Properties of novel silicon nitride-based materials

Our research on the mechanical and thermal properties of magnesium silicon nitride (MgSiN2)-silicon nitride (Si3N4) composite specimens has been reviewed in this paper. This specimen was fabricated by hot-pressing the compressed powder at a temperature between 1550oC and 1700oC for 90 min under a pressure of 75 MPa in a nitrogen atmosphere, using 1 mol% ytterbium oxide (Yb2O3) additions a sintering aid. Mechanical and thermal properties of MgSiN2 specimen without Si3N4 addition were as follows: Vickers hardness, 18.3 GPa; flexural strength, 371 MPa; fracture toughness, 2.2 MPa.m1/2; and thermal conductivity, 22.7 W m-1K-1. In order to improve these properties, MgSiN2 composite was fabricated with the addition of 0-89 mol% Si3N4. The fracture toughness of MgSiN2 specimen could be enhanced by the addition of Si3N4, e.g., 6.6 MPa m1/2 (4 mol% Si3N4 addition) and 8.7 MPa m1/2 (49 mol% Si3N4 addition). An increase in fracture toughness of MgSiN2-Si3N4 specimen was attributed to the elongation of Si3N4 grains. Moreover, te thermal conductivity of MgSiN2-Si3N4 specimen increased to 32.7 W m-1 K-1 for 29 mol% Si3N4 addition. (author)