Coated Diamond Particles Research Articles

Effect of different titanium addition methods on the properties of diamond/Cu composites

Due to the low bonding strength between diamond and copper, the thermal conductivity and mechanical strength of diamond/copper composites are affected. In order to improve the interface bonding strength, this paper prepared diamond/Cu composites with titanium element in two forms: adding titanium to the copper matrix and using titanium coated diamond particles, respectively. The microstructure and composition analysis of the materials were carried out through SEM, EDS, AFM, etc. The bending strength and thermal conductivity of titanium coated diamond/copper composites reached 230 MPa and 480 W/(m·K), respectively, which were higher than the bending strength and thermal conductivity of diamond/Cu composites with added titanium in the matrix (208 MPa and 127 W/(m·K) and significantly higher than the corresponding properties of pure diamond/Cu composites (69 MPa and 108 W/(m·K)). Pre coating a layer of titanium carbide on the surface of diamond can serve as a connecting bridge, effectively reducing interfacial thermal resistance and improving mechanical properties, which is more effective than adding titanium powder to the matrix to improve the bending strength and thermal conductivity of diamond/Cu composites.

Refractometric method to study the coating thickness of diamond nanoparticles

A method based on refractometric measurements of liquid nanodisperse systems has been developed to determine the quantitative composition of diamond-amorphous carbon colloidal particles. It was demonstrated that by measuring the changes in the refractive index and density of sols caused by changes in particle concentration it is possible to determine the thickness of the particle surface layer, assuming its composition is known. Within the framework of the Mie theory, the influence of the size of diamond particles with carbon coating on the refractive index of hydrosols was quantified. The limits of applicability of the developed method have been determined. For several polydisperse sols with coated diamond particles the thickness of carbon coating was determined.

Effect of uncoated and coated diamond on the compressive properties of porous aluminium composites

AbstractPorous aluminium composites are structural and functional materials that have vast potential, due to their lightweight and high energy absorption capacity, especially in automotive and aerospace applications. In this study, the effect of varying content of uncoated and titanium coated diamond particles on the compressive properties of porous aluminium composite was investigated. The composites were developed using powder metallurgy technique and porosity was attained by using polymethylmethacrylate (30 wt.%) as space holder material. The morphology of the pores was found to replicate the shape and size of polymethylmethacrylate particles, that were uniformly distributed in the composites. X‐ray diffraction analysis confirmed formation of aluminium carbide in uncoated diamond‐based aluminium composites while negligible amount was present in titanium coated porous composites during sintering. The porosities of composites decreased with an increase in diamond content due to the incomplete decomposition of polymethylmethacrylate particles. Moreover, the maximum plateau stress and energy absorption capacity of 9.96 MPa and 1.7 Mj/m3 were obtained for the composites with 8 wt.% of titanium coated diamond particles. Thus, coating inhibits the formation of undesirable compounds and contributes to better interfacial bonding between matrix and reinforcement.

Microstructure and Strengthening Effect of Coated Diamond Particles on the Porous Aluminum Composites.

In this work, porous Al alloy-based composites with varying Ti-coated diamond contents (0, 4, 6, 12 and 15 wt.%) were prepared, employing the powder metallurgy route and using a fixed amount (25 wt.%) of polymethylmethacrylate (PMMA) as a space holder. The effects of the varying wt.% of diamond particles on the microstructure, porosities, densities and compressive behaviors were systematically evaluated. The microstructure study revealed that the porous composites exhibited a well-defined and uniform porous structure with good interfacial bonding between the Al alloy matrix and diamond particles. The porosities ranged from 18% to 35%, with an increase in the diamond content. The maximum value of plateau stress of 31.51 MPa and an energy absorption capacity of 7.46 MJ/m3 were acquired for a composite with 12 wt.% of Ti-coated diamond content; beyond this wt.%, the properties declined. Thus, the presence of diamond particles, especially in the cell walls of porous composites, strengthened their cell walls and improved their compressive properties.

