Nano-polycrystalline Diamond Research Articles

Effect of micro-diamond and nano-polycrystalline diamond interfacial microstructure on OLC phase transition

The interfacial microstructure of micro-diamond and nano-polycrystalline diamond (nPCD), as well as their effect on the phase transition of complete structure onion-like carbon (OLC), were investigated using molecular dynamics simulations and experimental methods under high pressure and temperature (HPHT). Introducing micro-diamond disrupted the symmetric equilibrium structure of complete structure OLC, reduced the diamond nucleation process, and formed a coherent interface ((111)CD // (002)Gr), where cubic diamond (111) crystal plane was parallel to graphite (002) crystal plane. This transformed the initial diffusionless phase transition path of complete structure OLC into a low potential path for phase transition along the graphite crystal direction [002] by (111)CD // (002)Gr, thereby reducing the phase transition conditions. Additionally, due to different stacking orders or breakages in the graphite layers of the complete structure OLC, micro-diamond, and nPCD formed four interfacial microstructures containing twin boundaries (TB), cubic diamond, stacking fault (SF), and amorphous grain boundary (aB). Furthermore, under HPHT effects, numerous TBs and SFs were generated inside micro-diamonds as well as at their edges, resulting in a Vickers hardness of 167 GPa for polycrystalline diamond (PCD) composite. This simple yet effective method reduces synthesis conditions for OLC precursors while producing high-performance PCD composites with promising applications.

Kawai-type multianvil ultrahigh-pressure technology.

Since the large-volume press with a double-stage multianvil system was created by the late Professor Naoto Kawai, this apparatus (Kawai-type multianvil apparatus or KMA) has been developed for higher-pressure generation, in situ X-ray and neutron observations, deformation experiments, measurements of physical properties, synthesis of high-pressure phases, etc., utilizing its large sample volume and capacity in stable and homogeneous high temperature generation compared to those of competitive diamond anvil cells. These advancements in KMA technology have been made primarily by Japanese scientists and engineers, which yielded a wealth of new experimental data on phase transitions, melting relations, and physical characteristics of minerals and rocks, leading to significant constraints on the structures, chemical compositions, and dynamics of the deep Earth. KMA technology has also been used for synthesis of novel functional materials such as nano-polycrystalline diamond and transparent nano-ceramics, opening a new research field of ultrahigh-pressure materials science.

Discontinuous phase diagram of amorphous carbons.

The short-range order and medium-range order of amorphous carbons demonstrated in experiments allow us to rethink whether there exist intrinsic properties hidden by atomic disordering. Here we presented six representative phases of amorphous carbons (0.1-3.4g/cm3), namely, disordered graphene network (DGN), high-density amorphous carbon (HDAC), amorphous diaphite (a-DG), amorphous diamond (a-D), paracrystalline diamond (p-D), and nano-polycrystalline diamond (NPD), respectively, classified by their topological features and microstructural characterizations that are comparable with experiments. To achieve a comprehensive physical landscape for amorphous carbons, a phase diagram was plotted in the sp3/sp2 versus density plane, in which the counterintuitive discontinuity originates from the inherent difference in topological microstructures, further guiding us to discover a variety of phase transitions among different amorphous carbons. Intriguingly, the power law, log(sp3/sp2) ∝ ρn, hints at intrinsic topology and hidden order in amorphous carbons, providing an insightful perspective to reacquaint atomic disorder in non-crystalline carbons.

Dry etching of single-point cutting tool made of nanopolycrystalline diamond using oxygen plasma (Translated) (Shapeable cutting-edge radius)

Dry etching of single-point cutting tool made of nanopolycrystalline diamond using oxygen plasma (Translated) (Shapeable cutting-edge radius)

Self-Catalyzed Hydrogenated Carbon Nano-Onions Facilitates Mild Synthesis of Transparent Nano-Polycrystalline Diamond.

Transparent nano-polycrystalline diamond (t-NPD) possesses superior mechanical properties compared to single and traditional polycrystalline diamonds. However, the harsh synthetic conditions significantly limit its synthesis and applications. In this study, a synthesis routine is presented for t-NPD under low pressure and low temperature conditions, 10 GPa, 1600 °C and 15 GPa, 1350 °C similar with the synthesis condition of organic precursor. Self-catalyzed hydrogenated carbon nano-onions (HCNOs) from the combustion of naphthalene enable synthesis under nearly industrial conditions, which are like organic precursor and much lower than that of graphite and other carbon allotropes. This is made possible thanks to the significant impact of hydrogen on the thermodynamics, as it chemically facilitates phase transition. Ubiquitous nanotwinned structures are observed throughout t-NPD due to the high concentration of puckered layers and stacking faults of HCNOs, which impart a Vickers hardness about 140 GPa. This high hardness and optical transparency can be attributed to the nanocrystalline grain size, thin intergranular films, absence of secondary phase and pore-free features. The facile and industrial-scale synthesis of the HCNOs precursor, and mild synthesis conditions make t-NPD suitable for a wide range of potential applications.

