Nano-silver modified carbon nanotubes to reinforce the copper matrix composites and their mechanical properties

In ensuring the effective load transfer of carbon nanotubes (CNTs) reinforced copper (Cu)-based composites, good and stable interface contact is a key factor. Powder electrodeposition technology is used in the present study to coat silver (Ag) nanoparticles on CNTs for the first time. Subsequently, by ball milling and spark plasma sintering, uniform distribution of CNTs in the Cu matrix and tight Cu/C interface bonding are successfully achieved. It is found that Ag nanoparticles with a size of 5 nm are evenly embedded in the surface of CNTs. The results reveal that the agglomeration of CNTs is prevented by the addition of Ag nanoparticles and the adhesion between CNTs and Cu matrix is enhanced by the formation of coherent interface. Further, the load transfer of composite materials is effectively realized by the pinning effect of Ag particles on CNTs. The tensile strength, elongation, and conductivity of the 0.75 CNT-Ag/Cu samples were 314 MPa, 24.8%, and 93.6% IACS, respectively, which are 40.1%, 818%, and 3.3% higher than those of the CNT/Cu samples, respectively. The present method provides a new direction for the uniform coating powder materials and the synergistic strengthening of metal matrix composites.     

Mechanical Properties and Strain Hardening Behavior of Few-Layered Graphene Nanosheets-Reinforced Powder Metallurgy Nickel-Based Superalloy Metal Matrix Composites

Herein, few-layered graphene nanosheets (GNS) with approximately 3, 6, or 9 layers are used to reinforce high-performance nickel-based superalloy metal matrix composite. A powder metallurgy method comprising solution-mixing, hot isostatic pressing, and thermal processing is used to prepare GNS-FGH96 composites with different numbers of GNS layers as well as referential FGH96 matrix materials. Compared with those of unreinforced FGH96, the mechanical properties of the GNS-FGH96 composites are enhanced, specifically, the ≈6 layers GNS-FGH96 composite exhibits an ultimate tensile strength of 1660 MPa and a yield strength of 1229 MPa, which are 9.79% and 6.87% higher, respectively, than those without the addition of GNS. Furthermore, the ≈6 layers GNS-FGH96 composite exhibits the highest elongation-at-fracture of 29.9%. The as-prepared GNS-FGH96 composites show a good balance of strength and ductility owing to the increased dislocation density between the FGH96 matrix and GNS reinforcement interface area, as well as the high structural integrity of the GNS. Thus, this study provides a novel approach for designing and creating high-performance graphene-reinforced FGH96 metal matrix composites that exhibit exceptional strength and toughness.     

Rheological and mechanical properties of carbon nanotube/Graphite/SS316L/polypropylene nanocomposite for a conductive polymer composite

Highly filled conductive fillers (>60 vol%) for conductive polymer composites (CPCs) cause the degradation of rheological and mechanical properties. This study investigated the rheological properties of highly filled metal powder (SS316L) in a polymer matrix composite combined with carbon nanotubes (CNTs) and Graphite (G). The effects of filler concentrations and chemical functionalization on the mechanical and electrical properties of the resulting CPC were determined. Feedstocks with different concentrations were injection molded, and the molded specimens were subjected to tests of tensile strength, three-point bending, hardness, and three-point probe electrical conductivity. The feedstock of CNTs/G/SS316L can be injection molded from 28 vol% polypropylene (PP). The functionalized CPC shows higher strength and elongation than as-produced CPC based on the tensile and flexural tests. The highest flexural and tensile strengths are 80 and 35 MPa, respectively. The functionalized CPC also exhibits higher hardness and better electrical properties than as-produced CPC. Thus, functionalization with CNTs and Graphite enable the reinforcement and formation electrical conducting networks between metal- and carbon-based fillers within a polymer matrix.     

Effect of size and shape of metal particles to improve hardness and electrical properties of carbon nanotube reinforced copper and copper alloy composites

Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT–metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved.     

Technology development and applications of composites at HAL

Composite materials for aerospace applications through in-house R & D and through collaboration with overseas aerospace organizations and National Laboratories covering a wide spectrum including glass/carbon/kevlar fibre reinforced plastics, metal and Nomex honeycomb sandwich structures, laminated composites, metal matrix composites and metallo-ceramic composites.     

