24 results found
Lin CJ, Wang D, Peng L, et al., 2024, Carbides in AZ91 and their role in the grain refinement of magnesium, Journal of Alloys and Compounds, Vol: 971, ISSN: 0925-8388
Carbon inoculation is a well-known method to grain refine Mg-Al-based alloys, but the underlying mechanisms remain unclear. Here we study carbides and their relationship with the surrounding magnesium in inoculated Mg-9Al-0.7Zn-0.2Mn (wt.%, AZ91) by combining controlled solidification experiments with analytical electron microscopy. Up to three carbides formed depending on the solidification conditions: T1-Al2MgC2, T2-Al2MgC2 and Al4C3. All carbides grew with their basal planes as the largest facet and the trigonal carbides, T2-Al2MgC2 and Al4C3, often contained basal planar growth faults and growth twins. In many cases there was evidence of eutectic-like Al4C3 growing off T2-Al2MgC2, indicating that Al4C3 formed later in the solidification sequence after α-Mg had nucleated, consistent with recent phase diagram calculations. A basal-to-basal OR was measured between α-Mg and T2-Al2MgC2 for approximately 10% of particles, indicating that T2-Al2MgC2 is the heterogeneous nucleant for α-Mg. Particles with the OR had diverse locations including near grain boundaries and near the centre of grains, suggesting that the OR can form by pushing and engulfment as well as by heterogeneous nucleation.
Lin CJ, Peng L, Xian JW, et al., 2023, Eutectic solidification in Mg-9Al-0.7Zn: from divorced to coupled growth, Journal of Alloys and Compounds, Vol: 938, Pages: 1-16, ISSN: 0925-8388
In hypoeutectic Mg-Al-based alloys, Mg17Al12 forms in the last stages of solidification by a eutectic reaction that is usually fully or partially divorced. Here we investigate the nucleation, growth and morphology of the Mg17Al12-containing eutectic in a multicomponent Mg-9Al-0.7Zn-0.2Mn alloy. Under all solidification conditions studied, Mg17Al12 formed an interconnected skeleton in 3D and Mg17Al12 orientation domains spanned multiple α-Mg grains, indicating that Mg17Al12 nucleation events are relatively infrequent. While most regions of α-Mg+Mg17Al12 had no preferred orientation relationship (OR), occasional eutectic regions had the Burgers OR that may be related to the nucleation of Mg17Al12 on α-Mg during solidification. It is shown that the degree of partially divorced growth depends on a simple geometrical measure for the space available for eutectic growth involving the dendrite arm spacing, the eutectic fraction and the eutectic spacing. We then demonstrate that fully coupled eutectic microstructures can be generated in this alloy by independently manipulating the magnesium dendrite solidification time and the eutectic cooling rate.
Yin H, Li Q, Iannucci L, 2022, Meso-scale Finite Element (FE) modelling of biaxial carbon fibre non-crimp-fabric (NCF) based composites under uniaxial tension and in-plane shear, Composite Structures, Vol: 290, Pages: 1-17, ISSN: 0263-8223
Non-crimp-fabrics (NCF) are promising materials in aerospace applications. The complex internal structure of NCF composites could influence the in-plane performances, which needs to be comprehensively studied. The novel three-dimensional (3D) meso-scale repeated unit cell (RUC) models were proposed for biaxial NCF composites based on the Finite Element (FE) method to conduct a systematic parameter study, including layup sequence, out-of-plane tow waviness, resin-rich areas, transverse tow placements and delamination. The meso RUC model could effectively predict the homogenised uniaxial tensile and in-plane shear properties of biaxial NCF composites based on their meso-scale constituent and material properties. A multiscale framework was also developed for biaxial NCF composites. A micromechanical representative volume element (RVE) model provided homogenised mechanical properties for tows, and a macroscopical FE model validated the test results using the homogenised results obtained from meso RUC models. The numerical results were in good agreement with the experiment results. Therefore, the multiscale framework provides an insight into the critical parameters influencing the in-plane properties of NCF composites and an analysis tool for NCF material design.
