Single Diamond Research Articles

Numerical study on optimal impact angle of a single PDC cutter in impact rock cutting

In previous work (Liu et al., 2020), we studied the differences between conventional rock cutting and cutting with compound vertical and horizontal impact force. In this work, we investigated the relationship between the impact force direction and cutting efficiency, which is the key to the impactor design. We established an impact rock cutting model with a single sharp polycrystalline diamond compact (PDC) cutter, and the direction of the impact force was described by an impact angle (β), which ranged from 0 to 90°. Simulations with different β were conducted, and the fragmentation process, forces, and mechanical specific energy (MSE) were analyzed. We also investigated the effects of the amplitude and duration of the impact forces on the MSE. The results showed that there is an optimal β, for which the MSE is the lowest and cutting efficiency is the highest. The effects of the vertical and horizontal impact forces on the rock cutting process were different, and excessive vertical or horizontal impact forces were not conducive to improving the cutting efficiency. The optimal β decreased with an increase in the impact amplitude, and a similar relationship was found between the optimal β and the duration of the impact force. In practice, designers are suggested to set the β of the impactor between 30° and 60°, and a lower β may be necessary to adapt to a higher impact amplitude and lower frequency.

Single diamond scribing of SiCf/SiC composite: Force and material removal mechanism study

SiC fiber-reinforced SiC ceramic matrix (SiCf/SiC) is an advanced high-temperature material widely used in the heat-resistant componets of the aerospace engine and nuclear reactor, which are generally precisely ground to achieve the designed dimensional and geometrical tolerances. This research investigates the scribing force and material removal mechanism of 2.5D woven SiCf/SiC with the flat and sharp diamond grits, which present the new dressed and worn grinding wheel. The results show that the sharp grit has larger wear on the cutting edge and generates lower force than that of the flat grit at the same scribing depth and groove cross-section area. In both sharp and flat grits, the SiC matrix is mainly removed by the fracture cracks, peeling off, fiber exposure and powdering. In transverse diamond scribing of the SiCf, the fiber debonding and shear breakage are dominant removal feature for the flat grit scribing. Two additional removal patterns, the ductile scratch and fiber cracking, are observed for the sharp grit. In parallel diamond scribing of the SiCf, the shear and bending fractures in the cut-in and cut-out points are two key material removal modes, respectively, especially in the fiber woven structure. This research provides a fundamental understanding of interaction force and the material removal process of SiCf/SiC in grinding.

Experiment and Smooth Particle Hydrodynamics Simulation for the Wear Characteristics of Single Diamond Grit Scratching on Sapphire

Abrasive single crystal diamond (SCD) grit is widely used in the machining process of sapphire. The wear of SCD grit has a significant influence on the surface quality of sapphire. In this paper, smooth particle hydrodynamics (SPH) method is employed to reveal the wear mechanism of SCD grit with Steinberg constitutive equation and Grüneisen state equation. The wear morphology, wear volume and scratching forces are measured and analyzed by combination of SPH simulations and experiments. The results show that the scratching forces fluctuate in a certain range and decrease with the increasing of workpiece material removal volume. Different degrees of cleavage and fracture appear in the front and rear of SCD grit. The shear stress and extrusion stress are the main stresses of SCD grit during the scratching process. The wear progress and wear form are mainly determined by the stress state. Different stress state leads to different wear progress of the SCD grit. The SPH method is able to reflect and illustrate the wear characteristics of SCD grit scratching on sapphire.

Multiple metasomatic diamond-forming events in a cooling lithosphere beneath Voorspoed, South Africa

