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Ni3Si-based composites with different TiC contents are fabricated by in situ reaction sintering method. The phase composition, microstructure, microhardness, and tribological properties of the composites are studied. The results show that the addition of TiC particles prevents the formation of γ-Ni31Si12 phase, and the composites mainly consist of β1-Ni3Si and TiC phases. The composites have high hardness and relative density, and the values are above 580 HV and 87%, respectively. The friction coefficients are as low as 0.22. The wear rates of the composites are in the order of 10–6 mm3 m−1, which are two orders of magnitude lower than that of Ni3Si alloy. The primary wear mechanism of Ni3Si alloy is oxidation wear and slight abrasive wear, and the composites with TiC addition are oxidation wear and fatigue wear. The incorporation of TiC particles improves the tribological performance of Ni3Si alloy significantly. The composite with 20 wt.% TiC has the optimal tribological property. [ABSTRACT FROM AUTHOR]

The paper considers the process of creation of an aluminum bronze-based metal-matrix composite straightened with tungsten carbide particles by the method of electron-beam additive manufacturing. To create composites, a combined printing method with powder and wire material feeding has been used. The microstructure study showed that varying the printing parameters during the process has made possible to achieve a homogeneous distribution of particles of the strengthening phase in the matrix. Carbide particles undergo refining caused by the electron beam. The particles size of obtained composite is 4 times finer compared to the initial powder size. Dry sliding wear studies showed strong wear character and dependence of the friction coefficient on the hardening particles size. [ABSTRACT FROM AUTHOR]

Many process parameters of air plasma spray, such as deposition power, speed, and working distance, significantly influence the resulting microstructural, mechanical, tribological, and corrosion properties of the deposited coatings. Among these parameters, the feed rate plays a vital role in the microstructural evolution and achieved properties. Thus, this study investigates the effect of feed rates (10, 20, and 45 g/min) on the microstructure, tribological, and corrosion of Fe–Cr–Mo–B–C composite coatings fabricated using air plasma spray. The results showed that as the powder feed rate was reduced, the thickness, porosity, and amorphous fraction of the coating decreased due to a higher temperature and velocity of the particles at the point of impact. The lower feed rate increased the formed crystalline phases (Fe, Cr, Mo)23C6 and (Fe, Cr, Mo)7C6, which were embedded in the amorphous matrix. As a result, the hardness increased from about 0.72 GPa (at 45 g/min feed rate) to about 1.0 GPa (at 20 g/min feed rate) and 1.3 GPa (at 10 g/min feed rate). Similarly, the elastic modulus increased from about 40 GPa at 45 g/min feed rate to about 52 and 68 GPa at 20 and 10 g/min feed rates, respectively. Consequently, the sliding wear resistance was improved by up to 27 and 50% at a reduced feeding rate of 20 and 10 g/min, respectively. The principal wear mechanisms were adhesion and oxidation. The electrochemical corrosion resistance in a 3.5% NaCl solution was significantly increased at the lowest feed rate. [ABSTRACT FROM AUTHOR]

Since the last few decades, plasma spraying has gained its reputation to produce excellent metallic glass coatings because of its high process controllability. Present work studies the effect of various plasma spray parameters on the mechanical, tribological and the corrosion properties of plasma sprayed Fe-based bulk metallic glass (BMG) coating. The in-flight particle velocity and temperature were monitored using the accuraspray diagnostic sensor. Among different sets of parameters, combination of higher power at lower feed rate and higher gas flow provided the maximum density of the coating due to better melting of the particles. XRD analysis showed that high-temperature exposure of the in-flight particles incepted few traces of oxides and carbides in the coating, apart from the intrinsic α- and γ-phases of the Fe-based feedstock. The corrosion resistance of the coatings was highly influenced by the stand-off distance, keeping all the other parameters at higher values. The reason may be attributed to the more number of powder particles melting at higher power and impinging on the substrates at quite lesser time. Current work concludes that the various properties of the Fe-based BMG coating are seriously tailored by different sets of plasma parameters that urge to govern the overall coating properties. [ABSTRACT FROM AUTHOR]

