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

New self-sealed Si3N4/BN-based laminated structures were 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 micron. The composition of Si3N4 layers consisted of 7 wt% Y2O3 and 3 wt% Al2O3. The BN-based interfaces consisted of 90 wt% BN and 10 wt% Si3N4 in SN-(BN + SN) laminates and 50 wt% BN and 50 wt% Al2O3 in SN-(BN + Al2O3) laminates. Si3N4/BN-based laminates were densified by pressureless sintering at temperatures ranging from 1720 to 1820 C for 1 h under static N2 atmosphere. The highest density was achieved with samples having three Si3N4 layers in SN-(BN + SN) laminates and five Si3N4 layers in SN-(BN + Al2O3) with an average layer thickness of 260 and 320 micron, respectively. Samples with the highest density exhibited 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 consisted mainly of YAG phase with BN and Si3N4 as minor phases, while the microstructure of the (BN + SN) interface consisted of BN and Si3N4 as major phases. A much higher level of porosity was observed in (BN + SN) interfaces than in (BN + Al2O3) interfaces. 22 refs.