Profiling interfacial reaction features between diamond and Cu-Sn-Ti active filler metal brazed at 1223 K

• When the TiH 2 content is below 5 wt.%, completely uncoated and partially coated diamond particles with sharp edges can still be observed. When above 5 wt.%, all diamond particles are completely coated, indicating sufficient wettability has been achieved. • The interfacial reaction layer is found to be composed of TiC, the thickness of which is demonstrated to increase as a function of TiH 2 content, arriving at the peak value of 1.70 µm and remaining almost constant afterwards. • Further increasing TiH 2 content above 5 wt.% is unnecessary or even harmful, as it may encourage the formation of brittle Cu 41 Sn 11 phase, leading to significantly reduced wear resistance and potentially downgraded grinding efficiency. Diamond/Cu-Sn-Ti composites have been successfully prepared by cold-press forming in conjunction with high-temperature vacuum active brazing at 1223 K. Ensuing wetting behaviors between diamond and filler metal, interfacial characteristics of the reaction layer, and wear resistance of the bulky composite have been fully investigated. It is revealed that all diamond particles can only be fully coated when the TiH 2 content exceeds 5 wt%, below which sharp edges on diamond can still be observed. The interfacial reaction layer is found to be composed of TiC, the thickness of which is demonstrated to increase as a function of TiH 2 content, arriving at the peak value of 1.70 µm and remaining almost constant afterwards. It is further shown that the maximum wear resistance occurs approaching 5 wt% TiH 2 content. Potential mechanisms responsible for such interesting phenomena have been postulated.

Comparison of tribological behaviors of polycrystalline diamonds synthesized by titanium- and boron-coated diamond particles

In this study, the influence of the coating of diamond particles on the tribological behaviors of polycrystalline diamond (PCD) was investigated. Titanium- (Ti)- and Boron- (B)-coated diamond particles were sintered under high pressure-high temperature condition to obtain Ti-PCD and B-PCD, respectively. The Ti and B coatings were deposited via magnetic sputtering. The PCD specimens were characterized through scanning electron microscopy, X-ray diffraction, impact tests, thermal gravimetric analysis-differential scanning calorimetry and tribological tests. The results indicate that uniform titanium carbide (TiC) and boron carbide (B4C) phases are generated during the sintering processes of Ti-PCD and B-PCD, respectively. The as-obtained TiC phase promotes the tribological behaviors of Ti-PCD in vacuum, including a considerable enhancement of wear resistance. The TiC phase inhibits diamond exfoliation by strengthening interface bonding, which involved transforming the mechanical interaction between the diamond grains and cobalt binder to chemical bonding. However, massive pores are formed during sintering that weakens the interface bonding in B-PCD, and thus the induced wear resistance is low. Therefore, the Ti coating of diamond particles promotes the tribological behaviors of PCD, whereas B coating deteriorates it. This study lays a foundation for the development of suitable technology for the fabrication of PCD.

Laser powder bed fusion of diamond/N6 MMCs enabled by Ni-Ti coated diamond particles

Metal matrix composites (MMCs) have received increasing attention and there is a growing interest in additive manufacturing (AM) of MMCs with complex shapes recently. However, it remains challenging to control the quality of composite powder for MMCs. In this study, the diamond particles are firstly coated with thin layers of Titanium and Nickel to ensure strong interface bonding with the Nickel matrix. The influence of ball milling parameters on the Ni-Ti coated diamond/N6 composite powder particles preparation and the effect of processing parameters during laser powder bed fusion (LPBF) on the densification of and defects in the fabricated samples are analyzed. In the ball milling stage, the results show that highly flowable composite powder particles for LPBF can be obtained under a ball milling time of 4 h, a speed of 250 rpm, and a ball-to-powder ratio of 2:1. With the optimized composite powder, a set of Ni-Ti coated diamond/N6 MMCs are further manufactured under the laser powers of 150, 160, and 170 W and scanning speed of 250 mm/s, the MMC samples have relative densities higher than 99%. Our study demonstrates the feasibility of manufacturing dense diamond/N6 and other similar MMCs with appropriate coating, ball-milling and LPBF parameters.