Metallic matrix composites (MMCs) reinforced with carbon nanotubes (CNTs) significantly strengthen the base matrix. CNTs-MMCs are light in weight and very small fractions (vol% or wt%) of well-dispersed CNTs enhance mechanical properties effectively. The research on it is now broadening in different directions. Few parameters dominate the CNTs-MMCs properties that needed to be known before creating new composites. CNTs percentage, types, matrixes, production methods are some of them. A broad detail of the present CNTs-MMCs is helpful for the future. No statistical data is available so far to demonstrate the recent trends of CNTs-MMC. Since CNTs-MMCs are major composite groups applied for many engineering applications, an overview of the present prospects of these composites will be helpful for future research. In this paper, we have strived to gather information about the CNTs-MMCs and presented it through appropriate statistical illustrations to outline various data on this research field. [ABSTRACT FROM AUTHOR]

Evolution of structure of two-phase sintered Al-Sn composites during equal channel angular pressing (ECAP) without rotation of the sample between the passes (route A) was studied. The macrostructure with alternating thin Al and Sn interlayers was formed in the flow plane of the samples under the ECAP processing. It was found that the law of the changes in the parameters of the structure of the composites can be described using the geometry of ECAP. The greatest changes in the macrostructural parameters and increase in the strength of the composites were observed during the first two passes. The consequence of the thinning of aluminum interlayers is an increase in the depth of deformation of the subsurface layer and decrease in distance between tin interlayers which are sources of solid lubricant. As a result, the wear intensity of the sintered Al-Sn composites is additionally decreased under dry friction against steel if the sliding direction is perpendicular to the elongated phases interlayers. It was established that the composite containing about 40% Sn has the highest wear resistance. [ABSTRACT FROM AUTHOR]

Two types of graphite nanoflakes (GNFs), GNFA for 30-100 μm in diameter and less than 100 nm in thickness, and GNFB for 0.5-10 μm in diameter and less than 20 nm in thickness, were used to fabricate GNF/6061Al matrix composites with GNF fractions ranging from 5 to 15 wt.% via spark plasma sintering (SPS) at 610 °C under a load of 35 MPa. The effects of GNF size and content on microstructures and properties of the composites were investigated. The results show that uniform mixing of GNFs in the 6061Al powder was achieved through mechanical and ultrasonic stirring. When the GNFs were well dispersed, the composites were dense. An interfacial zone of 15-18 nm in thickness was formed and composed of two layers, a poorly crystalline layer and an amorphous layer. No Al4C3 was detected in the interfacial zone. The relative densities, bending strengths, thermal conductivities (TCs), and coefficients of thermal expansion (CTEs) (room temperature to 100 °C) of the 10 wt.% GNFA/6061Al matrix composites were 98.5%, 120 MPa, 155 W m−1 K−1 in the X–Y direction and 61 W m−1 K−1 in the Z direction, and 14.2 ppm K−1 in the X–Y direction and 12.1 ppm K−1 in the Z direction, respectively. Those of the 10 wt.% GNFB/6061Al matrix composites were 97.8%, 70 MPa, 110 W m−1 K−1 in the X–Y direction and 90 W m−1 K−1 in the Z direction, and 15.4 ppm K−1 in the X–Y direction and 14.7 ppm K−1 in the Z direction, respectively. The GNFB/6061Al matrix composites showed lower differences of TC and CTE between the X–Y and Z directions. Therefore, the anisotropy of the microstructures and properties of the composites in three dimensions were significantly reduced. [ABSTRACT FROM AUTHOR]

In the present study, porous titanium-20 wt.% hydroxyapatite nanocomposites were produced by the combination of mechanical alloying and powder metallurgical process with the addition of titanium hydride particles as the blowing agent. The powder mixture of Ti, HA and spacer particles were milled, pressed and heat-treated to decompose the hydride particles and to sinter into highly porous Ti-HA materials. The resulting microstructures were characterized using x-ray diffraction and scanning electron microscope with energy-dispersive spectrometry. The porosity, compressive strength and corrosion resistance of the porous nanocomposites were investigated. The results show that the compressive strength of porous Ti-HA can be tailored between 210 and 497 MPa by changing the content of blowing agent between 25 and 75%. The increase in the weight ratio of titanium hydride (from 25 to 75%) causes almost a twofold increase in the porosity and decreases the corrosion resistance (by almost two orders of magnitude). The present study has demonstrated that the porous Ti-HA nanocomposites are promising scaffold biomaterials for bone tissue engineering by virtue of their appropriate mechanical and corrosion properties and highly porous structure. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthening(ODS) copper has the characteristics of both high strength and high conductivity. The porosity is an important factor influencing the electrical conductivity. 0.9Al2O3/Cu powder was compacted by a high velocity compaction(HVC) technique. The influence of impact velocity on the green density of Al2O3 dispersion strengthening copper was studied,and the green density of 8.46 g·cm-3 was got at the impact velocity of 9.4 m·s-1. The dependence of the electrical conductivity on sintering temperature was investigated. The results from sintering steps showed that the higher the sintering temperature was,the higher the electrical conductivity was at the same green density level. Fracture surface and SEM observations indicated that the samples were inadequately sintered at the sintering temperature of 950℃,with particle boundaries and some pores being visible obviously. When the sintering temperature rose up to 1080℃,the pores tended to spheroidize,the particle boundaries disappeared,and the dimples appeared on the fracture surface,showing a typical plastic fracture characteristic. The electrical conductivity of the sintered compacts was measured to be 71.3% IACS.

