Microstructure and Mechanical Properties of Carbon Fiber Phenolic MatrixComposites containing Carbon Nanotubes and Silicon Carbide

Effect of carbon nanotubes and silicon carbide particles on ablative properties of carbon fiber phenolic matrix composites

Mechanical and wear properties of SiCp/CNT/Al6061 hybrid metal matrix composites

This study highlights the influence of carbon nanotubes (CNT) and silicon carbide (SiC) particles on microstructure, nanohardness and tribological behavior of copper nanocomposites. All the samples were fabricated via conventional powder metallurgy process involving high-energy ball milling, consolidation, sintering and hot forging. Microstructure of copper matrix composites was analyzed using both Transmission and Scanning Electron Microscope along wtih X-ray diffraction that was used to study the dispersion, bonding of reinforcements with matrix and identify the different phases formed during fabrication. Nanoindentation test was conducted to obtain nanohardness as a function of multiple reinforcement's content. Sliding wear test in dry conditions was conducted using pin-on-disc tribometer as per ASTM G99 standards. SEM microstructure revealed uniform dispersion of CNTs and SiC particles in the copper, which led to significant improvement in nanohardness. Nanocomposite with 3wt.% CNTs had nanohardness of 1.82 GPa while pure copper had 0.94 GPa indicating significant improvement. The tribological test showed that nanocomposites had excellent wear resistance in comparison with pure copper.

Carbon nanotube (CNT) and silicon carbide particles (SiCp) can work together as a double-scale hybrid reinforcement for new metal matrix composites. In this paper, nano nickel (Ni) particle catalyst was precipitated by carbamide to achieve uniform dispersion on micron SiCp. And then a CNT-covered SiCp hybrid was synthesized by a conventional Chemical Vapor Deposition (CVD) method. We found that the content of Ni catalyst has great effects on the size and production of CNT. The yield of CNT reached 20.73 wt.% with 5.0 wt.% Ni under the condition of 923 K and 1 h for CVD process. The diameter and average length of the as-grown CNT are 20~30 nm and 3 μm, respectively. Meantime, the chemistry during the controllable growth of CNT was analyzed on the basis of experimental results.

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.

In this work, an epoxy-based microwave absorbing coating (MAC) containing carbon nanotube (CNT), silicon carbide (SiC), and carbonyl iron (CI) particles was prepared. In order to achieve some optimum key properties such as high and broadband microwave absorbing properties, low density, and relatively low cost, a gradient structure and alternating multilayer structure are used simultaneously. The effect of a single layer containing one type of filler, single layer containing several types of fillers, and multilayer structures on mentioned key parameters are investigated. The electromagnetic parameters and the reflection loss (RL) versus frequency of samples were tested by network analyzer in the range of 2–18 GHz using the transmission/reflection method. As a final result, the multilayer MACs included nine layers in which each of the layers contained one type of the fillers (CNT, CI, and SiC) and three neat resin interlayers 2 mm in total thickness compared to other samples and provided a maximum return loss value of 17.6 dB at 08.50 GHz and an absorption bandwidth (RL < − 5 dB) of 16 GHz (2–18 GHz) with a density of 1.61 g/cm3. So, it is simply possible to obtain an efficient MAC due to suitable microwave absorbing filler distribution in multilayer coatings for any respective application.

Production of aluminium foams reinforced with silicon carbide and carbon nanotubes prepared by powder metallurgy method

In this contribution, an epoxy resin based composites which synergistically modified by carbon fiber (MCF) and silicon carbide (SiC) particles were prepared. The chemical structure of MCF and SiC before and after surface treated using silane coupling agent were analyzed by Fourier transform infrared spectroscopy and X-ray diffraction, respectively. The mechanical properties including tensile, flexural, and compression of the composites were investigated. Moreover, the friction and wear performances were studied on a ball-on-ring wear tester. The results indicated that the best tensile, compressive, and friction and wear properties of composites were obtained when SiC particles content is 3.0 wt.%. Compared to the pure epoxy resin, when the SiC particles content is 4.0 wt.%, the best flexural strength and modulus were obtained, which increased by 8.7% and 52.97%, respectively. Both the average coefficient of friction (COF) and the wear mass losses of the composites decreased significantly with the addition of the modified SiC particles. In addition, the main wear mechanism of pure EP is adhesive and fatigue wear, while the SiC/MCF/EP composites exhibit abrasive and fatigue wear.

In this study, hybrid composites of AZ91 Mg alloy reinforced with carbon nanotubes (CNTs) and silicon carbide particles (SiCps) were successfully fabricated by the squeeze infiltration method. For this fabrication, hybrid preforms of CNTs (5, 10, and 15 vol%) and SiCps (30 vol%) were produced by vacuum suction from slurry mix containing organic and inorganic binders. Hybrid CNT+SiCp/AZ91 Mg composites were fabricated by squeeze infiltration, and the melt infiltrated well between the reinforcements during squeeze infiltration to produce a hybrid MMC with virtually no pores. Their microstructural and thermal expansion properties were evaluated The resulting CNT+SiCp/AZ91 Mg hybrid composites were found to exhibit a significant decrease in their coefficients of thermal expansion with an increase in the CNT volume fraction, owing to the near-zero thermal expansion of the CNTs and the CTE mismatch between them and the AZ91 Mg matrix.

