Fracture toughness of concentric Si 3N 4-based laminated structures

Abstract

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 Si 3N 4 with 7 wt.% Y 2O 3 and 3 wt.% Al 2O 3 as sintering aids, and of interlayers consisting of 50 wt.% BN and 50 wt.% Al 2O 3 designated as SN-(BN + Al 2O 3). The other class of laminates has the same Si 3N 4 layer composition but different interlayer composition of 90 wt.% BN and 10 wt.% Si 3N 4 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 + Al 2O 3) laminates the highest apparent fracture toughness of 22 MPa m 1/2 was found in the samples with 7 Si 3N 4 layers and for the SN-(BN + SN) laminates the highest apparent fracture toughness of 19.5 MPa m 1/2 was found in the samples with 4 Si 3N 4 layers.