Relationship between Microstructure, Toughening Mechanisms and Fracture-Toughness of Reinforced Silicon-Nitride Ceramics

Different microstructures in Si3N4 ceramics containing Y2O3 and Al2O3
as sintering additives were prepared by two-step sintering, Pull-out
and elastic bridging were most frequently observed as the toughening
mechanisms in samples with fine-grained microstructures having
needlelike beta-Si3N4 grains with diameters of <1 mu m. Crack
deflection was the main toughening mechanism observed in samples with
coarse-grained microstructures having grains with diameters of >1 mu m.
The values of fracture toughness mere varied from 6.1 to 8.2 MPa .
m(1/2) with respect to the microstructural characteristics,
characterized by the volume fraction of needlelike grains and their
diameter.