T. YENER et al.: ELECTROMAGNETIC-SHIELDING EFFECTIVENESS AND FRACTURE BEHAVIOR ...
899–902
ELECTROMAGNETIC-SHIELDING EFFECTIVENESS AND
FRACTURE BEHAVIOR OF LAMINATED (Ni–NiAl3)
COMPOSITES
U^INKOVITOST ELEKTROMAGNETNE ZA[^ITE IN OBNA[ANJE
PRI LOMU LAMINIRANEGA KOMPOZITA (Ni-NiAl3)
Tuba Yener1, Suayb Cagri Yener2, Sakin Zeytýn1
1Sakarya University, Engineering Faculty, Department of Metallurgy and Materials Engineering, Serdivan, Sakarya, Turkey
2Sakarya University, Engineering Faculty, Department of Electrical and Electronic Engineering, Serdivan, Sakarya, Turkey
syener@sakarya.edu.tr
Prejem rokopisa – received: 2015-07-01; sprejem za objavo – accepted for publication: 2015-12-01
doi:10.17222/mit.2015.189
In this research Ni–NiAl3 multilayer composites were produced through reactive sintering in an open atmosphere using Ni and
Al foils with a 250-μm initial thickness. The sintering was performed at 700 °C under 2 MPa of pressure for 6 h. The micro-
structure and phase characterizations of the samples were performed. The hardness values of samples were determined using the
Vickers indentation technique for the intermetallic and metallic regions as 765±60 HV and 90±10 HV, respectively. For the
mechanical examinations, a perpendicular load was applied to the composite in order to observe the fracture behavior of the
metallic-intermetallic laminate composites. SEM fracture surface analyses indicated that cracks initiated in the intermetallic
region, and the crack propagation stopped when it reaches the ductile nickel phase. In addition, shielding-effectiveness measure-
ments were performed. The MIL composite exhibits over 50 dB electromagnetic-shielding effectiveness against a very wide
frequency range, from a few GHz to over 18 GHz.
Keywords: intermetallics, MIL composites, fracture behavior, electromagnetic interference shielding
V raziskavi so bili izdelani Ni–NiAl3 ve~plastni kompoziti z reakcijskim sintranjem na atmosferi in z uporabo Ni- in Al-folij z
za~etno debelino 250 μm. Sintranje je bilo 6 h na 700 °C, pri tlaku 2 MPa. Na vzorcih je bila izvedena karakterizacija mikro-
strukture in faz. Trdota vzorcev je bila dolo~ena po Vickersu, 765±60 HV, za podro~ja intermetalnih faz in 90±10 HV pri
osnovi. Za mehanske preiskave je bila uporabljena navpi~na obremenitev, za opazovanje obna{anja kompozita pri lomljenju
kovinskih in intermetalnih lamel. SEM-preiskave prelomov so pokazale, da je za~etek razpoke v podro~ju intermetalne faze in
da se {irjenje razpoke ustavi, ko pride v duktilno fazo niklja. Izvedene so bile tudi meritve u~inkovitosti za{~ite sevanja. MIL
kompozit ka`e u~inkovitost pred elektromagnetnim sevanjem, vi{jo od 50 dB v zelo {irokem obmo~ju frekvenc od nekaj GHz
do preko 18 GHz.
Klju~ne besede: intermetalne zlitine, MIL kompoziti, obna{anje pri lomu, elektromagnetna interferen~na za{~ita
1 INTRODUCTION
Layered metallic-intermetallic laminate (MIL) com-
posites are a new multifunctional materials group based
on open air reactive sintering of chemically active metal
foils under pressure.1,2 Laminate composites are being
intensively studied for a number of potential applica-
tions: electronic devices, structural components, armor,
etc. Ceramic–ceramic, metal–ceramic, metal–metal, me-
tal–ceramic–intermetallic and metal–intermetallic sys-
tems have shown desirable properties.3–5 They are
designed to optimize the desirable mechanical properties
of intermetallics by incorporating layers of ductile rein-
forcement.6 The combination of these types of materials
makes the MIL composites candidates for the armament
industry as armor materials that require improved
mechanical and electromagnetic properties.1,6,7
In particular, nickel–tri-nickel aluminide (Ni–NiAl3)
metal–intermetallic laminate (MIL) composite systems
have a great potential for aerospace, automotive and
military applications because of their combination of
high strength, toughness and stiffness at a lower density
than monolithic titanium or other laminate systems.7,8
Intermetallics of NiAl and NiAl3 have a high melting
point, a low density, high strength, good corrosion and
oxidation resistance at high temperature.9,10 The nickel-
aluminum system is one of the most well known in terms
of the formation of intermetallic phases. This system is
also a priority among laminate composite systems.2,5,11
The aim of the present study is to synthesize nickel-
nickel aluminide metallic-intermetallic composites and
analyze their mechanical, fracture and electromagnetic
shielding behaviors. The organization of the paper is as
follows. After this introduction, in the second section the
methodology and production of materials ear sum-
marized. In the third section the experimental results are
presented. In this section, the fracture behavior in terms
of "physical-shielding" and then electromagnetic-shield-
ing behavior of the composites are provided after expe-
rimental processes. Finally, the paper ends with a con-
clusion section.
