition forms the secondary Fe₃AlC phase during melt processing.