Utilizing a HPHT Hydraulic Cubic Press for producing large-diameter PCD compacts primarily involves the following four key technologies: raw material selection; formula, mixing, and purification treatment; assembly structure design; and high-temperature, high-pressure sintering process. Optimizing and improving these four key technologies can enhance the yield and quality of large-diameter PCD compacts.

1. Main Raw Material Selection
The quality of raw materials directly affects the performance and yield of PCD compacts.
A、Diamond Micron Powder
Cleanliness is key: It determines the defects and sintering quality of the diamond layer in the compact. Non-diamond particles, impurities on the diamond surface, and non-metallic components within the diamond can cause pinholes, impurity enrichment [Figure 1(a)], and a reduction in the bonding ratio of the diamond layer, significantly lowering the quality of the PCD compact.
Selection requirements: The premise for synthesizing high-quality PCD compacts is to select diamond micron powder with low content of non-catalytic impurities and clean particle surfaces [F.

B、Cemented Carbide Substrate
Function: During the use of PCD compacts, the cemented carbide substrate primarily provides support for the diamond layer.
Key influencing factors: The cobalt content, free carbon, and strength indicators in the cemented carbide are important factors affecting PCD stress and performance.
Free carbon: If the cemented carbide contains free carbon, it will grow into diamond within the cemented carbide under the catalytic action of cobalt during the PCD sintering process. This leads to the PCD being prone to overall fracture during use.
Excessively low cobalt content: This increases the brittleness of the cemented carbide, leading to PCD being prone to overall fracture.
Excessively high cobalt content or low strength: This can cause large-area spalling or delamination of the diamond layer when the PCD compact is used in high-impact environments. Moreover, excessively high cobalt content can further widen the difference in thermal expansion coefficients between the cemented carbide substrate and the diamond layer, leading to the easy formation of cracks in the diamond layer of the sintered PCD compact.
Selection requirements: Therefore, the key to selecting a cemented carbide substrate is reasonable cobalt content, absence of free carbon, and high strength.

C、High Melting Point Metal Shielding Cup
Function: To prevent external impurities from contaminating the PCD and to prevent cobalt from leaking out of the cemented carbide and the diamond layer.
Selection principles:
Structure and size: Must ensure uniform and enclosed loading.
Material: The metal used must have a eutectic temperature with cobalt and carbon that is higher than the PCD high-temperature, high-pressure sintering temperature.
Performance: It should have good shielding properties and a certain oxygen absorption and purification effect under high temperature and high pressure.
Plastic deformation ability: It should have good plastic deformation ability to prevent rupture during the ultra-pressure synthesis process, which could lead to external impurities contaminating the PCD compact.