Formation of stainless steel–carbon nanotube composites using a scalable chemical vapor infiltration process

Carbon nanotubes (CNTs) are among the strongest materials known, making their use in composites, a field with very high commercial potential for structural applications. Many of the methods reported to date to form metal composites have an excessive number of steps. Here, a facile chemical vapor deposition method to infiltrate multiwalled carbon nanotubes directly into pure stainless steel pellets and pellets from stainless steel mixed with iron particles is reported. The iron powder was dry-coated before vapor filtration with nanosized iron oxide catalyst precursor, a critical step to increase catalytic activity. This CVD method results in a substantial increase in the elastic modulus, yield strength, and hardness by 47, 104, and over 93 %, respectively, for composites made from mixed, dry-coated particles compared with corresponding control samples without nanotubes. This is the highest enhancement reported, to the best of our knowledge, of the mechanical properties for a metal–nanotube composite prepared using a metal other than copper. The addition of CNTs results in a relatively small increase in corrosion rate which can be mitigated to negligible levels by coating with a thin epoxy–carbon nanotube composite.     

Carbon nanotube dispersion in aluminum matrix composites—Quantification and influence on strength

Carbon nanotube (CNT) incorporation in metal matrix composites is hampered by the development of attractive van der Waals forces, which lead to the formation of CNT agglomerates. Therefore, a detailed quantification and characterization of CNT agglomerates and consequently CNT dispersion can enlighten their influence in composites strength. This work presents a comprehensive study, quantifying agglomerates by size, for three different composites (2, 4, and 6 CNT vol%), made with an aluminum-silicon matrix by a powder metallurgy route. From the obtained experimental data, an empirical model that attempts to predict the tensile strength of these composites from CNT agglomerates analysis is presented.     

高能球磨法制备高性能均一分散CNTs/Al5083复合材料

采用卧式高能球磨法制备0%~2%CNTs/Al5083(质量分数)复合材料,研究球磨时间和CNTs含量对复合材料性能的影响。采用扫描电镜(SEM)和透射电镜(TEM)对复合材料的形貌进行表征,测试复合材料的抗拉强度及硬度。结果表明:当球磨时间为1.5h时,CNTs可均匀分散在Al5083基体中;CNTs质量分数为1.5%时,CNTs/Al5083界面结合力最好,复合材料的抗拉强度和硬度分别为188.8MPa和136HV,比未加CNTs的Al5083合金基体分别提高了32.2%和36%。     

A comparative study of the coated filler method and the admixture method of powder metallurgy for making metal–matrix composites

Copper–matrix composites were made by powder metallurgy (PM). The reinforcements were molybdenum particles, silicon carbide whiskers and titanium diboride platelets. The coated filler method, which involves a reinforcement coated with the matrix metal, was used. In contrast, conventional PM uses the admixture method, which involves a mixture of matrix powder and reinforcement. For all the composite systems, the coated filler method was found to be superior to the admixture method in providing composites with lower porosity, greater hardness, higher compressive yield strength, lower coefficient of thermal expansion (CTE), higher thermal conductivity and lower electrical resistivity, though the degree of superiority was greater for high than low reinforcement contents. In the coated filler method, the coating on the reinforcement separated reinforcement units from one another and provided a cleaner interface and stronger bond between reinforcement and matrix than the admixture method could provide. The highest reinforcement content attained in dense composites (<5% porosity) made by the coated filler method was 70 vol% Mo, 60 vol% TiB2 and 54 vol% SiC. The critical reinforcement volume fraction above which the porosity of composites made by the admixture method increases abruptly is 60% Mo, 42% TiB2 and 33% SiC. This fraction increases with decreasing aspect ratio of the reinforcement. Among Cu/Mo, Cu/TiB2 and Cu/SiC at the same reinforcement volume fraction (50%), Cu/Mo gave the lowest CTE, highest thermal conductivity and lowest electrical resistivity, while Cu/SiC gave the greatest hardness and Cu/TiB2 and Cu/SiC gave the highest compressive yield strength. Compared to Cu/SiC, Cu/TiB2 exhibited much higher thermal conductivity and much lower electrical resistivity. This revised version was published online in November 2006 with corrections to the Cover Date.     