Development and characterization of Al5083-CNTs/SiC composites via friction stir processing

Polycrystalline zirconia (3Y-TZP grade) unreinforced and reinforced with multiwalled carbon nanotubes (CNTs) or silicon carbide whiskers (SiCw) or silicon carbide particles (SiCp) have been processed and studied by mechanical spectroscopy with complementary observations of electron microscopy and creep tests. Moreover, for comparison with zirconia, polycrystalline alumina specimens, unreinforced and reinforced with silicon carbide nanoparticles, have also been studied. The high-temperature mechanical loss spectrum of pure zirconia presents an exponential background (exponential increase with temperature) accompanied by a decrease of the dynamic shear modulus above 1200 K. A dissipation peak, which transforms into an exponential increase, appears in the spectra obtained as a function of frequency (isothermal spectrum). The peak does not depend on the amplitude of the applied stress, whereas the exponential increase is stress dependent above a certain threshold. This result has been linked to the interface reaction, which plays an important role in deformation accommodation during creep. The high-temperature mechanical loss is grain size dependent. Smaller the grain size, higher the mechanical loss. The presence of the impurities in the starting powder of zirconia leads to a shift of the entire mechanical- loss spectrum towards lower temperatures. Doping zirconia with different amounts of CNTs results in a decrease of the isothermal-mechanical loss level with respect to pure zirconia. A dissipation peak that transforms into an exponential increase is present for a higher amount of CNTs in the mechanical-loss spectrum as a function of temperature. Zirconia doped with CNTs exhibits a lower creep strain than pure zirconia when submitted to a compressive stress at high temperature. Also, addition of different amounts of SiCw to zirconia leads to a decrease of the mechanical-loss level. A high-temperature dissipation peak is presents in the isochronal spectrum. The peak is better resolved for a higher amount of SiCw. The creep-strain curve is lower in SiCw-doped zirconia than in pure zirconia at high temperature. Addition of SiCp to zirconia may shift or not the mechanical-loss spectrum towards lower temperatures. Doping zirconia with different amounts of SiCp results in the appearance of a peak or peaks in the high temperature isochronal and isothermal spectrum. The height of the peaks depends on the amount of SiCp to zirconia. Similar to zirconia, the high-temperature mechanical loss spectrum of alumina consists of an exponential increase of the mechanical loss and a decrease in the dynamic shear modulus above 1200 K. Additions of SiCp lower the high-temperature mechanical loss with respect to the one in pure alumina. High-temperature plastic deformation of pure zirconia and alumina is interpreted in terms of a theoretical model of GB sliding. When GB sliding is not limited by obstacles like multiple junctions, GB asperities or other defects, creep occur and an exponential background is observed in the mechanical-loss spectrum. Addition of nano-sized reinforcements on the GBs results in a decrease of the exponential background. This means that the GB sliding is more difficult and as a consequence a better creep resistance is observed. The activation parameters obtained from the Arrhenius plots were apparent. Two methods are used to correct the apparent values. However, even if the corrected values seem more reasonable than the values obtained from the Arrhenius plots, they do not bring useful information. It is proposed that apparent too high values of the activation enthalpy account for the evolution of the GB microstructure with temperature. Thermal evolution of the GB microstructure is believed to offer short circuit paths for GB diffusion, which allows the pinning nano-sized reinforcements to be overcome. Then pinning effect is less efficient.

Fabrication of ultra-light LM13 alloy hybrid foam reinforced by MWCNTs and SiC through stir casting technique

Effect of carbon nanotubes (CNTs) and silicon carbide (SiC) on mechanical properties of pure Al manufactured by powder metallurgy

AZ91 magnesium alloy hybrid composites reinforced with different hybrid ratios of carbon nanotubes (CNTs) and silicon carbide (SiC) nanoparticulates were fabricated by semisolid stirring assisted ultrasonic cavitation. The results showed that grains of the matrix in the AZ91/(CNT + SiC) composites were obviously refined after adding hybrid CNTs and SiC nanoparticles to the AZ91 alloy, and the room‐temperature mechanical properties of AZ91/(CNT + SiC) hybrid composites were improved comparing with the unreinforced AZ91 matrix. In addition, the tensile mechanical properties of the AZ91 alloy‐based hybrid composites were considerably improved at the mass hybrid ratio of 7 : 3 for CNTs and SiC nanoparticles; in particular, the tensile and yield strength were increased, respectively, by about 45 and 55% after gravity permanent mould casting. The reason for an increase in the room‐temperature strength of the hybrid composites should be mainly attributable to the larger hybrid ratio of CNTs and SiC nanoparticles, the coefficient of thermal expansion (CTE) mismatch between matrix and hybrid reinforcements, the dispersive strengthening effects (Orowan strengthening), and the grain refining (Hall‐Petch effect).

Microstructure and synergistic-strengthening efficiency of CNTs-SiCp dual-nano reinforcements in aluminum matrix composites