Mechanism of phase transition from OLCs with different structures to nPCD at high temperature and high pressure

The molecular dynamics (MD) calculation and experimental research methods were used to study the phase transition from onion-like carbon (OLC) with and without a diamond crystal core to nano-polycrystalline diamond (nPCD) under high temperature and high pressure (HTHP) conditions. The results showed that the transformation from OLC to nPCD was mainly a diffusionless transformation at the heating stage and a diffusional transformation at the cooling stage. There were two main paths for diffusionless transformation from the OLC phase to nPCD. The path (PATH1) was that the diamond grew along the graphite crystal direction [002] with the coherent interface formed by the cubic diamond crystal plane (111) parallel to the graphite crystal plane (002). Another path (PATH2) was that the diamond grew along the graphite crystal direction [120] with the coherent interface formed by the cubic diamond crystal plane (11–1) intersecting the graphite crystal plane (002). The initial path of diffusionless transformation of OLC with and without a diamond core was PATH1 and PATH2, respectively. Increasing the PATH1 phase variable can reduce the sintering conditions of the OLC phase to nPCD. The twin boundary content of nPCD can be improved by increasing the grain size consistency of the OLC and the stacking faults density of the OLC structure.

Diamond-TiC composite with an ultrahigh Hugoniot elastic limit

The Hugoniot elastic limit (HEL) is widely adopted as an important criterion for assessing the dynamic strength of materials, representing the transition stress from elastic to plastic response prior to failure under shock compression. Nano-polycrystalline diamond currently holds the highest HEL of 208 (±14) GPa. Here, we report a diamond-TiC composite (∼11.5 wt. % TiC) showing an ultrahigh HEL of at least 195 (±3.5) GPa, which is comparable to that of nano-polycrystalline diamond. All measured velocity profiles on the diamond-TiC free surface exhibited a single-wave structure at shock pressures of 48–195 GPa. Moreover, the measured Us–Up (shock wave velocity–particle velocity) relation can be linearly fitted, indicating no elastic–plastic transition or solid–solid phase transition up to a shock pressure of 195 GPa. The diamond-TiC composite's compression ratio was similar to that of TiC but significantly higher than that of diamond. These extraordinary dynamic responses are intrinsically attributed to the unique microstructure in which diamond polycrystals are encased in a TiC matrix, providing protection against yielding. Our findings not only developed a mechanically reliable, lightweight, and high-performance armor material at low synthesis costs, but also provided new insights into the shock compression behavior of diamond composites.

Super Strengthening Nano‐Polycrystalline Diamond through Grain Boundary Thinning

AbstractIntroducing nanostructures into diamonds is quite appealing for the synthesis of superhard materials with superior properties. However, as the grain size decreases to nanoscale, grain boundary effects become crucial yet complicated in the nanopolycrystalline diamond (NPD), making it challenging to tailor nanostructures. Here, atomistic simulations are combined with experiment to demonstrate a strengthening strategy for the sintered NPD by introducing thin amorphous grain boundary (AGB). The additive of small percentage of fullerene into precursors during sintering can significantly reduce crushed amorphous‐like nanodomains in diamond nanocrystals, leading to the formation of thin AGB. Such sintered NPD exhibits a significant hardness and fracture toughness enhancement, exceeding that of single crystal diamonds. These atomistic simulations show that upon straining the plastic deformation, crack initiation and propagation in NPD is AGB thickness dependent, and thin AGB can reduce crack nucleation and block crack propagation, well explaining the experimental observations. This study indicates that grain boundary modulation provides a promising approach for rational designs of high‐performance superhard materials with desired high strength.