Alignment of carbon nanotubes and reinforcing effects in nylon-6 polymer composite fibers

Alignment of pristine carbon nanotubes (P-CNTs) and fluorinated carbon nanotubes (F-CNTs) in nylon-6 polymer composite fibers (PCFs) has been achieved using a single-screw extrusion method. CNTs have been used as filler reinforcements to enhance the mechanical and thermal properties of nylon-6 composite fibers. The composites were fabricated by dry mixing nylon-6 polymer powder with the CNTs as the first step, then followed by the melt extrusion process of fiber materials in a single-screw extruder. The extruded fibers were stretched to their maxima and stabilized using a godet set-up. Finally, fibers were wound on a Wayne filament winder machine and tested for their tensile and thermal properties. The tests have shown a remarkable change in mechanical and thermal properties of nylon-6 polymer fibers with the addition of 0.5?wt% F-CNTs and 1.0?wt% of P-CNTs. To draw a comparison between the improvements achieved, the same process has been repeated with neat nylon-6 polymer. As a result, tensile strength has been increased by 230% for PCFs made with 0.5% F-CNTs and 1% P-CNTs as additives. These fibers have been further characterized by DSC, Raman spectroscopy and SEM which confirm the alignment of CNTs and interfacial bonding to nylon-6 polymer matrix.     

Development and analysis of high density poly ethylene (HDPE) nano SiO2 and wood powder reinforced polymer matrix hybrid nano composites

ABSTRACT

The Hybrid composites are the emerging materials which uses two or more reinforced particles or fibres simultaneously. As potential applications of the composites, wood reinforced thermoplastic composites are commercially attractive for high volume applications, but their properties can be enhanced by adding Nano SiO₂ particles. Wood powder and nano SiO₂ were mixed with high density polyethylene as matrix material. Wood powder with fixed 5 wt. % and Nano SiO₂ with varying weight % (3, 5, 7 wt. %) are reinforced in HDPE to manufacture composite materials by compression moulding process. Mechanical properties including tensile strength, flexural strength and Izod impact strength were evaluated and it was revealed that tensile strength and flexural strength were obtained maximum at 5 wt. % of Nano SiO₂ and impact strength was obtained maximum at 3 wt. % of Nano SiO₂.     

AlN添加量对BN基复合陶瓷热学性能与抗热震性的影响

以BN、SiO₂、AlN为原料, 采用热压工艺制备出BN基复合陶瓷。研究了AlN添加量对复合陶瓷热学与抗热震性能的影响。结果表明: 随着AlN添加量的增加, 复合陶瓷的热膨胀系数呈现先降低后升高的趋势。当AlN的添加量为5vol%时, 复合陶瓷的平均热膨胀系数最小, 为2.22×10^-6/K; 复合陶瓷的热导率则随着AlN添加量的增加呈先升高后降低的趋势, 当AlN的添加量为10vol%时达到最大值。未添加AlN的复合陶瓷热震后的残余强度随着热震温差的增大而升高; 随着AlN的引入, 复合陶瓷热震后的残余强度呈下降的趋势。对于添加5vol%AlN的复合陶瓷, 经1100℃热震后其残余强度为219.7 MPa, 强度保持率为88.9%, 抗热震性良好。     

