Diamond Volume Fraction Research Articles

Processing of diamond particle reinforced silicon(Ti) matrix composites by in-situ reactive sintering and their thermal properties

An innovative method of in-situ reactive preparation of diamond/silicon(Ti) matrix composites by spark plasma sintering (SPS) process was applied to produce specimens and the effect of Ti-addition to Si matrix was demonstrated. The relative density of diamond/Si(Ti) matrix composite was >98.1% in a volume fraction of diamond ranging from 40% to 60%. Actually, Si(Ti)/diamond composites containing 60% in volume diamond particles yielded a thermal conductivity (TC) of 525Wm−1K−1 at room temperature along with a thermal expansion coefficient (TEC) of 1.643×10−6K−1 at 573K. TC and TEC of the experimental data were compared with the predictions from several theoretical models. Microstructures of these materials were studied by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Ti addition lowered the melting point and resulted in the formation of TiSi2 phase in Si matrix. The results show that Ti addition is an effective approach for promoting the relative packing density and improving thermal conductivity of sintered samples.

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 copper–diamond composites with chromium carbide coatings on diamond particles for heat sink applications

Cr7C3 coatings were formed on diamond particles for improving the wettability between diamond particles and copper. The coatings were formed with a reaction medium of chromium in mixed molten salt. Copper–diamond composites with Cr7C3 coatings on diamond particles have been fabricated by vacuum pressure infiltration method. The microstructure of interfacial bonding between diamond and copper was discussed. Thermal conductivity and thermal expansion behavior of the obtained copper–diamond composites with various fractions of diamond particles were investigated. The as-fabricated composite exhibit a thermal conductivity of 562 W m−1 K−1 associated with coefficient of thermal expansion of 7.8 × 10−6 K−1 with a Cr7C3-coated diamond volume fraction of 65%. These results indicate that the obtained composites are suitable for being heat sink applications.

Mean and Instantaneous Thermal Expansion of Uncoated and Ti Coated Diamond/Copper Composite Materials

Heat sink materials not only should have higher thermal conductivity, but also have smaller difference of thermal expansion with cooled material. diamond/copper composites were made by the powder metallurgy method. Vacuum slowly vapor deposition technique was employed to deposit a titanium film on diamond particles before mixing with Cu powder in order to improve the bonding strength between Cu and diamond particles during sintering. The thermal expansion of diamond/Cu d composite was measured in the temperature range from 50 to 600 °C. The results show that the titanium film on diamond improves the interfacial bonding and reduces the coefficient of thermal expansion (CTE) of Cu/diamond composites. The CTE of diamond/Cu composites decreases with increasing diamond volume fraction as the results of mixture rule and the intense restriction effect of diamond reinforcement on the copper matrix. The residual stresses and pores in the composites affect instantaneous thermal expansion of diamond/Cu composites.

Rapid ascent conditions of diamond-bearing kimberlitic magmas: Findings from high pressure–temperature experiments and finite element modeling

This paper deals with the problem of rapid ascent mechanism of kimberlite magmas with a multi-directional approach: 1) the kinetics of diamond–graphite transition; 2) settling velocity of diamond phenocrysts in magmas and 3) formation of ruptures required for magma ascent with a high speed. Based on the diamond–graphite transition, we present an estimate of the ascent rates from high pressure and temperature experiments using Walker-type multi-anvil apparatus. The experiments were conducted with diamond, placed within a synthetic kimberlitic assemblage, keeping an initial pressure and temperature of 6GPa and 1350°C, respectively. It was observed that the volume fraction of diamond to graphite conversion strongly depended on the ascent rates. Using electrical resistivity and X-ray diffraction studies, we measured the degree of graphitization as a function of the ascent rate (u). For u<3m/s, diamond underwent almost complete graphitization (conversion>90%), whereas it remained nearly intact (conversion<10%) when u>10m/s. Our theoretical calculations of the settling velocity of mantle xenoliths again confirm that diamond can exist when u>3m/s. We performed numerical experiments with finite element (visco-elastic) models to analyze the dynamics of tensile failure at the tip of magma pools, leading to dilatational vertical fractures for magma transport. Considering the tensile strength of mantle in the order of 0.5kb, our models show this failure process as a function of the critical shape (Ar: ratio of vertical and horizontal dimensions) and density contrast (Δρ) of magma pools. The critical Δρ is estimated nearly 200kg/m3 when Ar is very large (>4).