AA7075 matrix composite was obtained by mechanical alloying using ZrO2 particles as reinforcement. After that, the powders were cold-compacted into an aluminum tube and consolidated by equal channel angular pressing at 220 °C. The temperature influence was analyzed, and it was found by scanning electron microscopy that this route gave the minimum pore percentage. Besides, it was noticeable that the hardness was wide superior in comparison with the AA 7075 aged bulk alloy. In addition, there was no evidence of any chemical reaction between ZrO2 and alloying elements at the temperature employed. On the other hand, it was numerically and experimentally demonstrated that the more strained regions exhibited a higher relative density values. [ABSTRACT FROM AUTHOR]

TiAl matrix composites reinforced with Ti2AlN were fabricated by in situ reactive method of powder metallurgy. Microstructures, bending properties at room temperature and compressive properties at elevated temperatures were investigated in contrast with those of TiAl alloy. The results reveal that the microstructure of TiAl matrix is significantly refined due to the synthesis of Ti2AlN. 15 vol.%Ti2AlN/TiAl exhibits excellent bending properties at room temperature, with bending strength of 753 MPa and fracture strain of 0.74%, which are 24.3 and 19.7% higher than those of TiAl alloy. The compressive strength of Ti2AlN/TiAl is markedly improved in comparison to that of TiAl alloy at elevated temperatures. Noticeably, the compressive strength of 15 and 35 vol.%Ti2AlN/TiAl increases by 67.4 and 58.7% at 1000 °C, respectively. The remarkable enhancement of mechanical performance is mainly due to the noteworthy refinement of TiAl matrix and the efficient obstruction of Ti2AlN particles to crack propagation, as well as the effective load-carrying role of Ti2AlN with high elastic modulus. [ABSTRACT FROM AUTHOR]

MgLiAl base composites strengthened with graphene platelets were prepared by semisolid processing of ball-milled alloy chips with 2% of graphene platelets. Composites strengthened with graphene platelets show higher hardness and yield stress than the cast alloys, i.e., 160 MPa as compared to 90 MPa for as-cast alloy MgLi9Al1.5. Mechanical properties for MgLiAl-based composites were similar or higher than for composites based on conventional AZ91 or WE43 alloys. The strengthening however was not only due to the presence of graphene, but also phases resulting from the reaction between carbon and lithium, i.e., Li2C2 carbide. Graphene platelets were located at globules boundaries resulting from semisolid processing for all investigated composites. Graphene platelets were in agglomerates forming continuous layers at grain boundaries in the composite based on the alloy MgLi4.5Al1.5. The shape of agglomerates was more complex and wavy in the composite based on MgLi9Al1.5 alloy most probably due to lithium-graphene reaction. Electron diffraction from the two-phase region α + β in MgLi9Al1.5 indicated that [001]α and [110]β directions are rotated about 4° from the ideal relationship [001] hex || [110] bcc phases. It showed higher lattice rotation than in earlier studies what is most probably caused by lattice slip and rotation during semisolid pressing causing substantial deformation particularly within the β phase. Raman spectroscopy studies confirmed the presence of graphene platelets within agglomerates and in addition the presence mainly of Li2C2 carbides in composites based on MgLi4.5Al1.5 and Mg9Li1.5Al alloys. From the character of Raman spectra refinement of graphene platelets was found in comparison with their initial size. The graphene areas without carbides contain graphene nanoplatelets with lateral dimension close to initial graphene sample. Electron diffraction allowed to confirm the presence of Li2C2 carbide at the surface of agglomerates found from Raman spectroscopy results. [ABSTRACT FROM AUTHOR]

