Search

Diamond possesses a unique combination of excellent optical, thermal, and mechanical properties, and is therefore an ideal transparent ceramic material for harsh and extreme environments. Due to its important applications in technology, transparent diamond ceramic (TDC) has been explored and prepared by chemical vapor deposition (CVD) or direct conversions of non-diamond carbon precursors at high pressure and high temperature (HPHT), but the preparation of large-size TDC with high mechanical strength remains a challenge. Here, we report for the first time, a transparent polycrystalline diamond ceramic from diamond powder with a transmittance of ∼60 % at wavelengths of 400–1600 nm. The analyses of phase composition, residual stress and microstructure evolution of the sintered samples with different sintering conditions indicate that compression at high temperatures (>2000 ⁰C) facilitates the deformation of diamond grains, allowing for densification and diamond-diamond bonding formation. The sintering pressure of the diamond powders with an optimized particle size distribution was dramatically reduced from 16 GPa to 10 GPa. Our results, based on successfully preparing centimeter-sized TDC, set the standard and the precedent for the large-scale preparation of larger TDC in proximity to industrial conditions. [ABSTRACT FROM AUTHOR]

Single-phase BC4N can be formed at high pressure and temperature, starting with either a mixture of diamond and cubic boron nitride or graphite and hexagonal boron nitride. The samples exhibit extreme Vickers hardness (85±4GPa), reaching the hardness of single crystal diamond. Within a random solid solution model, the X-ray diffraction patterns of cubic BC x N solid solutions were calculated. The results indicate that the prepared B–C–N materials are continuous solid solutions with a zinc-blende structure. [Copyright &y& Elsevier]

Hardness is an important indicator of the wear resistance of tool materials. The study of the effect of hardness on the wear resistance of tool materials has significant practical applications. In this experimental work, a series of polycrystalline cubic boron nitride (PcBN) and diamond (PCD) compacts with different hardness are sintered under high temperature and pressure, and these samples were fashioned into turning tools, used for edge wear testing in the granite turning process. Based on the measurements above, the relationship between hardness and wear resistance in two materials with identical grain sizes (1–2 µm) was examined, and the results reveal a significant positive correlation between the hardness and wear resistance of the two materials. Remarkably, the relationship between hardness and wear resistance in two materials complies with the same type of fitting function. But incredibly, the wear resistance of the two materials exhibits inconsistency as the hardness increases. Specifically, below 40 GPa Vickers hardness, both materials exhibit comparable wear resistance. However, above 40 GPa, the difference in wear resistance between the two materials becomes more pronounced with increasing hardness. At the Vickers hardness of 70 GPa, the abrasion ratio of the PCD is approximately 3.5 times that of the PcBN, and it is anticipated that the disparity between them will continue to expand within the broader range of hardness. Further analysis reveals that the intrinsic hardness of the crystal grains significantly impacts the wear resistance of polycrystalline materials. [ABSTRACT FROM AUTHOR]

Micro-grained diamond-SiC composites have been prepared by sintering a mixture of micro-grained diamond and Si powder using high-temperature and high-pressure method at 1100–1500 ° C , and 5.5 GPa. Plate impact experiments in reverse—and forward—impact geometry were used to investigate the shock response of the micro-grained diamond-SiC composites within a shock pressure range from 22 to 195 GPa. The obtained plot of shock velocity (D) vs particle velocity (u) indicated that the double elastic wave responses are observed in the pressure range of 22–170 GPa, which is consistent with the previously reported diamond-SiC composites containing a small amount of tungsten carbide (WC) under shock compression up to ∼ 110 GPa [Li et al., J. Appl. Phys. 128, 245901 (2020)]. The results of shock experiments demonstrate that the Hugoniot elastic limit of micro grained diamond in SiC matrix is as high as 170 GPa, which is nearly twice as high as that of single crystal diamond. [ABSTRACT FROM AUTHOR]

