Uncoated Diamond Research Articles

Interfacial characteristics of titanium coated micro-powder diamond abrasive tools fabricated by electroforming-brazing composite process

In this study, abrasive tools were fabricated by an electroforming-brazing composite process. The abrasive tools were prepared using micro-powder diamond (MPD) grits with and without titanium (Ti) coatings. The interface characteristics of the MPD diamond grits and filler alloy were investigated. The results show that the diamond grits are uniformly dispersed on the surface of the steel substrate without visible agglomeration, and the NiCr filler alloy has good wetting toward diamond grits. Compared to the uncoated diamond grits, the abrasive grains with a Ti coating have an ideal grain distribution and brazed joints, and no aggregation of Si element observed at its edge. There is a more stable carbide TiC that formed on its surface in addition to the chromium carbide. Furthermore, the coated diamond grits are not graphitized and show a better residual stress state. In the abrasive tools with Ti-coated diamond, numerous intermetallic compounds (IMCs) are formed in the brazing layer, but the formation of theγ-Ni-based solid solution is relatively slight. The IMCs increase the microhardness of the filler alloy and help improve the wear resistance of the solder layer.

Effect of Ti/Ni Coating of Diamond Particles on Microstructure and Properties of High-Entropy Alloy/Diamond Composites.

In this study, an effective way of applying Ti/Ni deposited coating to the surface of diamond single crystal particles by magnetron sputtering was proposed and novel high-entropy alloy (HEA)/diamond composites were prepared by spark plasma sintering (SPS). The results show that the interfacial bonding state of the coated diamond composite is obviously better than that of the uncoated diamond composite. Corresponding mechanical properties such as hardness, density, transverse fracture strength and friction properties of the coated diamond composite were also found to be better than those of the uncoated diamond composite. The effects of interface structure and defects on the mechanical properties of HEA/diamond composites were investigated. The research directions for further improving the structure and properties of high-entropy alloy/diamond composites were proposed.

Improvement of ZrC/Zr Coating on the Interface Combination and Physical Properties of Diamond-Copper Composites Fabricated by Spark Plasma Sintering.

In this study, diamond-copper composites were prepared with ZrC/Zr-coated diamond powders by spark plasma sintering. The magnetron sputtering technique was employed to coat the diamond particles with a zirconium layer. After heat treatment, most of the zirconium reacted with the surface of diamond and was transformed into zirconium carbide. The remaining zirconium on the zirconium carbide surface formed the outer layer. Owing to the method used to produce the ZrC/Zr-coated diamond in this study, the maximum thermal conductivity (TC) of 609 W·m−1·K−1 was obtained for 60 vol. % diamond-copper composites and the corresponding coefficient of thermal expansion (CTE) reached as low as 6.75 × 10−6 K−1. The bending strength of 40 vol. % ZrC/Zr-coated diamond-copper composites reached 255.95 MPa. The thermal and mechanical properties of ZrC/Zr-coated diamond-copper composites were substantially superior to those of uncoated diamond particles. Excellent properties can be attributed to the strengthening of the interfacial combination and the decrease in the interfacial thermal resistance due to the improvement associated with the ZrC/Zr coating. Theoretical analysis was also proposed to compare the thermal conductivities and CTE of diamond-copper composites fabricated with these two kinds of diamond powders.

Influence of tungsten coating on microstructure and thermal damage of brazed diamonds

ABSTRACTDegradation of diamond strength resulting from thermal damage in vacuum brazing process constrains the application of Ni-based brazed diamond tools. To reduce the thermal damage to brazed diamonds, the effectiveness of coating diamond with tungsten was investigated by scanning electron microscopy, Raman spectroscopy and friability test. Tungsten coating was deposited on diamond surfaces by vacuum diffusion method. The experimental results show that tungsten coating, as a buffering layer, plays a stress-relaxing role and brings about fewer cracks in the Ni-based matrix near diamond grains. Graphitization of W-coated diamond after brazing is much slighter than that of uncoated diamond and Ti-coated diamond, according to the morphology and Raman spectra. The isolation of diamond from nickel catalyst by tungsten coating inhibits the graphitization of diamond, which can further explain the increase in the toughness index of brazed diamonds.

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.