The influence of rolling temperature on the microstructure and mechanical properties of AA5083-1% Al2O3 composites has been analyzed in this study. The alloy was deformed with the method of warm accumulative roll bonding in various temperature conditions, i.e., at ambient temperature, 200°C, and 300°C up to 5 cycles (휀 = 4). The structure has been studied with scanning electron microscopy (SEM), and mechanical properties of the deformed material have been measured by tensile test as well as Vickers microhardness test. It was established that the rolling temperature had a significant effect on the mechanical properties and microstructure of the manufactured MMCs. High strength, low elongation, and high average Vickers microhardness were obtained for the material processed at lower temperatures, i.e., at ambient temperature. Whereas, by increasing the rolling temperature to 300°C, the toughness and elongation ranges were greater than for the MMCs manufactured at lower temperatures. [ABSTRACT FROM AUTHOR]

This paper discusses the influence of the chemical composition on the microstructure, mechanical and corrosion properties of mechanically alloyed and sintered (Mg-4Y-5.5Dy-0.5Zr)- x wt.% HA composites. Mechanical alloying for 25 h of the Mg-4Y-5.5Dy-0.5Zr composition, followed by sintering under argon at 550 °C for 2 h, led to the formation of a bulk alloy with an ultrafine grained microstructure. With the increase of the hydroxyapatite content in the (Mg-4Y-5.5Dy-0.5Zr)- x wt.% HA composite, a reduction of the grain sizes of the bulk material was noticeable. In the case of the bulk (Mg-4Y-5.5Dy-0.5Zr)-10 wt.% HA composite, the grain sizes of approx. 60 nm have been recorded by atomic force microscopy. The final microstructure of the synthesized composites strongly influenced the mechanical and corrosion properties. The Mg-4Y-5.5Dy-0.5Zr alloy was characterized by higher average values of Young's modulus (36.6 GPa). In the case of the (Mg-4Y-5.5Dy-0.5Zr)-5 wt.% HA scaffolds with the porosity of 48%, the Young's modulus was equal to 7.1 GPa. The (Mg-4Y-5.5Dy-0.5Zr)-10 wt.% HA composite was more corrosion resistant ( I = 5.849 × 10 A cm, E = −1.565 V versus SCE) than Mg-4Y-5.5Dy-0.5Zr alloy ( I = 4.838 × 10 A cm, E = −1.555 V versus SCE). The influence of hydrofluoric acid treatment on the corrosion behavior of the (Mg-4Y-5.5Dy-0.5Zr)-5 wt.% HA composite was also investigated. The electrochemical test showed that the corrosion resistance of fluoride-treated specimens was higher, compared with the untreated samples in the Ringer's solution. In conclusion, fluoride-treated (Mg-4Y-5.5Dy-0.5Zr)-HA composites are biodegradable materials with adjustable mechanical and corrosive properties. [ABSTRACT FROM AUTHOR]

An in situ TiO/AlO-reinforced Al composite is successfully prepared using a powder metallurgy route by the reaction of TiCO and Al powder. The TiCO powder is produced by carrying out a carbothermic reduction of titanium dioxide at 1000 °C. XRD results show that the final product is composed of Al, TiO, AlO, and AlTi. Morphology examination of the composite reveals the presence of bigger blocks of TiO and fine particles of AlO and the volume fraction of reinforcement is found to range between 18 and 55%. As the volume fraction of the reinforced materials approaches 50%, the particles start to agglomerate. Dry sliding wear tests conducted using a conventional pin-on-disk testing machine show that the wear resistance of the composite is higher than that of the pure aluminum ingot. The wear rate of the composite increases almost linearly with the increase in the wear distance. The sliding wear test shows that as the volume fraction of the reinforced phase increases, the coefficient of friction decreases. The wear mechanism is also discussed. [ABSTRACT FROM AUTHOR]

Four kinds of C f /Mg composites with different fabric architectures were fabricated by liquid–solid extrusion following vacuum infiltration (LSEVI) technique. The influence of fabric architecture on compressive properties of C f /Mg composites was investigated, and the microstructure and failure surfaces were examined by SEM. The results showed that C f /Mg composites were anisotropic material and the fabric architecture had great influence on their compressive performance. Moreover, fabric crimp had a negative influence on compressive properties of C f /Mg composite. The composite with non-woven carbon fabric perform had the highest compressive strength ( XY direction). Compared with 3 K plain-woven carbon cloth composite whose fiber bundles had 3000 monofilaments, 1 K plain-woven carbon cloth composite had better compressive properties. The analysis of failure surface indicated that the failure modes of C f /Mg composites were mainly shear failure and delamination failure. [ABSTRACT FROM AUTHOR]