The enhanced optical properties of chemical vapor deposited (CVD) diamond have been pursued in academia and industry for many applications. However, the barrier of CVD technology limits the application field of diamond. Herein, the performance of CVD polycrystalline diamond thick films was improved by high-pressure and high-temperature (HPHT) treatment. The microstructures of CVD polycrystalline diamond films before and after HPHT treatments were thoroughly examined using optical microscope, UV–visible and infrared absorption, Raman spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). It is found that the transparency of the CVD samples at 10 GPa increases dramatically with processing temperatures, from the original opacity to almost full optical transparency. Through spectroscopic and microstructural analyses, the modification mechanism of CVD polycrystalline diamond under HPHT conditions is proposed. The results show that the HPHT treatment can significantly enhance the optical properties of the starting CVD polycrystalline diamond films. [ABSTRACT FROM AUTHOR]

We have synthesized the well-performance bulk diamond–SiC composite by the high-temperature and high-pressure method and employed the light gas gun launched flyer plates to investigate shock compression response of the diamond–SiC composite. The plots of shock velocity vs particle velocity demonstrate the presence of double elastic waves in the diamond–SiC composite under shock compression. The first elastic wave travels at 13.1 ∼ 13.6 km / s and leads to yielding at ∼ 12.75 GPa. The second elastic wave propagates at 12.8 ∼ 13.0 km / s and does not display the yielding up to ∼ 110 GPa. Such a Hugoniot elastic limit is apparently higher than that of the single crystal diamond. The strengthening mechanism underlying the diamond–SiC composite has been discussed. By simulations of the lattice-spring model, the results revealed that under shock compression, the silicon carbide matrix yields first in the composite, resulting in damage to the substructure surrounding the diamond particles. This damage releases the intense shear stress and protects the diamond from severe crushing. Due to diamonds being hydrostatically confined by the silicon carbide matrix, both dislocation migration and slip band sliding are suppressed significantly, which enhances the strength of diamonds. [ABSTRACT FROM AUTHOR]

Although it has been nearly 70 years since iron-based catalysts were used to synthesize diamond from graphite at high pressure and high temperature (HPHT), the graphite to diamond transformation mechanism in this process is still a mystery. It is found that the formation of a eutectic melt between carbon and an iron-based catalyst plays a critical role in the graphite to diamond transformation at HPHT. In this work, the eutectic temperature of Fe–Ni–C (diamond and graphite) was determined using the in situ high-pressure temperature measurement (HPTM) and the high-pressure differential thermal analysis (HPDTA) method up to 8 GPa in a large-volume cubic press. The experimental results of XRD, Raman, SEM and XPS indicate that the transformation of graphite to diamond occurs in the Fe–Ni–C eutectic melt: the C–C bonds in graphite are broken in the eutectic melt, and the free carbon atoms in the melt form sp3 bond states in the thermodynamically stable region of diamond. In this process, the role of iron-based catalysts is to reduce the environmental conditions, in which the C–C bonds in graphite are destroyed, and to make the carbon atoms that are separated from the sp2 bond state form the sp3 bond state in the diamond P–T phase stable region. [ABSTRACT FROM AUTHOR]

