Al CNT Research Articles

Investigation of the Wear Behavior of Dual-Matrix Aluminum–(Aluminum–Carbon Nanotube) Composites

Aluminum (Al)–aluminum–carbon nanotube (Al–CNT) dual-matrix (DM) composites are a novel class of nanocomposite materials that combine the ductility of the Al matrix with the hardness and wear resistance of the Al–CNT composite and thus can offer a unique combination of properties that make them suitable for a wide range of wear applications such as cutting tools, bearings, brake pads, wear-resistant coatings, etc. However, the specific properties of the DM Al–(Al–CNT) composite will depend on several factors related to the material’s composition and the friction conditions. This study investigates the wear behavior of DM Al–(Al–CNT) composites consisting of a primary matrix of soft aluminum in which milled hard particles of (Al–CNT) are dispersed as affected by five parameters: (1) wt.% CNT in the reinforcement particles, (2) mixing ratio between the reinforcement particles and the soft Al matrix, (3) sliding speed, (4) applied load, and (5) distance. The experimental design used a Taguchi fractional factorial orthogonal array (OA) L27 to reduce the number of experiments, and analysis of variance (ANOVA) was used to determine the significance and to model the effect of each control parameter. Results showed that the wear rate could be reduced by up to 80% by tailoring the composition and controlling the friction conditions. It was found that the mixing ratio significantly impacts the wear behavior of DM Al–(Al–CNT) composites. A mixing ratio of 50% and a CNT content of 3 wt.% at the lowest applied load gave the lowest wear rate and coefficient of friction. Scanning electron microscopy investigations showed fragmentations in the reinforced matrix at higher loads and mixing ratios, which negatively impacted the wear behavior. Our findings confirm that DM Al–(Al–CNT) composites are promising for wear applications. However, the wear behavior depends on the composition and microstructural design of the composite, which needs to be carefully studied and understood.

Study of interfacial behavior on the damping characteristics of aluminum (Al)-Carbon nanotubes (CNTs) nanocomposites

In this work, MWCNTs-multi-walled carbon nanotubes of distinct reinforcement with Al matrix composite were fabricated by a novel route of dispersing Al-CNTs precursor, then integrated with compaction technique and sinter-forged process. The microstructural and dynamic behavior of as-produced Al-MWCNT composites were investigated, and the interfacial reaction was studied on the damping behavior of Al-CNT nanocomposite. Findings reveal a formation of aluminum carbide (Al4C3) formation at Al-CNT interface layers. A reaction arose at locations with an amorphous carbon coating at open ends of CNTs, in as-produced Al–CNT composites, carbon nanotubes with a wt. % of 0.75 has a solid interfacial interaction and obtained a damping capacity of 875 × 10−3 and a storage modulus of 82.9 GPa with a frequency of 1 Hz. This results in effective load transmission between the Al matrix and CNT, improving the dynamic behavior of the composite. However, the formation of the aluminum carbide phase contributes to the damping capacity of the aluminum reinforced with the wt. % of 0.75 and 1.0 CNT composite, which increases by 40 % and 21 % as compared to pure Al, whereas CNTs are identified as a capable coating for Al matrix to raise high absorb capacity at elevated temperatures subjected to the formation of Al4C3 phase without losing the mechanical behavior of the Al matrix.

Understanding the effect of bimodal microstructure on the strength–ductility synergy of Al–CNT nanocomposites

The research work presents a novel methodology to fabricate Al–CNT nanocomposites possessing excellent amalgamation of strength and ductility. A unique combination of processing techniques comprising of ball milling and spark plasma sintering was utilized for consolidating the samples. High-energy ball milling of as-received Al powder and subsequent addition of CNT into the milled Al powder led to a substantial enhancement in the mechanical properties of the resultant composites. Al compact comprising of as-received microcrystalline powder displayed a tensile strength of 105 MPa, which increased to 161 MPa for Al compact with ball-milled nanocrystalline powder. The respective values of ductility reduced from 41.9 to 6.6%. Adding 0.5 wt% CNT in the later compact led to a further upsurge in the tensile strength to 217 MPa; however, the nanocomposite exhibited a further reduction in the ductility to 4.7%. To address this problem, bimodal microstructure was introduced in Al–CNT nanocomposites by using a mixture of nanocrystalline and microcrystalline Al powders (10, 20, 30, 40 and 50 wt%) as the matrix. Al–CNT nanocomposite containing 30 wt% microcrystalline Al powder exhibited a remarkably improved strength–ductility synergy showing 149% higher yield strength and 78% higher tensile strength than the Al compact with microcrystalline grained matrix and 130% higher elongation than the Al–CNT nanocomposite with nanocrystalline grained matrix. Furthermore, to assess the effectiveness of bimodality and CNT reinforcement, experimentally determined value of yield strength of Al30M70N–CNT was assessed with respect to the theoretically calculated value. It was found that the experimentally obtained yield strength of the nanocomposite was about 94% closer to the predicted value endorsing the effectiveness of the designed fabrication route.

