Carbon Nanotube Reinforced Aluminum Matrix Research Articles

A coupled ductile damage model for metal matrix composites: Development and application

The prediction of failure behavior in metal matrix composites remains a significant challenge in both composition design and process optimization. An accurate prediction of metal matrix composites damage evolution is a crucial for enhancing the quality of metal matrix composites forming. As the material undergoes plastic deformation, it experiences void initiation and growth, resulting in consequential microstructural transformations, stiffness degradation, and mechanical property shifts. In this work, we employed a model to predict damage progression and stiffness decay in metal matrix composites. Leveraging the Gurson-Tvergaard-Needleman framework, this homogenization model accounts for the impact of the evolution of voids and reinforcing phases, on the composite's mechanical properties. The influences of reinforcing phases on voids nucleation and growth were particularly considered, and also the interaction of voids, matrix, reinforcing phases, and stiffness were integrated to discuss their impacts on damage evolution and mechanical performances of the metal matrix composites. The model was implemented as an Abaqus VUMAT subroutine, with its validity gauged by analyzing the influence of model parameters on failure mechanisms and inherent elastoplastic traits. Utilizing the flanging process of carbon nanotube-reinforced aluminum matrix composites as a case study, a significant agreement was observed between experimental and simulated force-displacement profiles, as well as crack evolution routes.

Re-dissolution behavior of secondary phases and mechanical response of CNT/2024Al composites

Heat treatment is one of the most effective strategies for regulating microstructure and enhancing the mechanical properties of aluminum matrix composites. In this work, the effects of solution treatment on the static recrystallization behavior, characteristics of secondary phases dissolving, and mechanical response of carbon nanotubes reinforced aluminum matrix composites (CNT/2024Al) were systematically investigated using transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). Since plenty of deformation stored energy in as-extruded composites is consumed, the residual energy is insufficient to induce static recrystallization during solution treatment. Besides, various interfacial phases aggregated around the Al2Cu phases, which reduced the effective contact area between the Al2Cu phases and matrix, and severely hindered the dissolution process of the Al2Cu phases. The yield strength, tensile strength, and elongation of as-solution treated composites were 23.2%, 44.9%, and 23.0% higher than those of as-extruded composites, respectively. The enhanced yield strength is attributed to solid solution strengthening induced by the dissolution of secondary phases, thermal mismatch strengthening, and the strengthening originating from the formation of Al4C3 phases.

Chemical and mechanical treatments for enhancement of carbon nanotube reinforced aluminum matrix composites

A widespread application of carbon nanotube (CNT) and its metal matrix composites (MMCs) has not been achieved due to difficulty to disperse CNT in the matrix to efficiently obtain the excellent properties of CNT. In this study, CNT/Al composites were fabricated by uniformly dispersing CNT in Al matrix using chemical and mechanical treatments, which include untangling CNT in an organic solvent (DMAc) with a certain dispersant such as potassium carbonate (K2CO3) or ammonium carbonate ((NH4)2CO3)), dry ball milling and post-sintering repeated hot rolling. The composites were consolidated by spark plasma sintering (SPS). It was found that chemical treatments with ammonium carbonate were more effective to untangle CNT with less damage, while CNT/Al composites with CNT treated by potassium carbonate showed higher dispersibility of CNT in Al matrix. It was also seen that the post-SPS repeated hot rolling can highly improve dispersibility of CNT as well as mechanical properties such as hardness, tensile strength and deformability of the composites.

Structural modeling and mechanical research of carbon nanotube reinforced aluminum matrix composites using strain gradient theory

Carbon nanotube (CNT)-reinforced aluminum alloys (Al) are considered to be the ideal metal-matrix composites owing to their high strength and elastic moduli. However, they have low ductility. In addition, the inhomogeneity of the structure makes a strong strain gradient during deformation. In this research, a series of simulations under uniaxial tension and shear loading paths were conducted to investigate the mechanical properties of CNT/Al6061 composite. The novel multiple mechanism-based strain gradient models (MMSG) were proposed to study and analyze the correlation between microstructure evolution and macro mechanical responses. The interfacial bonding, grain size, and dislocation density were mainly considered during the simulation. The results of this study can be used to reveal the synergetic strength and ductility of all the structural microstructure, which also affects the strain partition and failure of different phases in CNT/Al6061 composites.

