Processing strategy to trigger grain growth in silicon nitride

Abstract Large silicon nitride (Si 3 N 4 ) grain can enhance thermal conductivity and fracture toughness in the Si 3 N 4 ceramics. In this study, in order to use pores as a grain growth trigger and to achieve final densification, a limited amount of pores were introduced into the green compact. The pores were introduced by using four types of pore formers with diameters of 2, 20, 30, and 100 µm, and the pore volume was in the range of 3–18 vol%. The presence of pores promoted grain growth regardless of their diameter and volume, because no collisions occurred among the grains in the pores, and larger pores formed larger elongated grains. However, their large volume and diameter inhibited densification. Based on this tradeoff, the pore formers with a diameter of 30 µm exhibited superior properties, and fracture toughness and thermal conductivity increased to 10.2 MPa·m 1/2 and 118.2 W/(m·K), respectively, as the pore volume increased to 5 vol%. These results revealed that the pores in the compacts before sintering could improve the thermal conductivity and fracture toughness if they promoted grain growth during the sintering procedure and finally disappeared.