Slow crack growth behavior in Si3N4 sintered with Yb2Si2O7 tie-line composition additives

Slow crack growth behavior of two gas pressure sintered Si3N4 ceramics with different additives; a Yb2Si2O7 composition and an Al2O3–Y2O3 composition, was investigated by constant stress-rate (“dynamic fatigue”) testing at 1400°C. The slow crack growth parameter, n, was 14.7 and 6.3 for Si3N4 with Yb2Si2O7 and Al2O3–Y2O3 compositions, respectively. Superior crack growth resistance of Si3N4 with Yb2Si2O7 composition was due to its higher refractoriness of intergranular glassy films, compared to Si3N4 with Al2O3–Y2O3 composition.