Effects of solid-state interfacial reaction on the mechanical properties of carbon nanotubes reinforced aluminum matrix composites with heterogeneous structure

To overcome strength-ductility trade-off in carbon nanotubes (CNTs) reinforced Al matrix composites, we developed a novel and controllable strategy via a combination of different length of CNTs and fine/coarse-grained matrices. Microstructure analysis showed that Al4C3 nanorods about 100 nm were distributed in the fine grain zone (FGZ), while CNTs of micron length were distributed in the coarse grain zone (CGZ). Different sizes of reinforcements play different strengthening roles, and the bimodal grains can effectively coordinate deformation, thereby achieving a good combination of strength and ductility. Heat treatment does not affect the microstructure of the FGZ, but significantly affect the CNT/Al interface bonding in the CGZ. Heat treatment at an appropriate temperature can further improve the strength of the composite by improving the interface bonding. When the heat treatment temperature is too high, the coarsening of Al4C3 in CGZ will deteriorate the mechanical properties of the composite.

Effects of Solid-State Interfacial Reaction on the Mechanical Properties of Carbon Nanotubes Reinforced Aluminum Matrix Composites with Heterogeneous Structure

Effects of Solid-State Interfacial Reaction on the Mechanical Properties of Carbon Nanotubes Reinforced Aluminum Matrix Composites with Heterogeneous Structure

Improving the mechanical properties of carbon nanotubes reinforced aluminum matrix composites by heterogeneous structural design

A novel aluminum matrix composites with different lengths of CNTs and heterogeneous structural were prepared in this paper. The synergistic effect of reinforcements with different lengths improves the mechanical properties of composites. Meanwhile, the heterogeneous structure design introduced fiber-like reinforcement to enhance the strength and toughness of composite.

Machine-learning-assisted microstructure–property linkages of carbon nanotube-reinforced aluminum matrix nanocomposites produced by laser powder bed fusion

Abstract In this study, the cellular microstructural features in a subgrain size of carbon nanotube (CNT)-reinforced aluminum matrix nanocomposites produced by laser powder bed fusion (LPBF) (a size range between 0.5–1 μm) were quantitatively extracted and calculated from scanning electron microscopy images by applying a cell segmentation method and various image analysis techniques. Over 80 geometric features for each cellular cell were extracted and statistically analyzed using machine learning techniques to explore the structure–property linkages of carbon nanotube reinforced AlSi10Mg nanocomposites. Predictive models for hardness and relative mass density were established using these subgrain cellular microstructural features. Data dimension reduction using principal component analysis was conducted to reduce the feature number to 3. The results showed that even AlSi10Mg nanocomposite specimens produced using different laser parameters exhibited similar Al–Si eutectic microstructures, displaying a large difference in their mechanical properties including hardness and relative mass density due to cellular structure variance. For hardness prediction, the Extra Tress regression models showed a relative error of 2.47% for prediction accuracies. For the relative mass density prediction, the Decision Tress regression models showed a relative error of 1.42% for prediction accuracies. The results demonstrate that the developed models deliver satisfactory performance for hardness and relative mass density prediction of AlSi10Mg nanocomposites. The framework established in this study can be applied to the LPBF process optimization and mechanical properties manipulation of AlSi10Mg-based alloys and other additive manufacturing newly designed alloys or composites.

Study on Properties of Multi Walled Carbon Nanotube Reinforced Aluminum Matrix Composite through Casting Technique

Composite materials are defined as material systems consisting of mixture of or combination of two or more micro constituents insoluble in each other and differing in form and or material composition. In this study Metal Matrix Composite (MMCs) has been produced using stir casting method for performing the mechanical properties. Most of the engineering industries want light and better mechanical properties of components; this can be achieved by MMCs of Aluminium because of its excellent performance. In this research work we fabricate the Aluminium by liquid route. Here Al 7075 is used as a base metal and Multi Walled Carbon Nanotubes (MWCNT) used as sub metal with various percentages. Experiments were conducted to analyze microstructure, hardness & tensile strength. By using optical microscope and Scanning Electron Microscope (SEM) we analyze the sample specimens are well dispersion in MWCNT with AA 7075. Hardness and tensile strength increases with increasing of wt. %. Hardness of material increases with increase in percentages of MWCNT, whereas tensile strength of the material increases with increase in percentages of MWCNT and Elongation reduces

