Reinforced Metal Matrix Nanocomposites Research Articles

Folded graphene reinforced metal matrix nanocomposites with comprehensively enhanced tensile mechanical properties

It is urgent to develop advanced materials with high strength, high toughness and good ductility for modern engineering structures. Graphene reinforced metal matrix nanocomposites exhibit significantly enhanced strength and toughness, but their ductility remains relatively low due to the inherent tensile brittleness of graphene. Inspired by the origami concept, we utilize the surface hydrogenation method to develop an armchair-like folded graphene (AFG) structure as reinforcement for metal matrix composites. Molecular dynamics simulations show that the AFG structure can simultaneously enhance the tensile strength, stiffness, ductility, and toughness of copper (Cu) matrix composites. Compared with pristine graphene/Cu nanocomposites, AFG/Cu nanocomposites exhibit better ductility and toughness, while maintaining comparable strength and stiffness. Furthermore, the mechanical properties of AFG/Cu nanocomposites can be tuned by altering the degree of AFG folding and the distances between adjacent hydrogenated zones. The strengthening and toughening mechanism is that mechanically strong AFG can effectively block dislocation propagation across the metal-graphene interface before it unfolds to fracture. Such mechanism can be extended to other 2D nanomaterials reinforced metal matrix nanocomposites, opening up an avenue for developing high-performance nanocomposites.

Effect of TiC-CNT precipitates on the microstructure and hardness of coatings welded by the GTAW process

Carbon nanotubes (CNT)-reinforced metal matrix nanocomposites balance toughness and ductility and, therefore, can reduce maintenance costs of industrial equipment. In this sense, flux-cored made of low carbon steel filled with CNT/Ti6Al4V/CaF2 were used as filler metal to coat an A131 grade A steel sheet via GTAW process. SEM and Raman spectroscopy analyses evidence the partial phase transformation between Ti and CNT in TiC-CNT precipitates, which can act as barriers to dislocation movements in a ferritic matrix. Consequently, the hardnesses of the coatings were up to 33.9–77.4 % higher than the base metal. Therefore, incorporating TiC-CNT precipitate-based reinforcements via arc welding can improve the hardness of conventional steels.

Toughening and strengthening of Cu-coated carbon nanotubes reinforced AZ61 magnesium matrix nanocomposites by improving interfacial bonding

Interfacial modification without damaging the structure of carbon nanotubes (CNTs) is urgently needed to improve the performance of CNTs reinforced metal matrix nanocomposites. To fabricate CNTs/AZ61 nanocomposite with strong interfacial bonding, copper-coated CNTs (0.15–2.4 vol%) and AZ61 powder were employed through the process of ball milling mixing, vacuum hot pressing and extrusion. The powder and nanocomposites were characterized by HRTEM, SEM, XRD and compressive test to study the distribution of reinforcements, microstructures, interfacial structure and compression behavior. During the high-temperature fabrication process, in-situ interfacial reactions occurred between Cu particles of CNTs and Mg, Al and Zn elements in AZ61 matrix. As a result, the formation of interfacial reaction phases, such as AlCu3, Al2Cu, Cu2Mg, CuMg2, Cu0.61Zn0.39 and MgAl2C2 phases, and their diffused and/or coherent interface significantly strengthen the interfacial bonding. With only 0.15 vol% CNTs, the work of fracture and compression strength of the composite are 40 % and 20 % higher than those of pure AZ61, respectively. The dominating toughening mechanisms are the load transfer role of scattered CNTs and fine-grain effect. The dominating strengthening mechanisms are thermal mismatch and Orowan strengthening.

Boron Nitride Nanotubes Reinforced Metal Matrix Nanocomposites: A Review

Multiwalled Boron Nitride Nanotubes (BNNTs) reinforced Metal Matrix Nanocomposites (MMNCs) are discussed in this work. It is noticed that the reaction of BNNTs with Aluminum (Al) to form a compound at the interface depends on the processing condition. The processing methods include sintering, solidification, rolling, High-Pressure Torsion (HPT) and heat treatment have influenced the microstructure and mechanical properties of BNNTs filled MMNCs. The review suggests that BNNTs filled MMNCs have the potential to be used in various applications.

