Role of powder treatment and carbon nanotube dispersion in the fracture toughening of plasma-sprayed aluminum oxide-carbon nanotube nanocomposite

Al2O3 ceramic reinforced with 4-wt% multiwalled carbon nanotube (CNT) is plasma sprayed for improving the fracture toughness of the nanocomposite coating. Two different methodologies of CNT addition have been adopted in the powder feedstock to assist CNT dispersion in the nano-Al2O3 matrix. First, spray-dried nano-Al2O3 agglomerates are blended with 4 wt% CNT as powder-feedstock, which is subsequently plasma sprayed resulting in the fracture toughness improvement of 19.9%. Secondly, spray dried composite nano-Al2O3 and 4 wt% CNT powder was used as feedstock for attaining improved dispersion of CNTs. Plasma sprayed coating of composite spray dried powder resulted in increase of 42.9% in the fracture toughness. Coating synthesized from the blended powder displayed impact alignment of CNTs along splat interface, and CNTs chain loop structure anchoring the fused Al2O3 melt whereas coating synthesized from composite spray dried powder evinced anchoring of CNTs in the solid state sintered region and CNT mesh formation. Enhanced fracture toughness is attributed to significance of CNT dispersion.     

A simple approach to prepare Al/CNT composite: Spread–Dispersion (SD) method

In carbon nanotube (CNT) reinforced metal matrix composites (MMCs), the good dispersion of CNTs in the matrix as well as the processing problems are the major challenges inhibiting the development of these composites. In this study, well-dispersed CNTs reinforced aluminum (Al) matrix nanocomposite was fabricated by a novel Spread–Dispersion (SD) method. Specimens with ultra-fine grain size down to 20 nm were obtained. The tensile strength of the CNT nanocomposite was 66% greater than the base matrix with a minor decrease in ductility. Such enhancement was analyzed on the basis of segregation and uniform distribution of clustered CNTs, disappearance of the CNT-free zones, eliminated porosity, stronger Al/CNT bonding and the retention of CNT graphitic structure.     

Mechanical characterization of copper coated carbon nanotubes reinforced aluminum matrix composites

In this investigation, carbon nanotube (CNT) reinforced aluminum composites were prepared by the molecular-level mixing process using copper coated CNTs. The mixing of CNTs was accomplished by ultrasonic mixing and ball milling. Electroless Cu-coated CNTs were used to enhance the interfacial bonding between CNTs and aluminum. Scanning electron microscope analysis revealed the homogenous dispersion of Cu-coated CNTs in the composite samples compared with the uncoated CNTs. The samples were pressureless sintered under vacuum followed by hot rolling to promote the uniform microstructure and dispersion of CNTs. In 1.0 wt.% uncoated and Cu-coated CNT/Al composites, compared to pure Al, the microhardness increased by 44% and 103%, respectively. As compared to the pure Al, for 1.0 wt.% uncoated CNT/Al composite, increase in yield strength and ultimate tensile strength was estimated about 58% and 62%, respectively. However, in case of 1.0 wt.% Cu-coated CNT/Al composite, yield strength and ultimate tensile strength were increased significantly about 121% and 107%, respectively.     

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.     

球磨工艺对原位合成碳纳米管增强铝基复合材料微观组织和力学性能的影响

将原位化学气相沉积法合成的碳纳米管(CNTs)与铝的复合粉末进行球磨混合,进而粉末冶金制备CNTs/Al复合材料,研究球磨工艺对复合材料的微观组织和力学性能的影响。结果表明:球磨过程中不添加过程控制剂所得到的复合材料力学性能优异;随着球磨时间的增加,CNTs逐步分散嵌入铝基体内部,复合材料的组织也变得更加致密均匀。CNTs/Al复合材料的硬度和抗拉强度均随球磨时间的延长持续增加,但是伸长率先增后减。经90min球磨的CNTs/Al复合材料展现了强韧兼备的特点,其硬度和抗拉强度较原始纯铝提高了1.4倍和1.7倍,并且具有17.9%的高伸长率。     

Tensile strength of glass fibres with carbon nanotube–epoxy nanocomposite coating

A study has been made of a concept of ‘healing’ coatings applied onto the brittle fibre surface to reduce the stress concentrations and thus to improve the reinforcing efficiency in a composite. Coatings made from neat epoxy and carbon nanotube (CNT) reinforced epoxy nanocomposite were applied onto the individual glass fibres as well as rovings. It is shown that the 0.3 wt.% CNT–epoxy nanocomposite coating gave rise to a significant increase in tensile strength of the single fibre for all gauge lengths, better than the neat epoxy coating. The results on glass fibre roving also indicated a clear beneficial effect of nanocomposite impregnation on tensile strength. The rovings impregnated with the CNT nanocomposite exhibited a more uniform strength distribution and higher strengths than those impregnated with the neat epoxy. The changes in prevailing failure mechanisms influenced by the epoxy and nanocomposite coatings have been identified.     