Laser Powder Bed Fusion of Diamond/N6 Mmcs Enabled by Ni-Ti Coated Diamond Particles

Laser Powder Bed Fusion of Diamond/N6 Mmcs Enabled by Ni-Ti Coated Diamond Particles

Enhanced thermal conductivity of copper/diamond composites by fine-regulating microstructure of interfacial tungsten buffer layer

In this paper, tungsten (W) coatings were deposited on surface of diamond particles by magnetron sputtering for fabricating copper/diamond composites with high thermal conductivity. To reveal the influence of interfacial microstructure on performance of the composites, the W coated diamond particles subjected different annealing process before the composites were fabricated via pressure-assisted infiltration. The evolution of interfacial microstructure and composition of the coating layer were studied. Thermal conductivity of the composites exhibited increasing firstly and decreasing subsequently with the interfacial phase transformed from metallic W to corresponding carbides. Compared with diamond/WC/Cu interfacial microstructure, constructing diamond/WC/W2C/Cu interfacial microstructure via fine regulation is a critical factor for the optimized thermal conductivity of the composites. When the interfacial coating layer was composed of WC phase (97.6 wt.%) and W2C phase (2.4 wt.%), the highest thermal conductivity of the composite reached to 836 W⋅m−1⋅K−1. Based on the theoretical calculation, the W2C sublayer in diamond/WC/W2C/Cu interfacial microstructure reduces the acoustic impedance mismatch between Cu and the carbide buffer layer, resulting in higher interfacial thermal conductance.

Enhanced thermal conductivity in diamond/copper composites with tungsten coatings on diamond particles prepared by magnetron sputtering method

Tungsten coatings of 45–300 nm thickness were sputtered deposited on diamond particle surfaces, and diamond/Cu composites were obtained through pressureless infiltration of liquid copper into a bed of coated diamond particles. The composition of the as-deposited coatings was investigated. The effects of coating characteristics on the microstructure, gas tightness and thermal conductivities (TC) of the diamond/Cu composite were also discussed. Results showed that the originally smooth diamond surface are uniformly covered by nanosized tungsten cone arrays. Tungsten coatings with a thickness above 93 nm was found to be the most effective in improving the densification of overall composites and minimizing the interface thermal resistance between reinforcement and matrix. The thermal conductivity of composites reached 731 ± 10 W m−1 K−1 with a 300 nm tungsten coating and achieved a maximum of 796 ± 11 W m−1 K−1 with 218 nm coating. In addition, the interface thermal resistance between matrix and coated diamond particles was discussed in accordance with the calculations using a theoretical model.

Effect of diamond surface treatment on microstructure and thermal conductivity of diamond/W-30Cu composites prepared by microwave sintering

W-30Cu composites added with different amount (0–8 wt%) of diamond were fabricated by electroless copper plating and microwave sintering. The effects of sintering condition and diamond addition on the densification and thermal conductivity of the composites were investigated. The results show that the temperature, holding time, diamond content, and diamond-metal interface state all have effects on the properties of the diamond/W-30Cu composites. The relative density of the diamond/W-30Cu composites with 4 wt% coated diamond particles reached 94.99% after sintering at 1200 °C for 30 min, and the thermal conductivity reached 239.56 W·m−1 K−1, which is 42% higher than that of uncoated diamond/W-Cu composites.

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.

Effect of tungsten based coating characteristics on microstructure and thermal conductivity of diamond/Cu composites prepared by pressueless infiltration

Tungsten coatings were deposited on diamond particles by vacuum magnetron sputtering. The coated diamond particles were firstly heat treated at different temperatures, and diamond/copper (Cu) composites were fabricated by using a pressureless infiltration method afterwards. The influences of heat treatment on the microstructure and composition of tungsten based coating surface and diamond/copper composites were analysed. Notable differences were found in the microstructure with heating temperatures. Moreover, the tungsten based coating surface contained large quantities of oxidised tungsten, and the phase composition of the coatings varied within the range of tungsten–W2C–WC as the heat treatment temperature increased. The fracture surface morphologies in the copper matrix composites reinforced with diamond particles with coatings were identically characterised with the presence of ductile fracture of matrix accompanied by dissociation of diamond particles from the matrix. The thermal conductivity (TC) and gas tightness behaviours of the diamond/copper composites were also explored. A maximum TC of 768 W m−1 K−1 and a fine gas tightness of 2.5 × 10-10 Pa m3/s were obtained with reinforcement of tungsten-coated diamond particles treated at 800 °C. The value of the interface thermal resistance between copper and diamond particles was also estimated and specifically discussed.

