Effects of MgSiN2 addition and post-annealing on mechanical and thermal properties of Si3N4 ceramics

Si3N4 ceramics with 10 mol% (MgSiN2 + Y2O3) additives were prepared by sintering at 1900 degrees C for 8 h in 1 MPa N-2 atmosphere. Both the bending strength and thermal conductivity of the ceramics increase with increasing content of MgSiN2, and reached 689 MPa and 97 Wm(-1) K-1 with the addition of (7 mol% MgSiN2 + 3 mol% Y2O3). The bending strength and thermal conductivity were enhanced to 698 MPa and 105 Wm(-1) K-1 by post annealing at 1400 degrees C for 20 h. By annealing at 1600 degrees C, the thermal conductivity could be further improved to 117 Wm(-1) K-1, but the strength decreased to be 517 MPa. From the experimental results, adding more MgSiN2 and increasing the annealing temperature are helpful to improve the thermal conductivity, by reducing the grain boundary phase and increasing the grain size.