AN EXPERIMENTAL AND THEORETICAL INVESTIGATION OF THE RAPID CONSOLIDATION OF CONTINUOUSLY REINFORCED, METAL-MATRIX COMPOSITES

The feasibility of the rapid consolidation of T-14Al-21Nb/SCS-6 foil/f iber/foil composites using a forging approach was established as an al ternative to slower and more expensive processes such as those based o n hot isostatic pressing (HIP) or vacuum hot pressing (VHP). A firm ba sis for the technique was developed through theoretical analyses of te mperature transients, forging pressures, and fiber fracture. These ana lyses demonstrated that there exists an optimal forging speed at which the consolidation stresses are a minimum. It was also shown that the flow stress of the encapsulation material relative to that of the dens ifying layup is an important consideration in achieving full consolida tion during forging. Specifically, the difference in flow stress betwe en the two materials influences the magnitude and sign of the in-plane (secondary) stresses that are developed during forging and therefore the rate of pore closure during the latter stages of the process. With regard to fiber fracture, analyses were performed to estimate the axi al and tangential stresses during rapid consolidation. The theoretical work was validated by experimental trials using the Ti-14Al-21Nb matr ix/silicon carbide fiber system. Measured forging pressures were in go od agreement with predictions. Fiber fracture observations indicated t hat tangential tensile stresses developed in the fiber control failure ; a forging window to avoid such failures was thus developed. Finally, it was demonstrated that matrix microstructures and mechanical proper ties similar to those of conventionally consolidated Ti-14Al-21Nb/sili con carbide composites can be achieved by the forge-consolidation tech nique.