Fracture toughness and crack bridging of a silicon nitride ceramic

Toughening processes and mechanisms of a gaspressure-sintered silicon nitride ceramic with s-phase rod-like microstructure are studied by the quantitative measurement of the R-curve in the form of the crack growth resistance, KR, versus the crack extension, Δa, KR being 4·3 M Pam 1 2 at crack initiation and then increasing to 6·5 M Pam 1 2 for its plateau value after a crack extension of about 1 mm. It is concluded that the toughness improvement of silicon nitride ceramics with rod-like microstructure arises from the crack bridging of the intact grains, but not from the crack-tip deflection and bowing processes which have been believed to date to be the key microfracture processes for toughening silicon nitride ceramics with ample rod-like s-phase grains.