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.

SPS 成形したAg/ ダイヤモンド複合材料の熱物性に及ぼすダイヤモンドのバイモーダルな粒度分布の影響

Diamond-particle-dispersed-silver (Ag) matrix composites were fabricated in solid-liquid co-existent state by Spark Plasma Sintering (SPS) process from the mixture of diamond powders, Ag powders and Si powders. As the diamond powders, two kind of powders, monomodal diamond powders of 310 µm in diameter and a bimodal diamond powder mixture of 310 µm and 34.8 µm in diameter, were used. The microstructures and thermal conductivities of the composites fabricated were examined. These composites were all well consolidated by heating at a temperature range between 1113 K and 1188 K for 0.45 ks during SPS process. No reaction at the interface between the diamond particle and the Ag matrix was observed by scanning electron microscopy for the composites fabricated under the sintering conditions employed in the present study. Although the relative packing density of the monomodal composite decreased from 97.4 % to 93.4 % with increasing diamond volume fraction between 50 % and 60 %, that of the bimodal composite was higher than 97 % in a diamond volume fraction range up to 65 %. The thermal conductivity of the bimodal composite was higher than that of the monomodal composite in a diamond volume fraction range between 55 % and 65 %. The coefficient of thermal expansion of the composites falls in the upper line of Kerner's model, indicating strong bonding between the diamond particle and the Al matrix in the composite.

J045053 SPS成形したAl/ダイヤモンド複合材料の熱伝導率に及ぼすダイヤモンドのバイモーダルな粒度分布の影響([J045-05]知的材料・構造システム(5))

Diamond-particle-dispersed-aluminum (Al) matrix composites were fabricated in solid-liquid co-existent state by Spark Plasma Sintering (SPS) process from the mixture of diamond powders, Al powders and Al-5mass%Si powders. As the diamond powders, two kind of powders, monomodal diamond powders of 310μm in diameter and a bimodal diamond powder mixture of 310μm and 34.8μm in diameter, were used. The microstructures and thermal conductivities of the composites fabricated were examined. These composites were all well consolidated by heating at a temperature range between 798K and 876K for 1.56ks during SPS process. No reaction at the interface between the diamond particle and the Al matrix was observed by scanning electron microscopy for the composites fabricated under the sintering conditions employed in the present study. Although the relative packing density of the monomodal composite decreased from 99.1% to 87.4% with increasing the diamond volume fraction in a diamond volume fraction range between 50% and 60%, that of the bimodal composite was higher than 99% in a diamond volume fraction range up to 65%. The thermal conductivity of the bimodal composite was 455-581W/mK, which is higher than that of the monomodal composite in a diamond volume fraction range higher than 60%, and it is 530-58 lW/mK in a diamond volume fraction range between 60 and 70vol.%. -

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455Wm−1K−1 associated to a coefficient of thermal expansion of 12×10−6°C−1 and a density of 6.6gcm−3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λCu=400Wm−1K−1, αCu=17×10−6°C−1, ρCu=8.95gcm−3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.

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%.

Thermal properties of diamond/SiC/Al composites with high volume fractions

The diamond/SiC/Al composites with high volume fractions and a large ratio of diamond to SiC particle size (7.8:1) were fabricated by gas pressure infiltration. The results show that the fine SiC particles occupy efficiently the interstitial positions around coarse diamond particles; the main fracture mechanism of the composite is matrix ductile fracture, and diamond brittle fracture was observed which confirms a high interfacial bonding strength; the diamond/SiC/Al composites with 80% and 66.7% volume fraction of diamond in the reinforcement have the higher volume fraction in the reinforcement and lower coefficient of thermal expansion compared to the diamond/Al composite. Turner and Kerner models are not in good agreement with the experimental data for the composites based on reinforcement with two phases different in shape and component. When the effect of the coating layer considered, differential effective medium (DEM) model is confirmed a reliable model in designing a composite with a given thermal conductivity based on reinforcement with two phases different in size.