碳纳米管增强镁基复合材料导热性能研究

镁及其合金是目前最轻的金属结构材料,合金化虽然提升了镁合金的力学性能,但导致其导热性能严重下降,限制了镁合金的应用。碳纳米管(CNTs)因具有优异的力学、热学等性能,是最理想的增强体之一,可以用于改善镁合金的力学性能和热学性能。采用粉末冶金法分别以纯Mg、Mg-9Al合金、Mg-6Zn合金为基体制备了不同CNTs含量的镁基复合材料,利用光学显微镜、扫描电子显微镜、透射电子显微镜对复合材料微观组织、基体与增强体界面及析出相进行表征,并对复合材料的拉伸性能和热学性能进行测试。研究结果表明,当CNTs质量分数不超过1.0%时,可提高纯镁基复合材料的导热性能,力学性能仅有稍微降低;将CNTs添加到Mg-9Al合金中,可以促进纳米尺度β-Mg 17 Al 12相在CNTs周围析出,降低了Al在Mg基体中的固溶度,使CNTs/Mg-9Al复合材料的导热性能有所提高。此外,在CNTs/Mg-6Zn复合材料界面处存在C原子和Mg原子的相互嵌入区,这种嵌入型界面不仅有利于复合材料力学性能的提高,也使CNTs起到加速电子移动的“桥”的作用,有利于该复合材料热导率的提高。当CNTs质量分数为0.6%时,CNTs/Mg-6Zn复合材料具有较为优异的热学性能和力学性能,其热导率为127.0 W/(m·K),抗拉强度为303.0 MPa,屈服强度为204.0 MPa,伸长率为5.0%。     

Reinforcing brittle and ductile epoxy matrices using carbon nanotubes masterbatch

In this study, the mechanical and thermal properties of epoxy composites using two different forms of carbon nanotubes (powder and masterbatch) were investigated. Composites were prepared by loading the surface-modified CNT powder and/or CNT masterbatch into either ductile or brittle epoxy matrices. The results show that 3 wt.% CNT masterbatch enhances Young’s modulus by 20%, tensile strength by 30%, flexural strength by 15%, and 21.1 °C increment in the glass transition temperature (by 34%) of ductile epoxy matrix. From scanning electron microscopy images, it was observed that the CNT masterbatch was uniformly distributed indicating the pre-dispersed CNTs in the masterbatch allow an easier path for preparation of CNT-epoxy composites with reduced agglomeration of CNTs. These results demonstrate a good CNT dispersion and ductility of epoxy matrix play a key role to achieve high performance CNT-epoxy composites.     

Preparation and properties of the powder SBR composites filled with CNTs by spray drying process

Carbon nanotubes (CNTs) filled powder styrene-butadiene rubber (SBR) composites were prepared by spray drying of the suspension of CNTs in SBR latex. The powder was spherical like and uniform with an average diameter of less than 10 μm. The dispersion of CNTs in the rubber matrix was improved remarkably compared with that in the rubber composites obtained by the conventional mechanical mixing method. Further study about the effect of CNTs on the prepared SBR composites was performed by analyzing the vulcanization process of the SBR powder, thermal and mechanical properties of the vulcanized SBR composites. Differential scanning calorimeter (DSC) analysis indicated that the glass transition temperatures of SBR composites increased with the increasing ratio of CNTs. The vulcanization process showed that CNTs could decelerate the vulcanization of the SBR composites. Dynamic mechanical analysis indicated that the storage modulus of the composites was improved with the CNTs additions, especially when the CNTs addition exceeded 30 phr. Compared with pure SBR composites, the hardness, tensile and tear strengths of the composites filled with 60 phr CNTs enhanced 73.9%, 327.7% and 191.1%, respectively, which should be ascribed to the excellent mechanical properties of CNTs and uniform dispersion of CNTs in the rubber matrix.     

高性能SiC—AlN复相陶瓷

采用热压烧结工艺,通过合理的组成设计和烧结温度控制,制备出了高性能SiC-AlN复相陶瓷,在较佳条件下,复合材料的室温强度、断裂韧性、显微硬度分别高达1130MPa、6．2MPa·m^1/2、28．6GPa．显微结构研究表明,随着AlN的加入,复合材料的晶粒尺寸明显细化,并呈多层次效应,即由固溶体的形成所引起的一次晶粒细化和晶内亚晶界所引起的二次晶粒细化．     

Dispersion assessment and studies on AC percolative conductivity in polymer-derived Si–C–N/CNT ceramic nanocomposites

