Diamond Fraction Research Articles

Effect of hot forging temperature and diamond volume fraction on TiC interface evolution and thermal conductivity of hot-forged Ti-coated diamond/Cu composites

Diamond/Cu composites are developed as a solution to the challenge of dissipating heat in electronic devices, due to the potential to have a high thermal conductivity (TC) and a coefficient of thermal expansion (CTE) close to that of the electronic devices. In this study, Ti-coated diamond/Cu composites were fabricated by hot forging. Fabrication parameters were manipulated by altering the volume fraction of diamond and adjusting the hot forging temperature to determine the optimal combination of parameters to produce Ti-coated diamond/Cu composites with high TC. The microstructure of the hot-forged composites and the interface characteristics were characterized by SEM, and the interfacial bond strength between the copper and the diamond was assessed based on tensile test results. Compared to other fabrication temperatures of 700 °C and 850 °C, 800 °C is the optimal hot forging temperature to facilitate the dynamic formation of TiC interface layer and ensure a high interface coverage rate on the diamond particles. Additionally, the volume fraction of diamond affects the interface microstructure and TC of the hot-forged composites by affecting the heating behaviour of the composites during induction heating. As a result, 800 °C hot-forged composites with a composition of 45vol%Ti-coated diamond achieved the highest TC (455 W/mK) among the fabricated composites and exhibited good ductility at a high tensile strength of 124 MPa. The findings indicate that the high TC of the Ti-coated diamond/Cu composites are ensured by the synergy of uniform distribution of diamond in the matrix, a rough interface, and strong interfacial bonding between the copper and the diamond. This paper provides insights into the TiC interface formation mechanisms occurring during the induction heating and hot forging fabrication process.

Effect of Interfacial Coatings on Thermal Conductivity of Diamond/Al Composites

In this paper, the acoustic mismatch model and the differential effective medium scheme were applied to predict the influence of different interfacial coatings (Si and SiC) on the interfacial thermal conductivity and thermal conductivity of the Diamond/Al composites, respectively. With the increase of the thickness of interfacial coatings, the interfacial thermal conductivity and of the thermal conductivity of Diamond/Al composites decreased. In order to obtain ideal thermal conductivity of Diamond/Al composites, the thickness of the coating should be controlled below 1 μm. When the volume fraction of diamond was 60% and the average particle size was 100 μm, the interfacial thermal conductivity of Si and SiC coated Diamond/Al composites were in the range of 1.77×107∼1.1×108 W/(m2 · K) and 2.44×107∼1.29×108 W/(m2 · K), respectively; the thermal conductivity of Si and SiC coated Diamond/Al composites were in the range of 541.58∼764.15 W/(m· K) and 594.45∼777.3 W/(m· K), respectively. The thermal conductivity of Si and SiC coated Diamond/Al composites increased with the volume fraction and average particle size of Diamond, and the thermal conductivity of SiC coated Diamond/Al composites was higher than that of Si coated composites. SiC interface coating was proposed to be the most promising candidates to improve the thermal performance of Diamond/Al composites.

Hyperbolic Tangent Fluid Model for Stagnation Flow of Hybrid Nanofluid Over a Stretching Sheet

The problem of hyperbolic tangent fluid model for stagnation flow of hybrid nanofluid over a stretching sheet is investigated. Constitutive relation of an incompressible hyperbolic tangent model as well as consideration of thermal radiation and Newtonian heating is taken into account. The boundary layer problem is formulated to nonlinear partial differential equations which is then transformed into ordinary differential equations by using similarity transformation. The equations including the boundary conditions are solved numerically using bvp4c in the MATLAB software. A comparison with previous findings shows an excellent agreement. The effect of governing parameters such as power law index, Weissenberg number, suction/injection, radiation and Biot number is investigated. The changes in the value of volume fraction of diamond and silicon dioxide are also analyzed. Characteristics for the significant variables are graphically presented and the numerical results are tabulated. The velocity behavior is significantly influenced by the volume fraction of diamond and silicon dioxide and other physical parameters. Meanwhile, the temperature is influenced by the radiation parameter. This study provides conclusive evidence that increasing the volume fraction of diamond nanoparticles significantly enhances the heat transfer rate. The increment by 0.1 (10%) of the volume fraction of diamond nanoparticles increases the heat transfer rate approximately by 3%. These findings underscore the potential of integrating these nanoparticles to improve thermal performance across diverse applications.