Al–CNT–Ni composite with significantly increased strength and hardness

In this study, aluminium–carbon nanotube–nickel (Al–CNT–Ni) composite was prepared by powder metallurgy from pure Al powder and Ni-encapsulated CNT. Previously, carbon nanotubes were coated with nickel following ultraviolet-assisted electroless deposition method. Tensile strength and hardness of the composites were found to increase in proportion to the CNTs addition. For an addition of 7 wt.% Ni-coated CNTs containing 2.5 wt.% nanotubes of 8–15 nm diameter (Ni to CNT ratio was 1–0.357), resultant tensile and yield strength were increased by 129.26% and 157.48% respectively compared to pure aluminium. Hardness was also increased by 171.39%. These results were obtained while conventional sintering was followed by further consolidation by Hot Isostatic Pressing (HIP). Enhanced mechanical properties are attributed to the well dispersion of CNTs in aluminium matrix and strong interfacial bonding between CNT and aluminium. Well dispersion of CNTs and strong interfacial bonding was resulted from the uniform Ni-encapsulation as verified by red shift in Raman Spectroscopy.

Effect of nano-TiO<sub>2</sub> particles on mechanical performance of Al–CNT matrix composite

In this study, a brief review of the effects of the various types of TiO2 nanoparticles and a fixed addition of CNTs to the aluminum matrix on the mechanical, microstructural, and wear characteristics of the resulting composites. Classical powder metallurgy technique was utilized to fabricate the hybrid nanocomposites in this study, while the hybrid nanocomposites were characterized using SEM and XRD. The mechanical properties of the hybrid nanocomposites were evaluated by testing their microhardness, wear tests, and diametral compressive strength. From the SEM and XRD analysis, there was a proper and homogenous distribution of the reinforced particles. Although there was some agglomeration, no intermetallic compounds were found. The study also revealed that the microhardness, diametral compressive strength, and wear resistance significantly improved when the TiO2 nanoparticle content was increased. Also, it was explained that the wear resistance negatively correlated with the applied loads.

Processing, characterization, and properties of aluminum–carbon nanotube open-cell foams

This paper discusses the processing, characterization, and properties of aluminum–carbon nanotube (Al–CNT) open-cell foams. The effect of spark plasma sintering temperature on the developed internal surface macro/microstructure and local mechanical response is discussed. Grain size and amount of oxygen-rich internal scales increased with an increase in sintering temperature. Room temperature spherical indentation tests showed a general decline in load-bearing capacity of the foams with increase in sintering temperature. Cell-wall failure was found to be due to brittle fracture rather than plastic collapse. Analyses of the indentation unloading curves showed Al–CNT foams to be ~16% stiffer than Al foams processed at the same condition.

Friction stir processing of Al–CNT composites

Friction stir processing (FSP) is a solid-state process with the ability to refine grain sizes and uniformly disperse particles to improve the mechanical properties of the base material. In this study, FSP was performed on AA6061-T6 with and without additions of multi-walled CNTs. For FSP on monolithic Al plates, dendrites were broken down and dispersed uniformly with the increase in number of passes. As for FSP of Al–CNT composites, the CNTs have been successfully dispersed with three FSP passes. Dispersion is more uniform with increasing number of passes. The Vickers hardness and tensile yield strength were found to have improved after performing FSP with the addition of CNT as compared to FSP of AA6061-T6 without CNT.

Long-term post-processing disintegration of aluminum–carbon nanotube composites

This paper reports on the post-processing disintegration of melt-infiltrated aluminum–carbon nanotube (Al–CNT) composites. The paper shows that un-optimized processing conditions can lead to the deterioration of the consolidated composite into micro-scale powder over time. Extensive characterization of the disintegration process over unprecedented post-processing times of ~2.5 years was conducted. The effect of post-processing time on the morphological and phase changes is discussed. The paper points to the importance and need to evaluate the long-term properties of Al–CNT composites.

Design of A Setup of Cvd* For Cnt Synthesis and Study of Properties of Cnts Reinforced With Aluminium Based Composites

The physics of Carbon Nanotubes has rapidly evolved into a research field since their discovery by lijima (4) in multiwall form in 1991. In this research we have attempted an approach to obtain homogeneously dispersed CNTs in Al powders for preparing Al/CNTs nanocomposite. Ball milled Al and CNTs mixture has been compacted by universal testing machine under the load of 3 tons. Micro hardness and relative density of compacted composites of different weight percentage ratio of CNTs has been measured. By using Vicker hardness test, Optical Microscope, Scanning Electron Microscope (SEM) techniques we analyzed the hardness, micro structures and grain boundaries of casted Al-CNTs composites and compared the hardness of pure Al and CNTs reinforced Al composites at different weight percentages of CNTs. Also we checked the mixing pattern of Al CNT composites using X-Ray Diffraction (XRD) technique.

