Effect of loading rate on the fracture toughness and failure mechanisms of polycrystalline diamond (PCD)

•Quasi-static and dynamic fracture toughness of polycrystalline diamond was measured.•Influence of secondary cobalt phase investigated.•Cobalt phase has negative influence on measured fracture toughness at high rates.

Quasi-static and dynamic fracture toughness tests are performed on four grades of PCD to evaluate the effect of rate and identify dominant failure mechanisms. The results indicate that the presence of the secondary phase cobalt has a significant negative influence on the fracture toughness of PCD grades at high rates of loading. An apparent rate insensitivity was exhibited for coarse grain specimen, where appreciable amounts of secondary phase cobalt were removed, or leached from the crack-tip region. The beneficial effect of cobalt removal on dynamic toughness was observed to be dependent on grain size, with fine grain microstructures exhibiting a similar negative rate sensitivity to corresponding non-leached grades. SEM analysis was used to evaluate the resulting fracture surfaces of both static and dynamic fractured specimens. The effect of rate on the prevailing fracture mode was analysed using a dynamic fracture mechanics approach.