Thermal properties of tungsten/tungsten carbide-coated double-size diamond/copper composite

Diamond‑copper composites with high thermal properties and low density show huge potential applications in thermal management. Solving the interface between diamond and copper and increasing the volume fraction of diamond in the composite are crucial for its thermal conductivity. In this work, tungsten/tungsten carbide (W/WC) was used as an interface and fabricated on diamond surface by the molten salt method. Well-coating with higher than 95 % of coverage was obtained at the mass ratio of diamond and W of 3:3, which owns a 200 nm ± 10 nm thickness of W/WC layer. Meanwhile, double-size diamonds with 200 μm and 40 μm were compounded with the copper matrix to increase the volume fraction of the diamond. Theoretical calculation displays only 14.5 % of porosity in the bimodal diamond composite when 74.2 vol% of the large-size diamond is in the total volume fraction of the diamond. Microstructure characterization displays that the interfacial bonding was enhanced by the W/WC interface and morphology was improved by using the double-size diamonds even at 70 % of the volume fraction. Compared with single-size diamond/copper composite, the thermal conductivity was also increased and obtained the highest value of 640 Wm−1 K−1 for the double-size diamonds/copper composites. Finite element analysis and testing of actual scenarios further confirm the excellent thermal performance of double-size diamonds/copper composite, which meets the requirements of thermal management in high-power devices.

Thermal conductivity of 2D diamond superstructures in interlayer-bonded twisted bilayer graphene

We report results from a systematic analysis of thermal transport in 2D diamond superstructures in interlayer-bonded twisted bilayer graphene (IB-TBG) based on molecular-dynamics simulations. We find that the introduction of interlayer C–C bonds in these bilayer structures causes an abrupt drop in the thermal conductivity of pristine, non-interlayer-bonded bilayer graphene, while further increase in the interlayer C–C bond density (2D diamond fraction) leads to a monotonic increase in the thermal conductivity of the resulting superstructures with increasing 2D diamond fraction toward the high thermal conductivity of 2D diamond (diamane). We also find that a similar trend is exhibited in the thermal conductivity of interlayer-bonded graphene bilayers with randomly distributed individual interlayer C–C bonds (RD-IBGs) as a function of interlayer C–C bond density, but with the thermal conductivity of the IB-TBG 2D diamond superstructures consistently exceeding that of RD-IBGs at a given interlayer bond density. We analyze the simulation results employing effective medium and percolation theories and explain the predicted thermal conductivity dependence on interlayer bond density on the basis of lattice distortions induced in the bilayer structures as a result of interlayer bonding. Our findings demonstrate that the thermal conductivity of IB-TBG 2D diamond superstructures and RD-IBGs can be precisely tuned by controlling interlayer C–C bond density and have important implications for the thermal management applications of interlayer-bonded few-layer graphene derivatives.

High hardness and high fracture toughness B4C-diamond ceramics obtained by high-pressure sintering

The B4C-diamond composite with high hardness and toughness was first prepared by high-pressure sintering of B4C and diamond powders at 5 GPa and 1600 °C. The effect of the diamond fraction on the densification, microstructure and mechanical properties of B4C-diamond composite were investigated. The results indicated that the hardness of the as-prepared composite ceramics increased gradually with the increase in diamond content. The composite having 40 vol% diamond exhibited excellent comprehensive mechanical properties with a relative density of 98.3%, a density of 2.86 g/cm3, Vickers hardness of 39.8 GPa and fracture toughness of 8.1 MPa·m1/2. The use of superhard diamond enhanced the fracture toughness of the B4C while maintaining its lightweight and high hardness. The main toughening mechanisms were crack bridging, crack deflection and pull-out of homogeneously dispersed diamond grains. Superhard second phase dispersion high-pressure sintering provides a new technical route to improve the properties of advanced composites.

