Conductivity Of Metal Matrix Composites Research Articles

An analytical model to ascertain A.C. electrical conductivity of metal matrix composites

ABSTRACT With regard to an inherent understanding of electrical conductivity exhibited by monolithic metals and alloys system and metal matrix composite system under alternating current field, a long-standing unresolved issue, an analytical model is developed following classical free electron theory along with a typical conceptualisation of ‘effective relaxation time’ that combines conventional relaxation time (in view of collision of free electrons with lattice defects) and the time between successive cyclic reversals of electric field (the inverse of frequency). Two prime phenomena (electron scattering and polarisation at particle–matrix interface) are further conceived for metal matrix composite system containing particles. The developed model is found to closely follow (% deviation << 10) the available experimental result in the literature on A.C. electrical conductivity of 6063Al alloy and 6063Al–TiO2 composite systems. The model further ascertains certain system-specific parameters; such as, relaxation time under A.C. field, effective scattering factor and effective relaxation time aid from interface polarisation to specify the system behaviour under alternating current field. Accordingly, the model adequately explains the declining trend of A.C. electrical conductivity with increasing frequency in monolithic alloy system and an enhancement of A.C. electrical conductivity in metal matrix composite system in the presence of particles together with a non-declining trend even on increasing frequency.

Connection between strength and thermal conductivity of metal matrix composites with uniform distribution of graphite flakes

The paper focuses on the connection between thermal conductivity and overall strength of metal matrix composites on example of Al2024 and Mg-0.9Ca alloys reinforced with graphite flakes. We combine theoretical and experimental approaches to analyze the maximal stress concentration in such composites as a function of minimal distance between graphite flakes. The latter is linked to the volume fraction of the inhomogeneities, which governs overall thermal conductivity. Elimination of the volume fraction parameter leads to the explicit cross-property connection. This approach is possible if inhomogeneities in the material have the same shape and are uniformly distributed with no distinguishable clusters. The agreement between the theoretical predictions and experimental observations is very good.

Evaluation of Effective Thermal Conductivity of Metal Matrix Composites by Using Image-Based Calculation

Interfacial thermal resistance in Al-SiC composites was evaluated by comparing the measured thermal conductivity and the calculated thermal conductivity. Al-20vol.%SiC composites changing SiC particle size, 3 μm to 30 μm, was fabricated by spark plasma sintering and heat treatment. Effective thermal conductivity was measured with the steady state thermal conductivity measuring device. Effective thermal conductivity was also calculated by using SEM image and the measured relative density. Comparing the measured thermal conductivity and the calculated thermal conductivity, interfacial thermal resistance in Al-SiC composites was evaluated as about 1.0x10-8 (m2K)/W.

Thermal conductivity of metal matrix composites with coated inclusions: A new modelling approach for interface engineering design in thermal management

Despite the importance of interface engineering in technological metal matrix composites, both systematic experimental studies and modelling approaches are still lacking to predict some of their properties. This paper presents an insight into experimental results and modelling of the thermal conductivity in metal matrix composite materials with coated inclusions. Two types of composites of technological importance, Al/diamond and Mg/cobalt, have been interfacially engineered either by deposition of a 0-14.6 μm TiC layer on the diamond particles or by oxidative formation of a 0-21.4 μm Co3O4 layer on the cobalt particles, respectively. The experimental results of thermal conductivity can be properly accounted for by a new modelling approach that consists in a multi-step application of the GDEMS model. This modelling scheme demonstrates a predictive capacity far superior to the few current models available in the literature and allows an accurate calculation of the critical interface thickness, such that it outlines a proper interface engineering tool to design high thermally conductive composite materials.

Cumulative influence of nanoparticles on MMCs’ time–temperature history curve

Modern automobiles require materials with high thermal properties and less weight for extraordinary performance. Metal matrix composites (MMCs) possess the mechanical properties required for automobile applications. The present work focuses on developing a mathematical model using the finite-difference technique to examine the cumulative and individual influence of silicon carbide (SiC)/aluminum oxide (Al2O3) nanoparticle weight percentage on the MMCs’ time–temperature history curve. The thermophysical properties of MMCs are considered to be isotropic and homogeneous and are calculated using the mixture rule and the Maxwell model. The results reveal that increment in the weight percentage of the nanoparticles (silicon carbide/aluminum oxide) makes the time–temperature history curve steeper. The cumulative effect of the nanoparticles results in a less steep time–temperature history curve compared to the individual nanoparticle, indicating a decreased solidification rate due to low effective thermal conductivity. The two thermal conductivity models show the same time–temperature history curve due to less deviation in the thermal conductivity of MMCs. The mathematical model developed in the present work predicts the time–temperature history curve accurately which matches well with the experimental results.

