TEMPERATURE EFFECT ON C/SiC COMPOSITE WITH SiC NANOWIRES GROWN IN
SITU
Bingbing Pei1,2, Yunzhou Zhu1,* , Zhengren Huang1
1
The State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai
Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, PR China
2
Graduate Schools of the Chinese Academy of Sciences, Beijing 100049, PR China
ABSTRACT
The SiC nanowires were introduced in ceramic matrix to improve the strength and toughness
of C/SiC composites through polymer impregnation and pyrolysis process. The effects of
temperature on the in situ growth and morphology of SiC nanowires were evaluated. The
important effects of SiC nanowires grown in situ on properties of the composite, such as density,
flexural strength and interface characters were studied. C/SiC composites show better and higher
flexural strength and fracture toughness incorporation of SiC nanowires.
INTRODUCTION
C/SiC composite is considered as a promising high-temperature structural material in
aerospace industry and aircraft components, due to their low density, low coefficient of thermal
expansion, abrasion resistance and high reliability.1-2 Although the fracture tolerance of bulk SiC
can be readily improved by the incorporation of carbon reinforcement fibers, such gains in
fracture tolerance are basically from the fiber/matrix interfacial debonding and
bridging/deflection of transverse matrix cracks by the fibers. However, the SiC matrix displays a
brittle behavior similar to its bulk counterparts.3-5 Therefore, it is of great importance and
interesting to strengthen and toughen these week points.
Silicon carbide (SiC) nanowires have been widely researched as reinforcing elements in
ceramic-matrix composites (CMCs) for their excellent performance in mechanical and thermal
properties.6-7 There could be properties unseen in conventional composites to combine SiC
nanowires and conventional fibers together for multi-scale reinforcement, including density,
flexural strength and fracture behavior.8-10 As few researches about the synthesis and properties
of SiC nanowires-C/SiC composite, this work estimates the temperature effect on the SiC
nanowires in situ growth and the induced fracture based on microscopic observation.
In our study, SiC nanowires were introduced into carbon fiber fabrics by pyrolysis of
polycarbosilane with ferrocene catalyst. The main interests were variation of SiC nanowires
grown in situ and as-prepared composites properties such as, density, flexural strength and
interface characters that affected by different in situ growth temperature.
EXPERIMENTAL
T700 carbon fiber (Toho Tenax Co., Japan) was used for composite preparation. Typical
parameters of the carbon fiber are listed in table 1. The preforms were fabricated by periodic
layers of 12K long fibers and disorder short fibers. The fiber volume fraction in the preform was
controlled at about 26%. The PCS (National University of Defense and Technology, China) was
chosen as the preceramic polymer for matrix derivation in the present experiment. The ceramic
yield is 60.5% by TG test. The preforms were first infiltrated by a kind of slurry containing
catalyst ferrocene, which had a mass ratio 3:97 with PCS. After drying, the samples underwent
different high temperature to convert the polymer into ceramic matrix and in situ growth SiC
nanowires in argon atmosphere. One preform was underwent slurry without catalyst for
comparison. Subsequently, another five PIP cycles using PCS as precursor (without catalyst)
were undertaken to densify the samples. The pyrolysis step was conducted at 1300℃ in flowing
argon atmosphere. The as-prepared composites were cut and ground into 3 mm × 4 mm × 36 mm
rectangles for open porosity, bulk density and three-point-bend testing. The Archimedes method
was used to measure the density and open porosity of samples. The flexural strength by
three-point-bend testing was conducted on the Instron 5566 (Canton, MA) universal testing
machine, with a cross-head speed of 0.5 mm/min and a span of 30 mm. Yong’s modulus was
calculated from the data recorded during three-point-bend testing. Fracture toughness was
measured by single edge notched beam (SENB)，with a notch depth of 3.00 mm, dimension of 3
mm × 6 mm × 36 mm, a cross-head speed of 0.05 mm/min and a span of 20 mm. The fracture
surface was investigated by Field emission scanning electron microscope (FESEM, JEOL 6700F,
Tokyo, Japan).
TableⅠ. Properties of T700 carbon fiber.
Type
Diameter
(μm)
Density
(g/cm3)
Filaments
/yarn
Tensile
strength
(MPa)
T700
6
1.80
1200
4900
Elastic strength
（GPa）
296
RESULTS AND DISCUSSION
Size And Morphology
The thermodynamics indicates that the thermal reduction reaction in the pyrolysis of PCS
only happen when temperature goes to 1772.4K.
SiO2（s）+3C(s)SiC(s)+2CO(g)
(Eq. 1)
It contains two steps
SiO2（s）+C(s)SiO(g)+CO(g)
(Eq. 2)
SiO（s）+2C(s)SiC(s)+CO(g)
(Eq. 3)
SiC matrix would change to SiC nanowires in equation 3 in case of the existence of catalyst.
Figure 2 shows the surface morphology of the carbon fiber fabric underwent different in situ
reacting temperatures. It can be seen that SiC nanowires cannot be observed when temperature
below 1300℃. SiC nanowires start to grow when temperature comes to 1500℃, which become
shorter but thicker as temperature increase to 1700℃. The spherical cap on the tip of the
nanowires indicates that the nanowires grew through vapor-liquid-solid (VLS) mechanism.10-11
Figure 2. The surface morphology of the carbon fiber fabrics after the first cycle. (a) 1100℃; (b)
1300℃; (c) 1500℃; (d) 1700℃; (e and f) Partially enlarged morphology of SiC nanowires.
