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 TiCx 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.