Stability analysis of a spinning soft-core sandwich beam with CNTs reinforced metal matrix nanocomposite skins subjected to residual stress

The stability of a soft-cored spinning viscoelastic sandwich beam and carbon nanotubes (CNTs) reinforced metal matrix nanocomposites (MMNCs) skin subjected to residual stress have been investigated. The metal matrix nanocomposites (MMNCs) skins are symmetrical and isotropic. In addition, these skins reinforced with uniform and functionally graded (FG) distributions of carbon nanotubes (CNTs) are considered. The soft-core of the sandwich beam is deemed to be elastomeric and has internal damping of viscoelastic type. The skin layers of the sandwich beam are subject to residual stresses caused by the production process. Also, the effective material properties of skins are obtained using the rule of mixture (ROM) and Halpin-Tsai (H-T) micromechanics models. First, the governing equations of motion of a spinning viscoelastic sandwich beam are obtained using the Hamilton principle. Then, the sandwich beam's natural frequencies are calculated using the differential quadrature method (DQM). The effects of CNTs distribution, nanotube volume fraction, spinning speed, critical loading, the thickness of the core, axial force, and residual stress on the sandwich beam's natural frequency and stability regions are investigated. According to the results of this study, based on the sandwich beam's different spinning speeds, it is possible to estimate the optimal amount of core thickness to prevent instability, which can be very important in the design of spinning sandwich structures.

Micromechanical constitutive modeling of tensile and cyclic behaviors of nano-clay reinforced metal matrix nanocomposites

Metal matrix nanocomposites are emerging rapidly among both research and industry communities. Nonetheless, the studies for their use in Low-Cycle Fatigue (LCF) applications are rarely documented. Prior to tailoring the microstructure for the desired LCF performance, it is a fundamental task to understand the structure-property correlations of the nanocomposites. In the present paper, a continuum-based micromechanical model starting from the nanostructure is proposed to fulfill such a task. The proposed model is applied to a piston aluminum alloy reinforced with 1 wt% nano-clay subjected to fully-reversed strain-controlled LCF loading at room temperature. The model, formulated within Eshelby's inclusion framework, considers the active clay/matrix interactions, the intercalation/exfoliation effect via the equivalent stiffness method, and the size effect through the introduction of the interphase thickness as a characteristic length scale. To render the model able to reproduce the cyclic hysteretic behavior of the nanocomposites, the isotropic/kinematic hardening rule is considered to describe the aluminum alloy plasticity. The model results are favorably compared to the experimental observations in terms of monotonic and cyclic elastoplastic stress-strain responses of the aluminum/clay nanocomposite. A parametric study is then carried out in order to understand the separate and synergic effects of clay weight fraction, clay geometrical parameters (e.g., shape and size), and clay structural parameters (e.g., number of silicate layers and interlayer spacing) on the overall monotonic and cyclic responses of the present nanocomposite. The reinforcing effect of each parameter is discussed concerning the micromechanical model.

Interface energy effect on effective elastoplastic behavior of spheroidal particle reinforced metal matrix nanocomposites

A nanomechanical framework is proposed to predict the effective elastoplastic behavior of the metal matrix nanocomposites (MMNCs) containing randomly distributed and randomly oriented spheroidal particles. The interface energy effect is investigated by considering both of the interface elastic stress and the interface residual stress on the idealized zero-thickness membrane interphase between the matrix and the inhomogeneities. The orientational average is performed to obtain the effective constitutive relations of the MMNCs with randomly oriented spheroidal particles. By employing the micromechanical homogenization approaches, an effective yield criterion is formulated, and the effective secant moduli of the MMNCs are derived. Comparisons are made between the present framework and the classical micromechanics theory. The interface energy effect on the effective secant moduli are discussed, and the particle size dependence of the effective secant moduli is revealed. Furthermore, the effects of the interface elastic stress and the interface residual stress on the plastic yielding of the nanocomposites are discussed. Lastly, the theoretical predictions obtained by the present framework are compared with the relevant experiments and numerical simulations.

Analytical models of the strength and ductility of CNT reinforced metal matrix nano composites under elevated temperatures

Carbon nanotubes (CNTs) can greatly enhance the strength of metal matrix composites while resulting in ductility loss. This strength-ductility tradeoff dilemma always confines the development of material design and real-life applications. In this work, a temperature dependent strengthening analytical model is proposed for CNT reinforced metal matrix composites which considers three common strengthening mechanisms: Orowan looping effect, thermal expansion mismatch effect, and load bearing effect. The proposed model can predict composite material strength with different volume fractions of CNTs and under different temperatures. Combining the strengthening model with the stress based modified Mohr-Coulomb (sMMC) ductile fracture model, a ductility analytical model is then derived. This ductility analytical model includes the influences of temperature, multi-axial stress loading conditions, as well as the aforementioned three strengthening mechanisms. A good agreement has been achieved between literature published experimental data and analytical predictions for both composite material strength and ductility loss. The proposed two analytical models can provide a straightforward way to study the strength-ductility relationship for CNT reinforced metal matrix composites over a wide range of temperatures and different stress states, and then provide guidance on new material design and processing.