Aluminum-based in situ composites suffer from the age-old issue of particle segregation along the grain boundaries after casting. In the present study, friction stir processing (FSP) was employed as a secondary process to improve the distribution of in situ formed TiB particles in Al-based composite. All the agglomerates of TiB were broken, and uniform distribution of particles was achieved after double-pass FSP. Also, FSP removed the casting defects and caused significant grain refinement of the Al matrix. The microstructure was characterized by equiaxed fine grains with average size of 3 µm and narrow grain size distribution. The microstructural refinements and homogenization after FSP not only enhanced the strength but also improved the ductility of the as-cast composite. [ABSTRACT FROM AUTHOR]

Two types of alumina dispersion-strengthened copper (ADSC) alloys were fabricated by a novel in-situ reactive synthesis (IRS) and a traditional internal oxidation (IO) process. The features of alumina dispersoids in these ADSC alloys were investigated by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. It is found that nano-sized γ-AlO particles of approximately 10 nm in diameter are homogeneously distributed in the IRS-ADSC composites. Meanwhile, larger-sized, mixed crystal structure alumina with rod-shaped morphology is embedded in the IO-ADSC alloy. The IRS-ADSC composites can obtain better mechanical and physical properties than the IO-ADSC composites; the tensile strength of the IRS-ADSC alloy can reach 570 MPa at room temperature, its electrical conductivity is 85% IACS, and the Rockwell hardness can reach 86 HRB. [ABSTRACT FROM AUTHOR]

The fabrication of copper (Cu) and copper matrix silicon carbide (Cu/SiC) particulate composites via the sinter-forging process was investigated. Sintering and sinter-forging processes were performed under an inert Ar atmosphere. The influence of sinter-forging time, temperature, and compressive stress on the relative density and hardness of the prepared samples was systematically investigated and subsequently compared with that of the samples prepared by the conventional sintering process. The relative density and hardness of the composites were enhanced when they were prepared by the sinter-forging process. The relative density values of all Cu/SiC composite samples were observed to decrease with the increase in SiC content. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of Al7075 metal matrix composites reinforced with SiC, and the characterization of their microstructure and mechanical behavior. The mechanically milled Al7075 micron-sized powder and SiC nanoparticles are dynamically compacted using a drop hammer device. This compaction is performed at different temperatures and for various volume fractions of SiC nanoparticles. The relative density is directly related to the compaction temperature rise and indirectly related to the content of SiC nanoparticle reinforcement, respectively. Furthermore, increasing the amount of SiC nanoparticles improves the strength, stiffness, and hardness of the compacted specimens. The increase in hardness and strength may be attributed to the inherent hardness of the nanoparticles, and other phenomena such as thermal mismatch and crack shielding. Nevertheless, clustering of the nanoparticles at aluminum particle boundaries make these regions become a source of concentrated stress, which reduces the load carrying capacity of the compacted nanocomposite. [ABSTRACT FROM AUTHOR]

Copper matrix composites consisting of chromium (Cr) or ferrochrome (Cr-Fe) as strengthening elements and molybdenum disulfide as a lubricant had been sintered in nitrogen and hydrogen atmosphere, respectively. Their morphology and energy-dispersive X-ray spectrometry (EDS) analysis showed that serious interaction occurred between MoS and Cr (or Cr-Fe) particles when the samples were sintered in hydrogen atmosphere. Chromium sulfide compound (CrS) was formed as a reaction product, which decreased the density and strength of the composites remarkably. This interaction was inhibited when the samples were sintered in nitrogen atmosphere; thus, the mechanical properties of the composites were improved. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of Al-4.5wt% Cu alloy reinforced with different volume fractions (1.5vol%, 3vol%, and 5vol%) of alumina nanoparticles, fabricated using stir casting method, were investigated. Calculated amounts of alumina nanoparticles (about ϕ50 nm in size) were ball-milled with aluminum powders in a planetary ball mill for 5 h, and then the packets of milled powders were incorporated into molten Al-4.5wt% Cu alloy. Microstructural studies of the nanocomposites reveal a uniform distribution of alumina nanoparticles in the Al-4.5wt% Cu matrix. The results indicate an outstanding improvement in compression strength and hardness due to the effect of nanoparticle addition. The aging behavior of the composite is also evaluated, indicating that the addition of alumina nanoparticles can accelerate the aging process of the alloy, resulting in higher peak hardness values. [ABSTRACT FROM AUTHOR]

