Uncoated Diamond Research Articles

Effect of addition of boron and B4C coated diamond on the microstructure and compressive behaviour of porous aluminium composites

Owing to the growing demand for lightweight materials in automotive and aerospace applications, porous aluminium composites are studied in-depth due to their high strength-to-weight ratio, higher stiffness and good compressive properties. The studies include enhancing their strength by the inclusion of strengthening reinforcements. In this study, the effect of boron addition in the matrix combined with uncoated diamond as reinforcements was compared with the effect of B4C coated diamond on the microstructure, density, porosity and compressive properties of porous AlSnMg matrix composites. The addition of boron in the matrix combined with using uncoated diamond showed least significant improvement in properties while the addition of B4C coated diamond revealed better results. The microstructure of porous composites revealed that the boron addition insignificantly affected the bonding at the interface of matrix and uncoated diamond reinforcement comparatively B4C coated diamond improved the bonding at the interface of aluminium matrix and diamond. As a result, the higher densities and compressive strength of 39.97 MPa and energy absorption capacity of 13.2 MPa were acquired for porous Al composites with 10 wt.% of B4C coated diamond suggesting the use of coated diamond in porous aluminium for enhancing their strength in applications as fillers in light weight structures for automotives.

An interior damage free approach for nanosecond pulsed laser ablation of single crystal diamond via metal film induced self-maintaining graphitization

When laser ablation was conducted on an uncoated single-crystal diamond (SCD) substrate, interior damage and random ablation were observed. Metal film-induced self-maintaining graphitization (MISG) was proposed as a generic approach to solve this problem. MISG was realized through coating a ∼ 100-nm-thick metal film on an SCD substrate. Experiments involving laser irradiation of metal films, such as Au-, Al-, Ti-, and Pt-coated SCD substrates, revealed that the material removal depths were the same when the output power was the same and that the surface was covered by graphite after laser irradiation. In addition, the laser-induced damage to the upper or lower surface in the case of the uncoated SCD substrate disappeared. A semitransparent model based on Beer-Lambert law and an opaque model based on modified Level-Set method were built to simulate laser irradiation on uncoated and metal–coated SCD substrates. In the case of the uncoated sample, the laser energy was largely absorbed by the areas with high-concentration defects, leading to preferential graphitization. In the case of the metal-coated sample, a graphite layer was thermally induced on the SCD surface via heat transition during the period of laser irradiation of the metal film. Subsequently, the graphite layer was self-maintaining, and the material removal acted like a graphite piston sinking to the interior of the SCD substrate. This study demonstrates the feasibility of MISG as a universal approach for avoiding interior damage during laser ablation of SCD substrates.

Thermal-mechanical evolution behaviors of metal matrix diamond composite by powder bed fusion-laser beam

The thermal damage of diamond and the residual stress have always been the critical issues to be resolved in the development of metal matrix diamond composites. In the presented study, FeCoCrNi high entropy alloys (HEAs)-diamond composites were fabricated by powder bed fusion-laser beam of metals (PBF-LB/M), using un-coated diamond and Ti–Ni coated diamond, respectively. Based on the numerical and experimental analysis, the effect of thermal-mechanical behavior on the microstructures and mechanical properties of the composites was systematically investigated. By establishing the temperature field of the PBF-LB molten pool, the defects, diamond graphitization and in-situ TiC formation were studied. The start-temperature for diamond graphitization in coated samples was 365 °C higher than that of un-coated samples, due to the diffusion barrier effect of TiC. Subsequently, by thermo-mechanical coupling, the property and value of the residual stress exhibited sudden change at the diamond/matrix interface. The TiC intermediate layer significantly relieved the stress concentration at interface, and effectively avoided cleavage fracture of the diamond and the initiation of interfacial cracks. At the moderate molten-pool temperature, the coated diamond composites exhibited optimal performance, as bending strength of 913 MPa, friction coefficient of 0.25 and worn mass loss of 0.67 mg. Finally, the quantitative relationship between PBF-LB molten-pool temperature and the relative density, graphitization degree, residual stress, retention(bending strength) and wear performance was established, to demonstrate the thermal-mechanical evolution of the HEAs-diamond composites by PBF-LB.

