Mechanisms, Models, and Simulations of Metal-Coated Fiber Consolidation

Recent experimental studies of the hot isostatic consolidation of Ti-6Al-4V–coated SiC fibers contained in cylindrical canisters have revealed an unexpectedly high rate of creep densification. A creep consolidation model has been developed to analyze its origin. The initial stage of consolidation has been modeled using the results of contact analyses for perfectly plastic and power-law creeping cylinders that contain an elastic ceramic core. Final stage densification was modeled using a creep potential for a power-law material containing a dilute concentration of cusp-shaped voids with a shape factor similar to that observed in the experiments. Creep rates were microstructure sensitive and so the evolution of matrix grain size and the temperature dependence of the a/b-phase volume fractions were introduced into the model using micromechanics-based creep constitutive relationships for the matrix. To account for load shielding by the deformation resistant canister, the consolidation model was combined with an analysis of the creep collapse of a fully dense pressure vessel. The predicted densification rates were found to agree well with the experimental observations. The high densification rate observed in experiments was the result of the small initial grain size of the vapor-deposited matrix combined with retention of the cusp shape of the interfiber pores.