Creep of silicon nitride-titanium nitride composites

The effect of particulate TiN additions (0–50 wt%) on creep behaviour of hot-pressed (5 wt%Y₂O₃ + 2 wt%Al₂O₃)-doped silicon nitride (HPSN)-based ceramics was studied. Creep was measured using a four-point bending fixture in air at 1100–1340 °C. At 1100 °C, very low creep rates of HPSN with 0–30 wt% TiN are observed at nominal stresses up to 160 MPa. At 1200 °C the creep rate is slightly higher, and at 1300 °C the creep rate is increased by three orders of magnitude compared to 1100 °C and rupture occurs after a few hours under creep conditions. It was established that the formation of a TiN skeleton could detrimentally affect the creep behaviour of HPSN. An increase in TiN content leads to higher creep rates and to shorter rupture times of the samples. Activation energies of 500–1000 kJ mol^?1 in the temperature range of 1100–1340 °C at 100 MPa, and stress exponentsn?4 in the stress range 100–160 MPa at 1130–1200 °C were calculated. Possible creep mechanisms and the effect of oxidation on creep are discussed.