Efficient manufacture of high-performance electroplated diamond wires utilizing Cr-coated diamond micro-powder

The slicing of silicon ingots using electroplated diamond wires is a fundamental process in the creation of semiconductor devices such as chips and photovoltaic cells. Composite electroplating, a process that uses nickel (Ni) plating to fix diamond particles onto a steel wire, is a critical step in the manufacturing of these diamond wires. In this work, chromium (Cr)-coated diamond was used to achieve rapid and high-quality composite electroplating, thereby aiding the production of high-performance diamond wire saws. The Cr-coated diamond micro-powder was prepared utilizing vacuum slow evaporation technology at a temperature of 850 °C. This resulted in a uniform and firm Cr coating that was firmly bonded to the diamond surface via Cr3C2. Subsequent electrochemical tests were conducted in the composite electroplating bath. Linear scanning voltammetric curves revealed that the Cr-coated diamond was capable of inducing a more positive shift in the overpotential of Ni deposition, thus enhancing the reaction beyond that of uncoated diamond micro-powder. Additionally, the electrochemical impedance spectra indicated a decrease in charge transfer resistance during composite electroplating, attributable to the conductivity of the Cr-coated diamond. Electroplated diamond wires incorporating Cr-coated diamond demonstrated a greater abrasive density per unit length. SEM results showed that Ni was able to deposit on the Cr-coated diamond surface, resulting in the abrasives being completely covered by the Ni plating. The Cr-coated diamond wire exhibits a stronger resistance to abrasive detachment after cutting, which could increase the diamond-protrusion of the wire. The utilization of Cr-coated diamond micro-powder as an abrasive is anticipated to enhance the manufacturing efficiency of diamond wires and improve product quality, thereby promoting advancements in hard and brittle material processing technology.

Improved Bending Strength and Thermal Conductivity of Diamond/Al Composites with Ti Coating Fabricated by Liquid-Solid Separation Method.

In response to the rapid development of high-performance electronic devices, diamond/Al composites with high thermal conductivity (TC) have been considered as the latest generation of thermal management materials. This study involved the fabrication of diamond/Al composites reinforced with Ti-coated diamond particles using a liquid-solid separation (LSS) method. The interfacial characteristics of composites both without and with Ti coatings were evaluated using SEM, XRD, and EMPA. The results show that the LSS technology can fabricate diamond/Al composites without Al4C3, hence guaranteeing excellent mechanical and thermophysical properties. The higher TC of the diamond/Al composite with a Ti coating was attributed to the favorable metallurgical bonding interface compounds. Due to the non-wettability between diamond and Al, the TC of uncoated diamond particle-reinforced composites was only 149 W/m·K. The TC of Ti-coated composites increased by 85.9% to 277 W/m·K. A simultaneous comparison and analysis were performed on the features of composites reinforced by Ti and Cr coatings. The results suggest that the application of the Ti coating increases the bending strength of the composite, while the Cr coating enhances the TC of the composite. We calculate the theoretical TC of the diamond/Al composite by using the differential effective medium (DEM) and Maxwell prediction model and analyze the effect of Ti coating on the TC of the composite.

Effect of Cu-coated diamond on the formation of Cu–Sn-based diamond composites fabricated by laser-powder bed fusion

In this study, Cu–Sn-based diamond composites were fabricated using L-PBF. The effects of the Cu-coated diamond on the melt-pool evolution, diamond–metal matrix bonding, thermal damage, and friction behavior of Cu in the Cu–Sn-based diamond composites were investigated. Moreover, the optimum L-PBF parameters for processing Cu-coated diamond/Cu–Sn composites were investigated. A convolutional neural network based on deep learning was used to process laser-scanned diamond images and evaluate the diamond thermal damage by model-feature visualization. The thermally damaged Cu-coated diamond and percentage of severely damaged parts were reduced compared to those of the uncoated diamond. Thick Cu coating changed the wettability of the diamond and matrix, thereby increasing the friction of the molten pool and unmelted metal particles and introducing the friction of the Cu microfluidic flow on the diamond. Hence, the mechanical holding force of the CuSn alloy matrix on the diamond substantially increased, and the bending strength of the Cu-coated diamond/Cu–Sn composites fabricated using L-PBF reached 720 MPa, which is approximately twice that of diamond/Cu–Sn (365 MPa).

