Multilayer graphene and β-Si3N4 whisker-reinforced porous Si3N4 ceramics by spark plasma incomplete sintering

Abstract

Combining the advantages of spark plasma sintering (SPS) and incomplete sintering (IS) in preparation of Si3N4 ceramics, the spark plasma incomplete sintering (SPIS) was presented to fabricate porous Si3N4 ceramics. Considering balancing the contradictory relationship between the porosity and toughness, 1 wt% multilayer graphene (MLG) was incorporated into porous Si3N4 ceramics. Meanwhile, for the sake of compensating for the decrease in the hardness of porous Si3N4 ceramics induced by MLG, 0–8 wt% β-Si3N4 whisker (β-Si3N4w) were synergistically added. The element distribution, phase constitutions and microstructures of MLG/β-Si3N4w-reinforced porous Si3N4 ceramics were characterized by energy dispersive spectroscopy (EDS), x-rays diffraction (XRD) and scanning electron microscope (SEM). The effects of β-Si3N4w content on porosity, hardness and fracture toughness of porous Si3N4-based ceramics were analyzed. Results indicated that the porosity of porous Si3N4-based ceramics reached 21%, and then decreased significantly after the β-Si3N4w content exceeded 4 wt%. The hardness of porous Si3N4-based ceramics obtained the maximum value 2.81 GPa when β-Si3N4w was added 8 wt%, which was 31.92% higher than monolithic porous Si3N4 ceramic. The mass transfer, diffusion and fusion induced by β-Si3N4w were considered to be the main responsible for the increase of hardness. The fracture toughness of specimen with 1 wt% MLG and 4 wt% β-Si3N4w was advanced to 3.14 MPa m1/2, which was 15.44% higher than monolithic porous Si3N4 ceramic. The markedly enhanced of the fracture toughness was attributed to the synergistic effects of crack deflection, pull-out and bridging resulted by MLG/β-Si3N4w.