Thermal events and metasomatic processes have influenced the Kaapvaal craton in South Africa. High-density fluids (HDFs) trapped as microinclusions in diamond are main metasomatic agents which provide an insight to these processes in the Earth's mantle. Here we present data for 15 fibrous, HDF-bearing diamonds from the Voorspoed mine, South Africa, reflecting multiple diamond-forming events in a cooling lithosphere. Analyzed by FTIR and EPMA, the Voorspoed fibrous diamonds reveal three populations that differ in their nitrogen aggregation and HDF composition. A silicic‑carbonatitic group containing 11–30% B-centers, a saline group containing 5–16% B-centers, and a single high-Mg carbonatitic diamond with 0% B-centers. The distinct nitrogen aggregation of the fibrous diamond groups in Voorspoed and the lack of clear major element evolutionary trends for each HDF type or intermediate compositions between the different types suggest different time-temperature formation histories. Thermobarometry of mineral inclusions in non-fibrous monocrystalline Voorspoed diamonds (Viljoen et al., 2018) indicates that the Voorspoed lithosphere cooled by 100–200 °C since their host diamonds crystallized at high initial temperatures. High temperatures in Voorspoed lithosphere can be correlated with the eruption of the Ventersdorp flood basalts at the central Kaapvaal (ca. 2.7 Ga) or the Bushveld complex (ca. 2.06 Ga), and cooling rates of the lithosphere provide a time frame for a cooling process that originated ~2–3 Ga. Combining these data with the nitrogen aggregation systematics of fibrous and monocrystalline Voorspoed diamonds, we suggest that most Voorspoed diamonds formed during 4 metasomatic events: the oldest one recorded took place between 2 and 3 Gyr as a result of a major thermal perturbation, whereas the following three occurred between 200 and 600 Myr, 30–90 and < 30 Myr before kimberlite eruption in a cooling lithosphere. An even older (or deeper) event is hinted by a few diamonds where all nitrogen is in B-centers. The sequence of events implied by Voorspoed HDF compositional and nitrogen aggregation differences show affinities with other occurrences in South Africa (e.g. Kimberley, Finsch and Koffiefontein) and may reflect thermal and lithological variation between the central and southwest Kaapvaal lithosphere.

Modeling of the temperature field in nanosecond pulsed laser ablation of single crystalline diamond

In this paper, a comprehensive finite element (FE) simulation model of the heat transfer for laser ablation of a single crystalline diamond (SCD) with a scanning laser beam in Gaussian shape is developed. The model takes into account the material properties, the geometric structure, and the thermal boundary conditions. It is employed to study the dependence of the temperature distribution under varying laser machining parameters. The distribution characteristics of the temperature field, the temperature evolution, and the heat conduction on the diamond surface are obtained, analyzed, and discussed. The law describing the influence of the laser parameters on the temperature field on the diamond surface is established. After comparing the numerically estimated thermal penetration depth of the pulsed laser in the diamond with the experimentally ablated groove characterized by a scanning electron microscope (SEM), a white light interferometer (WLI) and the Raman spectroscopy analysis of the deposited metamorphic layer, it is found that the developed model shows an excellent predictive capability and provides a promising tool for the future optimization of the machining parameters.

Grinding characteristics of CVD diamond grits in single grit grinding of SiC ceramics

Single crystalline diamond (SCD) grits are usually made by a high-pressure and high-temperature (HPHT) method and exhibit cuboctahedral shapes and smooth surfaces. In this paper, we synthesized new kinds of SCD grits and nanocrystalline diamond (NCD) grits by a chemical vapor deposition (CVD) method and explored their grinding performance by single grit grinding of SiC ceramics. Grinding by HPHT grits was also conducted for comparison. The CVD-SCD grits exhibit cuboctahedral shapes, but surfaces are covered by protruded twin crystals of several microns, while the NCD grits are spherical agglomerations of nano-grains. We demonstrated that these morphological features have profound influences on material removal behavior. Results show that the wear of NCD grits is dominated by wear flat and intergranular cracks. The worn NCD grits can exert intense rubbing and ploughing effects on the workpiece. In contrast, the wear of CVD-SCD grits is dominated by fracture of the protruded twin crystals. It is proved that the twins on the grit surface are effective cutting edges to remove the material in a micro scale and thus lead to the formation of fine grinding striations and smaller cracking pits, but this process has little influence on specific grinding energy. Besides, grits with rough twins, especially on the flank face, tend to exhibit lower grinding force ratios and thus better sharpness. Moreover, for grits with smooth rake faces, there exists an explicit critical undeformed chip thickness value around 0.4–0.6 μm, above which the material removal mechanism changes from ductile to brittle rapidly. However, for grits with rough twins on rake faces, this transition process becomes vague.

Association of Nanodiamond Rotation Dynamics with Cell Activities by Translation-Rotation Tracking.

Correlated translation-orientation tracking of single particles can provide important information for understanding the dynamics of live systems and their interaction with the probes. However, full six-dimensional (6D) motion tracking has yet to be achieved. Here, we developed synchronized 3D translation and 3D rotation tracking of single diamond particles based on nitrogen-vacancy center sensing. We first performed 6D tracking of diamond particles attached to a giant plasma membrane vesicle to demonstrate the method. Quantitative analysis of diamond particles' motion allowed elimination of the geometric effect and revealed the net rotation on the vesicle. 6D tracking was then applied to measure live cell dynamics. Motion characteristics of nanodiamonds on cell membranes under various controlled physiological conditions suggest that the nanodiamonds' rotation is associated with cell metabolic activities. Our technique extends the toolbox of single particle tracking and provides a unique solution to problems where correlated analysis of translation and rotation is critical.