Materiali in tehnologije / Materials and technology 50 (2016) 6, 899–902 899
UDK 67.017:669.018.25:621.8.038 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(6)899(2016)
2 METHODOLOGY AND EXPERIMENTAL
PART
2.1 Materials and method
The MIL process consists of stacking commercial-
purity Ni and Al foils in alternating layers. The pro-
perties of the foils are listed in Table 1.
Table 1: Properties of foils used in experiments
Tabela 1: Lastnosti folij, uporabljenih pri preizkusih
Foil Ni Al
Thickness (ìm) 250 250
Purity (%) 99.5 99.5
Stack number 6 5
The nickel- and aluminum-foil dimensions were
initially selected to completely consume the aluminum in
forming the intermetallic compound with alternating
layers of partially unreacted Ni metal. Each foil sheet
was prepared as 10 mm × 10 mm and 60 mm × 40 mm
rectangular pieces for mechanical and electromagnetic
experiments, respectively. Contamination on the surface
of the foils was cleaned using ethanol. After drying ra-
pidly, they were laminated alternatively into nickel/alu-
minum multilayer samples. Each stack consisted of 6
nickel and 5 aluminum foils, as indicated in Table 1. An
initial pressure of 2 MPa is applied at room temperature
to ensure good contact between the foils. A schematic
representation of the Ni-Al stacks is shown in Figure 2a.
The sintering process was applied in the open air, in an
electrical resistance furnace at 700 °C for 6 h. After
sintering, samples were ground and polished using stan-
dard metallographic techniques.
2.2 Characterization
Microstructure analyses of the composites were per-
formed with a JEOL JSM-5600 model scanning electron
microscope (SEM). The presence of phases formed in
the sintered samples was determined by energy-disper-
sive spectroscopy (EDS). The microhardness of compo-
sites was determined using a Leica WMHT-Mod model
Vickers hardness instrument under an applied load of
300 g for the intermetallic zone, and 100 g for the me-
tallic zone. The composition of the phases was deter-
mined by comparing the results of the microprobe
analysis with the data in the binary Ni–Al phase diagram
(Figure 1).12
3 EXPERIMENTAL PROCESSES AND RESULTS
3.1 SEM-EDS Analysis
Figure 2b presents the cross-sectional micrographs
of representative laminated composites. The presence of
T. YENER et al.: ELECTROMAGNETIC-SHIELDING EFFECTIVENESS AND FRACTURE BEHAVIOR ...
900 Materiali in tehnologije / Materials and technology 50 (2016) 6, 899–902
Figure 2: a) Nickel-aluminum foils stack, b) SEM micrograph of la-
minated composites produced at 700 °C/6h
Slika 2: a) Sestav nikelj-aluminijevih folij, b) SEM-posnetek lami-
niranega kompozita, izdelanega pri 700 °C/6 h
Figure 1: The Ni–Al binary phase diagram12
Slika 1: Binarni fazni diagram Ni-Al12
Figure 3: SEM-EDS analyses of Ni-NiAl3 composites sintered at 700
°C/6h
Slika 3: SEM-EDS analize Ni-NiAl3 kompozita po sintranju 6 h na
700 °C
different regions indicates the different phases in the
composites. It can be seen that the laminated composites
consist of unreacted Ni layers (gray regions) and the
formed intermetallic NiAl3 layers (dark regions).
Moreover, the laminated composites are well-bonded and
remain nearly fully dense. The nickel aluminide phase
occurs due to the thermodynamics of the reaction bet-
ween Ni and Al. The existence of liquid Al phase plays
important roles in the nucleation and growth of NiAl
particles and the eventual formation of continuous alter-
native intermetallic layers.
3.2 Mechanical fracture behavior and hardness
Intermetallics and ceramics, in general, have very
little or no dislocation motion, and, hence, exhibit very
little inherent or intrinsic crack-propagation resistance.3
By using laminate design and proper composites, it is
aimed to produce intermetallic NiAl3 phase during the
process to give a high hardness to the composite, while
unreacted nickel provided moderate ductility.