Experimental Investigation on Tribological Behaviour of Copper Diamond Composites

In the present study, a range of copper diamond composites were prepared using powder metallurgy. The impact of volume fraction of diamond on tribological behaviour and its effective dispersion with copper powder was studied. Composites containing dispersion of hard particles in a metal matrix are widely used for automotive and other structural applications. Sliding wear has a vital role in the performance of electrical sliding contacts used in electric and electronic devices. Thermal considerations are also equally important for the sustainability of electronic parts. Product life and its reliability of sliding contacts are directly proportional to wear phenomenon. Due to these reasons and to meet the demands of improving thermal properties of materials for electronic components, a new composite material composed of diamond and copper was developed. The ball mill was used for 4 hours at 300 rpm for grinding and blending copper, diamond into fine powder. Being a cost-effective technique, normal sintering and powder metallurgy method were adopted for composite preparation where spark plasma sintering and other techniques were found to be very costly. Diamond was added in different volume fraction (1% wt., 3% wt. and 5% wt.) as reinforcement to analyse the influence of diamond particle concentration, distribution and its particle size on thermal conductivity and wear behaviour. A transmission electron microscope was used to characterize the morphology of powder. XRD analysis was used to identify the crystalline phases present in the composites. A wear test was performed on pin on disk test rig. The wear test illustrated that higher diamond content improves the wear resistance of the composite.

Synthesis of High Quality Transparent Nanocrystalline Diamond Films on Glass Substrates Using a Distributed Antenna Array Microwave System

Diamond is a material of choice for the fabrication of optical windows and for protective and anti-reflecting coatings for optical materials. For these kinds of applications, the diamond coating must have a high purity and a low surface roughness to guarantee a high transparency. It should also be synthesized at low surface temperature to allow the deposition on low melting-point substrates such as glasses. In this work, the ability of a Distributed Antenna Array (DAA) microwave system operating at low temperature and low pressure in H2/CH4/CO2 gas mixture to synthesize nanocrystalline diamond (NCD) films on borosilicate and soda-lime glass substrates is investigated aiming at optical applications. The influence of the substrate temperature and deposition time on the film microstructure and optical properties is examined. The best film properties are obtained for a substrate temperature below 300 °C. In these conditions, the growth rate is around 50 nm·h−1 and the films are homogeneous and formed of spherical aggregates composed of nanocrystalline diamond grains of 12 nm in size. The resulting surface roughness is then very low, typically below 10 nm, and the diamond fraction is higher than 80%. This leads to a high transmittance of the NCD/glass systems, above 75%, and to a low absorption coefficient of the NCD film below 103 cm−1 in the visible range. The resulting optical band gap is estimated at 3.55 eV. The wettability of the surface evolves from a hydrophilic regime on the bare glass substrates to a more hydrophobic regime after NCD deposition, as assessed by the increase of the measured contact angle from less than 55° to 76° after the deposition of 100 nm thick NCD film. This study emphasizes that such transparent diamond films deposited at low surface temperature on glass substrate using the DAA microwave technology can find applications for optical devices.

Research on maximizing the diamond content of diamond/SiC composite

Diamond content is a key factor affecting diamond/SiC composite performance, especially thermal and mechanical properties, but the composite with high diamond content manufacturing is still challenging issues. Hot mold pressing combined with liquid silicon infiltration to make diamond/SiC composites with high diamond content and relative density has been proposed in this paper. In addition, the effect of diamond particle size on the maximization of diamond content as well as properties of the composites were evaluated. The experiment shows that the content of diamond in the composites increases with the increase of the diamond particle size. When the particle size of diamond is 400 µm, the volume fraction of diamond reaches 59.08%. The highest thermal conductivity (ddia= 300 µm) and highest bending strength (ddia= 50 µm) are 616.77 W/m K (It is the maximum TC of diamond/SiC prepared by pressureless infiltration at present) and 380 MPa, respectively. This work provides a novel and efficient preparation method for further improving the thermal conductivity of diamond/SiC composites.

