st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Thick Metallic/Composite Coating on C-FRP Substrate by Plasma Spraying
Masahiro Fukumoto 1, Amirthan Ganesan1, Motohiro Yamada1 and Yoshiki Tsunekawa2
1
Department of Mechanical Engineering, Toyohashi University of Technology,
Toyohashi, Aichi, Japan
2
Toyota Technological Institute, Aichi, Japan
Abstract: C-FRP composite is most attractive candidate to fabricate large constructive bodies
like airplane, automobile, blade of the wind power generation and so on. One of the key issues
associated with these components is the lightning strike and consequent damage during practice. Therefore, in this study, atmospheric plasma spray and cold spray were used to fabricate
thick oxide free copper coatings onto the C-FRP substrate. Results showed that the coating
has sufficiency adhesion strength with improved electrical conductivity.
Keywords: Cold spray, Atmospheric plasma spray, C-FRP, Metallization
1. Introduction
Carbon fiber-reinforced plastic (C-FRP) has been vastly
used in aircraft fuselage due to its light weight, high
specific stiffness and high specific strength. However, the
poor electrical conductivity of the C-FRP may cause catastrophic failure in the fuselage and consequent casualties
if there is any lightning strike during the cruise. Therefore,
the conductive coating on the C-RRP substrate is essential
and inevitable. Although there are many coating techniques, namely vapor phase deposition, electro deposition,
and electroless deposition [1-4], the cold spraying is a
successful and promising coating technique for many engineering applications due to its high-rate and high-dense
coating development abilities. Nevertheless, their practical use in polymer substrate is still in the fledgling phase
due to the high erosion. Therefore, the direct cold spray
coating on the C-FRP substrate is literally difficult to
achieve. Recently, Affi et al. [5] used the plasma spray
and cold spray combination to deposit the aluminum
coating on the C-FRP composite. The aluminum coating
was fabricated on the C-FRP substrate using plasma aluminum interlayer. It was discussed that the cold spray
technique, preferably using lower gas temperature, could
result a coating with low volume resistivity. Even though,
there is no report available on the topic of making copper
coating on the C-FRP substrate, using above procedure,
owing to the high strength of the copper materials.
The present study showed the feasibility of making the
copper coating on the C-FRP substrate using carefully
controlled spray parameters and the proper selection of
the powder morphology. The coating mechanical properties and the electrical conductivity were evaluated.
2. Experimental Procedure
Commercially available pure copper powders of two
different shape and sizes were used (Fukuda Metal Foil
and Powder Co., Ltd., Japan) as the feedstock materials.
The details are shown in Table 1. The cold spray system
used in this study was commercially available with the de
Laval converging-diverging nozzle (Kinetics 4000, CGT,
Germany). Nitrogen was used as process gas. Spraying
parameters are shown in Table 2. C-FRP plate (provided
by Mitsubishi Rayon, Co. Ltd) was used as a substrate. It
has been made up of airplane grade epoxy resin having
heat resisting temperature of 180°C and PAN based carbon fiber as reinforcement (TR50S-6L). Details of CFRP
composite are shown in Table 3. An atmospheric plasma
spray system (APS: 9MB, Sulzer Metco) was used for
making an interlayer. The process conditions are given in
the Table 4. Long spray distance and sufficient substrate
cooling procedure were used to avoid C-FRP surface
damage by high temperature. Observation of coating surface and cross section was conducted using scanning
electron microscope (SEM: JSM-6390TY, JEOL Co. Ltd.).
The volume resistivity of sprayed coatings was measured
by four probe (terminals) method. The two outer probes
were used for sourcing current and the two inner probes
were used for measuring the resulting voltage drop across
the surface of the sample. To calibrate unit volume resistivity per-unit area cross-section, the measurement was
performed at several points with different distance of inner probe. Each sample was measured for three times and
the average was taken as a representative value.
Table 1. Powder properties
Powders
Spherical
Copper
Tin
Irregular
Copper
Epoxy
Shape
Size
(μm)
Spherical
+5 to -20
Spherical
+5 to -20
Dendritic
+5 to -45
Irregular
+10 to -70
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Table 2 Cold spray parameters
Gas
Pressure
MPa
Stand of
Distance
(mm)
Gun Traverse Speed
(mm/min)
2 and 3
30
500
Powder
Feed
Rate
(RPM)
5
Table 3 Properties of the CFRP
Fiber Trade Name
Fiber Tow Size
Linear Mass Density
Fiber Density
Strength
Modulus
Matrix
Curing Temperature
Composite Structure
Tow Density/25mm
Layer
Mass per Unit Area
Lay-Up Sequence
Layer
of
TR50S-6L Diameter 7μm
24000
400mg/m
1.82g/cm3
4900MPa
240GPa
Airplane Grade
Epoxy
180°C
Satin Pattern
Vertical 8.75 and
Horizontal 8.75
8
280g/mm2
[+45/90/-45/90]/
[90/-45/90/+45]
Table 4 Process parameters of plasma spray interlayer
Primary gas flow rate (l/min Ar)
Secondary gas flow rate (l/min
N2)
Arc current (A)
Arc voltage (V)
Spray distance (mm)
Traverse speed (mm/s)
47.2
1.89
Carrier gas and flow rate (l/min)
Ar and 2
Powder and Size (μm)
Cu and 75
Layers
2 and 4
500
56
150
202
3. Results and Discussion
The C-FRP substrate was treated mechanically prior to
the plasma spray coating; otherwise there was no coating
development on the C-FRP substrate. Figure 1 shows the
laser optical micrograph on surface profile of the C-FRP
substrate before and after the mechanical treatment and
their Ra roughness values were 6.6 and 9.3 μm, respectively. It is obvious from the figure that mechanical treatment leads to surface fracture and thus higher surface
roughness in m order.