Thermal damage mechanisms of Si-coated diamond powder based polycrystalline diamond

The polycrystalline diamond (PCD) composites were synthesized from Si-coated diamond or diamond powder mixtures with Si. The characterizations of phase structures, morphologies and thermal stability of PCD were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal gravimetric-differential scanning calorimetry (TG-DSC). The thermal damage mechanisms of PCD were studied under air condition up to 750 ℃ by thermal weight loss, XRD, SEM and wear tester. The results showed that the PCD was successfully synthesized by the Si-coated diamond with a homogeneous structure. The thermal stability and wear resistance of PCD with Si-coated diamond were better than those of PCD with uncoated diamond. It was determined that the chemical thermal damage mechanism with oxidation reaction dominated the damage of the PCD after high temperature annealing and the physical thermal damage mechanism also took effect on the exfoliation of binder and fine diamond grains from PCD.

Morphological features of W- and Ni-containing coatings on diamond crystals and properties of diamond-copper composites obtained by Spark Plasma Sintering

In the present study, W- and Ni-containing coatings on diamond crystals were obtained by rotary chemical vapor deposition (RCVD) using tungsten carbonyl W(CO)6 and nickelocene Ni(C5H5)2 as precursors. Morphological features of the coatings deposited under different processing conditions were investigated. For obtaining bulk diamond-copper composites, mixtures of the coated and uncoated diamond crystals with a copper powder were subjected to Spark Plasma Sintering (SPS). The effects of the presence of the coatings on the diamond crystals and the size of the initial diamond particles on the microstructure, relative density and thermal conductivity of the consolidated diamond-copper composites were investigated.

Spark plasma sintering of SiC-coated large-size diamond powder

A large-size (25 μm in diameter) diamond powder was coated with a SiC layer by rotary chemical vapor deposition. The SiC-coated diamond powder was consolidated with a SiO2 additive by spark plasma sintering (SPS) under a moderate pressure of 130 MPa at 1673–1973 K for 300 s. The relative density of the diamond body with 35 wt% SiO2 using the SiC-coated diamond powder was in the range 98–99% while that of the uncoated diamond powder was in the range 89–94%. The highest Vickers hardness of the SiC-coated diamond bodies was 36 GPa at 4.9 N.

Structure and performance of electroless composite plating Ni–P–RE and Ti coatings on diamond particles

The Ni–W–P, Ni–P–RE and Ti coatings on diamond surface were prepared by the process of electroless plating and electroless composite plating with heat treatment. The structure of metal plating and coating was tested by scanning electron microscope and X-ray diffraction. The results show that the finer coatings on diamond surface form after electroless plating and electroless composite plating process. The compressive strengths of the coatings increase by 38·57% comparing with the original diamond. The results of X-ray diffraction and thermodynamic analysis indicate that some carbides, such as WC and TiC, have been formed between diamond surface and the coatings after heat treatment. However, the compressive strength of diamonds with electroless composite plating after heat treatment is 16·43% higher than that of uncoated diamond because of high temperature oxidation.

Numerical investigation of the effect of interfacial thermal resistance upon the thermal conductivity of copper/diamond composites

Abstract Copper/diamond (Cu/D) composites are known for their applications in thermal management systems. This paper investigates the effect of interfacial thermal resistance (TR) upon the effective thermal conductivity of Cu/D composites through experimental and numerical means. The composite samples were made using uncoated, Cu-coated, and Cr-coated diamond particles. The transient plane source method was used to measure the thermal conductivity of the composite samples, while the micrographs of the specimens were used to develop the finite element models. Together with the experimental and numerical results, the interfacial TR was identified in each sample. Although Hasselman–Johnson model calculated the conductivity values with significant error, the trend shown by experimental results is still followed. The finite element model, however, led to an error of less than 1%. The numerical analysis showed that the TR depends not only upon the diamond volume fraction but also upon the coating material. Finally, it has been demonstrated that numerical simulation may be employed to reveal the appropriate combinations of diamond fraction and the coating material in order to attain the desired level of effective thermal conductivity.

