Young's modulus, density and phase composition of pressureless sintered self-sealed Si3N4/BN laminated structures

New self-sealed Si3N4/BN-based laminated structures have been produced by a modified slip-casting process in a form of square cross-sections, varying the number of layers from 3 to 20 and their thickness from 70 to 1000 mu m. The composition of Si3N4 layers consists of 7wt.% Y2O3 (yttria) and 3 wt.% Al2O3 (alumina). The BN-based interfaces consist of 90wt.% BN and 10 wt.% Si3N4 in SN - (BN + SN) laminates and 50 wt.% BN and 50 wt.% Al3O3 in SN - (BN + Al2O3) laminates. Si3N4/BN-based laminates were densified by pressureless sintering at temperatures ranging from 1720 to 1820 degrees C for 1 h under static N-2 gas atmosphere. The highest density was achieved with samples having 3 Si3N4 layers in SN - (BN + SN) laminates and 5 Si3N4 layers in SN - (BN + Al2O3) with an average layer thickness of 260 and 320 mu m, respectively. Also, it was found that samples with the highest density exhibit the highest Young's modulus of 315 GPa in SN - (BN + SN) laminates and 320 GPa in SN + (BN + Al2O3) laminates. The microstructure of the (BN + Al2O3) interface consists mainly of YAG phase with BN and Si3N4 as minor phases, while the microstructure of the (BN + SN) interface consists of BN and Si3N4 as major phases. A much higher level of porosity was observed in (BN + SN) interfaces than in (BN + Al2O3) interfaces. Crown Copyright (c) 2007 Published by Elsevier Ltd. All rights reserved.