Influence of inorganic coating over diamond particles on interaction force and dispersability in electroless solution

The inorganic coating of Al2O3 was introduced on nanoparticles to weaken their tendency of agglomeration in electroless plating bath. The influence of the coating on interaction energy and interaction forces between the coated particles was evaluated in this study. The Al2O3-coated diamond particles were prepared by the heterogeneous nucleation process. The attractive interaction and repulsive interaction between the coated particles in electroless nickel (EN) solution were calculated by the classical DLVO theory. Sedimentation tests were conducted to verify the modelling. The calculation predictions are well in agreement with the experimental results. The Al2O3 coating could reduce van der Waals attraction by enlarging the surface separation distance of diamond particles, and could increase electrical double layer repulsion by increasing the surface potentials in EN solution. Consequently, it could weaken the net attractive interaction, whose net attractive force decreased from −3.77×10−2N/m between bare particles to −1.12×10−2N/m between the coated ones, a reduction by 70%, at the separation distance of 1κ−1. The coated diamond particles in EN solution show a slower settling rate than bare ones. The Al2O3 coating contributes to the high dispersability of the coated particles under the agitation condition.

Thermal conductivity of copper-diamond composite materials produced by electrodeposition and the effect of TiC coatings on diamond particles

Copper matrix composite materials with diamond particles are considered to be among the leading candidates as the heat sink materials for future electronic devices. However, today, these materials are mostly produced by high temperature-high pressure (HTHP) processes, which can be very costly. In order to explore an economically more viable approach of producing copper-diamond composite materials, we used electrodeposition to synthesize such materials and measured their thermal conductivities. The maximum thermal conductivity observed was 454 W/mK at 68.2 vol % diamond. In an attempt to improve the thermal conductivity further, titanium carbide (TiC) coatings were implemented on the diamond particles. The TiC coated diamond particles embedded in the electrodeposited copper matrix improved the thermal conductivity to 557 W/mK at 34.7 vol %, which is ∼40 % higher than 400 W/mK for pure copper. This value is comparable to currently available commercial HTHP heat sink materials. These results show that there is a potential of using electrodeposition an alternative synthesis method for producing copper-diamond composite materials for thermal managements. However, the formation of the microstructure at different electrodeposition current densities suggests that a careful process optimization is required to obtain a void-free Cu matrix between the embedded diamond particles.

Microstructure and thermal behavior of diamond/Cu composites: Effects of surface modification

Copper matrix composites reinforced with dual-metal-layer coated diamond particles were prepared via hot-press sintering. The effects of W-Ni and W-Cu coatings on the microstructure and thermo-physical properties of the composites were analyzed. The thermal behavior of the composites was simulated using finite element models based on the experimental microstructure images. The results show that the dual-layer coatings not only favor the densification of the composites but also benefit the formation of excellent interfacial bonding. The thermal conductivity of the composites reinforced with 45 vol% W-Cu and W-Ni coated diamond particles reaches 661 and 563 W/mK, respectively. The simulation of the thermal behavior of the composites with dual-layer coatings shows that a temperature drop occurs when heat flows through the boundary between the diamond and copper. The heat flux transmits from one diamond to the nearest one and forms a heat transfer channel along the direction of the temperature gradient.