Polycrystalline diamond composites (PDC) have been used as a cutting material in a multitude of fields, from mechanical processing to oil and gas drilling. In this study, PDC samples were prepared under high pressure and high temperature (HPHT) conditions within a pressure interval of 5.5 to 10.5 GPa by sintering diamond powder (average grain size ~3 μm) with WC-10 wt% Co substrate. Samples obtained with varying sintering pressures and temperatures were characterized using Vickers hardness tester, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that: (1) within a specified material system, each distinct sintering pressure condition corresponds to a unique optimal sintering temperature that yields the pinnacle of consolidation efficiency in samples. This optimal temperature exhibits a linearly increasing trend with rising sintering pressure; (2) at the intersection where the sintering pressure attains its optimal match with temperature, an increase in pressure fosters more intimate contact and stronger inter-grain bonding among diamond particles, thus amplifying the D D bond formation effect, which consequently leads to a linear enhancement in the Vickers hardness values of PDC with increasing sintering pressure; (3) simultaneously, under conditions of optimal temperature matching, elevating the sintering pressure notably decreases the cobalt content within the polycrystalline diamond layer of PDC samples. These findings furnish crucial experimental evidence for optimizing PDC material properties, significantly contributing to the advancement of both theoretical exploration and technological innovation within the field, carrying profound academic value and practical guidance implications. [Display omitted] • At a given pressure, there is an optimal temperature for the peak sintering performance of PDC. • The optimal sintering temperature exhibits a linear increase with rising pressure. • Under optimal temperature conditions, increased pressure improves sample performance. [ABSTRACT FROM AUTHOR]

Porous diamonds have unique application prospects due to their flexible surface functionalities, high surface-area-to-volume ratio and high self-sharpening ability. Porous diamonds are usually prepared through microwave plasma chemical vapor deposition (MPCVD) techniques or through etching by transition metals, which are expensive and inefficient. Here, we report a simple and efficient method to grow large millimetre-scale porous single-crystal diamonds using high-pressure and high-temperature (HP-HT) techniques. The porous diamond crystal growth is driven by minimizing the surface energy through the attachment of small crystals to a large seed crystal surface in a metal solvent. Industrial-scale production of single-crystal porous diamonds is possible with this discovery. The porous single-crystal diamond is prepared by using high pressure and high temperature (HP-HT) technology. XRD, SEM, Raman spectroscopy and HRTEM observations illustrated the high quality of the porous diamond surface layer and confirmed the obtained diamonds as porous single crystals. [Display omitted] [ABSTRACT FROM AUTHOR]

Diamond is the hardest naturally occurring material found on earth but single crystal diamond is brittle due to the nature of catastrophic cleavage fracture. Polycrystalline diamond compact (PDC) materials are made by high pressure and high temperature (HPHT) technology. PDC materials have been widely used in several industries. Wear resistance is a key material property that has long been pursued for its valuable industrial applications. However, the inevitable use of catalysts introduced by the conventional manufacturing process significantly reduces their end-use performance and limits many of their potential applications. In this work, an ultra-strong catalyst-free polycrystalline diamond compact material has been successfully synthesized through innovative ultra-high pressure and ultra-high temperature (UHPHT) technology. These results set up new industry records for wear resistance and thermal stability for PDC cutters utilized for drilling in the oil and gas industry. The new material also broke all single-crystal diamond indenters, suggesting that the new material is too hard to be measured by the current standard single-crystal diamond indentation method. This represents a major breakthrough in hard materials that can expand many potential scientific research and industrial applications. [ABSTRACT FROM AUTHOR]

Polycrystalline diamond in the presence of silicon with different sintering times was investigated under high pressure and high temperature of 5.0 GPa and 1400 °C, respectively, using a multi-anvil apparatus. In this research, phase analysis demonstrated that the content of SiC increased and the amount of Si decreased clearly with the sintering time extending by X-ray diffraction (XRD). The characterization of the sintered body demonstrated that the electrical resistance decreased as the reaction time rose. Specimens with good conductivity of 17 Ω·cm−1 sintered for 20 min at 1400 °C under 5.0 GPa were successfully obtained. The measured Vickers hardness and thermal stability of the synthesized diamond-SiC composites in the present study were >40 GPa and 1450 K, respectively. • Diamond–SiC composites were investigated by sintering different times in the range of 1–20 min at 5.0 GPa and 1400 °C. • SiC was densely packed between the diamond's grain boundaries, preventing the contact between the oxygen and diamond. • Extending the sintering time, and the graphitization of diamond occurred in low pressure zone are gradually in process. [ABSTRACT FROM AUTHOR]