Exploiting the synergic strengthening effects of stacking faults in carbon nanotubes reinforced aluminum matrix composites for enhanced mechanical properties

Carbon nanotubes (CNTs) reinforced Al matrix composites containing high-density stacking faults were successfully fabricated through spark plasma sintering (SPS) and subsequently hot rolling with high strain rate. It is found that the inclusion of CNTs facilitate the formation of stacking fault in Al matrix. With increasing the CNTs from 0.5 vol% to 1.0 vol%, the density of stacking fault increases, which is mainly because of the reduced stacking fault energy of Al matrix in Al/CNTs composites, as revealed by the density functional theory simulation. Combined with the effective exploitation of the strengthening effectiveness of CNTs due to uniform dispersion of CNTs and well bonded Al-CNTs interface, the highest tensile strength (378 ± 8 MPa) together with good ductility (17.1 ± 1.5%) can be achieved for 1 vol% CNTs reinforced Al matrix composite. Moreover, the enhanced strength deriving from each strengthening mechanism relies on the CNTs content. When the CNTs content is 1.0 vol%, Orowan looping and stacking fault strengthening are the dominant strengthening mechanisms. The reported microstructure design and control can be informative for improving the mechanical properties of CNTs reinforced metal matrix composites.

Microscopic stresses in carbon nanotube reinforced aluminum matrix composites determined by in-situ neutron diffraction

One of the most desired strengthening mechanisms in the carbon nanotube reinforced aluminum matrix composites (CNT/Al) composites is the load transfer strengthening mechanism (LTSM). However, a fundamental issue concerning the LTSM is that quantitative measurements of load partitioning in these composites during loading are very limited. In this study, in-situ neutron diffraction study on the tensile deformation of the 3 vol.% CNT/2009Al composite and the unreinforced 2009Al alloy was conducted. The {311} and {220} diffraction elastic constants (DECs) of the 2009Al alloy were determined. Using those DECs the average stress in the 2009Al matrix of the composite was calculated. Then the average stress in the CNTs was separated by using the stress equilibrium condition. Computational homogenization models were also applied to explain the stress evolution in each phase. Predicted results agree with experimental data. In the present case, the average stress in the CNTs reaches 1630 MPa at the yield strength of the composite based on linear regression of the measured data, which leads to an increment of yield strength by about 37 MPa. As the result of this work, an approach to quantify load partitioning in the CNTs is developed for the CNT/Al composites, which can be applied to optimize the mechanical properties of the composites.

Carbon nanotubes reinforced aluminum matrix composites with high elongation prepared by flake powder metallurgy

High elongation aluminum matrix composites reinforced with carbon nanotubes (CNTs) were prepared by flake powder metallurgy, and densified by hot extrusion with a high extrusion ratio. After hot extrusion, fine and equiaxed grains were obtained in 2 wt% CNT/Al composite, and interfacial product (Al4C3) as well as bridge-connected CNTs aligned along the extrusion direction were found both in 1 wt% CNT/Al and 2 wt% CNT/Al composites. Both composites obtained high elongation while their strength was enhanced. Especially the elongation of 2 wt% CNT/Al composite is comparable to that of pure Al prepared by the same method, which reached about 30%. The good ductility mainly attributes to firm interfacial combination between CNTs and matrix, fine and equiaxed grains formed by dynamic recrystallization during hot extrusion, and bridge-connected CNTs aligned along the extrusion direction.

Effect of Milling Time on Dry Sliding Wear Behaviors of Carbon Nanotubes Reinforced Al Matrix Composites.

