Solid-State Reaction Between Titanium Carbide and Titanium Metal

The solid-state reaction between titanium and titanium carbide to form substoichiometric titanium carbide was studied by annealing single-crystal diffusion couples at T = 1350° to 1525°C. The thickness of the epitaxially grown carbide layer was almost an order of magnitude greater than that predicted from published values for chemical diffusion of carbon through titanium carbide. A value of 424 exp[–368 kJ/mol/RT] cm²/s is calculated for the chemical diffusivity of carbon from the diffusion-couple data of the present study. This anomalously rapid diffusion of carbon is associated with short-circuit diffusion along platelets of Ti₂C which develop parallel to {111} planes in TiC during the reaction. The Ti₂C platelets extend from the original Ti-TiC interface to the moving reaction front and also grow from the original interface into the original carbide crystal.