Influence of crack propagation path on the fracture toughness of polycrystalline Al2O3

Abstract

The influence of crack propagation path on the fracture toughness of polycrystalline Al2O3 was investigated. Polycrystalline Al2O3 with grain size from 1.8 μm to 50 μm 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 3.8 MPa√m at a grain size of 1.8 μm. It increased with the increase in grain size, and reached 4.5 MPa√m at grain sizes larger than 30 μm. 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 1.8 μm. It increased with the increase in grain size, and reached about 30% at grain sizes larger than 30 μm. 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 fracture toughness KIC of polycrystalline Al2O3 corresponded to the change in crack propagation path.