Processing strategy to trigger grain growth in silicon nitride

Large silicon nitride (Si3N4) grain can enhance thermal conductivity and fracture toughness in the Si3N4 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 mu m, 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 mu m exhibited superior properties, and fracture toughness and thermal conductivity increased to 10.2 MPa<middle dot>m1/2 and 118.2 W/(m<middle dot>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. This study investigates the effects of pores in the reactant compact on the microstructure, fracture toughness, and thermal conductivity of sintered Si3N4 ceramics. The results showed that the pores in the compacts before sintering could improve the thermal conductivity and fracture toughness if they disappeared and promoted grain growth during the sintering procedure. image