碳纳米管增强2024铝基复合材料的力学性能及断裂特性

为了研究碳纳米管对铝基复合材料性能的影响,采用冷等静压、热挤压方法制备了质量分数1.0%的多壁碳纳米管增强2024Al基复合材料.采用扫描电镜、透射电镜和拉伸试验对复合材料的显微组织进行了观察和分析,并对其力学性能进行了测试.结果表明,碳纳米管均匀地分布在复合材料中,碳纳米管和铝基体的界面结合良好,没有发现界面产物Al4C3的形成;复合材料的断口上存在大量的撕裂棱,韧窝,并涉及碳纳米管的拔出或拔断与桥接,与2024Al基体材料相比,复合材料的硬度、弹性模量和抗拉强度显著提高,同时复合材料的延伸率却并不下降.碳纳米管的加入可以显著提高铝基复合材料的力学性能.     

Tensile strength of glass fibres with carbon nanotube–epoxy nanocomposite coating: Effects of CNT morphology and dispersion state

The effects of carbon nanotube (CNT)–epoxy nanocomposite coating applied to glass fibre surface on tensile strength of single glass fibres are evaluated at different gauge lengths. The crack healing efficiencies obtained using two different types of CNTs with different structures, morphologies and dispersion characteristics in various concentrations are specifically studied. The results indicate that the tensile strength of single fibres increased significantly with increasing CNT content up to a certain level, depending on the type of CNTs. The crack healing efficiency was much higher for the fibres coated with straight, less entangled CNTs than those with highly entangled CNTs, indicating the CNT dispersion state in the coating played an important role. A strong correlation is established between the CNT dispersion state, the tensile properties of nanocomposite and the tensile strengths of fibres with the nanocomposite coating.     

Microstructures and tensile behavior of carbon nanotube reinforced Cu matrix nanocomposites

Carbon nanotubes (CNTs) have been considered as an ideal reinforcement to improve the mechanical performance of monolithic materials. However, the CNT/metal nanocomposites have shown lower strength than expected. In this study, the CNT reinforced Cu matrix nanocomposites were fabricated by spark plasma sintering (SPS) of high energy ball-milled nano-sized Cu powders with multi-wall CNTs, and followed by cold rolling process. The microstructure of CNT/Cu nanocomposites consists of two regions including CNT/Cu composite region, where most CNTs are distributed, and CNT free Cu matrix region. The stress–strain curves of CNT/Cu nanocomposites show a two-step yielding behavior, which is caused from the microstructural characteristics consisting of two regions and the load transfer between these regions. The CNT/Cu nanocomposites show a tensile strength of 281 MPa, which is approximately 1.6 times higher than that of monolithic Cu. It is confirmed that the key issue to enhance the strength of CNT/metal nanocomposite is homogeneous distribution of CNTs.     

A study on the tensile response and fracture in carbon nanotube-based composites using molecular mechanics

A study on the mechanical properties of polyethylene and carbon nanotube (CNT) based composites is presented using molecular mechanics simulations. The systems being investigated consist of amorphous as well as crystalline polyethylene (PE) composites with embedded single-walled CNTs. All the systems are subjected to quasi-static tensile loading, with the assumption that no cross-link chemical bonds exist between the CNT and polyethylene matrix in the case of nanocomposites. Based on the numerical simulations, we report Young’s moduli (C₃₃) of 212–215 GPa for crystalline PE, which closely match the experimental measurement. Furthermore, elastic stiffness of 3.19–3.69 GPa and tensile strength of 0.21–0.25 GPa are obtained for amorphous PE. The tensile responses are found to be highly isotropic. In the case of crystalline PE reinforced by long through CNTs, moderate improvements in the tensile strength and elastic stiffness are observed. However, the results differ from the predictions using the rule of mixtures. On the other hand, although significant increase in the overall tensile properties is observed when amorphous PE is reinforced by long through CNTs, the load transfer at the nanotube/polymer interface has negligible effect. Finally, degradations in both tensile strength and elastic stiffness are reported when amorphous PE is reinforced by embedded CNTs. The study presented indicates the importance of specific CNT and polymer configurations on the overall properties of the nanocomposite.     

