Young's modulus, density and phase composition of pressureless sintered self-sealed Si_3N_4/BN laminated structures

摘要

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 mu m. The composition of Si_3N_4 layers consists of 7 wt. percent Y_2O_3 (yttria) and 3 wt. percent Al_2O_3 (alumina). The BN-based interfaces consist of 90 wt. percent BN and 10 wt. percent Si_3N_4in SN - (BN + SN) laminates and 50 wt. percent BN and 50 wt. percent 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 deg 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 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 + 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.