ИЗУЧЕНИЕ ВЛИЯНИЯ СОСТАВА КОМПОЗИТОВ НА ОСНОВЕ СПЕЧЕННОГО ИМПАКТНОГО АЛМАЗА НА ИХ ИЗНОСОСТОЙКОСТЬ ПРИ ОБРАБОТКЕ КАРБИДА КРЕМНИЯ

The article presents the results of comparative tests on the wear resistance of composite materials (CM) sintered at high pressures and temperatures based on impact diamond (diamond-lonsdaleite abrasive — DLA) when processing silicon carbide (SiC). To assess the CM performance based on impact diamonds, a method has been developed for determining the wear resistance, based on the determination of the CM specific productivity. It is shown that for CMs based on impact diamond, it is expedient to use SiC as a binder. For CMs based on impact diamond with an additive of 40 vol.% SiC, specific productivity when machining a silicon carbide wheel is 25–30 % higher than for compositions containing dense BN phases — wBN and cBN. The decrease in the specific productivity of CM “impact diamond — cBN” relative to CM “impact diamond — SiC” is determined by the higher dispersion of crystals of dense BN phases in comparison with SiC, which generally impairs the abrasive ability of the material. In this case, the addition of a coarse fraction of impact diamond 100/63 μm to the charge composition does not lead to an increase in the specific productivity of the abrasive element as compared to CM based on DLA with a particle size of less than 40 μm. Preliminary mechanical activation of the initial charge also reduces the CM abrasive ability due to the formation of a highly dispersed structure of the material.

A New Way of Getting the Charge with Diamond Fraction

A New Way of Getting the Charge with Diamond Fraction

Enhanced thermal conductivity of diamond/copper composite fabricated through doping with rare-earth oxide Sc2O3

Diamond/copper composite has been considered as one of the next generation thermal management materials. Interfacial modification is an essential means of ameliorating interface wettability and bonding of diamond/copper composite for improving its thermal conductivity. In the present work, Diamond/copper composite was manufactured by using spark plasma sintering (SPS) technology with 60% volume fraction of diamond mixed with 40% volume fraction of copper power, chromium powder (0.7 wt%) and scandium oxide powder (0.21 wt%). A series of material analysis methods were used to characterize the microstructure, interfacial layer, phase compositions and distributions of Diamond/copper composite. The total and partial electron density of states (DOS) for Diamond-Cr-Sc2O3 interfacial model was investigated by means of first-principles calculations from CASTEP modules. The results showed Sc2O3 made a 5–20 nm well-arranged and uniformly distributed interfacial chromium carbide layer in the interface region, which played a critical role in increasing the amount of reactive interfacial bonding and decreasing defect. The addition of Sc2O3 brought the increasing number of heat transfer carriers at the interface and made the interface energy system more stable. The obtained diamond/copper composite exhibited that the wettability between diamond particles and copper was effectively improved. The thermal conductivity of diamond/copper is 872 W/(m·K) and the possible reasons for doping rare-earths Sc2O3 to improve the thermal conductivity were discussed.

