Modified embedded atom method study of the mechanical properties of carbon nanotube reinforced nickel composites

PHYSICAL REVIEW B 81, 104103 (2010)

Modified embedded atom method study of the mechanical properties of carbon nanotube
reinforced nickel composites
Jamal Uddin,1,2,* M. I. Baskes,3 S. G. Srinivasan,2'4 Thomas R. Cundari,1,2 and Angela K. Wilson1,2
'Department of Chemistry, University of North Texas, 1155 Union Circle #305070, Denton, Texas 76203, USA
2Center for Advanced Scientific Computing & Modeling, University of North Texas, Denton, Texas 76203, USA
3Materials Science and Technology Division, Los Alamos National Laboratory, MS G755, Los Alamos, New Mexico 87545, USA
4Department of Materials Science & Engineering, University of North Texas, Denton, Texas 76203, USA
(Received 12 October 2009; published 11 March 2010)
We report an atomistic simulation study of the behavior of nanocomposite materials that are formed by
incorporating single-walled carbon nanotubes (SWCNTs), with three different diameters, and a multiwalled
carbon nanotube (MWCNT) into a single-crystal nickel matrix. The interactions between carbon and nickel
atoms are described by a modified embedded atom method potential. Mechanical properties of these nanocom-
posite materials are predicted by atomistic calculations and compared with that of fcc nickel and pristine CNTs.
Our simulations predict that all Ni/CNT composites studied in this work are mechanically stable. Their elastic
properties depend on the volume fraction and diameter of embedded CNTs. The single-crystal Young's modu-
lus (El1) of Ni/SWCNT composites exhibit a large increase in the direction of CNTs alignment compared to
that of a single-crystal nickel. However, a moderate but gradual decrease is seen for E22 and E33 in the
transverse directions with increase in CNT diameters. As a consequence, Ni/SWCNTs show a gradual decrease
for the polycrystalline Young's, bulk and shear moduli with the increasing CNT diameters and volume frac-
tions. These reductions, although moderate, suggest that enhancement of mechanical properties for polycrys-
talline Ni/SWCNT nanocomposites are not achievable at any CNT volume fraction. The Ni/MWCNT com-
posite with high CNT volume fraction shows the highest increase in El1. Unlike the E22 and E33 for Ni/
SWCNTs, there is a significant increase in the E22 and the E33 for Ni/MWCNT. As a result, polycrystalline
Ni/MWCNT composites show slight increase in the elastic properties. This suggests that nickel nanocompos-
ites with enhanced mechanical properties can be fabricated using large volume fractions of larger diameter
MWCNTs. Depending on type, alignment and volume fraction, Ni/CNT composites show varying degrees of
elastic anisotropy and Poisson's ratio compared to pure Ni. Simulation predicts strong adhesion at the Ni/CNT
interface and a significant interfacial stress transfer between CNT and Ni matrix.

DOI: 10.1103/PhysRevB.81.104103
I. INTRODUCTION
Carbon nanotubes (CNTs) are among the stiffest and
strongest materials.' Their extremely small size, high aspect
ratios, and extraordinary structural and chemical stability
make CNTs a leading candidate for reinforcement fillers in
nanocomposite materials.2-6 As a result, there has been an
increasing scientific and technological interest in developing
nanocomposites by dispersing CNTs into a metal matrix or
by laser depositing metal matrix around the CNTs. Such
composites combine low density with high strength and stiff-
ness, and enhanced electrical and thermal properties. These
are particularly attractive for aerospace and other transporta-
tion applications2-4 where there is a renewed emphasis on
increasing fuel efficiency by "light weighting" the transport-
ers.
CNT-metallic composites offer distinct advantages over
polymeric composites for high-strength applications.5,6 Ku-
zumaki et al. were the first to study a aluminum/CNT
composite.7 Preparation and application of magnesium/CNT
composites was also reported.8'9 The mechanical strength of
nickel/CNTs nanocomposites was studied recently by Sun et
al.10 Some progress has also been made in the application of
atomistic simulations to predict the elastic and the mechani-
cal properties of such composite materials. For example,
molecular-dynamics (MD) simulations have been success-

PACS number(s): 62.23.Pq, 81.40.Jj, 68.35.Gy, 62.20.de
fully applied to predict the elastic properties of polyethylene/
CNT composites" and other polymeric CNT composites.'2
However, despite their potential superiority in mechanical
properties, the development of CNT-metal matrix composites
remains in its infancy. Development of metal matrix compos-
ites will be promoted from atomistic insights on the response
of their mechanical properties to chemical and material
modifications.
Nickel is the primary ingredient of numerous aerospace
superalloys,13,14 and therefore, is an attractive target for fab-
rication of ultrastrength materials with CNTs. This research
investigates the mechanical properties of pristine CNTs, a fcc
nickel matrix, and Ni/CNT composites at different CNT vol-
ume concentrations using quasistatic atomistic simulations.
Elastic properties of solids are important because they relate
to various fundamental solid-state properties. They deter-
mine the response of the crystal to external forces, as char-
acterized by elastic constants, bulk modulus, shear modulus,
Young's modulus, and Poisson's ratio. Therefore, elastic
properties play an important part in determining the strength
of the materials. We have calculated these properties and the
elastic anisotropy of Ni/CNT nanocomposite materials. Inter-
atomic interactions are described using a modified embedded
atom method (MEAM) initially developed by Daw and
Baskes'5,16 and later modified by Baskes.17

02010 The American Physical Society

1098-0121/2010/81(10)/104103(12)

104103-1

Uddin, Jamal; Baskes, Michael I.; Srivilliputhur, Srinivasan; Cundari, Thomas R., 1964- & Wilson, Angela K. Modified embedded atom method study of the mechanical properties of carbon nanotube reinforced nickel composites. [College Park, Maryland]. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc107769/. Accessed October 2, 2014.