Investigation on mechanical properties and microstructure of silicon nitride ceramics fabricated by spark plasma sintering

Abstract In order to prepare high-performance and stable performance silicon nitride-based ceramic cutting tools, orthogonal experiment was carried out firstly to study the influence of sintering temperature and sintering aids (MgSiN 2 , Y 2 O 3 and CeO 2 ) on the densification and mechanical properties of the Si 3 N 4 materials by spark plasma sintering. The results showed that Si 3 N 4 ceramics with 5 wt%MgSiN 2 , 3 wt%Y 2 O 3 and 1 wt%CeO 2 sintering aids had the best relative density and mechanical properties at 1650 ℃. Secondly, the effects of sintering temperature on the densification, microstructure and mechanical properties of Si 3 N 4 ceramics with 5 wt%MgSiN 2 , 3 wt%Y 2 O 3 and 1 wt%CeO 2 sintering aids were studied in detail. The results showed that the relative density of Si 3 N 4 ceramics reached the maximum of 99.40 ± 0.14% at 1650 ℃, the Vickers hardness and fracture toughness were 16.53 ± 0.12 GPa and 6.89 ± 0.20 MPa m 1/2 , respectively. The grain shapes were composed of equiaxed α-Si 3 N 4 and long columnar β-Si 3 N 4 , and the transformation rate of α-Si 3 N 4 to β-Si 3 N 4 was 42.5%. Finally, the statistical distribution of the relative density, phase transformation rate and mechanical properties of Si 3 N 4 ceramics with 5 wt%MgSiN 2 , 3 wt%Y 2 O 3 and 1 wt%CeO 2 sintering aids at 1650 ℃ was investigated. It was found that the mechanical properties of silicon nitride ceramics sintered by spark plasma sintering were less dispersive, and the hardness and fracture toughness obeyed the two parameters Weibull distribution well.