Effect of fiber transverse isotropy on effective thermal conductivity of metal matrix composites reinforced by randomly distributed fibers

The effective thermal conductivity of metal matrix composites (MMCs) reinforced by the randomly distributed transversely isotropic fibers is evaluated using the representative volume element (RVE) based finite element (FE) homogenization method. The modified random sequential absorption (RSA) algorithm is proposed to generate the periodic RVEs of MMCs and thus the periodic boundary conditions are introduced. The transversely isotropic thermal conductivity of fiber is considered and its numerical implementation in the FE analysis is detailed. The RVE based FE homogenization method to predict the effective thermal conductivity of MMCs reinforced by the randomly distributed fibers is verified by comparing against the experiment and the Hashin–Shtrikman bounds. The simulation results show that the effect of the transverse isotropy of fiber thermal conductivity on the effective thermal conductivity of MMCs reinforced by the randomly distributed fibers can be neglected owing to the large matrix/fiber thermal conductivity ratio. The effective thermal conductivity of MMCs reinforced by the randomly distributed fibers decreases with the increase of fiber volume fraction, while the effect of fiber aspect ratio on the effective thermal conductivity of MMCs reinforced by the randomly distributed fibers is not significant.

Thermal conductivity of metal-graphene composites

In this paper the results of numerical simulations and experimental studies are presented which describe potential and limitation of applications of single-layer (SLG) and multi-layer (MLG) graphene for thermal conductivity enhancement (TCE) of copper. A series of composite structures were studied which are representative of most widely used systems. The influence of structural parameters on the macroscopic thermal conductivity was analyzed, both experimentally and by numerical simulations. Analytical and Finite Element Method modeling were carried out to investigate a wide range of phenomena, including the effect of copper-MLG interface, copper grain size, volume fraction, thickness and orientation of MLG platelets as well as spatial distribution of MLG defined by percolation factor. Both modeling and the experimental results show that the volume fraction of MLG regions, their size, orientation and spatial distribution may significantly affect the thermal conductivity of metal matrix composites. TCE can be obtained for the laminate-like structure or particulate composites with highly aligned MLG regions. The thermal conductivity of such composites is strongly anisotropic and enhanced in the direction perpendicular to the layers. The results obtained in this study predict that SLG will have a negative effect on the thermal conductivity of copper matrix composites.

Electrical conductivity of a novel cast 6351 Al–Al4SiC4 in situ composite

In this research work, electrical conductivity of a novel cast 6351 Al–Al4SiC4 composite has been studied for varying Al4SiC4 particle content (2–7 vol%). Analytical models were developed on the basis of free electron theory and local resistance approach in order to predict electrical conductivity of metal matrix composites. The electrical conductivity of cast 6351 Al–Al4SiC4 composite was found to decrease with increasing Al4SiC4 content. Overprediction of results and more % deviation of the predicted electrical conductivity from experimental value were observed for local-resistance-approach-based model. However, the model developed on the basis of electron theory considering scattering of electrons at particle–matrix interface accurately predicted the experimental electrical conductivity data.

Thermal conductivity of advanced TiC reinforced metal matrix composites for polymer processing applications

Tools used for fabricating polymers are often required to have low thermal conductivities, e.g. for pelletizing, because this lowers the risk of the polymer nozzle being obstructed by molten polymer solidifying as it exits. Latterly, advanced corrosion and wear resistant metal matrix composites (MMCs) are used for pelletizing tools. Therefore, with respect to polymer processing it is important to know how the thermal conductivity of MMC gets influenced by hard phase and metal matrix contribution. In this study, the thermal conductivity of a TiC reinforced corrosion and wear resistant MMC gets analyzed. Especially the influence of chemical interdiffusion between TiC and metal matrix on the resulting thermal conductivity gets analyzed. It is shown that changes in the chemical composition lead to distinct decrease in thermal conductivity of the TiC which has to be considered when MMC thermal conductivities have to be examined.