Deposition of aluminium silicate film on diamond by sol-gel techniques

Diamond particles were coated with aluminium silicate film by sol-gel techniques, and characterised by X-ray diffraction, scanning electron microscope, energy-dispersive spectroscope and Differential Scanning Calorimetry and Thermogravimetric Analysis (DSC-TG). It was shown that amorphous aluminium silicate thin film was obtained, which encapsulated the diamond particles completely. As a good barrier, this film protected the diamond with enhanced oxidation resistance. Specifically, the initial oxidation temperature of the aluminium silicate film-coated diamond in air atmosphere was 715°C, 85°C higher than that of the uncoated diamond.

Study on induction brazing of diamond grits coated by physical vapor deposition

In this study, induction brazing was performed on diamond grits coated with amorphous NiCrBSi alloy (1.6-μm thick) deposited by physical vapor deposition (PVD). The brazing alloy exhibited better wetting toward the coated diamond grits than toward the uncoated diamond grits during induction brazing. The fine chromium-carbon compounds were evenly distributed between the brazed diamond grits with coating and the brazing alloy. However, the bulky chromium-carbon compounds were unevenly distributed between the brazed uncoated diamond grits and the brazing alloy. Cylindrical grinding of casting aluminum ZL102 plate with thickness of 15 mm was also performed using the brazed diamond burs fabricated with the coated diamond grits and uncoated diamond grits, respectively. The falloff percentage of brazed coated diamond grits was lower than that of brazed uncoated diamond grits. Accordingly, the temperature of processing arc area of the brazed diamond bur fabricated with the coated diamond grits was lower than that of the brazed diamond bur fabricated with the uncoated diamond grits, and its rate of removal of material was higher than that of the brazed diamond bur fabricated with the uncoated diamond grits.

Structure and Mechanical Properties of Impregnated Diamond Cutting Tools Using Cu-Based Metal Matrix

Cu-based metal matrix, Ti coated and uncoated diamond composite were prepared by hot-press sintering in vacuum. The effects of the mixing time and the sintering temperature on the relative density, hardness and transverse rupture strength (TRS) of the matrix were studied. Structures of specimens sintered at different temperatures were studied by XRD. The TRS and wear resistant of coated and uncoated diamond segment were compared. The results show that the optimum mixing time is 20 hours; with the increase of sintering temperature, the relative density, hardness and TRS of the matrix firstly increase and then decrease; the TRS of diamond segment is lower than the matrix sintered at the same temperature and TRS of Ti coated diamond segment increased by 6.18% as compared with uncoated diamond segment; moreover the wear resistance of Ti coated diamond segment is better than that of uncoated diamond segment.

Improved Thermal Performance of Diamond-Copper Composites with Boron Carbide Coating

B4C-coated diamond (diamond@B4C) particles are used to improve the interfacial bonding and thermal properties of diamond/Cu composites. Scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy were applied to characterize the formed B4C coating on diamond particles. It is found that the B4C coating strongly improves the interfacial bonding between the Cu matrix and diamond particles. The resulting diamond@B4C/Cu composites show high thermal conductivity of 665 W/mK and low coefficient of thermal expansion of 7.5 × 10−6/K at 60% diamond volume fraction, which are significantly superior to those of the composites with uncoated diamond particles. The experimental thermal conductivity is also theoretically analyzed to account for the thermal resistance at the diamond@B4C-Cu interface boundary.

Preparation of high thermal conductivity copper–diamond composites using molybdenum carbide-coated diamond particles

Molybdenum carbide (Mo2C) coatings on diamond particles were proposed to improve the interfacial bonding between diamond particles and copper. The Mo2C-coated diamond particles were prepared by molten salts method and the copper–diamond composites were obtained by vacuum pressure infiltration of Mo2C-coated diamond particles with pure copper. The structures of the coatings and composites were investigated using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicated that the Mo2C coatings effectively improved the wettability between diamond particles and copper matrix, and Mo2C intermediate layers were proved to decrease the interfacial thermal resistance of composites. The thermal conductivity of the composite reached 608 Wm−1 K−1 with 65 vol.% Mo2C-coated diamond, which was much higher than that with uncoated diamond. The greatly enhanced thermal conductivity is ascribed to the 1-μm-thick Mo2C coatings. Mo2C coatings on diamond particles are proved to be an effective way to enhance the thermal conductivities of copper–diamond composites.

