EXPERIMENTAL AND FINITE-ELEMENT ANALYTICAL GUIDELINES FOR FABRICATING CONTINUOUS FIBER (SCS-6) METAL-MATRIX (TI-6AL-4V) COMPOSITES VIA THE FOIL FIBER FOIL TECHNIQUE

The consolidation behavior of Ti-6Al-4V matrix SCS-6 silicon carbide fiber metal matrix composites fabricated using the foil/fiber/foil technique was studied by both experimental physical modeling and finite element analysis. The experiments were carried out at 875 degrees C (T/T-m = 0.597 for the matrix material) for varying levels of uniaxial compressive stress and times to characterize the stages of consolidation observed prior to reaching full density. Three stages of consolidation were identified: (1) instantaneous plasticity, (2) time-dependent foil deformation prior to establishing contact between neighboring foils, and (3) time dependent consolidation to close the pores at each side of the fiber that remain after neighboring foils have contacted between the fibers. Finite element analysis using the commercial code ABAQUS was employed to model the process and to examine the role of fiber spacing and applied stress level on the time required to densify the composite. The simulation predictions for the times necessary to achieve various densities were in good agreement with the experimental observations. The FFA results were used to establish analytical relations that describe the entire densification process. These equations are quite general and can be used to characterize any foil/fiber/foil composite fabrication process since they include as variables the matrix flow properties, processing stress and temperature, foil thickness and fiber diameter. The results predicted a slowing in densification at the latter stages of pore closure. This slowing was attributed to the low stresses in the matrix near a pore. Also, as the fiber spacing decreases, the time to densify increases because the load per fiber is now smaller.