Advances in graphene reinforced metal matrix nanocomposites: Mechanisms, processing, modelling, properties and applications

Graphene has been extensively explored to enhance functional and mechanical properties of metal matrix nanocomposites for wide-range applications due to their superior mechanical, electrical and thermal properties. This article discusses recent advances of key mechanisms, synthesis, manufacture, modelling and applications of graphene metal matrix nanocomposites. The main strengthening mechanisms include load transfer, Orowan cycle, thermal mismatch, and refinement strengthening. Synthesis technologies are discussed including some conventional methods (such as liquid metallurgy, powder metallurgy, thermal spraying and deposition technology) and some advanced processing methods (such as molecular-level mixing and friction stir processing). Analytical modelling (including phenomenological models, semi-empirical models, homogenization models, and self-consistent model) and numerical simulations (including finite elements method, finite difference method, and boundary element method) have been discussed for understanding the interface bonding and performance characteristics between graphene and different metal matrices (Al, Cu, Mg, Ni). Key challenges in applying graphene as a reinforcing component for the metal matrix composites and the potential solutions as well as prospectives of future development and opportunities are highlighted.

Oxidation weakens interfaces in carbon nanotube reinforced titanium nanocomposites: An in situ electron microscopy nanomechanical study

The interfacial binding interactions in fiber–reinforced metal matrix nanocomposites (MMNC) are involved with sophisticated physico-chemical​ phenomena that are sensitive to their commonly encountered high-temperature processing and/or working environments. The resulting interfacial load transfer characteristics, which play a vital role in achieving the anticipated bulk mechanical properties enhancements, remain elusive. Here we investigate the effect of thermal processing on the interfacial strength of carbon nanotube (CNT) reinforced titanium (Ti) nanocomposites by conducting in situ nanomechanical single-nanotube pull-out measurements inside a high resolution scanning electron microscope. Our nanomechanical measurements reveal that thermal annealing at 400 °C for two hours results in a 40% decrease of the interfacial load-carrying capacity. The measurements were analyzed using a micromechanics shear-lag model, and the results show that the thermal annealing reduces the maximum interfacial shear strength by about 42% from about 231MPa to about 135 MPa. The observed weakening of the CNT–Ti interface caused by thermal annealing is attributed to the formation of newly grown titanium oxide on the CNT–Ti binding interface. The findings reported here are useful to better understand the impact of thermal processing on the reinforcing efficiency of nanotubes in metal matrices, which is essential to the design and manufacturing of nanotube-reinforced MMNC with superior high-temperature performance.

Micromechanics-based modeling of elastic modulus and coefficient of thermal expansion for CNT-metal nanocomposites: effects of waviness, clustering and aluminum carbide layer

A micromechanical model is analytically developed to estimate the elastic modulus and the coefficient of thermal expansion (CTE) of the carbon nanotube (CNT)-reinforced metal matrix nanocomposites (MMNCs). The effects of two important microstructural features, including the CNT clusters and the waviness on the thermo-elastic response are investigated. The formation of aluminum carbide (Al4C3) layer due to the interaction between the CNT and the metal matrix is considered. A good agreement is found between the available experimental data and the simulation results considering the waviness, clustering, and Al4C3 interphase. The influences of volume fraction, and dispersion type of CNTs and Al4C3 layer thickness on the elastic modulus and the CTE of the CNT-metal nanocomposites are examined. The non-straight shape and the clustering of CNTs are two critical factors that can significantly degrade the thermo-elastic properties. From the mechanical viewpoint on designing the CNT-metal nanocomposites, producing the homogeneous microstructure without the CNT clusters and using the straight CNTs are necessary factors to obtain the maximum level of the thermomechanical performances. The numerical results show that the formation of the Al4C3 interphase may improve the MMNC macroscopic engineering constants. It is observed that aligning the CNTs into the metal matrixes leads to a significant improvement in the MMNC thermo-elastic properties. The proposed micromechanical approach can be a suitable model to predict the elastic modulus and the CTE of the CNT-reinforced MMNCs considering the important microstructural features.

