Aluminum and Nickel Matrix Composites Reinforced by CNTs: Dispersion/Mixture by Ultrasonication

An overview of the effect of stirrer design on the mechanical properties of Aluminium Alloy Matrix Composites fabricated by stir casting

In this study, a pre-mixing process was applied to assist a high-energy ball milling (HEBM) process to fabricate high-strength aluminium (Al) matrix composites reinforced with carbon nanotubes (CNTs) by powder metallurgy. Effects of initial state on the dispersion quality of CNTs in composites and resultant mechanical properties were investigated using electron microscopy and tensile testing, respectively. Results showed that after pre-mixing, raw CNT agglomerations became flattened CNT clusters, and evolved into individually dispersed CNT fragments on flaky Al powder surface after HEBM for 12 h. However, CNT clusters remained in the same HEBM process without pre-mixing. Both individual CNTs and CNT clusters were observed inside cold-welded Al particles with a prolonged milling time of 24 h. By applying pre-mixing, the reinforcing effect in CNT/Al composites increased by more than 100%. The distinct evolution processes of CNT dispersion during HEBM with different initial states have been discussed.

Unraveling the dispersion mechanism of carbon nanotubes in aluminum powder particles during high energy ball milling by FIB-TEM study

Dispersion characteristics, interfacial bonding and nanostructural evolution of MWCNT in Ti6Al4V powders prepared by shift speed ball milling technique

Fabrication and Characterization of Aligned Carbon Nanotubes Cluster Reinforced Magnesium Composite Based On Ultrasound/Magnetic Compound Field

An innovative multiscale (atomistic to mesoscale) model capable of predicting carbon nanotube (CNT) interactions and dispersion in water/surfactant/polymer systems was developed. The model was verified qualitatively with available experimental data in the literature. It can be used to computationally screen potential surfactants, solvents, polymers, and CNT with appropriate diameter and length to obtain improved CNT dispersion in aqueous medium. Thus the model would facilitate the reduction of time and cost required to produce CNT dispersed homogeneous solutions and CNT reinforced materials. CNT dispersion in any water/surfactant/polymer system depends on interactions between CNTs and surrounding molecules. Central to the study was the atomistic scale model which used the atomic structure of the surfactant, solvent, polymer, and CNT. The model was capable of predicting the CNT interactions in terms of potential of mean force (PMF) between CNTs under the influence of surrounding molecules in an aqueous solution. On the atomistic scale, molecular dynamics method was used to compute the PMF as a function of CNT separation and CNT alignment. An adaptive biasing force (ABF) method was used to speed up the calculations. Correlations were developed to determine the effective interactions between CNTs as a function of their any inter-atomic distance and orientation angle in water as well as in water/surfactant by fitting the calculated PMF data. On the mesoscale, the fitted PMF correlations were used as input An innovative multiscale (atomistic to mesoscale) model capable of predicting carbon nanotube (CNT) interactions and dispersion in water/surfactant/polymer systems was developed. The model was verified qualitatively with available experimental data in the literature. It can be used to computationally screen potential surfactants, solvents, polymers, and CNT with appropriate diameter and length to obtain improved CNT dispersion in aqueous medium. Thus the model would facilitate the reduction of time and cost required to produce CNT dispersed homogeneous solutions and CNT reinforced materials. CNT dispersion in any water/surfactant/polymer system depends on interactions between CNTs and surrounding molecules. Central to the study was the atomistic scale model which used the atomic structure of the surfactant, solvent, polymer, and CNT. The model was capable of predicting the CNT interactions in terms of potential of mean force (PMF) between CNTs under the influence of surrounding molecules in an aqueous solution. On the atomistic scale, molecular dynamics method was used to compute the PMF as a function of CNT separation and CNT alignment. An adaptive biasing force (ABF) method was used to speed up the calculations. Correlations were developed to determine the effective interactions between CNTs as a function of their any inter-atomic distance and orientation angle in water as well as in water/surfactant by fitting the calculated PMF data. On the mesoscale, the fitted PMF correlations were used as input in the Monte Carlo simulations to determine the degree of dispersion of CNTs in water and water/surfactant system. The distribution of CNT cluster size was determined for the CNTs dispersed in water with and without surfactant addition. The entropic and enthalpic contributions to the CNT interactions in water were determined to understand the dispersion mechanism of CNTs in water. The effects of CNT orientation, length, diameter, chirality and surfactant concentrations and structures on CNT interactions in water were investigated at room conditions. CNT interactions in polymer solution were also investigated with polyethylene oxide (PEO) polymer and water as a solvent. In all cases, the atomic arrangement of molecules was discussed in detailed. Simulations revealed that CNT orientation, length, diameter, and addition of surfactant and its structures can significantly affect CNT interactions (i.e., PMFs varied significantly) and in-turn the degree of CNT dispersion in aqueous solution. For all simulation cases, a uniform sampling was achieved by using the ABF method to calculate the governing PMF between CNTs indicating the effectiveness and convergence of the adaptive sampling scheme. The surfactant molecules were shown to adsorb at the CNT surface and contribute to weaker interactions between CNTs which resulted less CNT aggregate size at the mesoscale. Surfactant consisting with a benzene ring contributed much weaker interactions between CNTs as compared with that of without benzene ring. The increase in CNT length contributed the stronger CNT interactions where the increase in CNT diameter caused weaker CNT interactions in water. The interfacial characteristics between the CNT, surfactant and the polymer were also predicted and discussed. The model can be expanded for more solvents, surfactants, and polymers.

