Effect of processing parameters on the microstructure and mechanical behavior of a silicon carbide-silica composite

Abstract

Abstract Silicon carbide (SiC) is an inert material with excellent thermomechanical properties for many optoelectronic, structural, and ballistic applications. However, manufacturing SiC components is challenging due to the high temperatures (> 2000 deg C) and pressures (1000-2000 atm) required for traditional sintering processes. The objective of the present research study is to enable the additive manufacture of SiC components using a new powder bed, sodium hydroxide (NaOH) binder-jetting process. The innovation is the secondary crystal growth (SiO2) that serves to bridge and close the gaps between the SiC particles via a chemical attack (oxidation) of their surfaces by the NaOH solution. To evaluate the process, SiC powder was mixed with a NaOH-water solution at room temperature and shaped into 10 mm diameter by 15 mm long cylinders in a mold with compaction by hand pressure only. This approach was implemented to simplify testing while still mimicking the eventual powder bed, binder-jetting process where moderate pressure is applied by the roller from one powder layer to the next. Samples were thermally treated at moderate temperatures (approximately 1000 deg C) for a few hours. As the thermal treatment temperature and duration increased, the density also increased. In conjunction with the increase in density, the compressive strength increased. Scanning electron microscopy results are presented to validate the formation of secondary crystal growth.