Microstructure/processing relationships in reaction-synthesized titanium aluminide intermetallic matrix composites

Near-gamma TiAl- and Al3Ti-based intermetallic matrix composites have been produced using in-situ reaction- synthesis techniques. The intermetallic matrices have been reinforced with relatively high loadings (e.g., 20 to 50 Vol pct) of dispersed TiB2 particulates. It is shown that the as-synthesized TiB2 size is strongly dependent on the specific alloy formulation; specifically, the TiB2 size tends to increase as the nominal volume percent of TiB2 in the composite increases. The observed size effect is determined to be associated with the temperature that is attained during the synthesis event, which is established primarily by the net exothermicity of the participating synthesis reaction(s). The exothermicity of the reactions can be assessed through the calculation of a formulation's adiabatic temperature, which is found to increase with the percentage of TiB2 over the range of approximately 10 to 60 Vol pct. The coupling of a composite's characteristic adiabatic temperature with the resulting reinforcement size provides direct links among composition, processing, and mechanical performance, since the size of a reinforcing particle is influential in establishing the interparticle spacing, which, in turn, establishes the strengthening potency of the dispersed phase within the composite.