Young's modulus, density and phase composition of pressureless sintered self-sealed Si 3N 4/BN laminated structures

Abstract

New self-sealed Si 3N 4/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 μm. The composition of Si 3N 4 layers consists of 7 wt.% Y 2O 3 (yttria) and 3 wt.% Al 2O 3 (alumina). The BN-based interfaces consist of 90 wt.% BN and 10 wt.% Si 3N 4 in SN − (BN + SN) laminates and 50 wt.% BN and 50 wt.% Al 3O 3 in SN − (BN + Al 2O 3) laminates. Si 3N 4/BN-based laminates were densified by pressureless sintering at temperatures ranging from 1720 to 1820 °C for 1 h under static N 2 gas atmosphere. The highest density was achieved with samples having 3 Si 3N 4 layers in SN − (BN + SN) laminates and 5 Si 3N 4 layers in SN − (BN + Al 2O 3) with an average layer thickness of 260 and 320 μm, 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 + Al 2O 3) laminates. The microstructure of the (BN + Al 2O 3) interface consists mainly of YAG phase with BN and Si 3N 4 as minor phases, while the microstructure of the (BN + SN) interface consists of BN and Si 3N 4 as major phases. A much higher level of porosity was observed in (BN + SN) interfaces than in (BN + Al 2O 3) interfaces.