Numerical simulation of thermal conductivity of MMCs: effect of thermal interface resistance

The thermal conductivity of metal matrix composites is investigated by computational simulations, in which the effect of a thermal barrier resistance between the constituent phases is explicitly taken into account. A numerical unit cell approach, which is based on the finite element method, an analytical mean field method of the Mori–Tanaka type and bounding techniques are employed. To predict the effective conductivities of fibre composites two different types of unit cell are utilised for the numerical studies. Two dimensional unit cells are developed which allow for investigations of aligned, continuous fibre reinforced composites while three dimensional unit cells are employed to study a large variety of different arrangements of non-staggered and staggered aligned short fibres. In the case of short fibres the thermal barrier resistances of the end faces and of the cylindrical surfaces are modelled independently, which allows one to study both their individual and their combined influences on the overall behaviour. Results are presented for carbon fibre/copper composites and their overall thermal conductivities are investigated in terms of interfacial thermal barriers and microtopologies.

On the electrical conductivity of metal matrix composites containing high volume fractions of non-conducting inclusions

Different predictive models—the Maxwell mean field approach, the differential effective medium scheme, the 2- and 3-phase self-consistent, and 3-point model—for the electrical conductivity of two-phase materials are assessed based on electrical conductivity measurements of metal matrix composites with non-conducting inclusions produced by gas pressure infiltration. The volume fraction of non-conducting phase, namely equiaxed or angular alumina particles of various sizes and size-distributions embedded in a matrix of pure aluminum, is varied between 40 and 70 vol.-%. For a given volume fraction, the equiaxed particles yield consistently higher conductivity than their angular counterparts, by as much as 40%. The Maxwell/Mori-Tanaka estimate and the 3-phase self-consistent model are consistently too high for the case of equiaxed particles (approximated by spheres), while for this particle shape the 3-point bounds for the limiting case of symmetric cell materials and the differential scheme give good agreement. For angular particles, approximated by randomly oriented oblate spheroids, only the differential scheme yields accurate predictions, whereas the Maxwell mean-field approach largely, and the 3-phase self-consistent approach for randomly oriented spheroids slightly, overestimate the effective conductivity. The 3-point bound for symmetric cell materials with spheroidal cells also overestimates the effective conductivity significantly. Overall, the differential scheme is found to exhibit very good predictive capacity over the ranges of geometry and volume fractions covered in this study, unlike all other models examined.

Analytical modeling of the electrical conductivity of metal matrix composites: application to Ag–Cu and Cu–Nb

Modeling the electrical conductivity of composite materials is a complex matter, particularly if microstructural features lead to a size effect in electronic conduction or create an anisotropy. The method described in this article accounts for these circumstances by incorporation of appropriate phenomenological models. It provides a means to analyze and estimate the resistive behavior of two-phase or multi-phase micro-composites and nano-composites. A comparison with experimental data is carried out for two high-strength conductors, Ag–Cu and Cu–Nb, both of which have undergone extensive quantitative microstructure analysis to provide the required input for the model.

The longitudinal electrical conductivity of metal matrix composites at cryogenic temperature in the presence of a longitudinal magnetic field

Utilisation des resultats de la partie I pour deduire deux expressions integrales pour la conductivite electrique, quand un champ magnetique B est ajoute a un faible champ electrique egalement parallele aux fibres

Model of transverse electrical conductivity of metal matrix composites above liquid nitrogen temperatures

The present theories of transverse electrical conductivity of metal matrix composites (MMCs) containing nonconducting continuous cylindrical fibres are inadequate to predict experimental measurements. In this paper, we present a model of transverse electrical conductivity that predicts experimental data reasonably well for the case of an MMC material reinforced with nonconducting or poorly conducting continuous fibres. lt is based on the concept that transverse conductivity consists of two contributions: the electrical resistivity of the bulk material modified by periodic variations in the bulk cross-section due to the presence of nonconducting fibres; and a disturbance in electron transport due to nonuniformity in the electric field, caused by the presence of the fibres, that extends some distance away from and all around the fibres. To calculate this nonuniformity, we use the well-known solution of the potential field for a conducting cylinder in a uniform electric field and invert it so that it becomes a problem of nonconducting filaments in a conducting matrix. This gives a value of the transverse electrical resistivity for boron/aluminium (B/Al) containing 60 vol% fibre in nearly exact agreement with experimental data. The theory is compared to a modified capacitance model developed by Keller [1] for dielectric materials. The model discussed in this paper does not predict the trans-verse electrical resistivity of MMCs reinforced with very small-diameter fibres (Gr/Al, Al2O3, etc.) where the fibres are randomly distributed in a plane normal to their longitudinal axis. This problem will be discussed in a companion paper.