In this study, the effect of mechanical milling time on microstructure, hardness and dry sliding wear behaviors of carbon nanotube reinforced aluminum matrix composites was investigated.Multi-walled carbon nanotubes (amount of 1%) were added to gas atomized AA7075 alloy as a reinforcement material and it was mechanical milled five different times. Milled Al-CNTs composite powders were added in a steel mold and pre-formed by cold pressing and hot pressing. Pre-formed composites samples were sintered. Microstructures of produced samples were examined by Scanning electron microscope. Density and hardness values were measured 1 ms-1 sliding speed, 30 N loads and five different sliding distances were used in dry sliding wear tests on pin on disc type wear apparatus. As a result of the studies, it was found that the particle size increased as the milling time increased. Powders milled for 100 min had the largest particle size, whereas powders milled for 120 min had a smaller particle size. The results indicated that composites mechanically milled for 120 min had both the highest hardness value and the lowest weight loss.

Size-dependent effects of Ti powders in the pure aluminum matrix composites reinforced by carbon nanotubes

Carbon nanotube reinforced aluminum matrix (CNT/Al) composites with various microstructures were fabricated by powder metallurgy via introducing nano-sized and micron-sized Ti powders into the CNT-Al system. The size-dependent effects of Ti powders on the microstructure evolution and mechanical properties were further investigated. The results reveal that the best enhancement (∼51% of UTS) was obtained by adding 80 nm sized Ti powders into the CNT/Al composite compared with the composite without Ti addition, which mainly derives from the synergistic strengthening of the homogenously dispersed CNTs, a large quantity of in-situ formed nano-sized TiAl3 particles and fine grains. Meanwhile, it is also noted that the addition of micron-sized Ti powders can help the CNT dispersion in powder fabrication stage, and subsequently in-situ formed core-shell structured particles with different interface reaction degree in the Al matrix. Among them, 1 μm was determined to be the optimal size of Ti for the maximum formation of core-shell structured particles, which best exploits the load transfer ability of TiAl3 shell layers at their interfaces, and finally attributes to significant strength enhancement (∼35% of UTS). This research provides a valuable reference concerning the size effects of addition metal in future fabrication of CNTs reinforced metal matrix composites with alternative microstructure.

Investigation on forming limit of carbon nanotube reinforced aluminum matrix composite sheet at high temperature

The thermal forming limit curve of carbon nanotube reinforced aluminum matrix composite (CNT/2009Al) was theoretically and experimentally investigated in this work. The mathematical procedure was solved on basis of Marciniak-Kuczynski model by applying the two constitutive equations of Swift equation and Voce equation. The influence of yield functions on FLD was analyzed by employing the general form of Hill’s 1979 yield criterion. The thermal Nakajima test was performed to determine FLD of the composite sheet. The result shows that, CNT/2009Al sheet formability is in a low level even at high temperature, and the FLD predicted by Hill’s 1979 makes a reasonable agreement with experimental data in right-hand zone.

Effects of energy input during friction stir processing on microstructures and mechanical properties of aluminum/carbon nanotubes nanocomposites

Carbon nanotubes reinforced aluminum matrix nanocomposites were fabricated by friction stir processing. Raman spectroscopy, scanning electron microscope, transmission electron microscopy and tensile tests were used to characterize microstructures and mechanical properties of the nanocomposites. Effects of energy input during friction stir processing on microstructures and mechanical properties of the nanocomposites were investigated. It was found that the grain of aluminum matrix in the nanocomposites was coarsened slightly with the increase of energy input. Microstructure analysis showed that carbon nanotubes were successfully incorporated into aluminum matrix by friction stir processing and well bonded interfaces between the carbon nanotubes and aluminum matrix were formed. However, the carbon nanotubes dispersion and mechanical properties of the nanocomposites fabricated with different energy inputs were quite different, in which better carbon nanotubes dispersion and higher tensile strength could be obtained by applying higher energy input during the fabrication process. By applying the highest energy input, the tensile strength of the nanocomposite was 53.8% higher than that of the unreinforced aluminum. Meanwhile, the elongation of the nanocomposite was 31.2%, which showed an excellent ductility. The strengthening mechanisms were the synergy of Orowan looping, load transfer and grain refining. The present findings may provide the guidance on the optimization of the processing parameters during friction stir processing for fabricating the high performance aluminum/CNTs nanocomposites.