Li Q, Nasiri S, Yang G, et al., 2022, An Improved Approach to Manufacture Carbon Nanotube Reinforced Magnesium AZ91 Composites with Increased Strength and Ductility, Metals, ISSN: 2075-4701
Nasiri S, Wang K, Yang M, et al., 2022, Atomistic aspects of load transfer and fracture in CNT-reinforced aluminium, Materialia, Vol: 22, Pages: 101376-101376, ISSN: 2589-1529
This paper describes atomistic simulations of deformation and fracture of Al reinforced with carbon nanotubes (CNTs). We use density functional theory (DFT) to understand the energetics of Al-graphene interfaces and gain reference data for the parameterization of Al-C empirical potentials. We then investigate the load transfer between CNTs and Al and its effect on composite strengthening. To this end, we perform uniaxial tensile simulations of an Al crystal reinforced by CNTs of various volume fractions. We also study the interaction of the embedded CNTs with a crack. We show that the interaction between CNTs and Al is weak such that, under tensile loading, CNTs can easily slide inside the Al matrix and get pulled out from the cracked surface. This effect is almost independent of CNT length and volume fraction. Little load transfer and consequently no crack bridging are observed during the simulation of pristine CNTs threading the crack surfaces. CNTs that are geometrically fixated inside Al, on the other hand, can increase the fracture stress and enhance plastic dissipation in the matrix. CNTs located in front of a growing crack pin the crack and induce plastic deformation of the Al matrix. Depending on the CNT orientation, these processes can either increase or decrease the failure stress of the composite.
Xu Z, Tonry C, Beckwith C, et al., 2022, High-speed imaging of the ultrasonic deagglomeration of carbon nanotubes in water, JOM, Vol: 74, ISSN: 1047-4838
Ultrasonic treatment is effective in deagglomerating and dispersing nanoparticles in various liquids. However, the exact deagglomeration mechanisms vary for different nanoparticle clusters, owing to different particle geometries and inter-particle adhesion forces. Here, the deagglomeration mechanisms and the influence of sonotrode amplitude during ultrasonication of multiwall carbon nanotubes in de-ionized water were studied by a combination of high-speed imaging and numerical modeling. Particle image velocimetry was applied to images with a higher field of view to calculate the average streaming speeds distribution. These data allowed direct comparison with modeling results. For images captured at higher frame rates and magnification, different patterns of deagglomeration were identified and categorized based on different stages of cavitation zone development and for regions inside or outside the cavitation zone. The results obtained and discussed in this paper can also be relevant to a wide range of carbonaceous and other high aspect ratio nanomaterials.
Hisham NSN, Shaffer M, Li Q, 2022, THE APPLICATION OF CARBON NANOTUBES IN LIGHTWEIGHT METAL MATRIX COMPOSITES, Pages: 975-980
The main challenges in the development of CNTs reinforced metal matrix composites are the inhomogeneous distribution of CNTs in the metal matrix and the poor interfacial bonding between CNTs and metal. Thus, surface modification of CNTs with a suitable coating material prior to composite processing is a promising solution to overcome these issues. In this work, coated CNTs are used to improve the dispersion and the wettability of CNTs by the Mg matrix. This investigation found that a more homogeneous dispersion and better wettability could be achieved by using Ni-coated CNTs in comparison to pristine CNTs in AZ91 matrix.
Xu Z, Tonry C, Beckwith C, et al., 2022, HIGH SPEED IMAGING OF THE ULTRASONIC DEAGGLOMERATION OF NANOPARTICLES IN WATER, Pages: 1048-1055
Ultrasonic treatment is effective in deagglomerating and dispersing nanoparticles during composite manufacturing via liquid state processing route. However, the exact deagglomeration mechanisms were difficult to observe owning to opaque metal melt and containers. Here, an analogue experiment was carried out in de-ionize water to study the deagglomeration mechanisms and the influence of sonotrode amplitude during ultrasonication of multiwall carbon nanotubes in light-weight metal melt. Particle image velocimetry was applied to the captured images with a higher Field of View to calculate the average streaming speeds distribution. These data allowed direct comparison with modelling results. For images captured at higher frame rates and magnification, different patterns of deagglomeration were identified, and categorized based on different stages of cavitation zone development and for regions inside or outside the cavitation zone. The results obtained and discussed in this paper can be also relevant to a wide range of carbonaceous and other high aspect ratio nanomaterials.
