Analysis of the structure and magnetic behaviour of cobalt phase in polycrystalline diamond compacts

Abstract

Three variants of Polycrystalline Diamond (PCD) cutters were manufactured by High Pressure and High Temperature (HPHT) with varying diamond grain sizes ranging from 4 to 25 μm with a Tungsten Carbide (WCCo) substrate base. The structure and magnetic profiles of the PCD tables were analysed using KOERZIMAT 1.097 MS, Scanning Electron Microscopy (SEM), Image Analysis (IA), and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). The study revealed that the size of the PCD table specimen does not impact the magnetic saturation. A relationship was observed between the amount of metal phase and the magnetic saturation level and the cobalt mean-free path and coercivity were found to be correlated. The PCD layers separated from the substrates revealed that larger diamond compact grain sizes decrease metallic cobalt phase magnetic domains. However, this also leads to a decrease in coercivity due to a decrease in cobalt content. In addition, it is worth noting that the dissolved tungsten (W) remained constant in all three variants. This indicates that the diamond grain size and the presence of the cobalt phase did not impact the amount of dissolved W during the synthesis process. The starting fine grain size (average of 4 μm) led to a magnetic saturation value of 15.56 % after sintering, medium grain size (average of 13 μm) with a saturation value of 13.88 %) while the coarse grain size (average of 25 μm) resulted in a magnetic saturation value of 11.86 %. The observed phenomena can be explained by the increased size of the diamond grains, which leads to a decrease in the cobalt concentration.