Preparation,morphology and properties of acid and amine modified multiwalled carbon nanotube/polyimide composite

The precursor of polyimide, polyamic acid, was prepared by reacting 4,4′-oxydianiline (ODA) with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA). Unmodified, acid-modified and amine-modified multiwall carbon nanotubes (MWCNT) were separately added to the polyamic acid and heated to 300 °C to produce polyimide/carbon nanotube composite. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) microphotographs reveal that acid-modified MWCNT and amine-modified MWCNT were dispersed uniformly in the polyimide matrix. The effect of the acid and amine-modified MWCNTs on the surface and volume electrical resistivities of MWCNT/polyimide composites were investigated . The surface electrical resistivity of the nanocomposites decreased from 1.28 × 10¹⁵ Ω/cm² (neat polyimide) to 7.59 × 10⁶ Ω/cm² (6.98 wt% unmodified MWCNT content). Adding MWCNTs influenced the glass transition temperatures of the nanocomposites. Modified MWCNTs significance enhanced the mechanical properties of the nanocomposites. The tensile strength of the MWCNT/polyimide composite was increased from 102 MPa (neat polyimide) 134 MPa (6.98 wt% acid modified MWCNT/polyimide composites).     

Mechanical performance of epoxy matrix hybrid nanocomposites containing carbon nanotubes and nanodiamonds

A novel class of epoxy matrix hybrid nanocomposites has been developed containing multiwalled carbon nanotubes (MWCNTs) and nanodiamonds (NDs) to explore the combined effect of nanoreinforcements on the mechanical performance of nanocomposites. Both the nanofillers were functionalized before incorporating into epoxy matrix to promote interfacial interactions. The concentrations of both MWCNTs and NDs in the nanocomposites were increased systematically, i.e. 0.05 wt.%, 0.1 wt.% and 0.2 wt.% while composites containing individual nanoreinforcements were also manufactured for comparison. The developed nanocomposites were characterized microstructurally by scanning electron microscopy (SEM) and mechanically by tensile, flexural, impact and hardness tests. Homogeneous dispersion of MWCNTs and NDs was observed under SEM, which resulted in the enhancement of mechanical properties of nanocomposites. The composites containing 0.2 wt.% MWCNTs and 0.2 wt.% NDs showed 50% increase in hardness while tensile strength and modulus enhanced to 70% and 84%, respectively. Flexural strength and modulus also showed a rise of 104% and 56%, respectively. Interestingly, fracture strain also increased in both the tensile and flexural testing. The impact resistance increased to 161% showing a significant improvement in the toughness of hybrid nanocomposites.     

Preparation and characterization of carbon nanotube/polyetherimide nanocomposite films

Multi-walled carbon nanotube (MWCNT)/polyetherimide (PEI) nanocomposite films have been prepared by casting and imidization. A homogeneous dispersion of MWCNTs throughout the PEI matrix is observed by scanning electron microscopy of fracture surfaces, which shows not only a fine dispersion of MWCNTs but also strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTs) in the matrix and by the absence of debonding of CNTs from the matrix. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperature of PEI increases by about 10 °C by the addition of 1 wt% MWCNTs. Mechanical testing shows that for the addition of 1 wt% MWCNTs, the elastic moduli of the nanocomposites are significantly improved by about 250% while the tensile strength is comparable to that of the matrix. This improvement is due to the strong interfacial interaction between the MWCNTs and the PEI matrix which favors stress transfer from the polymer to the CNTs.     

