Microscale rising <i>R</i> ‐curve behavior of silicon nitride ceramics

Abstract This study investigated R‐ curve behavior when a crack extended several 100 nm for Y 2 O 3 –Al 2 O 3 doped Si 3 N 4 ceramics, using single‐edge notched microcantilever beam specimens. The serrate or sawtooth behavior was observed around the maximum load of the load‐displacement diagram, indicating the repetition of crack initiation and arrest. The toughness plots with crack extension from the diagram resulted in a rising R ‐curve fitting into one smooth line, which showed a 1.4 MPa m 1/2 toughness increase during crack extension equivalent to one‐grain diameter. The maximum bridging stress calculated from the R ‐curve, approximately 1.8 GPa, was also close to the previous results, while the stress was estimated to rise more steeply than previously thought.