Li Q, Markcoons D, Xu Z, et al., 2022, NANOPARTICLE REINFORCED LIGHTWEIGHT METAL COMPOSITES, Pages: 981-985
The interest to use carbon nanotubes (CNTs) to reinforce light metals has increased in recent years due to their potential application as lightweight high performance materials. One challenge in producing CNT composites is to achieve a homogenous dispersion of CNTs in the metal matrix. In order to effectively disperse CNTs in the Mg melt, we for the first time introduced the idea of using metal coated CNTs to promote the integration into Mg matrix. In this paper, Pt was selected to coat the CNT surface. TEM and EDX confirm that atomic Pt has been successfully deposited onto CNTs. The dispersion and stability of metal coated CNTs in solution have been investigated and compared to CNTs without metal coating. The Pt coated CNT reinforced Mg composites were also produced via a melt stirring process. The mechanical properties of such composites also showed a clear upward tendency, which we attribute to the Pt coating to help the dispersion of CNTs.
Nasiri S, Greff C, Wang K, et al., 2020, Multilayer structures of graphene and Pt nanoparticles: a multiscale computational study, Advanced Engineering Materials, Vol: 22, Pages: 1-11, ISSN: 1438-1656
Multiscale simulation study results of multilayer structures consisting of graphene sheets with embedded Pt nanoparticles is reported. Density functional theory is used to understand the energetics of Pt–graphene interfaces and provide reference data for the parameterization of a Pt–graphene interaction potential. Molecular dynamics simulations then provide the conformation and energetics of graphene sheets with embedded Pt nanoparticles of varying density, form, and size. These results are interpreted using a continuum mechanical model of sheet deformation, and serve to parameterize a meso‐scale Monte Carlo model to investigate the question under which conditions the free volume around the Pt nanoparticles forms a percolating cluster, such that the structures can be used in catalytic applications. This article is concluded with a discussion of potential applications of such multilayer structures.
Nasiri S, Wang K, Yang M, et al., 2019, Nickel coated carbon nanotubes in aluminum matrix composites: a multiscale simulation study, European Physical Journal B: Condensed Matter and Complex Systems, Vol: 92, Pages: 1-9, ISSN: 1434-6028
In this work we use density functional theory (DFT) calculations to benchmark empirical potentials for the interaction between nickel and sp2 bonded carbon nanoparticles. These potentials are then used in order to investigate how Ni decorated or coated carbon nanotubes (CNT) affect the mechanical properties of Al/CNT composites. In particular we look at the pull-out behaviour of pristine as well as Ni-decorated and Ni-coated CNT from an Al matrix. Our result shows that Ni coating may produce an extended interface (“interphase”) where a significant amount of energy is dissipated during CNT pull-out, leading to a high pull-out force. We also demonstrate that surface decorated CNT may act as efficient nano-crystallization agents and thus provide a novel strengthening mechanism not previously discussed in the literature. We discuss our results in view of promising approaches for engineering CNT-metal interfaces such as to achieve high strength metal-CNT composites.
Fomenko LS, Lubenets S, Natsik VD, et al., 2019, Investigation of the low-temperature mechanical behavior of elastomers and their carbon nanotube composites using microindentation, LOW TEMPERATURE PHYSICS, Vol: 45, Pages: 568-576, ISSN: 1063-777X
The micromechanical properties of epoxy resin elastomers and their carbon nanotube composites were studied using a microhardness tester equipped with low-temperature chamber. X-ray diffraction analysis indicated that all specimens were free of any crystalline components and were amorphous with only short-range order domains. The Vickers microhardness of all samples has been estimated in the temperature range 230–300 K. The measurements demonstrated that at room temperature these materials are elastomers (notably, they are in high-elastic state) and on cooling in the range of 250–270 K the glass transition takes place. Analysis of the temperature dependence of microhardness suggested that the thermomechanical and relaxation properties of the materials studied are consistent with a rheological model of a standard linear solid where the relaxation time (or viscosity) depends exponentially on the temperature in accordance with the Arrhenius equation for the rate of thermally activated process. Empirical estimates for the nonrelaxed and relaxed Young’s moduli and also for the activation energy (U = 0.75 eV) and the period of attempts (τ0 = 10–12 s) of the molecular process which determines the relaxation properties and the glasstransition of the materials have been obtained. The addition of carbon nanotubes into elastomeric epoxy resin had no effect on its micromechanical characteristics as measured by the microhardness tester. It is shown that the conventional microindentation method is an efficient tool of investigating the thermomechanical properties of elastomers nearby and below the glass transition temperature.
