| In this research, the beneficial effects of "shock compression of powders" and "reaction synthesis" were combined to investigate the possibility of net-shape solid-state synthesis of TiC ceramics with refined microstructures. Elemental titanium and carbon powder mixtures were shock-compressed to make green-density compacts for subsequent reaction synthesis experiments, which were performed in an induction-heated hot press at temperatures of 1000{dollar}spcirc{dollar}-1400{dollar}spcirc{dollar}C, with hold times of 30-180 minutes and a nominal pressure of 34.5 MPa (5000 psi). The unique combination of defect states and packing characteristics introduced during shock-compression, results in significant enhancement in the solid-state chemical reactivity of the powder mixtures. Consequently the reaction behavior of the powders is dominated by enhanced solid-state diffusion. Experimentally determined titanium carbide formation rates (measured based on depletion of elemental Ti), revealed that the otherwise-sluggish diffusion of Ti or C, through the initial C-deficient TiC{dollar}sb{lcub}rm x{rcub}{dollar} layer, is altered in the shock-compressed Ti + C powder mixtures. The apparent activation energy determined from reaction rate measurements and based on various kinetic and reaction synthesis models is observed to be reduced by four-to-six times the activation energy for diffusion of Ti into TiC{dollar}sb{lcub}rm x{rcub}{dollar} and two-to-three times that for diffusion of C into TiC{dollar}sb{lcub}rm x{rcub}{dollar}. Consequently consumption of Ti is achieved in time scales of about 1-3 hours at temperatures less than two-thirds of melting temperature of Ti. The resulting reaction synthesized compacts (80-85% of theoretical maximum density) have microstructures reminiscent of solid-state processes, with refined grain size ({dollar}<{dollar}6 {dollar}mu{dollar}m) and microhardness values approaching those of commercially available full-density TiC ceramics (2,000 KHN). In contrast, uniaxially pressed Ti + C (graphite) compacts undergo a combustion-type reaction (following initial solid-state reaction) generating products with {dollar}sim{dollar}70% of theoretical maximum density. |
