Metal- and Polymer-Matrix Composites: Functional LightweightMaterials for High-Performance Structures

NIKHIL GUPTA1,3 and MURALIDHARAN PARAMSOTHY2

1.—Composite Materials and Mechanics Laboratory, Mechanical and Aerospace EngineeringDepartment, Polytechnic School of Engineering, New York University, Brooklyn, NY 11201, USA.2.—Department of Mechanical Engineering, National University of Singapore, 9 EngineeringDrive 1, Singapore 117576, Singapore. 3.—e-mail: ngupta@nyu.edu

The special topic ‘‘Metal- and Polymer-Matrix Composites’’ is intended tocapture the state of the art in the research and practice of functional com-posites. The current set of articles related to metal-matrix composites includesreviews on functionalities such as self-healing, self-lubricating, and self-cleaning capabilities; research results on a variety of aluminum-matrix com-posites; and investigations on advanced composites manufacturing methods.In addition, the processing and properties of carbon nanotube-reinforcedpolymer-matrix composites and adhesive bonding of laminated composites arediscussed. The literature on functional metal-matrix composites is relativelyscarce compared to functional polymer-matrix composites. The demand forlightweight composites in the transportation sector is fueling the rapiddevelopment in this field, which is captured in the current set of articles. Thepossibility of simultaneously tailoring several desired properties is attractivebut very challenging, and it requires significant advancements in the scienceand technology of composite materials. The progress captured in the currentset of articles shows promise for developing materials that seem capable ofmoving this field from laboratory-scale prototypes to actual industrial appli-cations.

COMPOSITE MATERIALS

Increasing interest in lightweight and high-performance materials is leading to significantresearch activity in the area of composite materials.One recent focus area is to develop multifunctionalcomposites that have more than one property tai-lored as per the design requirements in addition toachieving low density. Automotive, aeronautics, andwind-energy sectors have been the major users ofcomposite materials. The transportation sector isespecially interested in such materials for structuralapplications due to steadily rising energy costs and adesire to reduce emissions. This interest in metal-and polymer-matrix composites for structural appli-cations inspired the Metal and Polymer-matrixComposites symposium that was organized as apart of Materials Science and Technology 2013

(MS&T’13) conference in Montreal, Canada. The to-pic of this issue is a follow-up to the symposium and isexpanded beyond the articles presented in Montrealto develop a more comprehensive overview of the field.

A brief snapshot of functional composites is pre-sented in Fig. 1. The upper half of the figure listsproperties that can be used to generate various func-tionalities in the material, whereas the lower halfpresents examples of functionalities. More propertiesand functionalities can be added to this diagram todevelop a comprehensive picture of the field. Damage-sensing and self-healing capabilities are of greatinterest to the aerospace structures. The self-cleaningand self-lubricating surfaces are relevant to the en-gine applications. The development of functioningcapabilities in the base material can reduce therequirements for additional systems on the applica-tion platform and can help in reducing the weight.

Carbon-fiber-reinforced polymer-matrix compositeshave seen strong growth in recent years in automobilebodies and wind turbine blades. However, the use of

Nikhil Gupta is the guest editor for the Composite Materials Committee ofthe TMS Structural Materials Division, and coordinator of the topicPolymer and Metal-Matrix Composites in this issue.

JOM, Vol. 66, No. 6, 2014

DOI: 10.1007/s11837-014-0969-0� 2014 The Minerals, Metals & Materials Society

862 (Published online May 1, 2014)

polymer-matrix composites in engine components islimited due to high temperatures. Metallic materialsare suitable for such applications. The development oflightweight metal-matrix composites with functionalproperties and high performance is very challenging,and studies ongoing in this area are captured underthis topic. Thirteen papers are included under thistopic in this issue. A summary of these articles ispresented in the following discussion.