Properties of SiO2-B2O3-Li2O-ZnO-Al2O3 glass-ceramic-coated diamond particles prepared by sol-gel method

During the process of sintering diamond/ceramic composites, the wettability between diamond and the ceramic matrix is poor, and there are many irregular pores in the composites, which leads a low bending strength of the composites and easy shedding of diamond. In order to solve these problems, SiO2-B2O3-Li2O-ZnO-Al2O3 glass-ceramic coated diamond was prepared by a sol-gel method, and the properties of the coated diamond abrasive particles were studied. The SBLZA glass-ceramic-coated diamond exhibited high thermal stability and excellent oxidation resistance, making it a good protective material for diamond. The oxidation resistance of the SBLZA glass-ceramic-coated diamond was determined by thermogravimetric analysis (TGA). The uncoated diamond abrasive particles began to oxidize at 723 °C, while the coated abrasive particles were resistant to oxidation at temperatures up to 1000 °C. The glass-ceramic coating significantly improved the bonding between diamond and the ceramic matrix. The use of SBLZA glass-ceramic-coated diamond instead of uncoated diamond in the composites sintered at 750 °C resulted in a decrease in the volume expansion rate of the diamond/ceramic composites from 37.2 % to 28.5 %, and an increase in the bending strength from 38.4 MPa to 61.5 MPa.

Improvement in effectiveness of diamond in strengthening the porous aluminium composite

In this study, an aluminum (Al) alloy matrix reinforced with uncoated and titanium (Ti) -coated diamond were developed using powder metallurgy technique where polymethylmethacrylate (PMMA) particles were employed as space holders. The weight % of uncoated and coated diamond varied as (0, 6, 9, 12, 15, and 20 wt.%). Microstructural and elemental analysis was examined using scanning electron microscopy and energy dispersive spectroscope, respectively. The relative density and porosity that were in the range of 0.72–0.92 and 31–44% respectively, were measured using Archimedes principle. The compressive properties were measured and correlated with microstructure observations. The microstructure of the composite samples revealed presence of well-defined macro pores with good interfacial integrity. The X-ray diffraction revealed the presence of strengthening phases such as Al2Ti, Mg2Sn, AlB12, Cu5Sn6, Al12Mg17 and MgB2 phases formed as a result of addition of metal additives in Al matrix. Further improvement in the strength was obtained by using Ti-coated diamond particles as reinforcement. As Ti formed a good interface between the Al alloy matrix and the diamond thereby preventing the formation of undesirable carbide phases. There was an improvement in plateau stress and energy absorption capacity of 82 and 88% as compared to unreinforced porous sample. The maximum values obtained for the plateau stress and energy absorption capacity were 45.12 MPa and 13.68 MJ/m3 respectively for 9 wt.% of Ti-coated diamond reinforced composites. Uncoated diamond reinforced composites, on the other hand, reduced the strength of porous Al alloy matrix due to the formation of brittle intermetallic compound such as carbides (Al2C3) at the interface. As a result, the coated diamond particle surface modifies and improves the wettability of the Al alloy matrix and diamond interface.

Preparation of Ti-coated diamond/WC-Co-based cemented carbide composites by microwave-evaporation titanium-plating of diamond particles and microwave hot-press sintering

Diamonds are considered ideal additives for improving the wear resistance of cemented carbide materials and thus for extending their service life. However, the poor wettability and thermal stability of diamonds limit their effectiveness. To solve this problem, in this study, microwave-evaporation technology, a low-cost and simple approach, was used to prepare a uniform titanium coating on diamond surface with an optimized diamond-to-titanium-hydride ratio of 5:3 and an optimized holding time of 1 h at 760 °C. The TiC interlayer with needle-rod microstructure was observed. The coating could increase the oxidation weight-loss temperature by 152.7 °C. The different steps of the high-temperature ablation process of Ti-coated diamond were also revealed. Then, Ti-coated diamond/WC-Co-based cemented carbide composites with uniform microstructure, good interfacial bonding, and no thermal burning loss of diamond were prepared using microwave hot-press sintering with a temperature of 1050 °C only and a pressure of 40 MPa, leading to good wear resistance. The wear rate of the composites prepared with Ti-coated diamond was 25.7% lower at room temperature and 50.7% lower at 400 °C than that of the uncoated diamond. This approach minimized the thermal damage to diamond since both Ti-coated diamond and the composites were prepared at low temperatures.

