A novel processing methodology that allows combined preheating and Flash-SPS (FSPS) of silicon carbide-based materials has been developed. Beta-SiC (+10 wt% B 4 C) powders were densified (Ф 20 mm) up to 96% of their theoretical density in 17 s under an applied pressure of 16 MPa (5 kN). The flash event was attributed to the sharp positive temperature dependence of the electrical conductivity (thermal runaway) of SiC, and a sudden increase in electric power absorption (Joule heating) of the samples after a sufficient preheating temperature (>600°C) was reached. The microstructural evolution was analyzed by examining materials densified by FSPS in the range of 82%-96% theoretical densities. FEM modeling results suggest that the FSPS heating rate was of the order of 8800°C/min. A comparative analysis was done between FSPS and reference samples (sintered using conventional SPS in the temperature range of 1800°C-2300°C). This allowed for a better understanding of the temperatures generated during FSPS, and in turn the sintering mechanisms. We also demonstrated the scalability of the FSPS process by consolidating a large aSiC disk (Ф 60 mm) in about 60 s inside a hybrid SPS furnace equipped with an induction heater, which allowed us to achieve sufficient preheating (1600°C) of the material to achieve FSPS.

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A novel processing route that induces simultaneous densification and texturing of SiC ceramics by Flash Spark Plasma Sintering (FSPS) is reported. Unlike hot forging (which produces texturing in a direction orthogonal to the load as a result of plastic deformation), FSPS produced texturing parallel to the pressing direction. The texturing was driven by a thermal gradient generated within the sample along its axial direction due to the higher electrical resistivity of SiC compared to the pressing graphite punch (the sample midthickness was hotter than the surfaces in contact with the graphite punches). In FSPSed SiC samples, the microstructure consisted of large SiC plate-like elongated crystals (thickness between 40 and 100 μm, width up to 500 μm) with their c-axis (slow growth direction) orthogonal to the Physical Vapor Transport (PVT) direction. The mechanisms producing densification and texture were studied for SiC with and without boron carbide sintering additives. In order to achieve a dense and textured portion of the sample, the presence of a liquid phase during sintering was necessary.

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