Enhancing mechanical properties of selectively laser sintered SiC/Si composites printed using electrostatic spraying microspheres with fine particles

The SiC/Si composites were prepared via selective laser sintering (SLS) combined with reactive melt infiltration (RMI) of liquid Si, using fine SiC particles with original particle sizes of 0.05, 0.8 and 5 mu m. A novel electrostatic spraying combined with phase inversion (ES-PI) method was developed to assemble SiC particles into spherical powders (40-60 mu m in diameter) before SLS, enabling SiC with excellent flowability. Commercial coarse SiC microparticles (similar to 40 mu m) were also adopted to prepare the SiC/Si reference composite for comparison. Then the effects of the fine original particle sizes of SiC on the microstructures, as well as mechanical performance of composites were studied. Compared to commercial SiC microparticles, the ES-PI SiC microspheres show superior sphericity and fluidity but a relatively high porosity. However, the pores in ES-PI SiC microspheres, which are potentially detrimental to mechanical properties of composites, will be totally filled and eliminated in the SiC/Si composites after RMI. The mechanical performance of the SiC/Si composites printed using the fine nano (0.05 mu m) and submicron (0.8 mu m) original particles was effectively improved than the reference composite. When printed using the ES-PI SiC microspheres with 0.05 mu m original particles, the flexural strength of the SiC/Si composite was enhanced by 25 %. This is attributed to the cracks deflection as well as the fracture mode transition from transgranular to intergranular rupture by the use of nano- or submicro-sized original SiC particles. This work provides an effective solution for preparing high strength SiC/Si composites with fine nano- or submirco particle sizes for space-based lightweight optical mirror using SLS.