Nanocomposites comprise polysilazane-derived SiCN ceramic charged with carbon nanotubes (CNTs) have been prepared by dispersion of multi-walled CNTs with a diameter of 80 nm in a cross-linked polysilazane (HTT 1800, Clariant) using a simple roll-mixer method. Subsequently, the composites were warm pressed and pyrolyzed in argon atmosphere. Scanning electron microscopy (SEM) and 3D Raman imaging techniques were used as major tools to assess the dispersion of CNTs throughout the ceramic matrix. Furthermore, studies on the effect of the volume fraction of CNTs in the nanocomposites on their electrical properties have been performed. The specific bulk conductivities of the materials were analyzed by AC impedance spectroscopy, revealing percolation thresholds (ρ_c) at CNT loadings lower than 1 vol%. Maximum conductivity amounted to 7.6 × 10⁻² S/cm was observed at 5 vol% CNT. The conductivity exponent in the SiCN/CNT composites was found equal to 1.71, indicating transport in three dimensions.     

3D打印制备碳纳米管/环氧树脂电磁屏蔽复合材料

采用3D打印技术制备具有连续通孔的环氧树脂基体,利用浸渍工艺将碳纳米管（CNTs）附着于环氧树脂基体孔壁,获得具有优异电性能和电磁屏蔽功能的CNTs/环氧树脂复合材料。研究结果表明,CNTs含量仅为2.86vol%时,CNTs/环氧树脂复合材料电导率高达35 S/m,总电磁屏蔽效能高达39.2 dB（厚度为2.0 mm）。研究表明,CNTs/环氧树脂复合材料对进入其内部电磁波的吸收占总屏蔽效能的98%,表现出吸收屏蔽为主导的电磁屏蔽机制。CNTs/环氧树脂复合材料的弯曲强度和弯曲模量相比环氧树脂基体也有一定的提高。该研究为具有优异电磁屏蔽性能的高分子基复合材料制备提供了新思路和方法。      

Mechanical and tribological behaviour of tungsten carbide reinforced aluminum LM4 matrix composites

Aluminum-based metal matrix composites (AMCs) play a vital role for potential applications in aerospace and automotive industries. This paper explores the experimental analysis of a composite with aluminum LM4 alloy as the matrix and tungsten carbide (WC) as the reinforcement material. The composite specimens were fabricated by the stir casting process. The reinforced ratios of 5, 10 and 15?wt.% of WC particulates were stirred in molten aluminum LM4 alloy (AALM4). Once the composite is solidified, the specimens are prepared to the required ASTM dimensions and tested for various mechanical properties such as tensile strength, impact strength and hardness. Moreover, the tribological behavior of the composite was studied using the pin-on-disc wear test apparatus. X-ray diffraction (XRD) analysis was conducted to analyze the various elements present in the composites. Finally, the scanning electron microscope (SEM) analysis reveals the uniform distribution of WC particles in Aluminum LM4 alloy matrix. The improvement in mechanical properties – hardness, impact strength and tensile strength – was achieved for the increase in the addition of wt.% of WC particles in the LM4 matrix. The decrease in mass loss was observed for the composite containing 15?wt.% of WC during the wear test among the various composites tested.     

碳纳米管/丁苯橡胶复合材料的电学性能

采用喷雾干燥法可制备不同配比的碳纳米管（Carbon nanotubes,CNTs）/粉末丁苯橡胶复合材料,观察CNTs在橡胶基体中的分散情况,检测复合材料的导电性能及介电性能,并进行了简要的理论分析。结果表明:CNTs在橡胶基体中获得了充分均匀的分散,有利于CNTs改性补强作用的发挥。与纯胶样品及填充炭黑（Carbon black,CB）样品相比, 填充CNTs样品在8~18GHz下具有较高的介电常数及低介电损耗。随着CNTs加入量的增加,CNTs/粉末丁苯橡胶复合材料的电导率逐渐升高,当CNTs加入量为60phr（per hundred rubber）时,与纯胶样品及添加60phr CB样品相比,电导率提高近10个数量级;复合材料内部导电同时存在隧道导电机制和渗逾导电机制。采用喷雾干燥法制备的CNTs/粉末丁苯橡胶复合材料,将是一种综合性能良好的新型纳米复合材料,有望在抗静电橡胶、电磁屏蔽及介电材料等领域获得应用。