Research on gold film-assisted ultraviolet nanosecond laser machining of diamond microgrooves

Diamond microgrooves have great application prospects in biomedicine, high-power semiconductor devices, optical imaging, chip thermal management, and cutting tools. In this work, the effect of gold film on ultraviolet nanosecond laser machining of single-crystal diamond microgrooves was investigated through simulation and experimental research. The simulation results show that the ablation width and depth gradually increase with the increase of gold film thickness, and the ablation depth reaches a maximum value when the thickness of gold film increases to 100 nm. The surface morphology and elemental analysis show that the gold film was first melted and then re-solidified around the microgrooves under ultraviolet nanosecond laser irradiation. The ablation threshold of Au-coated diamond is 4.05 J/cm2, 24 % smaller than that of uncoated diamond. The material removal rate of Au-coated microgrooves is always higher than that of uncoated microgrooves at the same laser intensity. At laser intensity of 8.5 J/cm2, it is 1.1 times higher than that of uncoated diamond microgrooves. Moreover, the physical mechanism of gold film during laser machining of diamond microgroove is analyzed. This study provides a new method for efficient machining of diamond microgrooves.

Reactive spark plasma sintering of SiC-TiC-diamond composites

SiC-TiC-diamond composites were fabricated via spark plasma sintering at hold temperatures of 1600 °C, 1625 °C, and 1650 °C from a powder blend containing by weight 30 % Si, 30 % Ti, and either 40 % uncoated or TiC-coated diamond. Due to the sintering conditions, sp3-diamond decomposed into thermodynamically favorable sp2‑carbon, reacting with Si and Ti to form SiC and TiC at T ≥ 1600 °C. As the hold temperature increased, the composite density reduced due to excess graphite formation for the uncoated diamond composites. However, at too low of a temperature the porosity fraction increased in the SiC-TiC matrix for the TiC-coated diamond composites. Overall, the results revealed that composites with ~97 % theoretical density and minimal (up to 5 vol%) graphite can be achieved by sintering Si-Ti-uncoated diamond at 1600 °C and Si-Ti-TiC-coated diamond at 1625 °C. X-ray diffraction, electron and x-ray microscopies with imaging analyses were carried out to quantify the volume fractions of each composite phase and used to explain the composite densification behavior. Conventional and energy filtered transmission electron microscopy, in addition to electron energy loss spectroscopy, were conducted to understand the nature of diamond graphitization with respect to the nucleation and growth of SiC, TiC, and nanoscale graphite.

Investigation of metal-coating-assisted IR nanosecond pulsed laser ablation of CVD diamond

Laser ablation is demonstrated to be a competent approach to processing chemical vapor deposition (CVD) diamond which is admitted to own poor machinability and is accordingly arduous to machine using conventional techniques. Notwithstanding, initial laser absorption by defects typically precipitates undesirable ablation quality and an increment in internal defects. The strategy of metal-coating-assisted laser ablation, which applies a coating on the diamond prior to laser irradiation to curtail defects and advance the quality of the ablated surface, is proposed in this study. In addition, an absorptivity-based laser energy distribution model is established to evaluate surface roughness and ablation depth. It can be concluded that the metal coating prevents local graphitization during the early ablation stage. The laser ablation of Ti-coated diamond surfaces resulted in a maximum reduction in surface roughness of 42.6% and 53%, respectively, for 100 and 500 nm coating, in comparison to that with the uncoated surfaces. Besides, the ablation depth of the laser-ablated 500 nm coating surface abates and reaches 21% in comparison with the uncoated diamond, while the 100 nm coating has a negligible effect on the ablation depth. In summary, the application of thin coatings on diamond prior to laser ablation results in homogeneous graphitization and a better surface finish with a marginal reduction in ablation depth.

