The influence of a strong/weak interface ratio on the mechanical properties
of Si3N4/BN-based layered composites was studied. The ratio was controlled
by the number of BN spots between the adjacent Si3N4 layers. By increasing
the BN interface area from 0% to 72%, fracture toughness increased from 7.
7 to 10.9 MPa.m(1/2), and bending strength decreased from 1275 to 982 MPa.
Fracture toughness was improved from 8.6 to 10.1 MPa.m(1/2) by additional h
eat treatment of samples containing 2 vol% beta-Si3N4 seed particles. The b
ending strength of samples with 35% weak BN interfaces, measured perpendicu
lar and parallel to layer alignment, was 1260 and 1240 MPa, respectively. T
his confirmed the two-directional isotropy of layered samples.