REACTION SYNTHESIS MECHANISM IN DYNAMICALLY DENSIFIED TI+C POWDER COMPACTS

Elemental titanium and carbon powder mixtures were statically and dyna mically densified to make similar to 88-90% dense compacts for subsequ ent reaction synthesis in an induction-heated hot press at 1100 degree s-1400 degrees C, with 60 minutes constant hold time and a nominal pre ssure of 34.5 MPa (5000 psi). The reaction behavior of the dynamically (shock) densified powder compacts was observed to be dominated by def ect-enhanced solid-state diffusion. Measurements of titanium carbide f ormation rates revealed that the otherwise-sluggish diffusion of Ti or C through the initial C-deficient TiCx layer is significantly altered in the dynamically compressed powders with activation energies for di ffusion reduced by 4-6 times. The reacted dynamically densified compac ts are similar to 85% dense, and have a similar to 5 mu m grain size. In contrast, statically pressed Ti + C compacts were observed to react via a combustion-type process (following initial solid-state reaction ) resulting in porous reaction products with >30% retained porosity. ( C) 1997 Acta Metallurgica Inc.