Improving the wear resistance of hoe blades by modifying of restoration coatings

The possibility of using a non-magnetic fraction of a detonation charge with a diamond fraction from the disposal of ammunition to modify the restoration coatings of a natural product – clay and secondary raw materials — was studied. Four different coating variants were investigated. For this, a T-620 electrode was used with its additional modification by coating with bentonite clay, as well as with a non-magnetic fraction of the detonation charge and applying it in the form of a slip coating on the cutting surface of the cultivator. It is shown that the use of such additives allows to increase the resistance of the working tool of agricultural machines, reduces its tendency to damage due to the minimum penetration of the thin-walled product of the hoe blade and a decrease in the cross section of the transition layer and the level of stress. Each modifier makes changes to increase the microhardness to varying degrees. An increase in microhardness is observed on the surface of the coating and its gradual decrease to the transition layer. The surface coating with the additional introduction of bentonite clay in a liquid bath has the highest microhardness. Its microhardness varies from HV-50-1009.7 to HV-50-615.2. Similarly, the effect of the modifying additive of the detonation charge, the microhardness varies from HV-50-969.6 to HV-50-633.26. When clay or a mixture is introduced into the restoration coating, the wear resistance increases by 1.3 - 2 times with respect to the deposited surfacing only by the electrode and by 2 - 3 times to the initial material of the cultivator. It was found that the lowest coefficient is characteristic for dry friction, as well as for hydroabrasive, for samples with additional modification with clay or a detonation charge

Predicting superhard materials via a machine learning informed evolutionary structure search

The computational prediction of superhard materials would enable the in silico design of compounds that could be used in a wide variety of technological applications. Herein, good agreement was found between experimental Vickers hardnesses, Hv, of a wide range of materials and those calculated by three macroscopic hardness models that employ the shear and/or bulk moduli obtained from: (i) first principles via AFLOW-AEL (AFLOW Automatic Elastic Library), and (ii) a machine learning (ML) model trained on materials within the AFLOW repository. Because H_{mathrm{v}}^{{mathrm{ML}}} values can be quickly estimated, they can be used in conjunction with an evolutionary search to predict stable, superhard materials. This methodology is implemented in the XtalOpt evolutionary algorithm. Each crystal is minimized to the nearest local minimum, and its Vickers hardness is computed via a linear relationship with the shear modulus discovered by Teter. Both the energy/enthalpy and H_{{mathrm{v,Teter}}}^{{mathrm{ML}}} are employed to determine a structure’s fitness. This implementation is applied towards the carbon system, and 43 new superhard phases are found. A topological analysis reveals that phases estimated to be slightly harder than diamond contain a substantial fraction of diamond and/or lonsdaleite.

Enhanced bending strength and thermal conductivity in diamond/Al composites with B4C coating

Diamond/Al composites containing B4C-coated and uncoated diamond particles were prepared by powder metallurgy. The microstructure, bending strength and thermal conductivity were characterized considering the B4C addition and diamond fraction. The influence of B4C coating and fraction of diamond on both bending strength and thermal conductivity were investigated. The bending strength increased with decreasing diamond fraction. Moreover, addition of B4C coating led to an obvious increase in bending strength. The peak value at 261.2 MPa was achieved in the composite with 30 vt.% B4C-coated diamond particles, which was about twice of that for 30 vt.% uncoated diamond/Al composite (140.1 MPa). The thermal conductivity enhanced with the increase in diamond fraction, and the highest value (352.7 W/m·K) was obtained in the composite with 50 vt.% B4C-coated diamond particles. Plating B4C on diamond gave rise to the enhancement in bending strength and thermal conductivity for diamond/Al composites, because of the improvement of the interfacial bonding between diamond and aluminum matrix.

Raman Scattering in Lonsdaleite

We present the results of our study of a polycrystalline diamond–lonsdaleite powder from the Popigai crater (Siberia) using UV micro-Raman scattering and synchrotron X-ray diffraction. By subtracting two experimental Raman spectra of diamond–lonsdaleite samples with a close ratio of the diamond and lonsdaleite fractions, when the maximum contribution to the difference spectrum is related to the difference of the lonsdaleite contributions and not to the change in the diamond band width, we have managed to obtain the spectrum of “pure” lonsdaleite. Its deconvolution has allowed us to identify all three Raman-active vibrational modes E2g, A1g, and E1g whose positions agree well with the results of ab initio calculations.