Brandley E, Greenhalgh E, Shaffer M, et al., 2018, Mapping carbon nanotube orientation by fast fourier transform of scanning electron micrographs, Carbon, Vol: 137, Pages: 78-87, ISSN: 0008-6223
A novel method of applying a two-dimensional Fourier transform (2D-FFT) to SEM was developed to map the CNT orientation in pre-formed arrays. Local 2D-FFTs were integrated azimuthally to determine an orientation distribution function and the associated Herman parameter. This approach provides data rapidly and over a wide range of lengthscales.Although likely to be applicable to a wide range of anisotropic nanoscale structures, the method was specifically developed to study CNT veils, a system in which orientation critically controls mechanical properties. Using this system as a model, key parameters for the 2D-FFT analysis were optimised, including magnification and domain size; a model set of CNT veils were pre-strained to 5%, 10% and 15%, to vary the alignment degree. The algorithm confirmed a narrower orientation distribution function and increasing Herman parameter, with increasing pre-strain.To validate the algorithm, the local orientation was compared to that derived from a common polarised Raman spectroscopy. Orientation maps of the Herman parameter, derived by both methods, showed good agreement. Quantitatively, the mean Herman parameter calculated using the polarised Raman spectroscopy was 0.42 ± 0.004 compared to 0.32 ± 0.002 for the 2D-FFT method, with a correlation coefficient of 0.73. Possible reasons for the modest and systematic discrepancy were discussed.
Li Q, Nasiri S, Zaiser M, 2017, Full paper – Magnesium composites reinforced by metal coated carbon nanotubes, 21st International Conference on Composite Materials
© 2017 International Committee on Composite Materials. All rights reserved. The interest to use carbon nanotubes (CNTs) to reinforce light metals has increased in recent years due to their potential application as lightweight high performance materials. One challenge in producing CNT composites is to achieve a homogenous dispersion of CNTs in the metal matrix. In order to effectively disperse CNTs in the Mg melt, we for the first time introduced the idea of using metal coated CNTs to promote the integration into Mg matrix. In this paper, Pt was selected to coat the CNT surface. TEM and EDX confirm that atomic Pt has been successfully deposited onto CNTs. The dispersion and stability of metal coated CNTs in solution have been investigated and compared to CNTs without metal coating. The Pt coated CNT reinforced Mg composites were also produced via a melt stirring process. The mechanical properties of such composites also showed a clear upward tendency, which we attribute to the Pt coating to help the dispersion of CNTs.
Brandley E, Li Q, Greenhalgh E, et al., 2017, Full paper – Alignment study of CNT veils and the influence on their composites, 21 st International Conference on Composite Materials
© 2017 International Committee on Composite Materials. All rights reserved. A methodology was developed to measure the alignment of carbon nanotubes in pre-strained samples of carbon nanotube veils via image processing techniques. The methodology was used on samples of as-received and pre-strained carbon nanotube veils and calculated an increased Herman parameter for the pre-strained sample relative to the as-received. A number of image processing techniques, specifically high and low pass filters, were tested in order to increase the signal of the carbon nanotubes in the scanning electron micrographs, however it was found filtering the micrograph prior did not enhance nanotube signal and did not improve the calculated orientation distribution function.
Li Q, Zaiser M, Blackford JR, et al., 2014, Mechanical properties and microstructure of single-wall carbon nanotube/elastomeric epoxy composites with block copolymers, Materials Letters, Vol: 125, Pages: 116-119, ISSN: 0167-577X
Single-wall carbon-nanotube (SWNT) reinforced elastomeric epoxy composites were fabricated by adding 0.03 wt% SWNTs and using 0.3 wt% block copolymer to obtain a good dispersion of carbon nanotubes in the epoxy matrix. Young׳s modulus, fracture stress and strain of the SWNT/epoxy composites with block copolymer were increased by 141%, 127% and 43%, respectively, compared to the pure epoxy resin. Scanning electron microscopy observation revealed that using the block copolymer as a dispersing agent significantly improved both SWNT dispersion in the epoxy matrix and interfacial bonding/load transfer.