Characterization
As can be seen in table 2, the bulk density increased when temperature below 1300℃, while
the open porosity had an opposite tendency. As the temperature increased from 1300℃ to
1700℃, the density of C/SiC composites with SiC nanowires decreased from 1.78 g/cm3 to 1.62
g/cm3 , and the corresponding open porosity increased from 19.4 % to 27.1 %, which may due to
the lower density of SiC than SiO2 in equation 3. The flexural strength and fracture toughness
were improved by incorporation of SiC nanowires. The as-prepared C-1500 exhibited better
properties than others even with a density of 1.66 g/cm3, which could due to the longer and more
SiC nanowires. The typical fracture behaviors of the different as-prepared C/SiC composites
subjected to flexural stress are shown in figure 3. The curves indicate a typical non-brittle
fracture behavior for all as-prepared composites. However, C/SiC composites with SiC
nanowires show better flexural strength. Figure 4 shows the fracture surface of C/SiC composites,
which indicates that interfacial debonding, pullouts and breaking of SiC nanowires are observed
in C-1500 and C-1700，a substantial contribution to the increased strength and toughness of the
matrix incorporation of the elastic deformation of SiC nanowires. The tough and strong SiC
matrix transfer loading effectively and suppress the crack propagation to the carbon fibers,
resulting high flexural strength and toughness of composites. C-1700 shows a little decrease in
properties due to the damage of carbon fiber in 1700℃. Figure 4 shows the fracture surface of
C-1500, SiC nanowires net structures are observed in SiC matrix and between carbon fiber,
resulting in the optimization of structure of inside pores and strengthen SiC matrix.
TableⅡ. Properties of as-prepared C/SiC composites.
Composite
Temperature
（℃）
Density
(g/cm3)
Porosity
(%)
C-1100
1100
1.72±0.01
19.7±0.3
Flexural
strength
(MPa)
69±5
Fracture
toughness
(MPa m1/2)
1.97±0.2
C-1300
C-1500
C-1700
1300
1500
1700
1.78±0.02
1.66±0.02
1.62±0.03
19.4±0.2
23.7±0.4
27.1±0.1
87±6
166±14
144±7
2.64±0.5
5.09±0.6
4.95±0.3
Figure 3. Flexural stress–displacement curves of the as-prepared C/SiC composites.
Figure 4. The fracture surface morphology of (a) C-1500 and (b) Partially enlarged morphology.
CONCLUTION
SiC nanowires were introduced into carbon fiber preform by impregnating of PCS precursor
with ferrocene catalyst, followed by the pyrolysis at different high temperature. The temperature
effects the in situ growth and morphology of SiC nanowires effectively. The density and flexural
strength were improved incorporation of SiC nanowires. The present results clearly show the
possibility of increasing strength by introducing SiC nanowires into carbon fiber preform.
Further investigation will be performed on optimization of carbon fiber fabric, fiber interface
layers and matrix modification to optimize the mechanical properties.
ACKNOWLEDGEMENT
This work has been supported by the National Natural Science Foundation of China under
Grant No. 51102256 and Institute Innovation Foundation under Grant No. Y12ZC2120G.
REFERENCES
1
S. Schmidt, S. Beyer, H. Knabe, H. Immich, R. Meistring, A. Gessler, Advanced ceramic matrix
composite materials for current and future propulsion technology applications, Acta
Astronautica , 55, 409-420 (2004).
2
R. Naslain, Design, preparation and properties of non-oxide CMCs for application in engines
and nuclear reactors: an overview, Composites Science and Technology , 64, 155-170 (2004).
3
Q. Feng, Z. Wang, H.J. Zhou, P. He, L. Gao, Y.M. Kan, X.Y. Zhang, Y.S. Ding, S. Dong,
Microstructure analysis of Cf/SiC–ZrC composites in both fabrication and plasma wind tunnel
testing processes, Ceramics International, 2013.
4
Y. Wang, H. Wu, Microstructure of friction surface developed on carbon fibre reinforced
carbon–silicon carbide (Cf/C–SiC), Journal of the European Ceramic Society, 32, 3509-3519
(2012).
5
R.R. Naslain, The design of the fiber-matrix interfacial zone in ceramic matrix composites,
Composites Part A, 29, 1145-1155 (1998).
6
S. Zhu, H.-A. Xi, Q. Li, R. Wang, In Situ Growth of beta-SiC Nanowires in Porous SiC
Ceramics, Journal of the American Ceramic Society, 88, 2619-2621 (2005).
7
J.-m. Pan, X.-h. Yan, X.-n. Cheng, Q.-b. Lu, M.-s. Wang, C.-h. Zhang, Preparation of SiC
nanowires-filled cellular SiCO ceramics from polymeric precursor, Ceramics International, 38,
6823-6829 (2012).
8
Y. Zhu, Z. Huang, S. Dong, M. Yuan, D. Jiang, Manufacturing 2D carbon-fiber-reinforced SiC
matrix composites by slurry infiltration and PIP process, Ceramics International, 34, 1201-1205
(2008).
9
X. Yao, S. Tan, Z. Huang, S. Dong, D. Jiang, Growth mechanism of β-SiC nanowires in SiC
reticulated porous ceramics, Ceramics International, 33, 901-904 (2007).
10
W. Yang, H. Araki, A. Kohyama, Q. Hu, H. Suzuki, T. Noda, Growing SiC nanowires on
Tyranno-SA SiC fibers, Journal of the American Ceramic Society, 87, 733-735 (2004).
11
W. Yang, H. Araki, C. Tang, S. Thaveethavorn, A. Kohyama, H. Suzuki, T. Noda, Single-crystal
SiC nanowires with a thin carbon coating for stronger and tougher ceramic composites, Advaced
Materials, 17, 1519-1523 (2005).