Modeling the effect of statistical variations in length and diameter of randomly oriented CNTs on the properties of CNT reinforced nanocomposites

A nano-mechanical model has been developed to calculate the tensile modulus and the tensile strength of randomly oriented short carbon nanotubes (CNTs) reinforced nanocomposites, considering the statistical variations of diameter and length of the CNTs. According to this model, the entire composite is divided into several composite segments which contain CNTs of almost the same diameter and length. The tensile modulus and tensile strength of the composite are then calculated by the weighted sum of the corresponding modulus and strength of each composite segment. The existing micro-mechanical approach for modeling the short fiber composites is modified to account for the structure of the CNTs, to calculate the modulus and the strength of each segmented CNT reinforced composites. Multi-walled CNTs with and without inter-tube bridging have been considered. Statistical variations of the diameter and length of the CNTs are modeled by a normal distribution. Simulation results show that CNTs inter-tube bridging, length and diameter affect the nanocomposites modulus and strength. Simulation results have been compared with the available experimental results and the comparison concludes that the developed model can be effectively used to predict tensile modulus and tensile strength of CNTs reinforced composites.     

Investigation of carbon nanotube reinforced aluminum matrix composite materials

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.     

Microstructure and mechanical properties of CNT/Ag nanocomposites fabricated by spark plasma sintering

Carbon nanotube/silver (CNT/Ag) nanocomposites include CNT volume fraction up to 10?vol.% were prepared by chemical reduction in solution followed by spark plasma sintering. Multiwalled CNTs underwent surface modifications by acid treatments, the Fourier transform infrared spectroscopy data indicated several functional groups loaded on the CNT surface by acid functionalisation. The acid-treated CNTs were sensitised and activated. Silver was deposited on the surface of the activated CNTs by chemical reduction of alkaline silver nitrate solution at room temperature. The microstructures of the prepared CNT/Ag nanocomposite powders were investigated by high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy and X-ray powder diffraction analysis. The results indicated that the produced CNT/Ag nanocomposite powders have coated type morphology. The produced CNT/Ag nanocomposite powders were sintered by spark plasma sintering. It was observed from the microstructure investigations of the sintered materials by HRSEM that the CNTs were distributed in the silver matrix with good homogeneity. The hardness and the tensile properties of the produced CNT/Ag nanocomposites were measured. By increasing the volume fraction of CNTs in the silver matrix, the hardness values increased but the elongation values of the prepared CNT/Ag nanocomposites decreased. In addition, the tensile strength was increased by increasing the CNTs volume fraction up to 7.5?vol.%, but the sample composed of 10?vol.% CNT/Ag was fractured before yielding.     

Electrically conductive carbon nanotube/polypropylene nanocomposite with improved mechanical properties

Conductive polymer nanocomposites based on carbon nanotubes (CNTs) have wide range of applications in the electronics and energy sectors. For many of these applications, such as the electromagnetic interference (EMI) shielding, high nanofiller loading is typically needed to achieve the desired properties. The high nanofiller concentration deteriorates the composite's tensile strength due to the increase in nanofiller aggregation. In this work, highly conductive CNT/polypropylene (PP) nanocomposite with improved tensile strength was prepared by melt mixing. The effects of CNT content on the processing behavior, microstructure, mechanical and electrical properties of the nanocomposite were investigated. Scanning electron microscopy was used to investigate the composite microstructure. Good level of CNT dispersion with remarkable adhesion at the CNT/PP interface was observed. Based on a theoretical model, the interfacial strength was estimated to be in the range of 36–58 MPa. As a result of this microstructure, significant enhancement in ultimate tensile strength was reported with the increase of CNT content. The tensile strength of the 20 wt.% CNT/PP nanocomposite was 80% higher than that of the unfilled PP. Moreover, and due to the good dispersion of CNT particles, an electrical percolation threshold concentration of 0.93 wt.% (0.5 vol.%) was obtained.     

Thermal conductivity of carbon nanotube reinforced aluminum composites: A multi-scale study using object oriented finite element method

In this study, object oriented finite element method (OOF) has been utilized to compute the thermal conductivity of plasma sprayed Al-12 wt.% Si containing 10 wt.% multiwall carbon nanotubes (CNTs). The computations have been made at micro- and macro-length scales which highlight the effect of CNT dispersion on thermal conductivity. Experimentally measured values at 50 °C indicate that CNT addition reduced the thermal conductivity of Al–Si matrix from 73 W m⁻¹ K⁻¹ to 25.4 W m⁻¹ K⁻¹ which is attributed to the presence of CNT clusters. OOF calculations at micro-length scale predicted an 81% increase in the conductivity of Al–Si matrix due to presence of well dispersed CNTs inside the matrix. At larger lengths scale, the decrease in the overall conductivity is related to the extremely low conductivity of CNT clusters. Thermal conductivity of CNT clusters could be up to three orders of magnitude lower than individual CNTs. OOF computed values match well with experimental results. OOF compute thermal conductivity of Al–CNT composite is also compared with theoretical two-phase models for CNT-composites at different length scales.     

