Tailoring structure and properties of composites synthesized in situ using displacement reactions

Displacement reactions can produce in situ intermetallic and ceramic matrix composites in a process where an intermetallic or ceramic phase(s) and a potential reinforcing phase(s) are grown together during a reactive phase transformation. Various forms of interpenetrating-phase and dispersed-phase microstructures are produced by means of these reactions. It is also apparent that both composition and morphology can be manipulated to some degree in order to tailor composite structures. The composition and morphology of MoSi2 reinforced with SiC particles was explored over a wide range by controlling starting reactant compositions and hot-pressing conditions. Preliminary results of a model for the formation of the MoSi2/SiC composite are presented in which both diffusion and interfacial reactions are included. Strength in bending and chevron-notch fracture toughness were determined as a function of temperature and composition and the measured properties are discussed with regard to the observed microstructures. A novel, graded composite structure in the NiAl/Ni3Al/Ni:Al2O3 system is also discussed.