TRANSIENT PLASTIC PHASE PROCESSING OF TITANIUM BORON CARBON COMPOSITES

Ceramic/ceramic composites in the Ti-B-C system were fabricated by a n ovel process referred to as transient plastic phase processing (TPPP). The basic concept is based on the following reaction: ''soft'' transi ent plastic matrix + reactant phase --> hard matrix + reinforcement ph ase where the transient plastic phase is a phase with a wide range of stoichiometry and a yield point that is a strong function of that stoi chiometry. The reactant phase is one that will react with the transien t phase in such a way so as to shift the composition of the latter tow ard its harder and more refractory composition. The composite is forme d in two stages: In the first, pressure is applied to shape and fully density the reactants while the transient phase is soft, i.e., before reaction. Once the reactants are densified, the reaction is allowed to proceed, forming a new phase and rendering the matrix more refractory . If the volume change upon reaction is small, then the density of the final compact will remain near theoretical. Using this approach ceram ic/ceramic composites in the Ti-B-C system were hot-pressed to full de nsity and complex shapes at temperatures as low as 1600-degrees-C.