THERMAL-CONDUCTIVITIES OF TI-SIC AND TI-TIB2 PARTICULATE COMPOSITES

Composites of commercial-purity titanium reinforced with 10 and 20 vol % of SiC and TiB2 particulates were produced by powder blending and e xtrusion. Heat treatments were conducted on each of these composites. The thermal diffusivities of the composites were measured as a functio n of temperature using the laser flash technique. Thermal conductiviti es were inferred from these measurements, using a rule-of-mixtures ass umption for the specific heats. It has been shown that, while an enhan cement of the thermal conductivity is expected to arise from the prese nce of both types of reinforcement, this behaviour is in fact observed only with the Ti-TiB2 composites. The thermal conductivity of Ti-TiB2 composites is significantly greater than that of the unreinforced mat rix and rises with increasing volume fraction of reinforcement. In con trast, the conductivities of the Ti-SiC composites were considerably l ower than that of the unreinforced titanium and decreased with increas ing volume fraction of SiC reinforcement. These results have been inte rpreted in terms of the thermal resistance of the reaction layers whic h exist between the matrix and two types of particulate reinforcements . The faster reaction kinetics between SiC and Ti gives rise to a thic ker reaction layer for a given heat treatment than that between Ti and TiB2 and is also accompanied by a much larger volume change (-4.6%). It is proposed that this volume decrease, giving rise to interfacial d amage and a network of microcracks, is at least partly responsible for a high interfacial thermal resistance, reducing the conductivity of t he Ti-SiC composite. These results indicate that TiB2 would be prefera ble to SiC as a reinforcement in Ti for situations where a high therma l conductivity would be beneficial.