ABSTRACTThe unique mechanical, thermal, and electrical properties of carbon nanotubes (CNTs) make them an ideal reinforcement for the metal matrix composites (MMCs). The successful incorporation of CNTs as reinforcement in MMCs can result in the development of lightweight and high-strength structures which can eventually result in weight savings for the automobile and aerospace industries. In the last two decades extensive research has been carried out to improve the dispersion of CNTs in metal and polymer matrices. Challenges remain to effectively disperse CNTs within the matrix materials with minimal damage during the composite processing stages. The ultra-high Young's modulus and other superior mechanical and thermal properties of CNTs have been attributed to the strong sp2 carbon-carbon (C-C) bonds present in their structures. In order to fully utilize the unique properties of CNTs as reinforcement, damages to CNTs in the form of damaging these sp2C-C bonds have to be minimized. A variety of processing techniques have been developed to fabricate CNTs reinforced MMCs but mechanical alloying (MA) via powder metallurgy (PM) is most widely used process to develop the nano-composites. The role of processing variables during PM and their effects on the structural integrity of CNTs have been reviewed in this work. Governing principles to predict the mechanical properties of CNTs with incorporating the key process variables are deduced. With the help of these governing equations, critical study of the processes parameters and their effects on the structural integrity of CNTs, it is possible to optimize the processing methodologies of CNTs reinforced MMCs and get the maximum benefit from the unique properties of CNTs. It is assumed that better dispersion of CNTs in the metal matrices, retaining the structural integrity of CNTs and optimization of process parameters would result in better mechanical and tribological properties of CNTs reinforced MMCs.

Fast innovations and improvements in the manufacturing sector continuously demand new and reliable materials to create higher quality goods faster. Metal matrix composites (MMCs) are one of the most conspicuous materials to achieve vital jobs in the manufacturing industry. They are growing as critical materials owing to their unique properties, such as higher strength, superior abrasion and wear resistance, and lower constants of thermal enlargement while maintaining greater corrosion resistance. Aluminium (Al) matrix composites (AMCs) are the most important candidates to fabricate intricate shapes of apparatus in different sectors such as aerospace, automobile, and marine industries. On the other hand, its poor hardness and decreased abrasion resistance have limited its application in some crucial engineering sectors. On the other hand, carbon nanomaterials, including graphene oxide (GO) and carbon nanotubes (CNTs) are considered excellent reinforcement nanomaterials for strengthening AMCs. In this research, we add 0.5 wt. % GO or 0.5 wt. % CNTs to strengthen the AMC. This study fabricates the composites through the powder metallurgical method. This study conducts different analyses related to texture, chemical structure, porosity, interface and reinforcement structure, and Electron Backscatter Diffraction (EBSD) of developed composites. EBSD is used to determine the local crystal configuration and crystal orientation at the surface of a specimen. Pole figure maps are used to analyze the texture of the developed composite specimen. The Al/0.5 wt. % GO material demonstrated a more enhanced surface morphology than pure Al sample owing to the restraining properties of GO, which led to better mechanical characteristics. While, the Al/0.5 wt. % CNT material possessed the equal average particle size as the pure Al sample and revealed a reduced engineering stress. This phenomenon was characterized by a lower performance of load transfer from the Al material to the strengthening materials, due to the deficiency of chemical reactions at the boundaries and the extensive agglomeration of the carbon nanotubes.

