Hot pressed SiC ceramics employing polymer-derived SiBCN as sintering aid

SiC ceramics were densified with 10 wt.% polymer-derived SiBCN additives by hot-pressing under a load of 40 MPa at 1850 degrees C for 90 min in a vacuum environment. Polyborosilazane was chosen as the SiBCN precursor and pyrolyzed at 1000 degrees C before use. The obvious densification process began at about 1700 degrees C during the sintering. The densification mechanism was different from the SiC ceramics densified by traditional sintering aids. When the temperature was above 1700 degrees C, particle rearrangement was accelerated because deformation and/or viscous flow of the SiBCN occurred under the external pressure. This procedure resulted in rapid increase of density. After particle rearrangement, B and C elements and nano SiC grains separating out from the SiBCN material led to SiC grain growth and further densification. The bending strength and Vickers hardness of the product were 562 +/- 36 MPa and 22.5 GPa at room temperature. (C) 2014 Published by Elsevier B.V.