Fracture toughness (K(sub Ic) and gamma wof) of a HIPed Si3N4 at elevated temperatures

Chevron-notched bend bars of a hot isostatically pressed (HiPed) silicon nitride (PY6) were tested in three-point flexure in air at 25, 1000, 1200, 1300, and 1400 C. Stable crack growth was consistently produced at all the test temperatures. Average fracture toughness, K(sub Ic), and work of fracture, gamma(sub wof), decreased from 6.4 MPa(sm bullet)(radical)m and 52 J/sq m, respectively, at 25C to 4.5 MPa(sm bullet)(radical)m and 44 J/sq m at 1200 C; a 29 percent and 15 percent decrease in K(sub Ic) and gamma(sub wof). Tests conducted at 1300 C and 1400 C activated high temperature deformation mechanisms, which effectively caused greater specimen ductility and apparent greater fracture resistances. At 1400 C, K(sub Ic) and gamma(sub wof) were 6.5 MPa(sm bullet)(radical)m and 159 J/sq m, respectively.