This chapter is devoted to studying the possibility of incorporating carbon nanotubes (CNTs) as reinforcing fillers in dissimilar metal matrices joints produced by friction stir welding (FSW), as well as the impact of this incorporation on the microstructural and mechanical properties of these joints. Carbon nanotubes are extensively used as a reinforcing material in nanocomposites, due to their high stiffness and strength. FSW is a solid-state welding process of joining aluminum and other metallic alloys and has been employed in the aerospace, rail, automotive, and marine industries. Recently, friction stir processing (FSP), a derivative method of FSW, has been employed as an alternative for the production of metal matrix composites (MMCs). In this work, the process parameters were optimized in order to achieve nondefective welds, with and without the addition of CNTs. Two main cases were studied: (1) FSP was optimized by changing the tool rotational and travel speed as well as the number and direction of FSW passes, and (2) a Taguchi design scheme was adopted to further investigate the FSP in relevance to three factors (number, direction of passes, and tool rotational speed). Mechanical behavior was studied, and the local mechanical properties of the produced MMCs were compared with their bulk counterparts and parent materials. More specifically, the measured mechanical properties in the micro- and nanoscale (namely hardness and elastic modulus) are correlated with the microstructure and the presence of fillers.

Aluminum matrix composites (AMCs) reinforced with carbon nanotubes (CNTs) are widely developed nowadays because they have superior properties. One method of manufacturing AMCs is stir-squeeze casting. This study investigated the effect of magnesium addition on 1% wt CNT reinforcement. Aluminum matrix composites made using Aluminum 6063 reinforced with 1% wt CNT added magnesium with variations (0%, 2%, 4%, 6% wt) were made by a casting method which combines stir-casting at 350 Rpm for 2 minutes with squeeze-casting at a pressure of 10 Mpa for 75 seconds, cast on a metal mold heated at 450°C and an AMC casting temperature of 750°C . The results of CNT-reinforced AMC casting were studied for physical properties, namely porosity and density, mechanical properties, namely tensile strength and hardness, and microstructure characterization, namely OM and SEM. The results showed that adding magnesium can reduce porosity and increase density. The results of hardness testing also show that increasing Mg can increase hardness, and the highest hardness value is 48.8 HV at the addition of 6% Mg, with an increase of 74% from the raw material. The microstructure observation results show that adding Mg functions as a wetting agent, which causes CNTs to be evenly distributed and no accumulation occurs.

Aluminum matrix composites (AMCs) are among the advanced materials that are employed in numerous industrial applications. AMCs have good stiffness and strength. They have low weight that makes them valuably handy for improving fuel efficiency and economy in the structures made from them. The friction stir processing (FSP) is a novel technique which is highly advantageous for producing composites, which are reinforced with particles that are sub-micron in size particularly in light weight metal matrix composites (MMCs). Current study is done to examine the potential of AA6061-based surface nanocomposites by reinforcing it with carbon nanotubes (CNTs) (as-received and purified) employing FSP. Fabrication of the composites is carried out by filling CNTs into the grooves of different sizes and friction stir processed (FSPd). Various parameters are investigated to attain best mechanical properties and dispersion of CNTs in the matrix. Metallography is used to reveal the material flow and grain size variation in the zones formed by the FSP. Micro hardness and tensile tests are conducted to evaluate the mechanical properties and an increase of 47.3% hardness and an increase of 32.4% ultimate tensile strength (UTS) are observed from the base FSPd material. Electron microscopic techniques are also employed to reveal the microstructural details.

Elemental powders and carbon nanotubes (CNTs) were mixed and milled in a high energy shaker mill (SPEX-8000M), to produce 2024 aluminum (Al2024) matrix composites reinforced with CNTs. Milled products were consolidated by uniaxial load pressing followed by pressure-less sintering under argon atmosphere for 2 h at 773 K. The effect of CNTs concentration and milling time on Vickers microhardness (µHV) was studied. Scanning electron microscopy (SEM) micrographs show that by milling process it is possible to obtain a homogeneous dispersion of CNTs into the aluminum matrix. The mechanical properties of the composites show an important improvement with respect to reference samples. The possible strengthening mechanisms are discussed in the present work.

