Production of Ni3Ti-TiC x intermetallic-ceramic composites employing combustion synthesis reactions

Combustion synthesis (CS) of nickel, titanium, and carbon (graphite) reactant particles can result in NiTi-TiC (stoichiometric) or Ni₃Ti-TiC _x (nonstoichiometric) composites. Since NiTi exhibits both superelasticity and shape memory properties while Ni₃Ti does not, it is important to understand the SHS reaction conditions under which each of these composite systems may be synthesized. The stoichiometry of TiC _x , for which 0.3 ≤ x ≤ 0.5, has an important controlling effect on the formation of either Ni₃Ti or NiTi; i.e., formation of TiC_0.7 results in a depletion of titanium and formation of Ni₃Ti. This deficiency should be considered when developing the SHS reaction. This article examines the SHS conditions under which Ni₃Ti-TiC _x composites are produced. Ignition, combustion, and microstructure characteristics of nickel, titanium, and carbon (graphite) particles were investigated as a function of initial relative density and thermophysical properties of the reactant mixture. Combination of the thermophysical properties and burning velocities controlled TiC _x particle size, yielding a dependence of particle size on cooling rate. Theoretical calculations were performed and are in good agreement with the experimental data presented.