2. Formula, Mixing, and Purification Treatment
These steps directly influence the uniformity of the PCD microstructure and the final product performance.
A、Formula：
Influencing factors: The formula of the diamond layer in a PCD compact is the main reason affecting the wear resistance, toughness, heat resistance, conductivity of PCD, and the surface finish of the machined workpiece.
When diamond particle size and grade are similar: PCD compacts with low metal content exhibit high wear resistance and heat resistance, low toughness, and difficulty in electrical discharge machining.
When metal content is similar: The finer the diamond particle size, the lower the wear resistance and heat resistance of the PCD compact, but the better its toughness and electrical discharge machining performance, and the higher the surface finish of the machined workpiece.
When formulas are identical: The higher the impact strength of the diamond, the higher the wear resistance of the PCD compact.
Optimization: A reasonable combination of diamond micron powders with different particle sizes can, to a certain extent, improve the product's wear resistance and toughness.
B、Mixing
Criticality: The purity, particle size, and dispersion degree of the metal binder in the diamond layer of a PCD compact are key factors affecting the uniformity of the PCD microstructure and the ultimate performance of the PCD compact.
High-grade PCD: In high-grade PCD compacts, the metal binder and diamond are highly dispersed, and metal particles are finely and uniformly distributed (Figure 2). This results in stable cutting, strong consistency in the surface finish of the machined workpiece, and stable and reliable service life.
Low-grade PCD: Low-grade PCD compacts generally have larger metal particles (Figure 3) and uneven metal distribution. This leads to increased friction and diamond particle shedding during use, which can cause localized reduction in surface finish and scratching of the machined workpiece. Such products can only be used in applications with low processing requirements, such as woodworking.
Mixing problems: The mixing methods commonly used in the industry often lead to uneven metal distribution. Due to the large difference in specific gravity between the metal binder and diamond, the metal binder tends to accumulate at the bottom and corners of the mixing barrel. Furthermore, repeated impacts from mixing balls can cause plastic deformation of the metal binder, with some particles sticking together to form larger particles. The difference in relative density can also easily lead to stratification of metal and diamond particles during loading, resulting in uneven distribution of the metal binder within the diamond layer.
Solution: Developing new mixing technologies to solve these problems is crucial for manufacturing high-grade large-diameter PCD compacts.
C、Purification Treatment
Purpose: After mixing and weighing, the material must undergo high-vacuum purification treatment. The main purpose is to eliminate organic residues that may have been introduced during the cleaning of the cemented carbide and metal shielding cup.
Process requirements: The vacuum purification treatment temperature should not exceed 600℃, and the vacuum chamber pressure should be no higher than 8×10⁻³ Pa. Before being removed from the furnace, inert gas protection must be employed to prevent oxidation of the metal binder.
3. HPHT Hydraulic Cubic Press High-Temperature and High-Pressure Assembly Structure Design
The overall integrity, deformation degree, and sintering uniformity of PCD compacts primarily depend on the pressure distribution, pressure transfer method, temperature field uniformity, and heating consistency during the synthesis process.
A、Challenges for HPHT Hydraulic Cubic Presses
Compared to two-sided presses, when synthesizing with high temperature and high pressure, the six top hammers of a HPHT Hydraulic Cubic Press move simultaneously towards the center, gradually compressing the pyrophyllite block to establish a sealed cavity. This causes the cylindrical core rod to be squeezed and transform into a square shape, resulting in irregular deformation.
The assembly structure of the HPHT Hydraulic Cubic Press adopts an inner-circle and outer-square insulation layer, leading to significant thickness differences in the insulation layer and non-uniform temperature fields.
Therefore, synthesizing large-diameter PCD compacts with a HPHT Hydraulic Cubic Press must address the issues of large deformation in the synthesis cavity and non-uniform temperature fields. The difficulty in solving these issues is significantly higher than with two-sided presses, which is the main reason for the large quality gap between large-diameter PCD compacts synthesized by domestic HPHT Hydraulic Cubic Presses and foreign two-sided presses.
B、Assembly Design Principles:
Design of conductive plugs, heaters, and carbon tubes: This is crucial for determining the uniformity of PCD compact sintering during the synthesis stage.
Design requirements: It must ensure that the axial and radial temperature difference of the compact and spacer parts is less than 4℃ during the high-pressure holding stage, and that the temperature difference between various parts of the compact is small during the heating process. During the heating process above 800℃, the temperature difference between the highest and lowest temperature regions within the cavity must not exceed 100℃.
Unreasonable consequences: An unreasonable temperature field distribution can lead to significant performance differences in PCD compacts at different locations within the cavity, and even cause phenomena such as edge chipping, surface cracks, delamination, fracture, and localized over-sintering or under-sintering of the PCD compact.
Assembly structure for uniform pressure transfer and prevention of PCD compact deformation: This is another critical design for synthesizing large-diameter PCD compacts using a HPHT Hydraulic Cubic Press.
Optimization method: By rationally selecting the formula and size of the insulating tube, the material of the spacers, and the material and size of the plugs (Figure 4), it is possible to not only improve the thickness uniformity of the diamond layer and reduce edge chipping of the PCD compact's diamond layer, but also to solve the problem of cemented carbide substrate fracture during the over-pressure process and reduce the residual stress in the synthesized PCD compact.
Reducing the probability of pressure release explosion: During the synthesis of large-diameter PCD compacts, the poor elasticity of the internal cavity materials can easily lead to pressure release explosions. A reasonable internal assembly structure can significantly reduce the probability of pressure release explosions, which is also a necessary consideration in assembly design.
4. High-Temperature and High-Pressure Sintering Process
The sintering process is a critical step in the formation of PCD compacts.
A、Pressure and Temperature
Pressure: Pressure is the fundamental condition that determines the temperature range and diamond bonding.
Binder: Cobalt is typically used as the binder for the diamond layer in PCD compacts.
Temperature determination:
Co-C eutectic temperature: The Co-C eutectic temperature is 1320℃ at atmospheric pressure (Figure 5). Considering the effect of high pressure on metal melting points and the need for diffusion, the high-temperature, high-pressure synthesis temperature generally needs to exceed 1350℃ to ensure the cobalt within the diamond layer exists in a liquid state.
Enhancing bonding strength: To improve the bonding strength between the diamond layer and the cemented carbide substrate, cobalt from the substrate needs to diffuse into the diamond layer to some extent. The WC-Co eutectic temperature is 1340℃ (Figure 6). Considering the high-pressure effect, to enhance the holding strength between the diamond layer and the cemented carbide, the synthesis temperature generally should not be lower than 1360℃.
Preventing cobalt enrichment: At the same time, appropriately controlling the cobalt content at the interface between the diamond layer and the WC-Co layer, especially preventing cobalt enrichment at the interface, is beneficial for improving the thermal stability of PCD materials. Therefore, the synthesis temperature should not be excessively high.
Optimal temperature range: Considering the temperature distribution within the cavity, diffusion requirements, sintering efficiency, and preventing cobalt from the cemented carbide from leaking outside the metal shielding cup during the synthesis stage (which could embrittle the cemented carbide), a sintering temperature of 1400～1500℃ is appropriate.
Corresponding pressure: Under these temperature conditions, an internal cavity pressure of 5.6～6.0GPa is relatively suitable, while also considering the wear of the top hammers.
B、Process Curve Design Principles:
Heating pressure: The heating pressure should be moderate; excessively low pressure during heating can cause the diamond in the PCD compact to revert.
Heating before sintering: Heating before the start of sintering is very important; a good design can quickly equalize the temperature field.
Holding time: The holding time should ensure sufficient diffusion of the metal binder but should not be too long. Otherwise, it can lead to abnormal diamond growth, increased surface cracks in PCD, and spalling of the cemented carbide base.
Cooling and depressurization: To reduce internal stress in PCD, it is best to use a process control curve that involves slow, simultaneous cooling and depressurization.
Through the research, development, and improvement of these four key technologies, the HPHT Hydraulic Cubic Press can not only significantly increase the yield of large-diameter PCD synthesis but, more importantly, can enhance the stability and overall quality of PCD products.