After indentation, the length of each of the two diagonals of the square-shaped Vickers
indentation was immediately measured by optical microscopy with a magnification of 500.
The values of the Vickers hardness were calculated, by the following equation:
The KIC values were determined using the direct crack measurement method. The Palmqvist
crack model equation was used to compute the fracture toughness (KIC). The Young's
modulus for high purity alumina ceramics is 386 GPa. The arithmetic mean of the all
measured c length (10 impressions) was 42 µm.
The calculated fracture toughness (KIC) value according to equation (2) is 2.69 MPa m