Thermal and Mechanical Properties of Magnesium Silicon Nitride-Silicon Nitride Composite

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Magnesium silicon nitride (MgSiN₂) compacts with 0 ∼89 mol% of silicon nitride(Si₃N₄) and 1 mol% ytterbium oxide(Yb₂O₃) as a sintering aid were hot-pressed at 1600^oC for 90 min under the pressure of 75 MPa. Relative densities of the MgSiN₂ composites with Si₃N₄ and Yb₂O₃ addition exceeded 95%, independent of the amount of Si₃N₄. With increasing amount of Si₃N₄, the number of elongated grains increased. Owing to the elongation of Si₃N₄ grains, the fracture toughness of the MgSiN₂ composite attained a maximum (8.7 MPa m^1/2) at 49 mol% of Si₃N₄addition. On the other hand, the bending strength increased gradually with increasing amount of Si₃N₄ and showed a maximum (1.0 GPa) at 89 mol% of Si₃N₄ addition. Consequently, the fracture toughness and bending strength of MgSiN₂composites with Si₃N₄ addition became 2.7 and 3.2 times as high as those of monolithic MgSiN₂ ceramic, respectively.