Evaluation of microstructure and mechanical properties of Al/Al2O3/SiC hybrid composite fabricated by accumulative roll bonding process

In this investigation, a new kind of metal matrix composites with a matrix of pure aluminum and hybrid reinforcement of Al₂O₃ and SiC particles was fabricated for the first time by anodizing followed by eight cycles accumulative roll bonding (ARB). The resulting microstructures and the corresponding mechanical properties of composites within different stages of ARB process were studied. It was found that with increasing the ARB cycles, alumina layers were fractured, resulting in homogenous distribution of Al₂O₃ particles in the aluminum matrix. Also, the distribution of SiC particles was improved and the porosity between particles and the matrix was decreased. It was observed that the tensile strength of composites improved by increasing the ARB passes, i.e. the tensile strength of the Al/1.6 vol.% Al₂O₃/1 vol.% SiC composite was measured to be about 3.1 times higher than as-received material. In addition, tensile strength of composites decreased by increasing volume fraction of SiC particles to more than 1 vol.%. Scanning electron microscopy (SEM) observation of fractured surfaces showed that the failure mechanism of broken hybrid composite was shear ductile rupture.     

Investigating effects of process parameters on microstructural and mechanical properties of Al5052/SiC metal matrix composite fabricated via friction stir processing

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite (MMC) was fabricated on surface of 5052 aluminum sheets by means of 5 μm and 50 nm SiC particles. Influence of tool rotational speed, traverse speed, number of FSP passes, shift of rotational direction between passes and particle size was studied on distribution of SiC particles in metal matrix, microstructure, microhardness and wear properties of specimens. Optimum of tool rotational and traverse speed for achieving desired powder dispersion in MMC was found. Results show that change of tool rotational direction between FSP passes, increase in number of passes and decrease of SiC particles size enhance hardness and wear properties.     

Microstructure and some mechanical properties of fly ash particulate reinforced AA6061 aluminum alloy composites prepared by compocasting

Fly ash has gathered widespread attention as a potential reinforcement for aluminum matrix composites (AMCs) to enhance the properties and reduce the cost of production. Aluminum alloy AA6061 reinforced with various amounts (0, 4, 8 and 12 wt.%) of fly ash particles were prepared by compocasting method. Fly ash particles were incorporated into the semi solid aluminum melt. X-ray diffraction patterns of the prepared AMCs revealed the presence of fly ash particles without the formation of any other intermetallic compounds. The microstructures of the AMCs were analyzed using scanning electron microscopy. The AMCs were characterized with the homogeneous dispersion of fly ash particles having clear interface and good bonding to the aluminum matrix. The incorporation of fly ash particles improved the microhardness and ultimate tensile strength (UTS) of the AMCs.     

Electromagnetic shielding effectiveness of aluminum alloy–fly ash composites

The cenosphere and precipitator fly ash particulates were used to produce two kinds of aluminum matrix composites with the density of 1.4–1.6 g cm⁻³ and 2.2–2.4 g cm⁻³ separately. The electromagnetic interference shielding effectiveness (EMSE) properties of the composites were measured in the frequency range of 30.0 kHz–1.5 GHz. The results indicated the EMSE properties of the two types of composites were nearly the same. By using the fly ash particles, the shielding effectiveness properties of the matrix aluminum have been improved in the frequency ranges 30.0 kHz–600.0 MHz and the increment varied with increasing frequency. The EMSE properties of 2024Al are in the range −36.1 ± 0.2 to −46.3 ± 0.3 dB while the composites are in the range −40.0 ± 0.8 to −102.5 ± 0.1 dB in the frequency range 1.0–600.0 MHz. At higher frequency, the EMSE properties of the composites are similar to that of the matrix. The tensile strength of the matrix aluminum has been decreased by addition of the fly ash particulate and the tensile strength of the composites were 110.2 MPa and 180.6 MPa separately. The fractography showed that one composite fractured brittly and the other fractured in a microductile manner.     

Tribological performance of carbon nanotube–graphene oxide hybrid/epoxy composites

An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr.     

