1993 Volume 101 Issue 1180 Pages 1384-1389
The influence of crack propagation path on the fracture toughness of polycrystalline Al2O3 was investigated. Polycrystalline Al2O3 with grain size from 1.8μm to 50μm was fabricated by hot pressing. Fracture toughness KIC was measured by the controlled surface flaw method and the chevron notched beam method. The value of KIC by the CSF method was 3.8MPa√m at a grain size of 1.8μm. It increased with the increase in grain size, and reached 4.5MPa√m at grain sizes larger than 30μm. The value of KIC by the CN method nearly agreed to the value of KIC by the CSF method. The fraction of transgranular fracture was 10% at a grain size of 1.8μm. It increased with the increase in grain size, and reached about 30% at grain sizes larger than 30μm. The critical energy release rate calculated from KIC linearly changed depending on the fraction of transgranular fracture. Consequently, it was shown that the change in frature toughness KIC of polycrystalline Al2O3 corresponded to the change in crack propagation path.
