Chapter 4. Reactant Compact and Product Microstructures for TiC, TiB₂, and TiC/TiB₂ from SPS Processing

Summary

Microstructures of TiC, TiB₂, and TiC/TiB₂ mixtures produced by self-propagating synthesis (SPS) were examined. Porosity levels were determined mainly by other process parameters, e.g., whether the part was unconstrained, constrained, or hot-pressed during the reaction. Pore sizes were determined mainly by outgassing in the former two. Grain sizes were mainly a function of the composition, and secondarily of fine residual porosity between grains. Thus, TiB₂ yielded larger grains for comparable densities than TiC because of higher reaction temperatures, while TiC/TiB₂ mixtures had finer grain sizes due to mutual inhibition of grain growth. However, these SPS-produced grain sizes tend to be somewhat greater than those commonly achievable by conventional hot-pressing. Considerable evidence of molten Ti is seen in these SPS products, including internal extrusion of Ti filaments. Evidence of thermal etching is seen on grains of TiC/TiB₂, and especially TiB_2.