MULTIFUNCTIONAL MATERIALS

The designers of automotive components usuallyhave a long wish list for properties that are requiredin a given part. As an example, an engine block isrequired to have high dimensional stability at dif-ferent temperatures, wear resistance, modulus, andfatigue life in addition to low weight. Such complexrequirements inspire the development of multi-functional materials, which is an important focusarea of research. In this issue, four articles focus ondiscussing multifunctionality in composite materi-als. The article by Ferguson et al.1 titled ‘‘Self-Healing Metals and Metal Matrix Composites’’ dis-cusses the current state of the art in the area of self-healing metallic materials. Self-healing in polymer-matrix composites has been demonstrated by sev-eral different approaches in the past two decades.However, achieving similar capabilities in metallicmaterials is much more complex. The article byDorri et al.2 titled ‘‘Functional Metal Matrix Com-posites: Self-Lubricating, Self-Healing, and Nano-composites—An Outlook’’ discusses the currentstatus and future perspective in multifunctionalmetallic materials. Self-lubrication through eithersolid- or liquid-phase lubricant that is released fromthe material microstructure can be useful. Self-healing can be achieved through approaches such asthe release of a healing agent or the use of shape-memory materials. The manuscript also discusseshollow-particle-filled composites called syntacticfoams, which are especially suitable for develop-ment with such functional capabilities. Syntacticfoams are synthesized by filling hollow particlesin polymer or metal-matrix. Syntactic foams are

further discussed by Orbulov and Majlinger3 intheir article, ‘‘Compressive Properties of MetalMatrix Syntactic Foams in Free and ConstrainedCompression.’’ They found that radial confinementof the specimens causes a remarkable difference inthe compressive properties of syntactic foams. Suchresults can be useful in automotive applications inwhich foam-filled channels are used for energyabsorption in crushing zones. The availability oftailored high-quality hollow particles is veryimportant in developing high-performance syntacticfoams. The article by Shunmugasamy et al.4 titled‘‘Compressive Characterization of Single Porous SiCHollow Particles’’ examines the recently developedhigh-quality particles through single-particle com-pression testing. Reliable information on the prop-erties of hollow particles can help in usingtheoretical models to accurately predict the prop-erties of syntactic foams. The hollow SiC particlescharacterized in this study have porous walls, whichmade it difficult to conduct direct measurement ofwall thickness and true particle density. Syntacticfoams with very low thermal expansion coefficientcan be developed by using hollow SiC particles.

ALUMINUM-MATRIX COMPOSITES

Lightweight aluminum-matrix composites forman important research area. A series of articles arefocused on aluminum-matrix composites. The arti-cle by Jiang et al.5 titled ‘‘The MicrostructuralDesign of Trimodal Aluminum Composites’’ discussesultrahigh-strength trimodal composites developedby their group. The matrix contains ultrafinenanocrystalline grains as well as coarser grains, inaddition to ceramic reinforcing particles, whichhelps in obtaining ultrahigh strength. The role ofinterface and grain boundaries on the properties ofthe composite is discussed. The study by Altinkok6

titled ‘‘Optimization of Mechanical Properties ofHybrid Al2O3/SiCp Reinforced Composites Producedby Pressure-Assisted Aluminum Infiltration’’ usedAl2O3/SiCp preforms to synthesize composite mate-rials. The effect of infiltration pressure and tem-perature was studied on the tensile properties of the

Fig. 1. A snapshot of the properties and functionalities of functional composites.

Metal- and Polymer-Matrix Composites: Functional Lightweight Materialsfor High-Performance Structures

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composite. Wear properties of the composites werealso characterized. The reinforcing mechanisms insuch hybrid composites can be complex. Anothereffective reinforcement for aluminum-matrix com-posites is diamond, which is investigated by Cacciaet al.7 in their article ‘‘Diamond Surface Modifica-tion to Enhance Interfacial Thermal Conductivity inAl/Diamond Composites.’’ The decreasing price ofsynthetic industrial diamonds is making them via-ble reinforcement for commercial composite mate-rials. The article is focused on studying thepossibility of modifying the surface of reinforcingdiamond particles to obtain sp2 hybridization, whichhas a better compatibility with aluminum than sp3

hybridized diamond surface. Corchado et al.8 stud-ied the effect of in situ-precipitated AlB2 particles inaluminum-alloy matrix composites in their article‘‘Effects of AlB2 Particles and Zinc on the AbsorbedImpact Energy of Gravity Cast Aluminum MatrixComposites.’’ They also studied the effect of zincconcentration on the impact and hardness of thismaterial system. There is a trade-off in the hard-ness and impact resistance with respect to theincreasing AlB2 concentration, and appropriatecompositions need to be determined as per the pri-mary requirements of the application.