A simple, space constrained NIRIM type reactor for chemical vapour deposition of diamond

In this paper the design of a simple, space constrained chemical vapour deposition reactor for diamond growth is detailed. Based on the design by NIRIM, the reactor is composed of a quartz discharge tube placed within a 2.45 GHz waveguide to create the conditions required for metastable growth of diamond. Utilising largely off-the-shelf components and a modular design, the reactor allows for easy modification, repair, and cleaning between growth runs. The elements of the reactor design are laid out with the CAD files, parts list, and control files made easily available to enable replication. Finally, the quality of nanocrystalline diamond films produced are studied with SEM and Raman spectroscopy, with the observation of clear faceting and a large diamond fraction suggesting the design offers deposition of diamond with minimal complexity.

Pressure-Temperature-Induced Transformations of Hydrocarbon- Fluorocarbon Mixtures into Nano- and Micron-Size Diamonds

Studies of thermal transformations of naphthalene (С10Н8), fluorographite (CF1.1) and octafluoronaphthalene (С10F8) and their binary mixtures (С10Н8 – CF1.1, С10Н8 – C10F8) under pressure of 8 GPa have been undertaken as models for gaining understanding of processes of carbonization, graphitization and diamond formation in pure hydrocarbon, fluorocarbon and carbon-hydrogen-fluorine-containing systems under high pressures. The studies found a significant reduction in the initiation temperature thresholds for all major thermal transformation processes in case of binary mixtures with respect to thresholds for pure hydrocarbon and fluorocarbon compounds. Another distinctive feature of the transformations of binary mixtures with respect to diamond formation stage of the transformations of pure hydrocarbons, has been the presence of massive quantity of nanosize (10–60 nm) diamond fraction in the products from binary mixtures along with the micron-size (5–20 μm) diamond fraction, typically observed in the transformations of pure hydrocarbons. The origin of nanodiamond was related to the specifics of carbonization of fluorocarbon compounds under pressure, which at 800–1000 °С produces, along with submicron particles of graphite-like material, a significant amount of closed shell 2–5 layer carbon nanoparticles of 5–15 nm size. These onion-like carbon nanoparticles act as precursors for formation of nano size diamond fractions in the transformations of binary mixtures of hydrocarbon and fluorocarbon compounds. These results potentially open a new direction for metal catalyst-free synthesis of pure and doped diamonds for broad applications. The present article gives an overview of this emerging area of rese arch.

Comparative Study of Condensation Routes for Formation of Nano- and Microsized Carbon Forms in Hydrocarbon, Fluorocarbon, and Fluoro-Hydrocarbon Systems at High Pressures and Temperatures

Thermal transformations of binary mixtures of hydrocarbons and fluorocarbons under high pressures demonstrate significantly lower initiation temperature thresholds for all major transformation stages, including carbonization, graphitization, and diamond formation, than the transformations of pure hydrocarbon and fluorocarbon components. In addition, along with the formation of micrometer-size diamond fraction, typical for transformation products of pure hydrocarbons, massive formation of nanosize diamond fraction has been observed in the products of conversion of mixtures. In order to gain understanding of the nature of simultaneous formation of micro- and nanosize fractions of diamond in the binary mixtures of hydrocarbon and fluorocarbon compounds, a comparative studies of the attributes of thermal transformations of pure hydrocarbon, fluorocarbons and their homogeneous and heterogeneous mixtures has been carried out under pressure of 8 GPa and temperatures up to 1500 °C. Naphthalene (C10H8) and octaflu...

Enabling Diamond Deposition with Cold Spray through the Coated Particle Method

This paper describes the application of Cold Spray to the deposition of a diamond grade pre-coated with Cu and Ni. Diamond powders are therefore used as the sole feedstock without the addition of separate binders (ductile phases) in cold spraying. The experimental results showed that it was possible to manufacture thick metal-diamond composite coatings with high diamond fraction in the coating but without phase change or graphitization. Results presented in this paper demonstrate the feasibility of a new methodology for the deposition of metal-diamond/ceramic composite coating with the cold spray technique.