Electrodeposition of pristine and composite poly(3,4-ethylenedioxythiophene) layers studied by electro-acoustic impedance measurements

Composite layers of poly(3,4-ethylenedioxythiophene) and diamond nanoparticles were prepared by an electrocodeposition procedure from an electrolyte containing the monomer 3,4-ethylenedioxythiophene and a suspension of diamond nanoparticles in acetonitrile/water mixtures. For the in situ monitoring of the deposition process we used piezoelectric quartz crystals with gold electrodes as substrates (electrochemical quartz crystal microbalance, EQCM). The inclusion of the diamond particles increases the stiffness of the layers. This effect can be directly quantified via the electroacoustic impedance of the quartz crystal. We use a mean field model for the interpretation of our EQCM data which yields the complex shear modulus of the composite layers. The volume fraction of diamond (as determined by ex situ XPS) enters as a parameter in the evaluation procedure. Finally, we could estimate the solvent content of the composite layers and the shear moduli of the pure dry PEDOT matrix.

Surface coating by diamond particles on an aluminum substrate by underwater shock wave

A new method for surface coating of an aluminum plate by diamond particles is developed. Underwater shock wave derived from the detonation of an explosive acts to accelerate an aluminum flyer plate to a desired velocity, the flyer plate collides with diamond particles and an aluminum base plate. Diamond particles are penetrated into aluminum. A diamond rich layer which of about 200 μm in depth was generated and the volume fraction of diamond was observed to gradually decrease from top to bottom. A simplified numerical simulation for observation of aluminum deformation at the collision was performed using Ls-Dyna software.

Diamond-Based Metal Matrix Composites for Thermal Management Made by Liquid Metal Infiltration — Potential and Limits

Diamond-based metal matrix composites have been made based on pure Al and eutectic Ag-3Si alloy by gas pressure infiltration into diamond powder beds with the aim to maximize thermal conductivity and to explore the range of coefficient of thermal expansion (CTE) that can be covered. The resulting composites covered roughly the range between 60 and 75 vol-% of diamond content. For the Al-based composites a maximum thermal conductivity at room temperature of 7.6 W/cmK is found while for the Ag-3Si based composites an unprecedented value of 9.7 W/cmK was achieved. The CTE at room temperature varied as a function of the diamond volume fraction between 3.3 and 7.0 ppm/K and 3.1 and 5.7 ppm/K for the Al-based and the Ag-3Si-based composites, respectively. The CTE was further found to vary quite significantly with temperature for the Al-based composites while the variation with temperature was less pronounced for the Ag-3Si-based composites. The results are compared with prediction by analytical modeling using the differential effective medium scheme for thermal conductivity and the Schapery bounds for the CTE. For the thermal conductivity good agreement is found while for the CTE a transition of the experimental data from Schapery’s upper to Schapery’s lower bound is observed as volume fraction increases. While the thermophysical properties are quite satisfactory, there is a trade-off to be made in these materials between high thermal conductivity and low CTE on the one side and surface quality and machinability on the other.

분말야금공정을 이용한 비정질 및 복합체 합금 분말의 벌크화 거동

In the present study, Zr-base metallic glass (MG) and Zr-base BMG/diamond composites were fabricated using a combination of gas atomization and spark plasma sintering (SPS). The microstructure, thermal stability and mechanical property of both the specimens as atomized and sintered were investigated. The experimental results showed that the SPSed specimens could be densified into nearly 100% and maintained the initial thermal stability at the sintering temperature of 630K. In addition, MG/diamond powder composites were successfully synthesised using SPS process. The composites, even a very low diamond volume fraction, generated a significant increase in compressive strength. With increasing the diamond volume fraction, the compressive strength was also increased due to the addition of hardest diamonds. It suggests that these composites would be potential candidates for a new cutting tool material.