Continuous real-time sensing with a nitrogen-vacancy center via coherent population trapping

We propose and theoretically analyze the use of coherent population trapping of a single diamond nitrogen vacancy (NV) center for continuous real-time sensing. The formation of the dark state in coherent population trapping prevents optical emissions from the NV center. Fluctuating magnetic fields, however, can kick the NV center out of the dark state, leading to a sequence of single-photon emissions. A time series of the photon counts detected can be used for magnetic field estimations, even when the average photon count per update time interval is much smaller than 1. For a theoretical demonstration, the nuclear spin bath in a diamond lattice is used as a model fluctuating magnetic environment. For fluctuations with known statistical properties, such as an Ornstein-Uhlenbeck process, Bayesian inference-based estimators can lead to an estimation variance that approaches the classical Cramer-Rao lower bound and can provide dynamical information on a timescale that is comparable to the inverse of the average photon counting rate. Real-time sensing using coherent population trapping adds a new and powerful tool to the emerging technology of quantum sensing.

Isotope Effect in Thermal Conductivity of Polycrystalline CVD-Diamond: Experiment and Theory

We measured the thermal conductivity κ(T) of polycrystalline diamond with natural (natC) and isotopically enriched (12C content up to 99.96 at.%) compositions over a broad temperature T range, from 5 to 410 K. The high quality polycrystalline diamond wafers were produced by microwave plasma chemical vapor deposition in CH4-H2 mixtures. The thermal conductivity of 12C diamond along the wafer, as precisely determined using a steady-state longitudinal heat flow method, exceeds much that of the natC sample at T&gt;60 K. The enriched sample demonstrates the value of κ(298K)=25.1±0.5 W cm−1 K−1 that is higher than the ever reported conductivity of natural and synthetic single crystalline diamonds with natural isotopic composition. A phenomenological theoretical model based on the full version of Callaway theory of thermal conductivity is developed which provides a good approximation of the experimental data. The role of different resistive scattering processes, including due to minor isotope 13C atoms, defects, and grain boundaries, is estimated from the data analysis. The model predicts about a 37% increase of thermal conductivity for impurity and dislocation free polycrystalline chemical vapor deposition (CVD)-diamond with the 12C-enriched isotopic composition at room temperature.

Cutting Force Prediction Models by FEA and RSM When Machining X56 Steel with Single Diamond Grit.

In the field of underwater emergency maintenance, submarine pipeline cutting is generally performed by a diamond wire saw. The process, in essence, involves diamond grits distributed on the surface of the beads cutting X56 pipeline steel bit by bit at high speed. To find the effect of the different parameters (cutting speed, coefficient of friction and depth of cut) on cutting force, the finite element (FEA) method and response surface method (RSM) were adopted to obtain cutting force prediction models. The former was based on 64 simulations; the latter was designed according to DoE (Design of Experiments). Confirmation experiments were executed to validate the regression models. The results indicate that most of the prediction errors were within 10%, which were acceptable in engineering. Based on variance analyses of the RSM models, it could be concluded that the depth of the cut played the most important role in determining the cutting force and coefficient the of friction was less influential. Despite making little direct contribution to the cutting force, the cutting speed is not supposed to be high for reducing the coefficient of friction. The cutting force models are instructive in manufacturing the diamond beads by determining the protrusion height of the diamond grits and the future planning of the cutting parameters.

Theoretical modeling and experimental analysis of single-grain scratching mechanism of fused quartz glass

Abstract Surface and subsurface damage, including cracks, scratches, microcracks, and residual stress, is inevitable when fabricating fused quartz glass because of their high brittleness and low fracture toughness. Single-grain scratching mechanism of fused quartz glass is examined using smoothed particle hydrodynamics (SPH) to clarify the mechanisms of material removal and produce crack-free optical surfaces. Single diamond grain experiments were conducted to validate the proposed SPH model, which predicts the critical depth of approximately 0.20 μm for ductile–brittle transition in fused quartz glass. Both simulation and experimental results indicate that three removal regimes, namely, complete ductile, ductile–brittle transform, and complete brittle modes, are involved in the material removal process. SPH simulation helps identify the location of crack formation and morphology of crack propagation during scratching. Thus, the SPH model is used to simulate the single grain scratching process under different conditions. Simulation results reflect that changing the scratching speed will lead to a remarkably different mechanism of crack initiation and propagation compared with changing the scratching depth. Effects of scratching depth and speed on scratching force and residual stress are also discussed thoroughly in the simulation analysis.

