Fig. 1.       Fracture surfaces of the sintered composites. (a) The Si3N4–graphene mixture powders. (b) The composites fabricated by hot pressing. (c, d) The composites fabricated by pressureless sintering. The arrows indicate GPLs embedded in the matrix.
Fig. 1. Fracture surfaces of the sintered composites. (a) The Si3N4–graphene mixture powders. (b) The composites fabricated by hot pressing. (c, d) The composites fabricated by pressureless sintering. The arrows indicate GPLs embedded in the matrix.

Silicon nitride (Si3N4) ceramic composites reinforced with graphene platelets (GPLs) were prepared by hot pressed sintering and pressureless sintering respectively. Adequate intermixing of the GPLs and the ceramic powders was achieved in nmethyl-pyrrolidone (NMP) under ultrasonic vibration followed by ball-milling. The microstructure and phases of the Si3N4 ceramic composites were investigated by Field Emission Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). The effects of GPLs on the composites' mechanical properties were analyzed. The results showed that GPLs were well dispersed in the Si3N4 ceramic matrix. β-Si3N4, O′-sialon and GPLs were present in the hot-pressed composites while pressureless sintered composites contain β-Si3N4, Si, SiC and GPLs. Graphene has the potential to improve the mechanical properties of both the hot pressed and pressureless sintered composites. Toughening effect of GPLs on the pressureless sintered composites appeared more effective than that on the hot pressed composites. Toughening mechanisms, such as pull-out, crack bridging and crack deflection induced by GPLs were observed in the composites prepared by the two methods.

This paper was originally published in Materials Science and Engineering:A 644 (2015) Pages 90-95

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