**3.1 Conventional high-pressure high-temperature (HPHT) technology**

The PCD material produced using traditional HPHT technology creates a unique superhard engineering tool material with high hardness, high wear resistance, and high impact resistance. PDC drill bits equipped with PDC cutters are widely recognized in oil and gas drilling due to their long drill life and ability to maintain high penetration rates (ROP) because the shear action of the fixed cutter on penetrating rock is more effective than crushing action of the roller cone bits. There are two main pressing technologies, including belt press and cubic press, which are currently used in the production of almost all synthetic diamond powders and sintered PCDs. Other techniques also exist, but due to the small size of the samples, their use is limited to research and development. The belt press was developed in the 1950s when GE successfully synthesized historically first man-made diamond crystals. Another important HPHT press technology is cubic press technology, which was originally developed as an alternative to generating diamond synthetic conditions, but it has been becoming the primary PDC manufacturing method. Diamond sintering requires extremely high heat and extremely high pressure, and metal systems use catalytic solvents to make the sintering process more economical (**Figure 5**). Typically, diamonds are sintered at temperatures around 1400°C. The source of the catalytic/solvent metal can be enhanced by an in-situ process that directly adds the original diamond powder or infiltrates from the substrate in a state where the catalytic/ solvent metal can flow with capillary force. The gap spacing of the diamond raw material is filled with a catalyst or solvent from the matrix, which sinters to bond adjacent diamond crystals together. Cobalt is commonly used as an adhesive phase for PDC presses.

At high temperatures and pressures, diamond-to-diamond bonding occurs, and the metal is relieved into diamond abrasive particles, which helps to catalyze the binding process. For catalytic/solvent metals to be effective, the temperature at which the carbon dissolves and re-precipitates must be reached. These temperatures typically exceed 1200°C [4, 12]. For catalytic solvent systems at active temperatures, diamonds are easily and significantly degraded to graphite at temperatures close to atmospheric pressure;

**Figure 5.** *P–T phase diagram of carbon showing conventional HPHT sintering region [4].*
