High-temperature fracture energy of superplastically forged silicon nitride

The fracture energy of superplastically forged silicon nitride, where rodli ke silicon nitride grains are aligned in one direction, was investigated at high temperatures from 1100 degrees to 1300 degreesC and at room temperatu re. Bending tests using chevron-notched beams were conducted at two displac ement rates, 0.05 and 0.005 mm/min. The superplastically forged silicon nit ride showed remarkably high fracture energies, 200-630 J/m(2). The fracture energy was largely dependent on the temperature and the displacement rate. The high fracture energy was attributed to grain pullout enhanced by the s oftened grain-boundary glassy phase and the aligned rodlike grains.