NUKLEONIKA 2006, 51(Suppl. 1):s55-s60

Our research on the mechanical and thermal properties of magnesium silicon nitride (MgSiN₂)-silicon nitride (Si₃N₄) composite specimens has been reviewed in this paper. The specimen was fabricated by hot-pressing the compressed powder at a temperature between 1550°C and 1700°C for 90 min under a pressure of 75 MPa in a nitrogen atmosphere, using 1 mol% ytterbium oxide (Yb₂O₃) addition as 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 m^1/2; and thermal conductivity, 22.7 W m^-1 K^-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 m^1/2 (4 mol% Si₃N₄ addition) and 8.7 MPa m^1/2 (49 mol% Si₃N₄ addition). An increase in fracture toughness of MgSiN₂-Si₃N₄ specimen was attributed to the elongation of Si₃N₄ grains. Moreover, the thermal conductivity of MgSiN₂-Si₃N₄ specimen increased to 32.7 W m^-1 K^-1 for 29 mol% Si₃N₄ addition.