Thermally reduced graphene oxide acting as a trap for multiwall carbon nanotubes in bi-filler epoxy composites

The effect of thermally reduced graphene oxide (TRGO) on the electrical percolation threshold of multi wall carbon nanotube (MWCNT)/epoxy cured composites is studied along with their combined rheological/electrical behavior in their suspension state. In contrast to MWCNT and carbon black (CB) based epoxy composites, there is no prominent percolation threshold for the bi-filler (TRGO–MWCNT/epoxy) composite. Furthermore, the electrical conductivity of the bi-filler composite is two orders of magnitude lower (∼1 × 10⁻⁵ S/m) than the pristine MWCNT/epoxy composites (∼1 × 10⁻³ S/m). This result is primarily due to the strong interaction between TRGO and MWCNTs. Optical micrographs of the suspension and scanning electron micrographs of the cured composites indicate trapping of MWCNTs onto TRGO sheets. A morphological model describing this interaction is presented.     

Effect of surface nanocrystallization induced by fast multiple rotation rolling on mechanical properties of a low carbon steel

Fast multiple rotation rolling (FMRR), a novel and efficient surface nanocrystallization technique, was used to fabricate a nanostructured layer in the surface of low carbon steel. The microstructure of the surface layer was characterized by transmission electron microscopy, optical microscope and scanning electron microscopy, and mechanical properties were investigated by microhardness measurements, tensile measurements and friction and wear tests. In addition, the fracture and wear scars morphologies were observed by scanning electron microscopy. Experimental results indicated that a deformation layer with thickness about 200 μm is clearly observed in the FMRR sample surface. A nanostructured layer of 30 μm thick is obtained, with grain size ranging from 8 to 18 nm and average grain size about 14 nm in the top surface layer. The microhardness of the FMRR sample change gradiently along the depth from about 316 HV in the top surface layer to about 160 HV in the matrix, which is nearly twice harder than that of the original sample. The ultimate tensile strength has also been markedly improved. And the friction and wear experiments show that tribological properties of the low carbon steel have been enhanced by FMRR treatment.     

Effect of surface functionalization on mechanical properties and decomposition kinetics of high performance polyetherimide/MWCNT nano composites

In this investigation, Polyetherimide (PEI) reinforced with multi-walled carbon nanotube (MWCNT) using novel melt blending technique. Surface of MWCNTs are modified by acid treatment as well as by plasma treatment. PEI nano composites with 2 wt% treated MWCNT shows about 15% improvement in mechanical properties when compared to unfilled PEI. The thermal decomposition kinetics of PEI/MWCNT nano composites has been critically analyzed by using Coats – Redfern model. The increase in activation energy for thermal degradation by 699 kJ/mol for 2 wt% MWCNT implies improvement in the thermal properties of PEI. Studies under Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM) depict significant interfacial adhesion with uniform dispersion of MWCNT in polymer matrix due to surface functionalization. 0.5 wt% chemically modified MWCNT shows typical alignment of MWCNT. There is a significant improvement in mechanical properties and thermal properties for surface functionalized MWCNT reinforced.     

In situ fabrication of titanium carbide particulates-reinforced iron matrix composites

Titanium carbide (TiC) particulates-reinforced iron matrix composites were prepared by in situ fabrication method combining an infiltration casting with a subsequent heat treatment. The effects of different heat treatment times (0, 1, 6 and 11 h) at 1138 °C on the phase evolution, microstructural features, and properties of the composites were investigated. The as-prepared composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microhardness and wear resistance tests. The XRD results showed that the composites consisted of graphite, α-iron and titanium carbide after heat treatment at 1138 °C for 11 h. The SEM observation revealed that the formed TiC particulates were homogenously distributed in the iron matrix. The average microhardness of the composite heat treated at 1138 °C for 6 h increased depending upon the region: 209 HV_0.1 (iron matrix) < 787 HV_0.1 (titanium wire) < 2667 HV_0.1 (composite region). After being heat treated at 1138 °C for 11 h, the composite indicated no considerable change in microhardness value, and the average microhardness of the composite region was about 2354 HV_0.1. The highest microhardness value obtained for the composite region was due to the formation of titanium carbide particulates as reinforcement phase within the iron matrix. Relative wear resistance was determined by a pin-on-disc wear test technique under different loads, and as a result, the composites containing higher volume fraction of hard titanium carbide particulates presented higher wear resistance compared with the unreinforced gray cast iron.     