Due to the deflection of cracks along the Ni/NiAl
interfaces, a non-catastrophic fracture was observed in
the laminated composites. A weak delamination and de-
bonding is seen at the metallic nickel and the inter-
metallic layers interface. In a large number of cleavage
cracks present in the brittle intermetallic layer. Despite
the severe plastic deformation, the nickel layer was not
torn. This clearly demonstrates the effect of crack
stopping of the ductile reinforcing phases (Figure 4).
When it comes to hardness, the values of samples
were determined by using the Vickers indentation tech-
nique for intermetallic and metallic region as 765±60 HV,
90±10 HV, respectively, whereas the hardness of metallic
aluminum and nickel, respectively, is about 45 HV and
90 HV
3.3 Electromagnetic-shielding effectiveness
Electromagnetic interference can lead to adverse con-
sequences, such as malfunction or crashing of electronic
systems and computers, unintentionally firing of
electrically explosive devices, or be the cause of the loss
of secret information to an enemy. In this respect, it is
essential to protect devices from disruptive electromag-
netic signals to guarantee their functionality in stable
operating conditions. It is also obvious that the electro-
magnetic shielding is vital in military applications.13–15
Shielding effectiveness is the ratio of impinging
energy to the residual energy. When an electromagnetic
wave passes through a shield, absorption and reflection
take place. The residual energy is part of the remaining
energy that is neither reflected nor absorbed by the
shield, but emerges from the shield. Shielding effective-
ness (SE) is the ratio of the field before and after
T. YENER et al.: ELECTROMAGNETIC-SHIELDING EFFECTIVENESS AND FRACTURE BEHAVIOR ...
Materiali in tehnologije / Materials and technology 50 (2016) 6, 899–902 901
Figure 5: Electromagnetic-shielding effectiveness characteristics of
laminated Ni–NiAl3 composites a) X Band (8.2–12.4 GHz), b) Ku
Band (12.4–18 GHz)
Slika 5: Zna~ilnost u~inkovitosti elektromagnetne za{~ite laminira-
nega Ni-NiAl3 kompozita a) X-pas (8,2 GHz-12,4 GHz), b) Ku-pas
(12,4 GHz – 18 GHz)
Figure 4: Cross-sectional micrographs of Ni-NiAl3 composites after
impact effect: a) 135× , b) 350×
Slika 4: Posnetek preseka kompozita Ni-NiAl3 po udarcu: a) 135×, b)
350×
attenuation of the electric and magnetic fields and can be
expressed as Equation (1):15,16
[ ]SE dB
E
E
i
t
= 20 lg (1)
Where Ei and Et refer to the transmitted and incident
waves, respectively. Shielding effectiveness is a function
of frequency, and from the Equation (1) it is measured in
dB.
The shielding-effectiveness characteristics of lami-
nated Ni–NiAl3 composites have been measured and the
results obtained are shown in Figures 5a and 5b for the
X band and Ku band, respectively.
From the results, the produced MIL composites
exhibit around or more 50 dB of electromagnetic-
shielding effectiveness against a very wide frequency
range from 8.2 GHz to over 18 GHz. That shielding level
means even 99.999 % of the incident power is prevented
by the produced composites. These shielding-effective-
ness levels indicate that laminated composites can be
remarkable candidates for shielding application also
thanks to their improved mechanical properties.
4 CONCLUSIONS
The conclusions of this research can be summarized
as follows:
• By controlling the duration of the reactive-foil sint-
ering process, composites can be fabricated in which
a tailored amount of residual aluminum remains at
the intermetallic centerline.
• Ni–NiAl3 metal–intermetallic laminate (MIL) com-
posites have been successfully synthesized by
reactive-foil sintering technique in open air at 700 °C
for 6 h under 2 MPa pressure. The laminated struc-
ture is well-bonded, nearly fully dense.
• Microstructural characterization by SEM and EDS
indicates that NiAl, NiAl3, Ni2Al3 are intermetallic
phases in the composite.
• The hardness of the fabricated laminated composite
was dramatically changed. Whereas the hardness of
metallic aluminum and nickel, respectively, is about
45 HV and 90 HV, the hardness of intermetallic zone
is approximately 765±60 HV.
• In this study the shielding effectiveness of laminated
Ni–NiAl3 composites was examined in a two-fre-
quency band at GHz levels and the results obtained
are shown. Around 50-dB shielding-effectiveness le-
vels were reached experimentally from the measure-
ments.
• Thus, experimental results obtained are promising for
MIL composites to be appropriate candidate mate-
rials for military applications with their electromag-
netic as well as mechanical properties.