Direct observation of carbon nanotube induced strengthening in aluminum composite via in situ tensile tests

In situ tensile tests inside a scanning electron microscope chamber are conducted on spark plasma sintered Al and Al-1vol.% CNT composites to understand the strengthening and deformation mechanisms due to long (25–30μm) CNT reinforcement addition. Al–CNT composite shows 40% higher tensile strength, and 65% higher stiffness for mere 1vol.% CNT addition. The failure occurs by CNT pullout from the matrix, which is directly imaged during the tensile testing. Telescopic sliding of CNT walls is also observed which aids to strengthening.

Wear and friction behavior of Al6061 alloy reinforced with carbon nanotubes

Friction and wear behavior of Al6061 monolithic alloy and 1wt% CNTs reinforced Al6061 composite prepared through ball milling and spark plasma sintering was investigated. It was found that, under mild wear conditions, the composite displayed lower wear rate and friction coefficient compared to the monolithic alloy. However, for severe wear conditions, the composite displayed higher wear rate and friction coefficient compared to the monolithic alloy. Analysis of worn surfaces revealed that, at lower loads, abrasion was the dominant wear mechanism for both materials. At higher loads, adhesion was found to be dominant for the monolithic alloy while excessive sub-surface fracturing and delamination were mainly observed for the composite. Also, it was clarified that the friction and wear behavior of Al–CNT composites is largely influenced by the applied load and there exists a critical load beyond which CNTs could have a negative impact on the wear resistance of aluminum alloy.

Differentiating the mechanical response of hybridized Mg nano-composites as a function of strain rate

Abstract The effect of strain rate change on tensile and compressive response of hybrid Mg/Al–CNT nano-composites synthesized through powder metallurgy route incorporating microwave assisted rapid sintering technique and hot extrusion is investigated in this work. It is important to characterize the effect of strain rate on mechanical response of a material that will be used in a structure which can undergo a high rate deformation (as in automobile crash) as well as during high velocity forming processes such as electromagnetic or electro hydraulic forming. Tensile and compressive tests for monolithic Mg along with its hybrid Mg/Al–CNT nano-composites counterparts at quasi-static and dynamic regimes were carried out using: (i) a servo hydraulic testing machine (MTS) and (b) a Split Hopkinson Pressure Bar (SHPB) apparatus with an average strain rate of 10−4 s−1 and 2 × 103 s−1, respectively. The tremendous increase in strain rate led to a considerable increase in strength of monolithic Mg alongside hybrid nano-composites in both tension and compression. The presence of hybrid Al–CNT particles significantly assisted in improving mechanical response of Mg in both quasi-static and dynamic regimes. Considering the crystallographic texture, the different mechanical response of Mg due to the presence of hybrid Al–CNT particles as a function of strain rate in both tension and compression is differentiated here.

Enhancing tensile and compressive strength of magnesium using ball milled Al+CNT reinforcement

In this work, Mg/Al–CNT nano-composites were fabricated using powder metallurgy route involving microwave assisted rapid sintering and hot extrusion. Ball milled Al–CNT particles comprising different contents of CNTs coated with fixed amount of Al were used for strengthening. Microstructural characterization of these Mg/Al–CNT nano-composites reveal reasonably uniform distribution of Al–CNT particles up to CNT content of 0.30% by weight, significant grain refinement and the presence of minimal porosity compared to monolithic Mg. Importantly, for the nominally identical processing conditions, the textures of as-extruded nano-composite specimens is significantly influenced by the presence of Al–CNT particles. Nano-composite configurations exhibit different tensile and compressive response as a function of CNT content. Among the different Mg/Al–CNT formulations synthesized, the Mg/Al–CNT configuration with Al–CNT particles composition of 1.00% Al and 0.30% CNT by weight (Mg/1.00Al–0.30CNT) exhibit higher tensile yield strength (0.2% YS), ultimate tensile strength (UTS) and failure strain (FS) (up to +72%, +48%, +9%, respectively) compared to monolithic Mg. In terms of compressive response, it exhibits the best overall compressive properties compared to the monolithic Mg with an improvement of 63% in the compressive yield strength (0.2% CYS) and 80% in ultimate compressive strength (UCS), but failure strain was compromised.