(a)
(b)
Fig. 1 Laser optical micrograph of the surface profile of
(a) untreated C-FRP and (b) mechanically treated C-FRP.
Figure 2 shows the copper coating developed on the
C-FRP substrate using plasma spray interlayer. As shown
schematically in Fig. 2(a), the first thin copper layer coating with 50-60μm thickness was made using the plasma
spray. Then, a thick copper coating with about 1mm
thickness was made by dendritic copper powder using
cold spray technique. The copper spike in Fig. 1(b) shows
the feasibility of making very thick copper coating on the
C-FRP substrate. Figure 1(c) shows the cross sectional
micrograph near interface region, at where the copper
coating and the substrate polymer adheres quite well
without any de-bonding.
(a)
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21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
(b)
(c)
Fig. 2 Copper coating on the C-FRP substrate (a) schematic diagram, (b) overview of the copper coating on the
C-FRP substrate and (c) cross section microstructure of
the coating.
strength values. The fracture surface analysis showed that
the fracture exactly occurred at the polymer-plasma interlayer for the both cases. It is inferred that the main bonding mechanism between the copper splat and the polymer
is mechanical anchoring.
Figure 4 shows the splat collection test on the C-FRP
substrate. There was no significant difference in the splat
morphology on the untreated and mechanically treated
samples, while there was no coating build-up on the untreated surface. It is believed that the surface roughness
plays a vital role on the coating build up on the mechanically treated samples. It has been stated that the high surface roughness, however, is believed to be beneficial for
the good wetting of the C-FRP substrate by the copper
splat due to the capillary action and therefore a conformal
contact with the polymer substrate.
(a)
(b)
Fig. 4 Copper splats on (a) untreated C-FRP and (b)
mechanically treated C-FRP substrate.
Fig. 3 Adhesion strength of the coating.
The plasma sprayed coating having thickness of
50-60μm was considered for the adhesion strength test.
As it can be seen in the Fig. 3, the plasma sprayed coating
with interlayer by plasma spraying has higher adhesion
strength as compared to the plasma-cold spray combined
coating. It is believed that the particle impact energy and
the thermal input by the cold spray may attribute to
weaken the interlayer and resulted in poor adhesion
Finally, Fig. 5 shows the electrical resistivity measurement results on the pure bulk copper, only plasma sprayed
interlayer coating and the plasma-cold spayed copper
coating. The plasma sprayed interlayer shows very high
electrical resistance. On the other hand, the electrical resistivity of the plasma-cold sprayed copper coating is well
improved, as compared to the earlier one. It is believed
that the high electrical resistivity of the plasma sprayed
interlayer coating may arise from the excess oxidation of
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
the copper particle while traveling in the plasma plume.
During the coating, as they impact on the surface to be
coated, these oxide scales are segregated along the grain
boundary and the inter-particle boundaries and resist the
electron path way. On the other hand, less oxidization,
due to low process temperature and the dense coating
structure may bring about the lower electrical resistivity
in the plasma-cold spray coating.
Acknowledgments
The authors greatly acknowledge the financial support
from the Aichi Prefecture Knowledge Hub Project, No.
P1-G1-S1. The authors are grateful to Mitsubishi Rayon,
Co. Ltd for supplying the C-FRP composite materials.
The authors are also acknowledging the support of Dr.
Mohammed Shahien while performing the atmospheric
plasma spray.
5. References
[1]
[2]
[3]
[4]
Fig. 5 Electrical resistivity of the copper coating on the [5]
C-FRP substrate.
4. Conclusion
Following conclusions were obtained in this study.
1) Thick copper coating was successfully fabricated using
plasma-cold spray combination.
2) The coating adhesion strength and the electrical conductivity were fairly improved.
3) Further study is needed to ascertain the bonding
mechanism which will help to improve further the adhesion strength and conductivity of the coating.
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W. Zheng, S. C. Wong, Composite Science and
Technology, 63 (2003).
F. A. Fisher, J. A. Plumer, R. A. Perala, Air- craft
Lightning Protection Handbook, Federal Aviation
Administration, 1989.
J. Affi, H. Okazaki, M. Yamada, M. Fukumoto, Materials Transaction, 9, 52 (2011).