Carbon nanotube-reinforced aluminum matrix composites enhanced by grain refinement and in situ precipitation

Carbon nanotubes-reinforced aluminum matrix (CNTs/Al) composites possess wide application prospects in many fields, and how to achieve a high performance is always a research hot spot. In this study, a novel high-performance Al matrix nanocomposite reinforced with short CNTs and in situ Al4C3 nanorods was fabricated by combining ball milling and hot extrusion, and they exhibit excellent comprehensive mechanical properties. The 2 wt% CNTs/Al composite reached a tensile strength of 312 MP and an elongation of 15.8%, showing an 102% strength improvement compared with the pure aluminum prepared by the same process. The remarkable improvement of the mechanical properties originates from the synergistical enhancement of fine-grained strengthening and dispersion strengthening of in situ Al4C3 nanorods and short CNTs.

Forming Mechanism and Mechanical Properties of Carbon Nanotube Reinforced Aluminum Matrix Composites by Selective Laser Melting

Forming Mechanism and Mechanical Properties of Carbon Nanotube Reinforced Aluminum Matrix Composites by Selective Laser Melting

Effect of aluminum carbide interphase on the thermomechanical behavior of carbon nanotube/aluminum nanocomposites

The objective of this work is to investigate the coefficient of thermal expansion of carbon nanotube reinforced aluminum matrix nanocomposites in which aluminum carbide (Al4C3) interphase formed due to chemical interaction between the carbon nanotube and aluminum matrix is included. To this end, the micromechanical finite element method along with a representative volume element, which incorporates, carbon nanotube, interphase, and aluminum matrix is employed. The emphasis is mainly placed on the effect of Al4C3 interphase on the coefficient of thermal expansion of aluminum nanocomposites with random microstructures. The effects of interphase thickness, carbon nanotube diameter, and volume fraction on the thermomechanical response of aluminum nanocomposite are discussed. The results reveal that the effect of Al4C3 interphase on the coefficient of thermal expansion of the aluminum nanocomposites becomes more significant with (i) increasing the coefficient of thermal expansion volume fraction, (ii) decreasing the coefficient of thermal expansion diameter, and (iii) increasing the interphase thickness. It is clearly observed that the coefficient of thermal expansion varies nonlinearly with the carbon nanotube diameter; however, it decreases linearly as the carbon nanotube volume fraction increases. Furthermore, the axial and transverse coefficient of thermal expansions of aligned continuous and discontinuous carbon nanotube-reinforced aluminum nanocomposites with Al4C3 interphase are predicted. Also, the presented finite element method results are compared with the available experiment in the literature, rule of mixture, and concentric cylinder model results.

Investigation of Mechanical Behavior of Carbon Nanotube Reinforced Aluminum Matrix AlMg / KNT Composites

Bu çalışmada, toz metalürjisi tekniği kullanılarak AlMg matriksine ağırlıkça farklı oranlar da (%2,5, %5 ve %10) KNT takviyesi ile güçlendirilmiş AlMg/KNT nano kompozit materyalleri sentezlenmiştir. Mekanik alaşımlama (MA) işlemi 7 saat ve 400 Rpm de Turbula karıştırma cihazında yapılmıştır. Mekanik alaşımlamanın ardından sırası ile toz karekterizasyonu, optik incelemeler, sertlik ve yoğunluk testleri yapılmıştır. XRD spektrometre cihazında 10-90 derecede taranarak hassasiyetle XRD incelenmiş ardından 200 Mpa basınç altında metal kalıpta numuneler üretilmiştir. Üretilen AlMg/KNT kompozit numuneleri yüksek vakum altında farklı (350 0C, 400 0C, 450 0C) sıcaklıklar da 120 dakika boyunca sinterlenerek üretilen numunelerin sertlik, yoğunluk ve metalografik incelemeleri yapılmıştır. Aynı atmosferde, farklı sıcaklık ve farklı KNT oranlar ile üretilmiş olan AlMg/KNT kompozit numunelerin pik şiddetlerinde artan KNT oranları ile birlikte 42,6º gözle görülür şekilde artış gözlemlenmiştir. Aynı şekilde artan KNT oranı ile birlikte sinterleme sıcaklığına bağlı olarak sertlik değerlerinde iyileşme ve buna karşılık artan KNT oranı ile birlikte yoğunluk düşüşü gözlemlenmiştir.