Interfacial characteristics and thermal damage of brazed W-coated diamond with Ni- based filler alloy

In this study, the brazing of W-coated diamond to 1045 steel with Ni-based filler alloy was investigated. In addition, the brazing thermal damage of W-coated diamond joints was compared to that of uncoated ones. After brazing, the coating was not fount to affect the good wettability of the Ni-based filler alloy to the diamond. Moreover, the cracks at the interface of W-coated diamond were less and smaller. An ordered and compact Cr3C2 layer was formed on the surface of the uncoated diamond, while a disordered Cr3C2 layer and rod-like Cr7C3 growing into the filler alloy were formed on the surface of the W-coated diamond. The chromium carbide layer on the W-coated diamond surface was thinner, the graphitization degree was lower, and the maximum residual compressive stress was reduced by 11.4% compared to those on the uncoated diamond. The mechanical properties of the W-coated diamond grits were better preserved after brazing, and the coating alleviated the thermal damage of the brazed diamond joint.

Characteristics of Diamond Abrasive Used in Magnetic Abrasive Finishing of Nickel-Based Superalloys

Abstract Nickel-based superalloys have a wide range of high-temperature applications such as turbine blades. The complex geometries of these applications and the specific properties of the materials raise difficulties in the surface finishing. Magnetic abrasive finishing (MAF) has proven effective in finishing the complex geometries. In MAF, the magnetic properties of the workpiece, tool, and abrasive play important roles in controlling finishing characteristics. This paper presents the effects of nickel coating on the abrasive behavior during finishing and resulting finishing characteristics of Ni-based superalloys. The Ni-coated diamond abrasive is more attracted to the magnet than the Ni-based superalloy surface. As a result, fewer Ni-coated diamond abrasive particles, which are stuck between the magnetic-particle brush and the target surface, participate in surface finishing. Because of this, coupled with the reduced sharpness of abrasive cutting edges due to the coating, Ni-coated diamond abrasive cannot effectively smooth the target surface in MAF. However, the Ni coating is worn off during finishing of the hard, rough, additively manufactured surface. Then, the diamond abrasive participates in finishing as uncoated diamond abrasive and facilitates the material removal, finishing the target surface.

Enhancement of fluorescence from nitrogen-vacancy center ensemble in bulk diamond with broadband antireflection coatings

The negatively charged nitrogen-vacancy (NV−) center in diamond is a promising platform for quantum sensing. However, fluorescence from the NV− centers suffers large energy loss at the diamond–air interface. Here, we propose a broadband antireflection coating to enhance the fluorescence intensity by simultaneously reducing the energy loss of the excitation laser and the fluorescence. The reflectance for normal-incidence light decreases from nearly 17% for bared diamond to below 0.33% for coated diamond in the wavelength range 500 nm–800 nm. The reflectance averaged over the fluorescence bandwidth is below 3% for angles of incidence less than 20°. The measured emitted fluorescence for the coated diamond is 1.44 times that of uncoated diamond, corresponding to nearly 20% improvement in the measurement sensitivity. The proposed method is significant for enhancing the signal-to-noise ratio of NV−-based sensors.

High-speed machining of aluminium alloy using vegetable oil based small quantity lubrication

In an attempt to investigate the effectiveness of vegetable oil based small quantity lubrication in high-speed machining of aluminium, this study finds that its usefulness is more significant in an intermittent cutting process like end milling than in turning, where continuous cutting happens. The investigation was carried out using small quantity lubrication aerosol, produced by air atomization of sunflower oil at the rate of 100 ml/h for each cutting zone. In the high-speed turning operations, uncoated and polycrystalline diamond–tipped WC inserts were used. 5%–20% reduction of cutting force could be realized by small quantity lubrication application, compared to dry environment. The highest order of reduction was observed when the cutting velocity was increased from 700 to 1000 m/min. At lower velocities, small quantity lubrication effect was almost insignificant. However, high-speed end milling operations received substantially superior benefit by small quantity lubrication application. The reduction of feed force was 30% or more among different cutting speeds. The beneficial effect of small quantity lubrication application was significantly more in machining commercially pure 1050 grade of aluminium than 7075 alloy. The required prevalence of the thick-film lubrication at the interface of chip and tool rake for arresting any possible diffusion of aluminium to tool material was significant in the intermittent cutting since every cutting edge drew in fresh micro-droplets of lubricant before resuming cutting in its next cycle of engagement with workpiece. Interestingly, the end milling performance of small quantity lubrication–assisted uncoated carbide was so good that diamond-coated tools were not necessary. Surface roughness profiles, chip morphology and traces of built up edge formation were critically investigated and the results clearly indicated the predominantly more favourable outcome of small quantity lubrication application in end milling, compared to turning.