Carbon nanotubes (CNTs), since the discovery by Iijima, have attracted tremendous interests in scientific research mainly due to their exceptional structure and physical properties. The high aspect ratio, light weight, extraordinary stiffness, and strength make CNTs a potentially very functional material to be used in polymer nanocomposites application. Carbon nanotubes are single or multilayered coaxial tubes of six-membered ring networks composed of carbon. It is an allotrope of carbon and is sometimes classified as a type of fullerene. Carbon nanotubes are expected to be applied to materials that normally do not conduct heat or electricity, such as resin, rubber, ink, and paint. In addition, it is expected to be applied to the electronics field because of its conductivity and thermal conductivity even in small quantities and high strength when made into long lengths. One of the problems of CNTs is the tendency of CNTs to aggregate with each other due to intermolecular interactions. In the aggregated state, CNTs cannot exhibit their inherently useful characteristics, and therefore, a technology to disperse CNTs at the nano-level is required. Currently, two major methods are being considered for dispersing CNTs: The first is dispersion by chemical modification. By introducing carboxylic acid into strong acid treated CNTs and introducing hydrophilic or hydrophobic substituents here, solubilization in water or organic solvents is possible. However, there is a problem that this destroys the structure of CNTs and thus greatly impairs their original properties.The other method is to physically disperse CNTs. This is a very simple method that uses ultrasonic irradiation to loosen bundled CNTs, but the dispersion is only temporary, and re-agglomeration occurs quickly. Problems have also been reported, such as excessive ultrasonic irradiation destroying the structure of the CNTs. We have succeeded in producing CNTs nano dispersion gels by adding an aromatic compound to agglomerated CNTs and applying agitation and ultrasonic irradiation. The following describes the process of preparing CNTs dispersion gels. After agglomerated CNTs are temporarily dispersed by ultrasonic irradiation, an aromatic compound (dispersant) is added and mixed and agitated. The dispersed CNTs and the aromatic compound are combined by π-π interaction, and the aromatic compound is adsorbed on the CNTs surface. When CNTs molecules adsorbed with aromatic compounds approach each other, the aromatic compounds on the surface form π-π interactions. At this point, the CNTs are in a gel-like state. Since this dispersion gel does not chemically modify the CNTs, it can be prepared without destroying the structure of the CNTs. The CNTs gel proved to be free from aggregation even after the dispersant component was removed, and the network structure was maintained. In addition, this dispersion gel shows high electrical conductivity because the CNTs are dispersed three-dimensionally and the CNTs form three-dimensional conductive paths in the gel.Next, we introduce the preparation of CNT composite resin. CNT composite resin is prepared by adding binder resin to the carbon nanotube dispersion gel prepared earlier, mixing, and stirring, and ultrasonic irradiation. A transparent conductive film is created by forming the prepared CNT composite resin on a glass slide. In recent years, transparent conductive films have been in high demand due to the development of electronics products, and the use of CNTs as the main material is expected to significantly reduce the cost of development, as they are less expensive than Metallic materials such as indium tin oxide and can be stably supplied. The challenge of this research is that the amount of black CNTs added, which imparts conductivity, significantly affects the transparency of the transparent conductive film. Therefore, it is necessary to select aromatic compounds and resin materials that achieve both high conductivity and transparency with low amounts of added CNTs from a molecular chemistry perspective. In our previous research, we focused on the chemical bonding between resin materials and CNTs for the first time and attempted to improve electrical conductivity by using hydrogen bonding for CNTs. In addition, by combining polycarbonate, which exhibits high transparency and impact resistance, with CNT dispersion gel, we attempted to fabricate a transparent conductive film with high durability. As a result, we succeeded in developing a transparent conductive film material with performance applicable to touch panels.In this study, CNTs dispersion gels prepared with aromatic compounds were evaluated using absorbance measurements and Raman spectroscopy. The Raman spectra measurements allowed us to quantitatively evaluate the interaction between SWCNTs and aromatic compounds. The possibility of charge-transfer complex formation was also suggested by the results of absorbance measurements. Figure 1

Carbon nanotube dispersion in metallic matrices has been a challenge for many years. This paper investigates for the first time whether shortened carbon nanotubes as a starting material could promote improved carbon nanotube dispersion and promote less carbon nanotube damage when dispersed in metals. Aluminum-carbon nanotube nanocomposites were prepared using two carbon nanotube lengths (644nm and 10–30 μm). The nanocomposites prepared with shortened carbon nanotubes showed less carbon nanotube damage, higher microhardness, smaller matrix grain size, and improved dispersion of the carbon nanotubes as compared to the nanocomposites prepared with longer carbon nanotubes. Results suggest major implications for the use of even shorter carbon nanotubes for metal matrix composites.

A comparison of mechanical and wear properties of plasma sprayed carbon nanotube reinforced aluminum composites at nano and macro scale