In situ observation of the formation of TiC from the elements by neutron diffraction

In situ neutron diffraction has been employed to investigate the formation of TiC x from the elements at relatively low temperatures, beginning at T ∼ 1073 K. Slow heating of the mixture of the elements precludes the generation of sufficient heat to induce a self-propagating high temperature synthesis (SHS), reported in the literature for this system. We observe that the reaction starts well before the α – β transition in Ti occurs, which implies that in this case this transition does not serve as a trigger mechanism for SHS. An extensive coexistence of both polymorphs of titanium suggests that a significant amount of carbon diffuses into the hexagonal α -Ti lattice and stabilizes it with respect to the cubic β -phase. This is supported by the observation of an anomalous increase of the c-lattice parameter of the α -Ti lattice above the transition temperature for pure α -Ti. Density functional theory (DFT) based calculations support this interpretation. The energetics of the carburization of α -Ti have been obtained from the DFT calculations.