Bending Strength and Cutting Performance of WB-Coated-Diamond/Fe-Ni Composites

Diamond particle with tungsten boride (WB) coating was synthesized by the molten salt method. Three different diamond/Fe-Ni composites made from pristine diamond, B4C coated diamond and WB coated diamond with Fe-Ni powders were prepared by powder metallurgy. The composition and microstructure of the tungsten boride coating were investigated. Both bending strength and cutting performance of the composites were investigated. Addition of the WB coating provided an increased bending strength (871.2 MPa) and relative density (93.54%), compared with the composites consist of uncoated diamond and Fe-Ni (746.8 MPa, 92.81%). Three different Fe-Ni-based impregnated diamond drill bits contained 20 vol.% pristine diamond, B4C coated diamond and WB coated diamond were manufactured by powder metallurgy, respectively. Drilling rate of bits was measured by XY-4 geological core drill on granite. The test results show that the drilling rate of bits with WB coated diamond (2.42 m/h) was 40% higher than that with pristine uncoated diamond (1.72 m/h).

Investigation on Drill Wear and Micro Hole Quality in High Speed Drilling of High Frequency Printed Circuit Board

Due to the severe wear of micro drill and the difficulty in controlling of hole quality, high speed drilling process of high frequency printed circuit board (PCB) was attracted comprehensive attention. In this investigation, the wear width of drills’ primary face was measured, and the wear morphologies of micro drills were studied at once. Furthermore, regularity of micro hole quality concerning drilling burr and nail heading while drilling with different types of drills were analyzed. The research results indicated that the wear width of diamond coating drill reduced slightly. Abrasive wear and adhesive wear were mainly occurred on uncoated drill and diamond like carbon coating drill, but some micro breaches and pits appeared on uncoated drill. Meanwhile, drilling with diamond like carbon coating drill could obtain better hole quality than drilling with uncoated ones. However, diamond coating drill performed well in terms of ability of wear resistance, as well as micro hole quality.

Thermal stability of polycrystalline diamond compact sintered with boron-coated diamond particles

The polycrystalline diamond compact (PDC), which consists of a polycrystalline diamond layer on a tungsten carbide (WC)/cobalt (Co) substrate, is extensively utilized as drilling bits. However, the poor thermal stability due to the graphitization and oxygen susceptibility of diamond severely limits the application of PDCs to high-temperature drilling work. In this study, a new PDC with improved thermal stability is successfully synthesized with boron (B)-coated diamond particles, which forms a uniform boron carbide (B4C) barrier. The as-received B4C phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperatures to 800 °C and 780 °C, respectively, which are ~100 °C and ~30 °C higher than those (700 °C and 750 °C) of the PDC sintered with uncoated diamond particles. The B4C barrier protects diamond grains from direct contact with the Co phase, prohibiting the cobalt-catalytic graphitization. In addition, the oxidation of the B4C barrier occurs prior to that of the diamond grains, which inhibits the PDC from oxidation.

Influence of B4C coating on graphitization for diamond/WC-Fe-Ni composite

Diamond/WC-Fe-Ni composite is a potential composition for impregnated diamond drill bits. It is necessary to avoid the graphitization of the diamond from Fe and Ni under the powder metallurgy process. Boron carbide (B4C) was coated on diamond, and diamond/WC-Fe-Ni composites were consolidated by hot pressing at different temperatures. The influences of sintering temperature and interfacial structure on bending strength and wear behavior were investigated. The bending strength for diamond/WC-Fe-Ni composite was dependent on matrix densification and interfacial graphitization. Un-coated diamond was eroded by Fe-Ni matrix and partially converted to graphite during the sintering process at all sintering temperatures. In opposite, B4C coating was beneficial to matrix densification at a lower sintering temperature, and delayed the appearance of graphitization to around 1300 °C. Therefore, the diamond/WC-Fe-Ni composites with B4C coating exhibited larger bending strength and better wear behavior at a relative low sintering temperature.