The mechanism of combustion synthesis of (TiC xN y-TiB 2)/Ni from a Ni-Ti-C-BN system

Abstract

The combustion reaction mechanism of the Ni-Ti-C-BN system was investigated by a combustion front quenching method. The results showed that the SHS reaction in the Ni-Ti-C-BN system starts with the formation of TiN x and TiB from the solid-state reaction between Ti and BN. Meanwhile, the solid-state reaction between Ni and Ti occurs at some locations to form Ni 3Ti. Subsequently, the resultant TiN x reacts with Ni to form the Ni-Ti compounds such as NiTi and Ni 3Ti. As the temperature increases further, Ni-Ti liquid appears between NiTi and Ni 3Ti, and some B atoms that diffused away from BN could dissolve into the Ni-Ti liquid to form TiB 2. The heat generated from these reactions promotes the further dissolution of the C, B and N atoms in the Ni-Ti liquid to form the Ni-Ti-B-N-C liquid. As the B, N and C atoms in the liquid become sufficiently supersaturated, precipitation of plenty of TiB 2 and TiC x N y grains occurs. In addition, the reasons for the prior formation of TiB 2 over TiC x N y and separated residence of the TiB 2 and TiC x N y grains in the microstructure were discussed.