Cutting edge radius of single-point cutting tool made of nano-polycrystalline diamond and phenomenon generated in ultraprecision cutting of oxygen-free copper

Cutting edge radius of single-point cutting tool made of nano-polycrystalline diamond and phenomenon generated in ultraprecision cutting of oxygen-free copper

Control of Spindle Position and Stiffness of Aerostatic-Bearing-Type Air Turbine Spindle

Air turbine spindles with aerostatic bearings are widely used in ultraprecision machining equipment. Ultraprecision grinding processes using air turbine spindles with aerostatic bearings include constant-pressure dry lapping of nano-polycrystalline diamond (NPD) tools and ultraviolet irradiation polishing of chemical vapor deposition diamond films. In the dry lapping of NPD tools, it is necessary to achieve constant-pressure grinding while flexibly adjusting the contact force between the NPD tool and the truer fixed on the end face of the aerostatic spindle to form a nose bite with a cutting-edge rounding radius, R, of 0.1 nm. However, it is common for operators to manually adjust the cut depth and the air pressure supplied to the aerostatic bearing by relying on the noise and rotation speed during machining. Moreover, aerostatic spindles without a control mechanism, such as active bearings, are widely used because of their low costs and versatility. For several years, the authors have been developing a method to control air bearing stiffness by controlling the bearing supply pressure with high speeds and precision using a high-precision quick response regulator for aerostatic spindles without a control mechanism, such as active bearings. In this study, the compliance control (control of spindle position and stiffness) of aerostatic bearings was investigated using the proposed method, and the effectiveness of the method to ultraprecision grinding applications was demonstrated.

Micro-scale abrasion investigations of single-crystal diamonds using nano-polycrystalline diamond wheels

A small grinding wheel of 3.2 mm in diameter was prepared from nano-polycrystalline diamond (NPD) obtained by direct conversion sintering under high pressure and high temperature. Using this NPD wheel as a grinding blade, a new useful method for investigating the micro-scale abrasive properties of single-crystal diamonds was developed. Since NPD has an extremely high hardness of about 130 GPa, the abrasive properties of various natural and synthetic single-crystal diamonds, whose hardness is usually around 70 to 125 GPa, can be appropriately evaluated. In addition, since the wheel diameter is very small, it is possible to measure the abrasion resistance in a minute region of several tens of μm in a diamond crystal. It was confirmed that the method can accurately evaluate the abrasive properties of minute regions of single-crystal diamonds using synthetic type IIa diamond. It was also demonstrated that it is possible to investigate how the abrasive properties of synthetic type Ib and natural type Ia diamonds change depending on the distribution of impurities or crystal defects in the crystals.

Improvement of nano-polycrystalline diamond anvil cells with Zr-based bulk metallic glass cylinder for higher pressures: application to Laue-TOF diffractometer

ABSTRACT Single-crystal neutron diffraction provides direct information about crystal structures such as hydrogen positions and magnetic structures. However, in-situ experiments conducted under high pressure entail technical difficulties such as attenuation correction, masking of parasitic diffraction, and limitations of sample volumes and accessible directions. For this study, we improved diamond anvil cells with a tubular frame made of Zr-based bulk metallic glass and nano-polycrystalline diamond anvils for single-crystal neutron diffraction. The thicker tubular frame was confirmed through experimentation as stably generating 4.5 GPa. Its feasibility for neutron diffraction was assessed at the Laue-TOF diffractometer at the BL18 (SENJU) beamline in the MLF J-PARC using time-resolved two-dimensional detectors covering wide solid angles. In addition to ambient-pressure measurements of NH4Cl, diffraction patterns of a high-pressure phase of ice were also collected in-situ. The obtained intensities are of refinable quality sufficient for structure analysis.

Ultraprecision grinding of microdimple array mold made of cemented carbide using nano-polycrystalline diamond tool

Ultraprecision grinding of microdimple array mold made of cemented carbide using nano-polycrystalline diamond tool

Dry etching of single-point cutting tool made of nano-polycrystalline diamond using oxygen plasma (Shapeable cutting edge radius)

Dry etching of single-point cutting tool made of nano-polycrystalline diamond using oxygen plasma (Shapeable cutting edge radius)

Plastic Deformation and Strengthening Mechanisms of Nanopolycrystalline Diamond.

Bulk nanopolycrystalline diamond (NPD) samples were deformed plastically within the diamond stability field up to 14 GPa and above 1473 K. Macroscopic differential stress Δσ was determined on the basis of the distortion of the 111 Debye ring using synchrotron X-ray diffraction. Up to ∼5(2)% strain, Debye ring distortion can be satisfactorily described by lattice strain theories as an ellipse. Beyond ∼5(2)% strain, lattice spacing d111 along the Δσ direction becomes saturated and remains constant with further deformation. Transmission electron microscopy on as-synthesized NPD shows well-bonded grain boundaries with no free dislocations within the grains. Deformed samples also contain very few free dislocations, while density of {111} twins increases with plastic strain. Individual grains display complex contrast, exhibiting increasing misorientation with deformation according electron diffraction. Thus, NPD does not deform by dislocation slip, which is the dominated mechanism in conventional polycrystalline diamond composites (PCDCs, grain size >1 μm). The nonelliptical Debye ring distortion is modeled by nucleating dislocations or their dissociated partials gliding in the {111} planes to produce deformation twinning. With increasing strain up to ∼5(2)%, strength increases rapidly to ∼20(1) GPa, where d111 reaches saturation. Strength beyond the saturation shows a weak dependence on strain, reaching ∼22(1) GPa at >10% strain. Overall, the strength is ∼2-3 times that of conventional PCDCs. Combined with molecular dynamics simulations and lattice rotation theory, we conclude that the rapid rise of strength with strain is due to defect-source strengthening, whereas further deformation is dominated by nanotwinning and lattice rotation.