Preparation and characterization of multi-walled carbon nanotube/hydroxyapatite nanocomposite film dip coated on Ti–6Al–4V by sol–gel method for biomedical applications: An in vitro study

In the present research, the introduction of multi-walled carbon nanotubes (MWCNTs) into the hydroxyapatite (HA) matrix and dip coating of nanocomposite on titanium alloy (Ti–6Al–4V) plate was conducted in order to improve the performance of the HA-coated implant via the sol–gel method. The structural characterization and electron microscopy results confirmed well crystallized HA–MWCNT coating and homogenous dispersion of carbon nanotubes in the ceramic matrix at temperatures as low as 500 °C. The evaluation of the mechanical properties of HA and HA/MWCNT composite coatings with different weight percentages of MWCNTs showed that the addition of low concentrations of MWCNTs (0.5 and 1 wt.%) had improved effect on the mechanical properties of nanocomposite coatings. Moreover, this in vitro study ascertained the biocompatibility of the prepared sol–gel-derived HA/MWCNT composite coatings.     

Reduction of thermal residual stresses of laminated polymer composites by addition of carbon nanotubes

This paper studies the effects of multi-walled carbon nanotubes (MWCNTs) on the thermal residual stresses in polymeric fibrous composites. Reinforced ML-506 epoxy nanocomposites with different amounts of homogeneously dispersed MWCNTs (0.1 wt.%, 0.5 wt.% and 1 wt.%) were fabricated using the sonication technique. Thermo-mechanical analysis and tensile tests of the specimens were carried out to characterize the thermal and mechanical properties of MWCNTs/epoxy composites. Due to the negative thermal expansion and high modulus of MWCNTs, addition of MWCNTs resulted in a great reduction of the coefficient of thermal expansion (CTE) of epoxy. The MWCNTs also moderately increased the Young’s modulus of the epoxy. Then, the effects of adding MWCNTs on micro and macro-residual stresses in carbon fiber (CF)/epoxy laminated composites were investigated using the energy method and the classical lamination theory (CLT), respectively. The results indicated that the addition of low amounts of MWCNTs leads to a considerable reduction in thermal residual stress components in both micro and macro levels.     

Fabrication of continuous carbon fiber-reinforced aluminum–magnesium alloy composite wires using ultrasonic infiltration method

In order to fabricate continuous carbon fiber-reinforced aluminum alloy matrix composites, various infiltration methods such as gas pressure infiltration, CVD-infiltration, and ultrasonic infiltration methods have been developed. Among these methods, the ultrasonic infiltration method is the simplest. In this study, the effects of ultrasonic power, the diameter of the hole of the horn, fabricating speed, and magnesium content on the ease of infiltration are investigated. As the results, both an ultrasonic power of 200 W and the addition of more than 2.4 mass% Mg are indispensable to infiltrate molten aluminum alloy into a PAN-based M40J carbon fiber bundle, which has 6000 filaments. Contrariwise, the tensile strength and relative strength (ROM ratio) of the obtained composites decreased from 1100 MPa (0.7) at both 2.4 and 4.7 mass% Mg contents to 800 MPa (0.5) at 10 mass% Mg content. This was probably caused by an increase in the content of the Al₃Mg₂ intermetallic compound. Consequently, the addition of magnesium is effective in improving the infiltration; however, it causes the strength of the composites to decrease. It is found that in this process, the optimum magnesium content in aluminum from the viewpoints of ease of infiltration and strength was 4.7 mass%.     