5 REFERENCES
1 K. S. Vecchio, Synthetic multifunctional metallic-intermetallic lami-
nate composites, JOM, 57 (2005) 3, 25–31, doi:10.1007/s11837-
005-0229-4
2 B. Besen, M. Kalayci, T. Yener, S. Zeytin, Some Properties Of
Ni-AlNi Metallic-Intermetallic Laminate Material, Journal of Inter-
national Scientific Publications: Materials, Methods & Technologies,
7 (2013) 2, 390–396
3 R. R. Adharapurapu, K. S. Vecchio, F. Jiang, A. Rohatgi, Fracture of
Ti-Al3Ti metal-intermetallic laminate composites: Effects of lamina-
tion on resistance-curve behavior, Metallurgical and Materials Tran-
sactions A, 36 (2005) 11, 3217–3236, doi:10.1007/s11661-005-
0092-5
4 L. Peng, H. Li, J. Wang, Processing and mechanical behavior of
laminated titanium–titanium tri-aluminide (Ti–Al3Ti) composites,
Materials Science and Engineering A, 406 (2005) 1, 309–318,
doi:10.1016/j.msea.2005.06.067
5 X. Yang, X. Peng, F. Wang, Size effect of Al particles on the struc-
ture and oxidation of Ni/Ni3Al composites transformed from electro-
deposited Ni–Al films, Scripta Materialia, 56 (2007) 6, 509–512,
doi:10.1016/j.scriptamat.2006.11.016
6 A. Rohatgi, D. J. Harach, K. S. Vecchio, K. P. Harvey, Resistance-
curve and fracture behavior of Ti–Al3Ti metallic–intermetallic lami-
nate (MIL) composites, Acta Materialia, 51 (2003) 10, 2933–2957,
doi:10.1016/S1359-6454(03)00108-3
7 Y. Cao, C. Guo, S. Zhu, N. Wei, R. A. Javed, F. Jiang, Fracture beha-
vior of Ti/Al3Ti metal-intermetallic laminate (MIL) composite under
dynamic loading, Materials Science and Engineering A, 637 (2015),
235–242, doi:10.1016/j.msea.2015.04.025
8 K. H. Zuo, D. L. Jiang, Q. L. Lin, Mechanical properties of
Al2O3/Ni laminated composites, Materials Letters, 60 (2006) 9–10,
1265–1268, doi:10.1016/j.matlet.2005.11.010
9 L. Z. Zhang, D. N. Wang, B. Y. Wang, R. S. Yu, L. Wei, Identifi-
cation of lattice vacancies in the B2-phase region of Ni–Al system by
positron annihilation, Journal of Alloys and Compounds, 457 (2008)
1–2, 47–50, doi:10.1016/j.jallcom.2007.03.065
10 F. L. Zhang, Z. F. Yang, Y. M. Zhou, C. Y. Wang, H. P. Huang, Fabri-
cation of grinding tool material by the SHS of Ni–Al/diamond/dilute,
International Journal of Refractory Metals and Hard Materials, 29
(2011) 3, 344–350, doi:10.1016/j.ijrmhm.2010.12.013
11 C. T. Wei, V. F. Nesterenko, T. P. Weihs, B. A. Remington, H. S.
Park, M. A. Meyers, Response of Ni/Al laminates to laser-driven
compression, Acta Materialia, 60 (2012) 9, 3929–3942,
doi:10.1016/j.actamat.2012.03.028
12 ASM Handbook, Vol. 3: Alloy Phase Diagrams, ASM International,
2001
13 P. Saini, M. Aror, Microwave Absorption and EMI Shielding Beha-
vior of Nanocomposites Based on Intrinsically Conducting Poly-
mers, Graphene and Carbon Nanotubes, Chapter 3, In: A. De Souza
Gomes (Ed.), New Polymers for Special Applications, InTech, 2012,
doi:10.5772/48779
14 C. R. Paul, Introduction to electromagnetic compatibility, 2nd Edition,
John Wiley & Sons, 2006, 184
15 S. Geetha, K. K. Satheesh Kumar, C. R. K. Rao, M. Vijayan, D. C.
Trivedi, EMI shielding: Methods and materials-A review, Journal of
Applied Polymer Science, 112 (2009) 4, 2073–2086,
doi:10.1002/app.29812
16 O. Cerezci, S. ªeker, ª. Yener, B. Kanberoðlu, M. H. Niºancý, Ev,
Ofislerde GSM Frekanslý Radyasyondan Bireysel Korunma,
EMANET, Yýldýz Teknik Üniversitesi, Beºiktaº, Ýstanbul 2013,
372–376
T. YENER et al.: ELECTROMAGNETIC-SHIELDING EFFECTIVENESS AND FRACTURE BEHAVIOR ...
902 Materiali in tehnologije / Materials and technology 50 (2016) 6, 899–902