COMBUSTION CHARACTERISTICS OF THE NI3TI-TIB2 INTERMETALLIC MATRIX COMPOSITES

Combustion synthesis (SHS) of Ni3Ti-TiB2 metal matrix composites (MMCs ) was selected to investigate the effect of gravity in a reaction syst em that produced a light, solid ceramic particle (TiB2) synthesized in situ in a large volume (>50 pct) of the liquid metallic matrix (Ni3Ti ). The effects of composition, green density of pellets, and nickel pa rticle size on the combustion characteristics are presented. Combustio n reaction temperature, wave velocity, and combustion behavior changed drastically with change in reaction parameters. Two types of density effects were observed when different nickel particle sizes were used. The structures of the combustion zones were characterized using temper ature profile analysis. The combustion zone can be divided into prefla me, reaction, and after-burning zones. The combustion mechanism was st udied by quenching the combustion front. It was found that the combust ion reactions proceeded in the following sequence: formation of liquid Ni-Ti eutectic at 940 degrees C --> Ni3Ti + NiTi phases --> reduction of NiTi with B --> TiB2 + Ni3Ti.