Si元素对碳纳米管增强铝基复合泡沫组织与性能的影响

针对金属基复合材料,添加合金元素是提升其综合性能的有效途径.本文通过高能球磨和填加造孔剂法,制备了添加Si元素的碳纳米管(CNTs)增强铝基(CNTs/Al-Si)复合泡沫,通过准静态压缩实验测试其压缩性能和吸能性能,进一步研究烧结温度和不同Si元素含量对CNTs/Al-Si复合泡沫微观组织、压缩性能和吸能性能的影响,...     

取向碳纳米管膜/氰基树脂复合材料的制备与性能强化机制

以浮动催化化学气相沉积法(FCCVD)碳纳米管(CNT)膜为原料,通过氰基树脂溶液浸渍法制备CNT预浸膜,然后采用热辅助牵伸和热压固化的方法制备高取向CNT膜复合材料。详细分析了热处理的温度和树脂溶液浓度对CNT预浸膜拉伸性能的影响,从而得到合适的热辅助牵伸工艺,并考察固化工艺对复合材料性能的影响。在此基础上,从浸润特性、CNT取向程度和层间剪切性能方面揭示CNT膜复合材料力学性能的强化机制。结果表明与传统CNT膜牵伸工艺相比,CNT预浸膜热牵伸工艺更有利于制备高取向CNT膜复合材料。热牵伸的温度和树脂溶液的浓度是制备高取向、低孔隙CNT预浸膜的关键因素。通过固化工艺的改变可有效调控氰基树脂的反应程度碳纳米管薄膜/氰基树脂复合材料的拉伸性能。经高温后固化处理后,CNT膜/氰基树脂复合材料的拉伸强度和模量分别高达2 748 MPa和302GPa。优异的树脂浸润特性、层间剪切强度以及高的CNT取向度使CNT膜复合材料中CNT更有利于协同承载,从而提高其力学性能。     

Microstructure and Properties of Spark Plasma Sintered Carbon Nanotube Reinforced Aluminum Matrix Composites

In this paper, spark plasma sintering (SPS) of multi‐walled carbon nanotube (CNT) reinforced aluminum matrix composites is reported. Ball milling of the Al‐CNT mixture with polyacrylic acid (PAA) dispersion agent followed by SPS resulted in uniform dispersion of CNTs in dense composite compacts. Significant improvement in microhardness, nanohardness, and compressive yield strength was observed with 2 wt% CNT reinforcement in aluminum matrix composites. The Al‐CNT composites further exhibited improved wear resistance and lower friction coefficient due to strengthening and self‐lubricating effects of CNTs.     

Influence of nano-sized carbon nanotube reinforcements on tensile deformation,cyclic fatigue,and final fracture behavior of a magnesium alloy

Magnesium alloy (AZ31) based metal matrix composite reinforced with carbon nanotubes (CNTs) was fabricated using the technique of disintegrated melt deposition followed by hot extrusion. In this research paper, the microstructure, hardness, tensile properties, tensile fracture, high cycle fatigue characteristics, and final fracture behavior of CNTs-reinforced magnesium alloy composite (denoted as AZ31/1.0 vol.% CNT or AZ31/CNT) is presented, discussed, and compared with the unreinforced counterpart (AZ31). The elastic modulus, yield strength, tensile strength of the reinforced magnesium alloy was noticeably higher compared to the unreinforced counterpart. The ductility, quantified both by elongation-to-failure and reduction in cross-section area of the composite was higher than the monolithic counterpart. A comparison of the CNT-reinforced magnesium alloy with the unreinforced counterpart revealed a noticeable improvement in cyclic fatigue life at the load ratios tested. At all values of maximum stress, both the reinforced and unreinforced magnesium alloy was found to degrade the cyclic fatigue life at a lower ratio, i.e., under conditions of fully reversed loading. The viable mechanisms responsible for the enhanced cyclic fatigue life and tensile behavior of the composite are rationalized in light of macroscopic fracture mode and intrinsic microscopic mechanisms governing fracture.