Si-Coated Diamond Particles Reinforced Copper Composites Fabricated by Spark Plasma Sintering Process

This article introduced a unique production process of diamond/Cu composite materials via spark plasma sintering. Moreover, effects of Si-coated diamond particles and diamond volume fraction on heat conduction of diamond/Cu composite materials were examined. This research presented Si-coated diamond/Cu composite materials yielded higher heat conduction than that of the samples with uncoated diamond particles. It was found that Si-coated composite materials, including a volume fraction of 50% Si-coated diamond particles, yielded a relatively higher heat conduction of 535 W/mK along with the relative density of 96.3%. The phases present were identified by X-ray diffraction and microstructures were studied by scanning electron microscopy. Additionally, the influence of interface on heat conduction of diamond/Cu composites was specifically discussed.

Effect of TiC Intermediate Layers on the Thermal Conductivity of Copper/Diamond Composites

TiC intermediate layers were formed on the surface of diamond particle with reaction of Ti powders in mixed molten NaCl-KCl salts. The copper/diamond composites with TiC-coated diamond particles were fabricated by pressure infiltration. Then the microstructure and thermal conductivity of the obtained copper/diamond composites were studied. The results showed the thermal conductivity of the composites with a density of 5.65 g/cm3reached 514 Wm-1K-1, which is much higher than with uncoated diamond. The TiC layers synthesized on diamond particles is shown to be an effective way to enhance the thermal conductivity of copper/diamond composite.

Effect of molybdenum as interfacial element on the thermal conductivity of diamond/Cu composites

As a carbide forming additive, molybdenum gets maximum benefit of high thermal conductivities of diamond and copper. Coating Mo on the diamond surface can promote the interfacial bonding in diamond/Cu composites. A Mo coated diamond/Cu composite with high thermal conductivity of 726W/mK is obtained, which is achieved by a thin nano-sized Mo2C layer. Mo coated diamond or un-coated diamond reinforced copper composites have been made by pressure assisted liquid copper infiltration method. The interfacial configuration, the bulk thermal conductivity and the evolution of interfacial thermal resistance are presented, indicating that the good adhesion at the interface can decrease the thermal boundary resistance and thus increase the thermal conductivity of the composites.

Investigation on Brazing of Carbon Film Deposited Diamond for Cutting Vehicle Tyre

The super brazed diamond saw was developed to cut efficiently vehicle tyre in the research. The carbon film deposited diamond and the uncoated diamond were brazed with NiCr alloy by high-frequency induction heating under argon atmosphere at 1030°C for 30 seconds respectively. The interfacial microstructures between the brazed diamond and the filler alloy were analyzed by the advanced testing technologies. The results shows that long-lath carbides with the definite orientation and better flatness are closely arrayed on the brazed uncoated diamond surface and Cr-carbides forms normally and compactly on the surface of carbon film deposited diamond brazed. That is because the carbon film has changed the mechanism of Cr-carbides forming on the surface of diamond brazed. The test of cutting vehicle tyre shows that the use life of the brazed deposited diamond saw is much longer than that of the brazed uncoated diamond saw.

Thermal conductivity and microstructure of Al/diamond composites with Ti-coated diamond particles consolidated by spark plasma sintering

Metal/diamond composites have been considered as the new generation of thermal management material. The critical challenge to obtain composites with high thermal conductivity (TC) is to improve the interfacial bonding between the matrix and diamond. In the present study, a titanium coating was plated on the surface of diamond particles via vacuum evaporation–deposition, and Al/diamond composites were consolidated by spark plasma sintering (SPS) technique. The TC and microstructure of composites, respectively, with coated and uncoated diamond particles are compared and discussed. The results show that the Ti coating can significantly increase the wetting property between Al and diamond, leading to a strong interfacial bonding. The diffusion of Ti into the matrix and the formation of TiC are detected at the Al–diamond interface. The properties of composites, respectively, with coated and uncoated diamond exhibit different trends with increasing sintering temperature or diamond volume fraction. Compared with composites with uncoated particles, the Al/Ti–diamond composites obtained the much higher relative density and TC as high as 491 W/mK. Based on the comparison between the experimental and theoretical values, it is found that the thermal conductivities of Al/Ti–diamond composites have reached or surpassed the theoretical calculations with the particle volume fraction not more than 50%.