The vacuum hot pressing behavior of silicon carbide fibers coated with nanocrystalline Ti–6Al–4V

Abstract

The vacuum hot pressing (VHP) of silicon carbide monofilaments coated with nanocrystalline Ti–6Al–4V has been studied. During consolidation, very high densification rates were observed, even at temperatures and pressures well below those normally used for processing conventional Ti–6Al–4V. From the cross-sections of partially consolidated specimens, the evolution of coated fiber–fiber contacts and pore shapes were determined. The pores were found to be cusp-shaped throughout the consolidation process. Columns of coated fibers were observed to form along the loading direction and resulted in regions of locally high fiber volume fraction. Simulations of the VHP experiments were performed using a model which incorporated time and temperature dependent microstructure relationships. In the model, the initial densification was based upon a recent micromechanical contact analysis for a metal coated fiber. Final stage densification was analyzed by modifying the Qian et al. strain rate potential for a power law creeping body containing isolated cusp-shaped pores. Overall, the simulations compared well with the experimental density data, although the load supported by the regions of locally high fiber volume fraction resulted in the model slightly overestimating the observed densification time response.