Static fatigue and fracture toughness of mullite ceramics at 1200°C

The fatigue behavior for mullite ceramics containing 71, 72 and 74 wt% Al 2 O 3 (71A, 72A and 74A) was measured at 1200°C by the static fatigue technique. The fracture toughness was evaluated from the slow crack growth magnitude (fatigue fracture surface) combined with the applied stress. The crack growth parameter (N) of 71A, 72A and 74A was 17, 23-24 and 26, and the fracture toughness (K IC ) was 4.3, 2.4 and 1.7 MPa.m 1/2 , respectively. These tendencies correspond to a decrease of the glass phase in the grain boundary. The fracture modes of the grains in the fatigue fracture surface for 71A was intergranular fracture in equiaxial crystals and transgranular fracture broken in the rod-like crystals, for 72A intergranular fracture in equiaxial crystals and transgranular fracture broken in slightly remained rod-like crystals, and for 74A only intergranular fracture (...)