Al-based composites reinforced with Al-Ti intermetallic compounds/Ti metal hierarchically spherical agents were successfully fabricated by powder metallurgy. This kind of structure produces strongly bonded interfaces as well as soft/hard/soft transition regions between the matrix and reinforced agents, which are beneficial to load transfer during deformation. As expected, the resultant composites exhibit promising mechanical properties at ambient temperature. The underlying mechanism was also discussed in this paper. [ABSTRACT FROM AUTHOR]

Fe-WC nanocomposites were successfully fabricated by high-frequency induction heated sintering of ball milled nanostructure powders. The ball milled powders were characterized by X-ray diffraction. Density measurements by the Archimedes method show that all sintered samples have the relative density higher than 95%. Studies on the effects of WC content, milling speed, and milling time indicate that a higher milling speed and a more WC content lead to the improvement of mechanical properties. There is a very good distribution of WC particles in the Fe matrix at the milling speed of 650 r/min. For the sintered sample 20-5-650 (20wt% WC, milling time of 5 h, and milled speed of 650 r/min), the maximum Brinell hardness and yield stress are obtained to be 3.25 GPa and 858 MPa, respectively. All sintered samples have brittle fracture during compression test except the sample 20-5-650. [ABSTRACT FROM AUTHOR]

Pure Cu composites reinforced with diamond particles were fabricated by a high pressure and high temperature (HPHT) infiltration technique. Their microstructural evolution and thermal conductivity were presented as a function of sintering parameters (temperature, pressure, and time). The improvement in interfacial bonding strength and the maximum thermal conductivity of 750 W/(m·K) were achieved at the optimal sintering parameters of 1200°C, 6 GPa and 10 min. It is found that the thermal conductivity of the composites depends strongly on sintering pressure. When the sintering pressure is above 6 GPa, the diamond skeleton is detected, which greatly contributes to the excellent thermal conductivity. [ABSTRACT FROM AUTHOR]

Magnesium matrix composites (MMC) reinforced with 5wt% tricalcium phosphate (TCP) particles were prepared by powder metallurgy. Pure magnesium (CP-Mg) was fabricated by the same procedure for comparison. Scanning electron microscopy and energy- dispersive X-ray spectroscopy analyses revealed that TCP particles were distributed homogeneously in the MMC. In order to investigate the corrosion properties, MMC samples were immersed in a simulated body fluid (SBF) at 310±0.5 K for 72 h. The mass loss of the samples in SBF and the pH values of the SBF were evaluated. Moreover, electrochemical measurements were conducted in the SBF. It was shown that the corrosion rate of the MMC decreased with the addition of TCP compared with CP-Mg. Hydroxyapatite was formed on the surface of MMC samples after immersion in the SBF for 72 h but not on the surface of CP-Mg. [ABSTRACT FROM AUTHOR]

Particulate reinforced metallic matrix composites have attracted considerable attention due to their lightweight, high strength, high specific modulus, and good wear resistance. Al/BC composite strips were produced in this work by a modified accumulative roll bonding process where the strips were rotated 90° around the normal direction between successive passes. Transmission electron microscopy and X-ray diffraction analyses reveal the development of nanostructures in the Al matrix after seven passes. It is found that the BC reinforcement distribution in the matrix is improved by progression of the process. Additionally, the tensile yield strength and elongation of the processed materials are increased with the increase of passes. [ABSTRACT FROM AUTHOR]

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature (HPHT) sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, B, and Ti. The thermal conductivity (TC) obtained exhibited as high as 688 W·m·K, but also as low as 325 W·m·K. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification. [ABSTRACT FROM AUTHOR]

The interfacial thermal conductance (ITC) and thermal conductivity (TC) of diamond/Al composites with various coatings were theoretically studied and discussed. A series of predictions and numerical analyses were performed to investigate the effect of thickness, sound velocity, and other parameters of coating layers on the ITC and TC. It is found that both the ITC and TC decline with increasing coating thickness, especially for the coatings with relatively low thermal conductivity. Nevertheless, if the coating thickness is close to zero, or quite a small value, the ITC and TC are mainly determined by the constants of the coating material. Under this condition, coatings such as Ni, TiC, MoC, SiC, and Si can significantly improve the ITC and TC of diamond/Al composites. By contrast, coatings like Ag will exert the negative effect. Taking the optimization of interfacial bonding into account, conductive carbides such as TiC or MoC with low thickness can be the most suitable coatings for diamond/Al composites. [ABSTRACT FROM AUTHOR]