Enhanced compressive response of hybrid Mg–CNT nano-composites

Uniaxial compressive properties of hybrid Mg/Al–CNT nano-composites are studied in the present paper. Hybrid nano-composites were fabricated using powder metallurgy route followed by microwave assisted rapid sintering technique and hot extrusion. The hybrid Mg/Al–CNT nano-composites exhibited slightly smaller grain sizes compared to monolithic Mg and reasonable hybrid Al–CNT nano-particle distribution up to Al content of 1.00 wt%. Compared to pure Mg, the Mg/Al–CNT nano-composites exhibited higher compressive yield strength (0.2% CYS), ultimate compressive strength (UCS) and work of fracture (WOF) (up to +36%, +76%, +36%) compared to pure Mg but failure strain was compromised. Inclusive of crystallographic texture changes, the effect of hybrid Al–CNT nano-particle integration on the enhancement of compressive properties of Mg is investigated in this paper.

Using integrated hybrid (Al + CNT) reinforcement to simultaneously enhance strength and ductility of magnesium

Magnesium nano-composites containing hybrid aluminium–carbon nanotube (Al–CNT) reinforcement were synthesized through powder metallurgy route using microwave assisted rapid sintering technique followed by hot extrusion. Compared to monolithic Mg, microstructural characterization revealed reasonably uniform distribution of Al–CNT particles in the matrix and reduction in average matrix grain size in the case of hybrid nano-composites. Compared to monolithic Mg, the Mg/Al–CNT nano-composites exhibited higher elastic modulus, strength and failure strain up to 1.00 wt.% Al content. The CNT content was kept constant at 0.18 wt.%. Among the different nano-composite formulations, the Mg/1.00Al–0.18CNT nano-composite exhibited the best improvement in elastic modulus ( E), tensile yield strength (0.2%YS), ultimate tensile strength (UTS) and failure strain (up to +3.6%, +38%, +36% and +42%, respectively) compared to pure Mg. The effect of hybrid Al–CNT reinforcement integration on the enhancement of mechanical properties of Mg is investigated in this paper.

Properties of polypropylene composites containing aluminum/multi-walled carbon nanotubes

Polypropylene/aluminum–multi-walled carbon nanotube (PP/Al–CNT) composites were prepared by a twin-screw extruder. The morphology indicates that the CNTs are well embedded or implanted within Al-flakes rather than attached on the surface. During preparation of composites, the CNTs came apart from Al–CNT so that free CNTs as well as Al–CNT were observed in PP/Al–CNT composite. The crystallization temperatures of PP/CNT and PP/Al–CNT composites were increased from 111 °C for PP to 127 °C for the composites. The decomposition temperature increased by 55 °C for PP/CNT composite and 75 °C for PP/Al–CNT composite. The PP/Al–CNT composite showed higher thermal conductivity than PP/CNT and PP/Al-flake composites with increasing filler content. PP/Al–CNT composites showed the viscosity values between PP/CNT and PP/Al-flake composites. PP/Al–CNT composite showed higher tensile modulus and lower tensile strength with increasing filler content compared to PP/CNT and PP/Al-flake composites.

Tensile properties of carbon nanotube reinforced aluminum nanocomposite fabricated by plasma spray forming

Uniaxial tensile tests were performed on plasma spray formed (PSF) Al–Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs). The addition of CNTs leads to 78% increase in the elastic modulus of the composite. There was a marginal increase in the tensile strength of CNT reinforced composite with degradation in strain to failure by 46%. The computed critical pullout length of CNTs ranges from 2.1 to 19.7 μm which is higher than the experimental length of CNT, leading to relatively poor load transfer and low tensile strength of PSF nanocomposites. Fracture surface validates that tensile fracture is governed strongly by the constitutive hierarchical microstructure of the plasma sprayed Al–CNT nanocomposite. The fracture path in Al–CNT nanocomposite occurs in Al–Si matrix adjacent to SiC layer on CNT surface.

Fabrication of Carbon Nanotube Reinforced Aluminum Composite by Powder Extrusion Process

This paper describes a fabrication process of Al/CNT composites and investigated their mechanical properties. CNT is a very useful reinforcement for composites since it has a very high strength and very high Young’s modulus. However, it is very difficult to distribute CNT in a metal matrix. Natural rubber was used as an elastomer and mixed with Al powder and CNT precursors to improve the distribution of the CNT in Al matrix. The resulting powder mixture was filled into Al alloy billets and encapsulated in vacuum atmosphere. The billets were then extruded with different extrusion ratios of 5, 10 and 20 at 673K. The composites were observed under optical microscope and FE-SEM, and the mechanical properties were evaluated by Vickers hardness and tensile tests. We succeeded in obtaining fully densified and finely extruded rod of Al/CNT composites of well distributed CNT by hot extrusion process. Observation of post extrusion micro structures revealed that CNT were not damaged by the hot extrusion process and their Vickers hardness and tensile strengths obtained were about twice compared to pure Al.