Micromechanical simulation and experimental investigation of aluminum-based nanocomposites

Ceramic reinforced metal matrix nanocomposites are widely used in aerospace and auto industries due to their enhanced mechanical and physical properties. In this research, we investigate the mechanical properties of aluminum/Nano-silica composites through experiments and simulations. Aluminum/Nano-silica composite samples with different weight percentages of silica nanoparticles are prepared via powder metallurgy. In this method, Nano-silica and aluminum powders are mixed and compressed in a mold, followed by sintering at high temperatures. Uniaxial tensile testing of the nanocomposite samples shows that adding one percent of Nano-silica causes a considerable increase in mechanical properties of nanocomposite compared to pure aluminum. A computational micromechanical model, based on a representative volume element of aluminum/silica nanocomposite, is developed in a commercial finite element software. The model employs an elastoplastic material model along with a ductile damage model for aluminum matrix and linear elastic model for nano-silica particles. Via careful determination of model parameters from the experimental results of pure aluminum samples prepared by powder metallurgy, the proposed computational model has shown satisfactory agreement with experiments. The validated computational model can be used to perform a parametric study to optimize the microstructure of nanocomposite for enhanced mechanical properties.

Applying a micromechanics approach for predicting thermal conducting properties of carbon nanotube-metal nanocomposites

Heat dissipation is a very important issue in the harsh thermal loads affecting the reliability of structures. In this study, the thermal conducting behavior of carbon nanotube (CNT)-reinforced metal matrix nanocomposites (MMNCs) has been analyzed using a micromechanical model based on the method of cell (MOC) approach. The critical role of interfacial thermal resistance between the CNT and metal matrix in the MMNC thermal conducting response has been extensively explored. Also, the effects of volume fraction, length, diameter and curvature of CNTs have been investigated. It has been found that forming a perfect CNT/matrix interface contact would enhance remarkably the overall thermal conductivities. Generally, the axial thermal conductivity of the CNT-reinforced MMNCs can be increased with (i) rising CNT length and (ii) using straight CNTs. Moreover, the transverse thermal conductivity of these nanocomposite materials are improved with (i) rising CNT diameter and (ii) using wavy CNTs. Besides, increasing CNT volume fraction leads to a significant increment in the effective thermal conductivities in the presence of a perfect bonding at the CNT/matrix interface. Effective thermal conductivities of the MMNCs estimated by the MOC approach have been compared with those predicted by the effective medium and Halpin-Tsai models. A quite good agreement has been observed between the predictions of the MOC approach and experimental data.

Micromechanical estimation of biaxial thermomechanical responses of hybrid fiber-reinforced metal matrix nanocomposites containing carbon nanotubes

A new approach combining three models is developed to evaluate the thermomechanical behavior of carbon nanotube-fiber reinforced metal matrix nanocomposites (CNT-FRMMCs). At first, the shear lag and Schapery models are modified to determine the mechanical and thermal characteristics of CNT-reinforced metal matrix, respectively. Then, the transverse elastic moduli and transverse/transverse biaxial initial yield envelope of CNT-FRMMCs are predicted using the simplified unit cell (SUC) micromechanical model together with a proper representative volume element (RVE) with r × c sub-cells. The effect of the mismatch in coefficients of thermal expansion (CTEs) between the constituents of the hybrid composite is considered. The results obviously reveal that both thermoelastic properties and initial yield surface of FRMMCs can be significantly improved with adding CNTs. The influences of volume fraction, geometrical and material properties of CNTs, fiber volume fraction, fibers arrangement type, temperature change and residual stresses (RSs) on the CNT-FRMMCs mechanical properties are explored extensively. It is observed that (i) increasing both CNT volume fraction and length and (ii) decreasing the CNT diameter can lead to a more improvement in the thermomechanical behavior of CNT-FRMMCs. The results show that adding CNTs into the FRMMCs can reduce the effect of thermal RSs on the biaxial initial yield envelope.