Multiwalled carbon nanotubes (CNTs) were coated by a molybdenum layer using carbonyl thermal decomposition process with a precursor of molybdenum hexacarbonyl. The Mo-coated CNTs (Mo-CNTs) were added into copper powders to fabricate Mo-CNT/Cu composites by means of mechanical milling followed by spark plasma sintering. The Mo-CNTs were uniform dispersion in the Cu matrix when their contents were 2.5 vol.%-7.5 vol.%, while some Mo-CNT clusters were clearly observed at additions of 10.0 vol.%-15.0 vol.% Mo-CNTs in the mixture. The mechanical, electrical, and thermal properties of the Mo-CNT/Cu composites were characterized, and the results showed that the tensile strength and hardness were 2.0 and 2.2 times higher than those of CNT-free specimens, respectively. Moreover, the Mo-CNT/Cu composites exhibited an enhanced thermal conductivity but inferior electrical conductivity compared with sintered pure Cu. The uncoated CNT/Cu composites were fabricated by the similar processes, and the measured tensile strength, hardness, thermal conductivity, and electrical conductivity of the CNT/Cu composites were lower than those of the Mo-CNT/Cu composites. [ABSTRACT FROM AUTHOR]

The thermal conductivity of diamond/copper composites with bimodal particle sizes was studied. The composites were prepared through pressure infiltration of liquid copper into diamond preforms with a mixture of 40 and 100 μm-size diamonds. The permeability of the preforms with different coarse-to-fine volume ratios of diamonds was investigated. The thermal conductivity of the diamond/copper composites with bimodal size distribution was compared to the theoretical value derived from an analytical model developed by Chu. It is predicted that the diamond/copper composites could reach a higher thermal conductivity and their surface roughness could be improved by applying bimodal diamond particle sizes. [ABSTRACT FROM AUTHOR]

lN/Al composites are a potentially new kind of thermal management material for electronic packaging and heat sink applications. The spark plasma sintering (SPS) technique was used for the first time to prepare the AlN/Al composites, and attention was focused on the effects of sintering parameters on the relative density, microstructure and, in particular, thermal conductivity behavior of the composites. The results showed that the relative density and thermal conductivity of the composites increased with increasing sintering temperature and pressure. The composites sintered at 1550°C for 5 min under 70 MPa showed the maximum relative density and thermal conductivity, corresponding to 99% and 97.5 W·m·K, respectively. However, the thermal conductivity of present AlN/Al composites is still far below the theoretical value. Possible reasons for this deviation were discussed. [ABSTRACT FROM AUTHOR]

Diamond reinforced copper (Cu/diamond) composites were prepared by a pressure infiltration technique. The composites show a super high conductivity of 713 W·m·K in combination with an extremely low coefficient of thermal expansion (CTE) of 7.72 × 10 K (25-100°C), which are achieved by modifying the copper matrix with adding 0.3 wt.% of boron to get a good thermal contact between the matrix and the diamond particles. By adopting a series of postmachining techniques the composites were made into near-net-shape parts, and an electroless silver coating was also successfully plated on the composites. Finally, their potential applications in the thermal management of light emitting diodes (LED) were illustrated via prototype examples. [ABSTRACT FROM AUTHOR]

Many traditional methods for strengthening martensitic stainless steel (SS) typically come at the sacrifice of ductility. Herein, we report a configuration design of ceramic particles for reinforcing additively manufactured 15-5 PH martensitic SS with an optimized combination of high-strength and impressively larger ductility via the micron-sized TiC addition. High strength is ascribed to grain refinement, Orowan bowing strengthening, and abundant nucleation of nanoscale (Nb,Ti)C precipitates, while high elongation correlates to the reduced oxide inclusion content, martensite/austenite duplex microstructure, and progressive transformation-induced plasticity effect. In addition, severe localized corrosion is completely inhibited. This work shows the great potential of additive manufacturing technology to fabricate Fe-based composites with unique microstructures, low residual stress levels, excellent corrosion resistance, and an exceptional combination of strength and ductility for practical applications. [ABSTRACT FROM AUTHOR]