Effect of Ultra-High Pressure Sintering and Spark Plasma Sintering and Subsequent Heat Treatment on the Properties of Si3N4 Ceramics

Xiaoan Lv, Xianhui Li, Junwei Huang, Changchun Ge, Qi Yu
2022 Materials  
In this study, coarse Beta silicon nitride (β-Si3N4) powder was used as the raw material to fabricate dense Si3N4 ceramics using two different methods of ultra-high pressure sintering and spark plasma sintering at 1550 °C, followed by heat treatment at 1750 °C. The densification, microstructure, mechanical properties, and thermal conductivity of samples were investigated comparatively. The results indicate that spark plasma sintering can fabricate dense Si3N4 ceramics with a relative density of
more » ... 99.2% in a shorter time and promote α-to-β phase transition. Coarse β-Si3N4 grains were partially fragmented during ultra-high pressure sintering under high pressure of 5 GPa, thereby reducing the number of the nucleus, which is conducive to the growth of elongated grains. The UHP sample with no fine α-Si3N4 powder addition achieved the highest fracture strength (822 MPa) and fracture toughness (6.6 MPa·m1/2). The addition of partial fine α-Si3N4 powder facilitated the densification of the SPS samples and promoted the growth of elongated grains. The β-Si3N4 ceramics SPS sintered with fine α-Si3N4 powder addition obtained the best comprehensive performance, including the highest density of 99.8%, hardness of 1890 HV, fracture strength of 817 MPa, fracture toughness of 6.2 MPa·m1/2, and thermal conductivity of 71 W·m−1·K−1.
doi:10.3390/ma15207309 fatcat:upkd7xirmzgbhdffow3cbyyj5m