Accumulative press bonding; a novel manufacturing process of nanostructured metal matrix composites

A new manufacturing process for metal matrix composites has been invented, namely accumulative press bonding (APB). The APB process provided an effective method to produce bulk Al/10 vol.% WC_p composite using tungsten carbide (WC) powder and AA1050 aluminum sheets as the raw materials. The microstructural evolutions and mechanical properties of the monolithic aluminum and Al/WC_p composite during various APB cycles were examined by scanning electron microscopy, X-ray diffractometry, X’pert HighScore software, and tensile test equipment. The results revealed that by increasing the number of APB cycles (a) the uniformity of WC particles in aluminum matrix improved, (b) the porosity of the composite eliminated, (c) the particle free zones decreased and (d) the cluster characteristics improved. Hence, the final Al/WC_p composite processed by 14 APB cycles showed a uniform distribution of WC_p throughout the aluminum matrix, strong bonding between particles and matrix, and a microstructure without any porosity and undesirable phases. The X-ray diffraction results also showed that nanostructured Al/WC_p composite with the average crystallite size of 58.4 nm was successfully achieved by employing 14 cycles of APB technique. The tensile strength of the composites enhanced by increasing the number of APB cycles, and reached to a maximum value of 216 MPa at the end of 14th cycle, which is 2.45 and 1.2 times higher than obtained values for annealed (raw material, 88 MPa) and 14 cycles APBed monolithic aluminum (180 MPa), respectively. Though the elongation of Al/WC_p composite lessened during the initial cycles of APB process, it increased at the final cycles of the mentioned process by 78%. Role of WC particles, uniformity of reinforcement, porosity, bonding quality of the reinforcement and matrix, grain refinement, and strain hardening were considered as the strengthening mechanisms in the manufactured composites.     

Properties of graphene nanopowder and multi-walled carbon nanotube-filled epoxy thin-film nanocomposites for electronic applications: The effect of sonication time and filler loading

Graphene nanopowder (GNP) and multi-walled carbon nanotube (MWCNT)-filled epoxy thin-film composites were fabricated using ultrasonication and the spin coating technique. The effect of sonication time (10, 20 and 30 min) and GNP loading (0.05–1 vol%) on the tensile and electrical properties of GNP/epoxy thin-film composites was investigated. The addition of GNP decreased the material’s tensile strength and modulus. However, among the tested samples, the GNP/epoxy composites produced using 20 min of sonication time had a slightly higher tensile strength and modulus, with a lower electrical percolation threshold volume fraction. The effect of sonication time was supported by morphological analysis, which showed an improvement in GNP dispersion with increased sonication time. However, GNP deformation was observed after a long sonication time. The GNP/epoxy composites at different filler loadings showed higher electrical properties but slightly lower tensile properties compared with the MWCNT/epoxy composites fabricated using 20 min of sonication time.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Increase of bending fatigue resistance for tungsten inert gas welded SS400 steel plates using friction stir processing

To improve the fatigue resistance of tungsten inert gas (TIG)-welded SS400 steel plates, friction stir processing (FSP) was performed on TIG weld beads. Although the tensile properties of the TIG-welded steel plates with FSP were similar to those without FSP, their bending strength exhibited about 1.4 GPa at room temperature, which was 40% higher than that without FSP (about 1 GPa). Similarly, FSP produced about 170% increase in the number of cycles to failure at an applied stress amplitude of 270 MPa during three-point bending fatigue at room temperature. A fine-grained FSP region (grain sizes of about 1–2 μm in diameter) enhanced grain-boundary strengthening, leading to the higher bending strength and bending fatigue resistance.     

Effect of ball-milling time on mechanical properties of carbon nanotubes reinforced aluminum matrix composites

Carbon nanotubes reinforced pure Al (CNT/Al) composites were produced by ball-milling and powder metallurgy. Microstructure and its evolution of the mixture powders and the fabricated composites were examined and the mechanical properties of the composites were tested. It was indicated that the CNTs were gradually dispersed into the Al matrix as ball-milling time increased and achieved a uniform dispersion after 6 h ball-milling. Further increasing the ball-milling time to 8–12 h resulted in serious damage to the CNTs. The tensile tests showed that as the ball-milling time increased, the tensile and yield strengths of the composites increased, while the elongation increased first and then decreased. The strengthening of CNTs increased significantly as the ball-milling time increased to 6 h, and then decreased when further increasing the ball-milling time. The yield strength of the composite with 6 h ball-milling increased by 42.3% compared with the matrix.