Pure diamond compacts with submicron grain size were prepared by sintering diamond powder at 14.0 GPa and 1600–2000 °C using a multi-anvil apparatus. The synthesis conditions were much milder than those required when using graphite as the precursor. The sintered polycrystalline diamond (PCD) displayed excellent mechanical properties comparable to those of nano-polycrystalline diamond. The highest Vickers hardness measured for PCD was 125.0 GPa. During sintering, the small diamond grains between larger grains transformed into graphite first at moderate sintering temperature, and then the graphite transformed into diamond at 14.0 GPa and higher temperature. The large amounts of nano-twins and stacking faults inside the diamond grains contributed to the high Vickers hardness of PCD. [ABSTRACT FROM AUTHOR]

Pure diamond powder and mixed powder of diamond and sodium chloride were treated at high pressures (5 GPa and 10 GPa) and high temperatures (1000–2700 °C), and then the graphitization behavior of diamond powder under non-hydrostatic (pure diamond powder) and quasi-hydrostatic (mixed powder of diamond and sodium chloride) compression was quantitatively studied by analyzing the X-ray diffraction peaks' area of treated samples. It is found that the graphitization under non-hydrostatic compression is much more easily triggered by heating due to the heterogeneous stress distribution within the diamond grains. Under the quasi-hydrostatic compression of 5 GPa, the starting graphitization temperature is about 1600 °C, which is 300 °C higher than that under non-hydrostatic compression. Under a pressure of 10 GPa, graphitization could be observed after pure diamond powder was treated at 1400 °C, but no graphitization occurred in the mixed powder even after a high temperature treatment at 2300 °C. Optimizing the stress distribution among diamond grains by the mixing of grain-size can significantly reduce the graphitization at high temperature even under non-hydrostatic compression. [Display omitted] • Graphitization of diamond was quantitatively studied by x-ray diffraction peak areas. • The graphitization behavior of diamond is affected by stress state. • Higher temperature of graphitization is under quasi-hydrostatic compression of 5 GPa. • No graphitization occurs under quasi-hydrostatic compression of 10 GPa at 2300 °C. • The graphitization degree is greatly weakened by the mixing of grain-size. [ABSTRACT FROM AUTHOR]

The diamond thick layers prepared using chemical vapor deposition (CVD) methods have been treated at high pressures and high temperatures (HP-HT). It was found that the Vickers hardness of the HP-HT treated bulks was nearly two times as high as that of the starting CVD diamond samples. The hardness of the samples treated at 8 GPa and 1800°C is ∼80 GPa at a loading force of 49 N, close to that of the single-crystal diamond (∼100 GPa). In addition, the oxidation resistance of CVD diamond samples was also enhanced greatly after HP-HT treatments, and the diamondization of sp2bonded carbon in the CVD diamond samples could occur at 7–8 GPa and 1600–1800°C. The HP-HT conditions of diamondization in our works are much lower than the case of the graphite-to-diamond direct transformation without the presence of catalyst (>15 GPa and 2000°C). [ABSTRACT FROM PUBLISHER]

Well-sintered polycrystalline diamond composite (PDC) is a hard material obtained from WC–Co substrate and diamond using a high-temperature high-pressure (HPHT) process. PDC has immense potential in aerospace, automobile, oil and gas, and tool manufacturing industries. In this study, PDC was formed by sintering diamond powder (average crystal size = 10 μm) and WC–15 wt% Co substrates at HPHT and the diamond layer thickness is 1.2 mm. The thicknesses of the diamond layer on the PDC cutter were varied, and their effects on the PDC cutter wear were examined. Wear experiments and hardness tests were conducted on samples with varying diamond layer thicknesses. They were characterized using scanning electron microscopy, X-ray diffraction, and Hall effect, and these revealed that (1) hardness of the PDC slightly increased with an increase in the thickness of the diamond layer, and (2) the PDC tool's life could be improved by appropriately increasing the thickness of the diamond layer. The findings of this study provide insights for future studies on designing and optimizing the properties of the PDC. [Display omitted] • Effect of diamond layer thickness on the wear rate of polycrystalline diamond composite (PDC) • PDC formed with diamond powder and WC-15 wt% Co substrate at HPHT. • PDC tool's life increased with increase in thickness of the diamond layers. [ABSTRACT FROM AUTHOR]