A STUDY OF FEMTOSECOND LASER POLISHING OF CVD NANOPOLYCRYSTALLINE DIAMOND FILMS

Femtosecond (fs) laser ablation has been recognized as an effective and promising technique for high-precision processing of natural and synthesized diamond. In this work, a study of femtosecond laser polishing for nanopolycrystalline diamond (NCD) films by chemical vapor deposition (CVD) is reported. The laser irradiation is induced by 200-fs laser pulses with a repetition frequency of 50[Formula: see text]MHz, and various laser fluences are employed to investigate their polishing effectiveness. The results show that the optimal laser fluence is 0.7[Formula: see text]J/cm2, at which the nanodiamond grains on top of the cauliflower-like clusters of NCD films can be ablated. With such laser fluence, the mean surface roughness of NCD films reduces from 73.84[Formula: see text]nm to 31.88[Formula: see text]nm, which presents a 57% reduction. Nevertheless, when the laser fluence rises beyond 0.7[Formula: see text]J/cm2, large amount of amorphous carbon (a-C) balls and porous lava-like morphology would come into being, resulting in severe degradation of the NCD surface.

Ultrahigh-pressure synthesis and applications of nano-polycrystalline diamond

Ultrahigh-pressure synthesis and applications of nano-polycrystalline diamond

Effect of sintering parameters on microstructure and properties of nanopolycrystalline diamond bulks synthesized from onion-like carbon

Additive-free nanopolycrystalline diamond (NPD) bulks were sintered from the onion-like carbon (OLC14) under industrial conditions of 4–6 GPa/1000–1400 °C/10–30 min. OLC14 was fabricated by annealing detonation nanodiamond (ND) at the conditions of 1400 °C/2 h/1 Pa (furnace cooling). The diamond content, average ND grain size, relative density and Vickers hardness of NPD bulk reached the maximum values of 81.56 wt%, 12 nm, 94% and 42 GPa sintered in the conditions of 5 GPa/1300 °C/20 min. Lots of nanotwins were formed in the NPD bulks due to the wrinkles and defects of OLC14 precursors. Because the carbon atom space and position of OLC14 spherical graphite layer was close to those of diamond, OLC14 could easily be transformed into ND, which grew larger and bonded with each other to form NPD bulks. The transformation of OLC14 into ND grain was martensitic transition. The sp3 carbon core of OLC14 as crystal seed had effect on this transformation. OLC14 with smaller grain size could be preferentially transformed into ND.

Shock Response of Full Density Nanopolycrystalline Diamond.

Hugoniot of full-dense nanopolycrystalline diamond (NPD) was investigated up to 1600GPa. The Hugoniot elastic limit of NPD is 208 (±14) GPa, which is more than twice as high as that of single-crystal diamond. The Hugoniot of NPD is stiffer than that of single-crystal diamond up to 500GPa, while no significant difference is observed at higher pressures where the elastic precursor is overdriven by a following plastic wave. These findings confirm that the grain boundary strengthening effect recognized in static compression experiments is also effective against high strain-rate dynamic compressions.

Development of a simulation method for three-dimensional shape generation by femtosecond laser ablation on binderless nano-polycrystalline diamond

One advantage of a femtosecond laser is that it enables the processing of materials that are otherwise difficult to process via conventional methods such as cutting, grinding, electric discharge machining, etc. However, it is difficult to predict a three dimensional shape processed by the laser. To achieve required three-dimensional shapes using femtosecond lasers with high accuracy and efficiency, it is essential to develop a computer-aided manufacturing (CAM) system that generates processing data (NC data). In this paper, a simulation method is proposed for femtosecond laser processing, which is the basis for the development of a CAM system. A binderless nano-polycrystalline diamond is used as the workpiece material to test the proposed method. Based on a comparison with the experimental results, it is confirmed that the processing shape could be simulated at a high accuracy for fixed-point irradiation as well as scanning irradiation.