The effect of degree of sintering on the structural and mechanical properties of Si3N4–SiO2 glass ceramics

Abstract

Silica-based glass ceramics have been extensively used in biomedical applications due to their superior biocompatibility and controllable properties. However, their low mechanical strength limits their application. This could be addressed by optimizing the crystalline phase which determines their final properties. Silicon nitride has attracted attention due to its combination of good mechanical and biological properties. Therefore, to combine the advantage of silica-based glass and silicon nitride ceramic, this study developed a silicon nitride-silicon dioxide (Si3N4–SiO2) glass ceramics. The effects of spark plasma sintering parameters on the structural and mechanical properties of Si3N4–SiO2 glass ceramics were investigated. Full densification was reached at a sintering temperature of 1300 °C, a holding time of 10 min and an applied pressure of 80 MPa (relative density = 99.19 %). No silicon oxynitride (Si2N2O) crystalline phase was formed in the sintered glass ceramics, as confirmed by XRD. The interface between the β-Si3N4 crystalline and amorphous SiO2 was investigated by HRTEM, and the results indicated that an amorphous interfacial oxide was formed at the interface. The mechanical properties increased with increasing sintering temperature, as a result of the increased density. The Si3N4–SiO2 glass ceramics sintered at 1500 °C exhibited the highest value of toughness and flexural strength, at 4.6 ± 0.28 MPa m1/2 and 360 ± 27 MPa. The indentation cracks observed by SEM showed that the large β-Si3N4 grains promoted crack deflection, while the equiaxed Si3N4 grains with a lower aspect ratio led to transgranular fracture. The mechanical properties of these Si3N4–SiO2 glass ceramics are comparable to commercial glass ceramics, indicating their promising aspects in biomedical applications.