High thermal conductivity of diamond/copper composites produced with Cu–ZrC double-layer coated diamond particles

A new method was proposed to fabricate diamond/Cu composites. Double-layer diamond particles were directly compressed at ultra-high pressure to prepare the preform and then sintered in a vacuum equipment for densification. The raw diamond particles were coated with zirconium carbide by magnetron sputtering for the inner layer and then deposited with copper by chemical method for the outer layer. Prepared with these particles, the composites had good interface bonding and homogeneously distributed particles in the copper matrix. The thermal conductivity of 65 vol% diamond/Cu composite was as high as 720 W m−1 K−1. When the diamond content increased to 70 vol%, the coefficient of thermal expansion was extremely low (4.33 × 10−6/K). With superb thermal–physical performance, diamond/Cu composites are potentially applicable to electronic packaging.

Regulating interface adhesion and enhancing thermal conductivity of diamond/copper composites by ion beam bombardment and following surface metallization pretreatment

A new pretreatment process, namely, Ar+ ion beam bombardment and following deposition of a tungsten coating layer on diamond particles for fabricating diamond/copper composites is proposed in this paper. The composites are fabricated by infiltration method, and exhibited excellent thermal properties. Composition of the tungsten coated diamond particles is characterized by the Micro-XRD to investigate the effect of ion beam bombardment on the selectivity of interfacial reaction between the diamond planes and the coating layer. Scanning electron microscopy (SEM) is used to investigate the effect of the ion beam bombardment on interface structure and composition of the composites. A good interfacial adhesion without micro-gaps or cracks in the interfacial region is obtained. In addition to that, the phenomenon of selective interfacial reaction in the composite is no longer taking place, and the metal matrix uniformly adheres to all diamond planes. Therefore, the further enhancing thermal conductivity of the composites reach up to 896 W m−1 K−1, and coefficient of thermal expansion is only 5.9 × 10−6 K−1. The excellent performance can be attributed to the regulated interfacial adhesion and the optimized effective interfacial thermal conductance.

Mo2C coating on diamond: Different effects on thermal conductivity of diamond/Al and diamond/Cu composites

Mo2C submicron layer coated diamond particles prepared by a molten salts route with Mo powder as the starting material were used as the filler in Cu- and Al- matrix composites. The microstructure and thermal property of the composites prepared by a vacuum pressure infiltration method were investigated. When introducing a 500nm thick Mo2C layer, the thermal conductivity of the composites with different matrix presented different performance. A high thermal conductivity (657Wm−1K−1) was obtained in diamond/Cu composites owing to the improved interfacial bonding and lower interfacial thermal resistance, while the thermal conductivity of diamond/Al composites decreased from 553Wm−1K−1 to 218Wm−1K−1 when introducing the Mo2C layer, which can be attributed to the formation of harmful granule-phase (Al12Mo) at the interface of diamond and aluminum. This work provides a promising approach to improve performance of diamond reinforced metal matrix composites by selecting carbide as an interface modifier.

Influence of heat treatment temperature on bonding and oxidation resistance of diamond particles coated with TiO2 film

In this paper, TiO2 films were coated on the surface of diamond particles using a sol–gel method. The effects of heat treatment temperature on the morphology, composition, chemical bonds, oxidation resistance and compressive strength of diamond particles coated with TiO2 films were characterized through scanning electron microscopy, Fourier transform infrared, Raman spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric–differential scanning calorimetry and compressive strength test. The results showed that when the temperature reached 600°C, the amorphous TiO2 on the diamond particles surface exhibited as a dense anatase film and the Ti–O–C bond formed between TiO2 and the diamond substrates. When temperature reached 800°C, TiO2 films were still in anatase phase and part of the diamond carbon began to graphitize. The graphitizated carbon can also form the Ti–O–C bond with TiO2 film, although TiO2 film would tend to crack in this condition. Meanwhile, the temperature had a serious influence on the oxidation resistance of diamond particles coated with TiO2 films in air. When the heat treatment temperature reached 600°C, the initial oxidation temperature of the coated diamond particles reached the maximum value of 754°C. When the diamond particles were oxidized at 800°C for 0.5 h in air, the weight loss rate reached the minimum value of 6.7 wt% and the compressive strength reached the maximum value of 15.7 N.