Interaction between edge dislocations and amorphous interphase in carbon nanotubes reinforced metal matrix nanocomposites incorporating interface effect

Dislocations mobility and stability in the carbon nanotubes (CNTs)-reinforced metal matrix nanocomposites (MMNCs) can significantly affect the mechanical properties of the composites. However, current processing techniques often lead to the formation of coated CNT (amorphous interphase exists between the reinforcement and metal matrix), which have large impact upon the image force exerting on dislocations. Even though the importance of the interphase zone formed in metal matrix composites has been demonstrated by many studies for elastic properties, the influence of interphase on the local elastoplastic behavior of CNT-reinforced MMNCs is still an open issue. This paper puts forward a three-phase composite cylinder model with new boundary conditions. In this model, the interaction between edge dislocations and a coated CNT incorporating interface effect is investigated. The explicit expressions for the stress fields and the image force acting on an edge dislocation are proposed. In addition, plastic flow occurring around the coated reinforcement is addressed. The influences of interface condition and the material properties of coated CNT on the glide/climb force are clearly analyzed. The results indicate that the interface effect becomes remarkable when the radius of the coated reinforcement is below 10nm. In addition, different from the traditional particles, the coated CNT attracts the adjacent edge dislocations, causing pronounced local hardening at the interface between the interphase and the metal matrix under certain conditions. It is concluded that the presence of the interphase can have a profound effect on the local stress field in CNT-reinforced MMNCs. Finally, the condition of the dislocations stability and the equilibrium numbers of dislocations at a given size grain are evaluated for considering the interface effect.

Novel nanoprocessing route for bulk graphene nanoplatelets reinforced metal matrix nanocomposites

It is extremely difficult to effectively incorporate and disperse graphene nanoplatelets into metal matrix by traditional processing methods. In this paper, a novel nanoprocessing method that combines liquid state ultrasonic processing and solid state stirring is presented for fabrication of bulk metal–graphene nanoplatelets nanocomposites. The obtained graphene nanoplatelets reinforced Mg-based metal matrix nanocomposite shows a uniform dispersion of graphene nanoplatelets and dramatically enhanced properties. This novel nanoprocessing route has great potential for the production of ultrahigh performance metal matrix nanocomposites.

Effect of Processing on the Dispersion of CNTs in Al-Nanocomposites

Agglomeration and poor distribution/dispersion of carbon nanotubes (CNTs) within the matrix remains a major problem in processing homogeneous CNT reinforced metal matrix nanocomposites. In this work, we examine the effect of processing on the dispersion of CNTs in Al6061 and Al2124 alloy based Nanocomposites. Three methods were used to prepare the nanocomposite powders. In the first, CNTs were mixed with the prealloyed powder through dry ball milling. In the second, CNTs were sonicated then the prealloyed powder was added followed by sonication of the mixture and wet milling. In the third, the CNTs were functionalized, sonicated, and then the prealloyed powder was added followed by sonication of the mixture and wet milling. The effect of functionaliztion, sonication and type of milling on the dispersion of CNTs was evaluated.

Interatomic potentials for atomic scale modeling of metal–matrix ceramic particle reinforced nanocomposites

Functionally graded particle reinforced metal–matrix nanocomposite materials show significant promise for use in protective structures due to their high strengths, stiffness, failure resistance, and the ability to mitigate damage during ballistic impact. Further improvement of the performance of these materials requires fine-tuning of the nanostructure which, in turn, necessitates a clear fundamental understanding of the deformation and failure mechanisms under conditions of dynamic loading. While the molecular dynamics simulation technique is an excellent tool for investigation of the mechanisms of plastic deformation and failure of the particle reinforced metal–matrix nanocomposites at the atomic scale, the predictive power of the technique relies on an accurate description of the interatomic interactions. This paper provides a brief review of a recently developed class of interatomic potentials capable of the computationally efficient description of multi-component systems composed of metals, Si, Ge, and C. The potentials are based on reformulation of the Embedded Atom Method (EAM) potential for metals and two empirical potentials commonly used for covalently bonded materials, Stillinger–Weber (SW) and Tersoff, in a compatible functional form. The description of the angular dependence of interatomic interactions in the covalent materials is incorporated into the framework of the EAM potential and, therefore, the new class of potentials is dubbed Angular-dependent EAM (A-EAM) potentials. The A-EAM potentials retain all the properties of the pure components as predicted by the original SW, Tersoff, and EAM potentials, thus eliminating the need for extensive testing and limiting the scope of the potential parameterization to only the cross-interaction between the components. The performance of the A-EAM potentials is illustrated for the Au–Si system, with good agreement with experimental data obtained for the enthalpy of mixing in the Au–Si liquid alloy and the Au–Si phase diagram. The A-EAM potentials are suitable for large-scale atomistic simulations of metal–Si/Ge/C/SiC systems, such as the ones required for investigation of the dynamic response of nanocomposite materials to a ballistic/blast impact.