Fourier-transform infrared spectroscopy for analysis of diamond materials of different origin

The study of impurity composition of diamond materials is an important element of their classification for use in various fields of science and technology. Many physical (thermal and electrical conductivity, optical purity), mechanical (hardness and strength) and aesthetic (color grade and clarity) properties of diamond depend on the presence of impurities in their structure; therefore, it is important to quickly and reliably determine each impurity in diamond. In this work, the method of FTIR spectroscopy is proposed as an express method for determining the impurity composition of diamonds. We examined three types of diamond materials: single crystal natural diamonds (before and after heat treatment), single crystal synthetic HPHT-diamonds and synthetic polycrystalline diamond CVD-films. We have established that the used technique allows to determine impurities in single crystals of natural and synthetic origin reliably and effectively, while the study of polycrystalline thin films is best performed using spectrophotometry.

Surface microstructuring of single crystalline diamond based on the accumulated energy homogenization in the nanosecond pulsed laser ablation

In this paper, surface microstructuring of single crystalline diamond (SCD) by a nanosecond pulsed laser is performed. The nanometric surface characteristics of the ablated micro-grooves on the diamond caused by the thermal effect are firstly studied, where the deposited metamorphic layer, the irregular cross-sectional profile of the ablated groove and the non-uniform surface morphology are involved, and the dependence of the obtained surface characteristics on the ablation parameters of the infrared nanosecond pulsed laser, including the laser energy density, the pulse frequency, the scanning speed and the scanning times, is then analyzed and discussed. Finally, based on the mathematic analysis of the laser energy distribution and the accumulated energy intensity homogenization, the scanning path of the laser beam is programmed and five different types of surface microstructures are then fabricated on the diamond by controlling the scanning path with the optimized laser machining parameters to achieve the high surface quality of less cracking and better uniformity.

Wideband Output Brewster Window for Terahertz TWT Amplifiers Application

A wideband terahertz (THz) output network consisting of a pyramidal horn and a diamond Brewster window has been developed for 0.7-1.0-THz traveling-wave tube (TWT) amplifier and is measured at 0.325-0.5 THz owing to the limitation of the measurement facility. A pyramidal horn is designed to convert the waveguide mode into a high-purity quasi-plane polarized mode to meet the demand of the Brewster window. A diamond Brewster window plate with low THz transmission loss is fabricated via chemical vapor deposition (CVD). The plate is directly placed on the pyramidal horn with a Brewster angle. A circular window plate supporter is intended to balance the stress distribution during diamond-metal brazing. The measurement shows transmission coefficient is better than 0.85 within a wide bandwidth of 0.325-0.5 THz. This letter provides a practical way for a single diamond window structure for THz TWT amplifiers.

Behavioral Contrast of Electron and Hole Transport in High-Resolution Diamond Detectors: A Biparametric Correlation Study

In this letter we investigate for the first time the behavioral differences of transport properties of electrons and holes observed in high-resolution radiation detectors fabricated on high-purity single crystalline diamond using biparametric (BP) correlation studies. The chemical vapor deposition (CVD) grown 500 μm thick diamonds exhibited an excellent energy resolution of 0.5% for 5486 keV alpha particles for both electron and hole transport in a vertical electrode geometry. Interestingly, the behavior of the electron and hole transport were found to be vastly different at bias voltages less than 100 V. No discernable detector signal was observed due to electron transit below an applied bias of -100 V. The hole transit on the other hand, resulted in resolvable pulse height spectrum (PHS) from bias voltages as low as +10 V. Digital biparametric correlation studies of the rise-times and induced charge from each interaction of the incident alpha particles, revealed that the observed difference is due to the excessive electron trapping below bias voltages of -100 V. At lower biases, the width of the alpha peak in the PHS due to hole movement, was hardly affected by trapping and was observed to be limited due to lower hole drift velocities. The developed method with new insights of correlating the biparametric plots and the detector performance can be extended to vast range of semiconductor detectors.

Wear characteristics of single diamond grit scratching on sapphire with different contact forms

Abrasive single crystal diamond (SCD) is widely used in the machining process of sapphire. The wear characteristics of SCD grit have a significant influence on the tool wear and machining precision of sapphire. However, the influence of grit-workpiece contact form on the wear characteristics of SCD grit scratching on sapphire is not clear. In this paper, the wear characteristics of single SCD grit scratching on sapphire with three different grit-workpiece contact forms (point/line/face) are systematically investigated. Wear volume, wear morphology and scratching force are measured and tracked. Stress models of different contact forms are further established and analyzed. The results show that the SCD grit with face contact form can remove the most sapphire volume and it is the most wear-resistant. The SCD grit with point contact form can remove the fewest sapphire volume and it is the most prone to cleavage and fracture. Smaller stress results in more wear-resistant of the SCD grit during scratching on sapphire. Contact form is closely related to the stress state and has an important influence on the wear characteristics of SCD grit. The investigation results could provide a theoretical basis for the fabrication of abrasive tools.

