Combustion synthesis of chromium nitrides by SHS of Cr powder compacts under nitrogen pressures

An experimental study on the preparation of chromium nitrides by self-propagating high-temperature synthesis (SHS) was conducted with powder compacts under nitrogen pressures of 0.45–4.24 MPa. The SHS process is characterized by the steady propagation of a self-sustained combustion front, followed by prolonged afterburning reactions. Nitrogen pressure was demonstrated to play an important role in the combustion characteristics as well as in the phase composition of synthesized products. Experimental evidence indicated that combustion temperature and flame-front propagation velocity were substantially increased by increasing the nitrogen pressure. It was found that multiphase products consisting of two nitride phases Cr2N and CrN were yielded by the self-sustained reactions conducted in this study. The combustion product contained only about 10 mol% of CrN when the reaction was performed under a low nitrogen pressure of 0.79 MPa. However, the CrN content was found to increase significantly with nitrogen pressure. Namely, the mole fraction of CrN in the final product increases up to about 54% at 1.83 MPa of nitrogen, and finally approaches an asymptotical value around 80% in nitrogen of 4.24 MPa.