Hippmann S, Li Q, Addinal R, et al., 2013, Carbon nanotubes–reinforced copper matrix composites produced by melt stirring, Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanoengineering and Nanosystems, Vol: 227, Pages: 63-66, ISSN: 1740-3499
<jats:p> Due to their geometry and extraordinary mechanical properties, carbon nanotubes have been envisioned as promising enhancements for metal matrix composites. In this article, we report on our melt stirring approach for incorporation of carbon nanotubes into a copper alloy matrix and on the experimental results obtained by assessing the material properties. The existence of carbon nanotubes in the copper matrix after processing was proven by Raman analysis. We found that the small amounts of carbon nanotubes (0.1 wt%) in the composites influenced mechanical and abrasive wear properties. </jats:p>
Li Q, Turhan MC, Rottmair CA, et al., 2012, Influence of MWCNT dispersion on corrosion behaviour of their Mg composites, MATERIALS AND CORROSION-WERKSTOFFE UND KORROSION, Vol: 63, Pages: 384-387, ISSN: 0947-5117
Turhan MC, Li Q, Jha H, et al., 2011, Corrosion behaviour of multiwall carbon nanotube/magnesium composites in 3.5% NaCl, ELECTROCHIMICA ACTA, Vol: 56, Pages: 7141-7148, ISSN: 0013-4686
Li Q, Rottmair CA, Singer RF, 2010, CNT reinforced light metal composites produced by melt stirring and by high pressure die casting, Composites Science and Technology, Vol: 70, Pages: 2242-2247, ISSN: 0266-3538
Light metal matrix composites are of great interest due to their potential for reducing CO2 emission through lightweight design e.g. in the automotive sector. Carbon nanotubes can be considered as ideal reinforcements, due to their high strength, high aspect ratio and thermo-mechanic properties. In this research, CNT reinforced light metal composites were produced by melt stirring and by high pressure die casting, which can be both easily scaled up. The light metal composites showed significantly improved mechanical properties already at small CNT contents. The influence of CNT concentration on the composites was also studied. © Elsevier Ltd.
Li Q, Viereckl A, Rottmair CA, et al., 2009, Improved processing of carbon nanotube/magnesium alloy composites, Composites Science and Technology, Vol: 69, Pages: 1193-1199, ISSN: 0266-3538
Carbon nanotubes (CNTs) are promising reinforcements for light weight and high strength composites due to their exceptional properties. However, until now, the main obstacle is to obtain a homogenous dispersion of the CNTs in the desired material matrix. Quite a few methods have been studied to help improving the dispersion of CNTs in a polymer matrix. But not much research has been conducted on how to disperse CNTs in metal matrices. In this study, a two-step process was applied. In the first stage, a block copolymer was used as a dispersion agent to pre-disperse multiwall carbon nanotubes (MWNTs) on Mg alloy chips. Then the chips with the well dispersed MWNTs on their surface were melted and at the same time vigorously stirred. The molten MWNT Mg alloy composites were poured into a cylindrical mould to solidify quickly. For the pre-dispersion step, the microstructures of the Mg alloy chips were studied under SEM. MWNTs were quite successfully dispersed on the surfaces of the Mg alloy chips. The mechanical properties of the MWNT/Mg composites were measured by compression testing. The compression at failure, the compressive yield strength and ultimate compressive strength have all been improved significantly up to 36% by only adding 0.1 wt% MWNTs to the Mg alloy. In order to predict the potential yield strengths of the MWNT reinforced Mg alloy composites, the contributions by load transfer, Orowan strengthening and thermal mismatch were added up. © 2009 Elsevier Ltd. All rights reserved.
Bright I, Koutsos V, Li Q, et al., 2006, Carbon nanotubes for integration into nanocomposite materials, Microelectronic Engineering, Vol: 83, Pages: 1542-1546, ISSN: 0167-9317
Li Q, Zaiser M, Koutsos V, 2004, Carbon nanotube/epoxy resin composites using a block copolymer as a dispersing agent, physica status solidi (a), Vol: 201, Pages: R89-R91, ISSN: 0031-8965
Lin C-J, Peng L, Xian J, et al., Eutectic Solidification in Mg-9al-0.7zn: From Divorced to Coupled Growth, SSRN Electronic Journal
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