Fracture toughness evaluation of polycrystalline diamond as a function of microstructure

•Fracture toughness of polycrystalline diamond was investigated.•Variation in potential characteristic length scales was examined.•Physical interpretation of critical distance is non-trivial to justify.•Cobalt removal from polycrystalline diamond material reduces fracture toughness.

The fracture toughness of polycrystalline diamond has been investigated with reference to the microstructure. The physical interpretation of the critical distance is examined, and it is illustrated that this becomes increasingly difficult to define for larger grain sizes. Consequently, the minimum notch root radius becomes an important parameter governing the accuracy of toughness for blunt notched specimens. A higher than expected toughness was observed for fine grain specimens, illustrating the influence of the combination of both intrinsic and extrinsic fracture mechanisms on the overall toughness. Finally, the process of cobalt removal was found to reduce toughness compared to conventional grades.