The design of high-strength and high-toughness materials that can sustain high shock-wave loadings is crucial for both armor and civil applications. We propose a bioinspired diamond composite that mimics the brick-and-mortar arrangement of nacre from mollusk shells and evaluate its performance for different diamond brick contents using lattice-spring model. In this work, we present a systematic investigation elucidating the effects of volume fraction of diamond brick, on the shock compression response of bioinspired diamond composites. By comparing the nacre-like diamond composite with traditional diamond composite, it was found that the nacre-like diamond composite can reduce damage degree in diamond composite, and improve dynamic strength of diamond composite. More importantly, the damage evolution analysis of the impacted nacre-like diamond composite indicated that there is large-scale crack deflection, which is only cause slight damage to the diamond brick. The obtained numerical results may provide valuable insights into the preparation of superhard composites for numerous engineering applications. • Superhard diamond composites with a nacre-like architecture were designed. • Macroscopic shock-wave propagation and mesoscopic damage evolution were analyzed. • The nacre-like diamond composites exhibited reduced localized damage under shock compression. • The nacre-like diamond composites displayed improved dynamic strength. [ABSTRACT FROM AUTHOR]

The thickness of the silicon carbide layer around diamond grains in the reaction sintering process of diamond/SiC composites starting from diamond and silicon was investigated at 1100–1400 °C and 5 GPa using two different sample assemblies. Dense silicon carbide layers with thicknesses from 60 nm to 350 nm were observed using energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) analysis. This demonstrated that the thickness of the silicon carbide layer increased with increasing sintering temperature and time. The surface morphology of diamond grains/single-crystal diamond wafers eroded by liquid silicon was analysed by field emission scanning electron microscopy (FESEM), and it was found that SiC growth was controlled by the diffusion of silicon and carbon atoms through the existing layer of SiC. [Display omitted] • The thickness of silicon carbide layer around diamond grains was measured at 1100–1400 °C and 5 GPa. Dense silicon carbide layers with thicknesses from 60 nm to 350 nm were observed using EDS and XRD analysis. • The thickness of silicon carbide layer increased with the increase of temperature and SiC growth was controlled by the diffusion of silicon and carbon atoms through the existing layer of SiC. • The quantitative data of the thickness of silicon carbide layer around diamond under high pressure is reported for the first time. [ABSTRACT FROM AUTHOR]

The stability and solubility of diamond in cobalt at a pressure of 5 GPa was investigated. At temperatures ranging from 1000 °C and 1350 °C, diamond can be dissolved in cobalt without graphitization. Meanwhile, the solubility of single diamond crystals in cobalt was measured at 5 GPa and temperatures of up to 1300 °C through weight analysis, and it was found to increase with the increase in temperature. The morphological changes of the diamond crystals after high-pressure and high-temperature (HPHT) treatments were observed using a scanning electron microscope. The resulting quantitative data and morphology analysis enabled the construction of a scheme for the morphological evolution of diamond crystals during their dissolution in cobalt at HPHT. The diamond formation process in cobalt solvent is discussed in relation to the dynamic equilibrium. Unlabelled Image • The solubility of diamond in cobalt was measured at 5.0 GPa and high temperatures up to 1300 °C. The temperatures region of diamond growth at 5 GPa is determined. • The solubility of diamond in cobalt increased with the increase of temperature and the diamond formation in metal solvents is a process of the dissolution and precipitation of carbon atoms. • The quantitative data of solubility of diamond in cobalt under high pressure is reported for the first time, which provides favorable evidence of solvent theory. [ABSTRACT FROM AUTHOR]