Abstract
The effect of silicon nitride (Si 3N 4) addition on the sintering of magnesium silicon nitride (MgSiN 2) powder has been examined using a hot-pressing technique. The MgSiN 2 powder compacts with 1, 4, and 9 mol% of Si 3N 4 addition [sintering aid: 1 mol% ytterbium oxide (Yb 2O 3)] were hot-pressed at a temperature between 1550 and 1800 °C for 90 min in a nitrogen (N 2) atmosphere under the pressure of 75 MPa. The relative density of a MgSiN 2 compact with 4 mol% of Si 3N 4 addition hot-pressed at 1600 °C for 90 min showed a maximum (98.6%), although the relative density was reduced by the addition of Si 3N 4 at other hot-pressing temperatures. The maximum fracture toughness (6.6 MPa·m 1/2) was achieved for the MgSiN 2 specimen with 4 and 9 mol% of Si 3N 4 addition hot-pressed at 1600 °C for 90 min. This value was 2.5 times higher than that of MgSiN 2 specimen without Si 3N 4 addition (2.6 MPa·m 1/2). The improvement of the fracture toughness appeared to be due to the elongation of the Si 3N 4 grains, which had occurred in the presence of a liquid phase during the hot pressing. The thermal conductivity of the MgSiN 2 specimen with 9 mol% of Si 3N 4 addition hot-pressed at 1750 °C for 90 min increased to 34.1 W m −1 K −1, which is to our knowledge, the highest among the values so far reported for MgSiN 2 ceramics.
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