COMPOSITE SYNTHESIS METHODS

Methods of composite synthesis are the primaryfocus in two articles. Borkar et al.9 studied the laser-engineered net shaping (LENS process for Ni-Ti-Calloy in the article ‘‘Laser-Deposited In Situ TiC-Reinforced Nickel Matrix Composites: 3D Micro-structure and Tribological Properties.’’ The Ni-10Ti-10C composite exhibits primary cuboidal TiC precipi-tates as well as eutectic carbide precipitates, whereasthe Ni-3Ti-20C composite exhibits an additional gra-phitic phase in the microstructure. A three-dimen-sional microstructural analysis reveals thedistribution and morphology of phases. Webb andCharit10 studied the spark-plasma sintering (SPS)process in their article ‘‘Fabrication of Cermets viaSpark-Plasma Sintering for Nuclear Applications’’ forW-UO2 cermets. The SPS process yielded denseW-CeO2 specimens with a finer microstructure thanother sintering techniques.

The infiltration of Cu-Si alloy in porous preformsof carbon is modeled by Iqbal et al.11 in the article‘‘Numerical Studies of Infiltration Dynamics ofLiquid–Copper and Silicon/Solid–Carbon System.’’Wetting of reinforcement by the melt is an impor-tant consideration in infiltration processes. Theeffect of various parameters such as preform poresize and infiltration rate on the wetting angle isincluded in the model.

POLYMER-MATRIX COMPOSITES

The article by Paramsothy12 discusses the pro-cessing and properties of carbon nanotube (CNT)-reinforced composite materials in his article ‘‘Dis-

persion, Interface, and Alignment of CarbonNanotubes in Thermomechanically Stretched Poly-styrene Matrix.’’ Obtaining uniform dispersion ofCNTs in the microstructure and a strong CNT-matrix interface is critical for obtaining improve-ment in mechanical properties of nanocomposites.Preferential orientation of CNTs can provide direc-tional properties in the composites.

Poveromo and Earthman13 discuss joining ofcomposites in their article ‘‘Analysis of ‘Kiss’ Bondsbetween Composite Laminates.’’ They show that‘kiss’ bonds can be formed using room temperaturecurable epoxy paste adhesives by creating an amineblush on the epoxy surface or by applying a releaseagent on the bonding surfaces. Bond line integrity isan important issue for any component containingadhesive joints.

SUMMARY

The rapid growth in the demand for lightweightand high-performance materials in all modes oftransportation has been a driving force behindnumerous recent innovations in the area of metal-and polymer-matrix composites. The new focus onmultifunctional material has resulted in the devel-opment of self-healing, self-lubricating, and self-cleaning materials. New reinforcement materials,including microscale and nanoscale materials, arebeing developed for various matrices. Theadvancements related to synthesis methods havehelped in developing new compositions and reduc-ing the cost of final products. Thirteen articlesincluded under the Metal- and Polymer-MatrixComposites topic discuss various aspects of theprocessing, microstructure, and properties of com-posite materials. Many studies are focused onaluminum-matrix composites because of interest inlightweight composites to replace heavier steelparts. Hollow-particle-filled syntactic foams werediscussed for compressive properties and for thepossibility of filling the hollow particles with liquidsfor generating self-healing and self-lubricatingcomposites.

ACKNOWLEDGEMENTS

This work was supported by the Office of NavalResearch Grant N00014-10-1-0988 with Dr. YapaD.S. Rajapakse as the program manager. Dr.Vasanth Chakravarthy Shunmugasamy and StevenEric Zeltmann are thanked for help with manu-script preparation.

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