An experimental and theoretical investigation of the rapid consolidation of continuously reinforced, metal-matrix Composites

Abstract

The feasibility of the rapid consolidation of T-14Al-21Nb/SCS-6 foil/fiber/foil composites using a forging approach was established as an alternative to slower and more expensive processes such as those based on hot isostatic pressing (HIP) or vacuum hot pressing (VHP). A firm basis for the technique was developed through theoretical analyses of temperature transients, forging pressures, and fiber fracture. These analyses 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 densifying layup is an important consideration in achieving full consolidation during forging. Specifically, the difference in flow stress between 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 axial and tangential stresses during rapid consolidation. The theoretical work was validated by experimental trials using the Ti-14Al-21Nb matrix/silicon carbide fiber system. Measured forging pressures were in good agreement with predictions. Fiber fracture observations indicated that 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 properties similar to those of conventionally consolidated Ti-14Al-21Nb/silicon carbide composites can be achieved by the forge-consolidation technique.