To estimation of temperature fluctuations in diamond grains when drilling with diamond bits

Abstract. If we consider the interacting pair: the matrix of a diamond crown, reinforced with protruding diamonds and rock, as a kind of system, then in the process of friction of the matrix against the bottom hole, external mechanical energy is converted into the energy of the heat and matter flows. The main concentration of the flows occurs in places where diamonds protrude above the matrix and take on an additional load. The rubbing system tries to smoothing itself by concentrating pressure and temperature on the diamonds. Diamonds, due to their higher hardness than the destructible medium, are pressed into the rock and destroy it. Since the process of cutting rocks is intermittent, the concentration of energy on diamonds occurs periodically, in the form of “flashes”. Each such “flash” is accompanied by a short-term increase in temperature in the contact zone (temperature fluctuation) and the spalling of a microparticle of the rock. In this work, from the standpoint of thermoelastic instability, the issue of temperature microflashes in single diamonds during the interaction of rough surfaces of the matrix of the diamond crown and the bottom of the borehole is considered, in order to take this factor into account in the mechanism of wear of the diamond of the drill bit. The value of temperature fluctuations on the surface of cutting diamonds was estimated and the size of the flash zone was determined. It is shown that temperature flashes of 400 (С &lt; T* &lt; 3650 (С are observed when drilling granite with a diamond crown on the diamond surface in an area of 5.8(10‑5 m, therefore, the presence of such “microflashes” on the diamond surface in a very small area in the process of interaction with the rock can lead to graphitization of the diamond in this place and separation from the surface of the grain. Such a mechanism should play a certain role in the wear and destruction of diamond surface areas during drilling. The magnitude of temperature fluctuations depends on the physical and mechanical properties of the contacting pair: diamond – rock, operating parameters of the tool and the nature of the placement of diamonds in the crown matrix. In this regard, the study of the assessment of temperature fluctuations in diamond grains when drilling with diamond bits may be of practical interest. Keywords: rock, thermal stresses, intensive cooling, macro- and microcrack system.

Fabrication of textured surface with ultrasonic vibration-assisted indentation

An ultrasonic vibration-assisted indentation system/method is proposed and developed to fabricate structured or textured surfaces more precisely and efficiently than the conventional micro-cutting process. Indenters made of single crystalline diamond (SCD) were fabricated by laser fabrication and polishing with diamond abrasives on a cast iron plate. In the experiments, the microarray molds of four-corner cone and semi-sphere shapes were generated precisely on the electroless Ni-P substrate with ultrasonic vibration-assisted indentation using the SCD indenters. From the indentation experiments, it is clear that the microtextured patterns were formed precisely and effectively by using the developed indentation system.

A novel experimental apparatus for single polycrystalline diamond compact cutter tests.

Polycrystalline diamond compact (PDC) bits are increasingly favored in the drilling field due to their high efficiency in rock breaking together with their longevity. To investigate the rock failure mechanism and further improve the performance of PDC bits, innovative experimental equipment is proposed in this paper. With its assistance, we can study the characteristics of rock-breaking using a PDC cutter under different conditions, e.g., high pressure and high temperature (HPHT), confining pressure, and jet impingement. The setup can be grouped into three parts: a rock cutting system, high-pressure jet generation system, and controlling system. A series of experiments was conducted to demonstrate the reliability of the setup. The results demonstrate the improvement in performance of PDC bits in the exploration of HPHT formations.

Experimental and statistical analysis of the wear of diamond impregnated tools

Diamond impregnated tools are considered which are used to machine concrete. During their application, the bonding as well as the diamonds need to wear down in a certain way to gain a sharp tool. This required wear is called self-sharpening and means a continuous exposure of new diamonds. Within the development phase of diamond tools, time and cost intensive testing is necessary for the assessment of the tool performance. Hence, an extrapolation based on a minimal amount of testing is desirable to forecast the tool lifetime. A further reduction of the development and testing cost can be achieved by reducing the data needed to forecast the tool performance. Within this paper, the development of a statistical model is shown which was used to forecast the lifetime of the single diamonds on the tool. The statistical analysis is based on single segment tests which were carried out with different segment specification. During the tests, the exposed and broken out diamonds were counted to serve as the necessary input data for the statistical analysis. The counting of the diamonds on the segment was done in two different ways: based on the 2-dimensional microscopic pictures made after every minute of drilling and based on the 3-dimensional surface measurements made after every 5 min of drilling. It turns out that these two approaches of the wear analysis provide similar results.