Effect of ZrB2 additions on the thermal stability of polycrystalline diamond

This study investigates the effect of ZrB$_2$ additions on the microstructure, thermal stability, and thermo-mechanical wear behaviour of polycrystalline diamond. Following high-pressure high-temperature (HPHT) sintering, the ZrB$_2$-PCD material showed a full conversion of the binder phase to cobalt-boride (Co2B and Co$₂₃$B$_6$) phases. In-situ PXRD and TEM vacuum annealing experiments observed that the onset of bulk graphitisation occurred above $1000^\circC$ for the ZrB$_2$-PCD material, compared to $850^\circC$ for the STD-PCD material. The ZrB$_2$-PCD tools showed excellent thermo-mechanical wear behaviour, exhibiting increased durability and a steady wear scar progression during high-temperature dry-VTL testing. However, lowered abrasion wear resistance was observed for the ZrB2-PCD tools during low-temperature wet-VTL testing, probably due the reduced diamond contiguity in the ZrB2 additive sample. Further optimisation of the ZrB$_2$ additive phase content, mixing methodology, or sintering conditions could be explored to improve the abrasive wear resistance of this novel PCD material.