Thermal conductivity of aluminum matrix composites reinforced with mixtures of diamond and SiC particles

Aluminum matrix composites reinforced with mixtures of diamond and SiC particles of equal size were produced by gas pressure assisted liquid metal infiltration. Replacing SiC gradually by diamond particles results in a steady increase of thermal conductivity from 220 W/mK to 580 W/mK. Electrical conductivity measurements indicate that the silicon content in the matrix decreases with increasing diamond volume fraction. Predictions of the differential effective medium scheme generalized for multiple types of inclusions agree well with experimental results.

Effect of diamond shapes and associated thermal boundary resistance on thermal conductivity of diamond-based composites

This work presents techniques to generate densely packed diamond-like particles, for example, as present in a metal matrix composite of Al, Cu, or Ag reinforced with single crystals of synthetic diamonds; as intended to be used for heat sinks or very efficient thermal conductors, spreaders, etc. Two different ways are described to predict the thermal conductivity of the composite: line tracing and surface-averaged Hasselman and Johnson. The effects of diamond volume fraction, size and, in particular, shapes on the composite thermal conductivity are discussed.

Thermal properties of diamond particle-dispersed Cu composites

This study describes the thermal properties of Cu composites containing diamond particles. Cu powder and diamond particles were mechanically mixed at 500rpm and then consolidated at 723K by vacuum-hot pressing. The particle size (0.005–7.7μm) and volume fraction (0–20%) of diamond were changed to investigate their effect on the thermal properties of Cu composites. Adding 1% diamond by volume to Cu can improve the thermal diffusivity and thermal conductivity, and a particle size of more than 0.95μm is more effective for improving those properties. For the case of Cu composite containing diamond particles with mean particle size of 7.7μm, the thermal diffusivity can be improved by 14% and the thermal conductivity can also be improved by 18%, compared with as-consolidated Cu powder. However, the thermal diffusivity and thermal conductivity of Cu composite decrease with an increase in the volume fraction of diamond because of the size reduction of grain in the matrix.

Thermal properties of diamond/copper composite material

Thermal considerations are becoming increasingly important for the reliabilities of the electronics parts as the electronics technologies make continuous progress such as the higher output power of laser diodes or the higher level of integration of ICs. For this reason the desire for improving thermal properties of materials for electronics component parts is getting stronger and the material performance has become a critical design consideration for packages. To meet the demands for a high performance material for heat spreader materials and packages, a new composite material composed of diamond and copper was successfully manufactured under high pressure and high temperature. The effects of diamond particle sizes and the volume fractions of diamond on both thermal conductivity and the coefficient of thermal expansion (CTE) were investigated. The thermal conductivity of the composite material was dependent on both the particle size and the volume fraction of diamond, while the CTE was dependent only on the volume fraction of diamond. At the higher diamond volume fraction, the experimentally obtained thermal conductivities of the composite materials were above the theoretically expected values and the experimentally obtained CTE were between the two theoretical Kerner lines. This may be due to the fact that at the higher diamond volume fraction the diamond particles are closely packed to form bondings between each particle. The composite of diamond and copper have a potential for a heat spreading substrate with high performance and high reliability because not only its thermal conductivity is high but its coefficient of thermal expansion can be tailored according to a semiconductor material of electronics devices.

Synthesis of WC/Co/Diamond Nanocomposites

ABSTRACT A new method had been developed for the synthesis of a triphasic WC/Co/diamond nanocomposite, comprising a high volume fraction of diamond in a WC/Co matrix. Starting with available nanophase WC/Co powder, the new process involves: (1) partial sintering of a WC/Co powder compact to develop a porous preform, (2) chemical vapor infiltration (CVI) of the porous preform with amorphous or graphitic carbon, and (3) high pressure/high temperature (HPHT) consolidation of the carbon-infiltrated WC/Co preform to develop a fully-dense WC/Co/diamond nanocomposite. In the critical CVI step of the process, the kinetics of the carbon deposition may be controlled to develop either an uniform or graded distribution throughout the porous WC/Co preform. A functionally-graded triphasic superhard material, comprising a nanophase WC/Co core and a diamond-enriched surface, should combine high strength and toughness with superior wear resistance.