The macroscopic combustion regimes, as well as the dynamics of phase formation, for the titanium-nitrogen system at low nitrogen pressures (0.1 kPa < p < 50 kPa) have been studied. Several combustion modes, including planar surface (high-temperature), surface spot, and planar layer-by-layer (low-temperature) mode, have been observed. Also, a chaotic spot mode was found at pressures below 2 kPa for conditions of high heat loss. Using the time-resolved x-ray diffraction method previously developed by the authors, it was shown in situ that different mechanisms of phase formation correspond to these combustion modes. For the high-temperature mode, titanium nitride appeared in the combustion front as the initial product. However, only solid solutions of nitrogen in titanium were formed during the low-temperature mode. A complex sequence of phase formation was observed for spot combustion.