Fracture toughness of concentric Si3N4-based laminated structures

A new concentric rectangular laminated structure was designed and fabricated by slip-casting method and densified by pressureless sintering process. One class of laminates consists of layers of Si3N4 with 7 wt.% Y2O3 and 3 wt.% Al2O3 as sintering aids, and of interlayers consisting of 50 wt.% BN and 50 wt.% Al2O3 designated as SN-(BN + Al2O3). The other class of laminates has the same Si3N4 layer composition but different interlayer composition of 90 wt.% BN and 10 wt.% Si3N4 designated as SN-(BN + SN). The objective of this paper is to investigate the effects of the number of layers and their thickness on apparent fracture toughness of these laminates. The interfacial layer composition was discussed in terms of its role in toughening of the laminates. For the SN-(BN + Al2O3) laminates the highest apparent fracture toughness of 22 MPa m1/2 was found in the samples with 7 Si3N4 layers and for the SN-(BN + SN) laminates the highest apparent fracture toughness of 19.5 MPa m1/2 was found in the samples with 4 Si3N4 layers.