AlSi11/ Si3N4 interpenetrating composites
Tribology properties of aluminum matris composites
Hongyan WANG, Shouren WANG*, Gaozhi LIU
School of Mechanical Engineering
University of Jinan
Jinan, China
Yingzi WANG
School of Materials Science
University of Jinan
Jinan, China
Abstract— In present work, the metal-ceramic
interpenetrating composites (IPCs) as AlSi11/ Si3N4 are
fabricated by infiltrating technique. IPCs exhibit special
characterization of brittle ceramic reinforced phase introduced
by ductile metal matrix phase. During the sliding wear
processes, IPCs exhibit four wear mechanism such as initial
adhesive wear, mixed adhesive and abrasive wear, adhesive
wear and final abrasive wear. Reinforcements inhibit plastic
flow and restrict propagation of wear cracks. Increase in the
volume fraction of reinforcement leads to improvement in the
wear resistance. Under higher load and lower round speed
conditions, the friction coefficients are lower than that of
relative conditions.
Keywords-interpenetrating composites; Si3N4; aluminum;
network structure;tribology
1. Introduction
It is well known that metal–ceramic interpenetrating
composites (IPCs) exhibit superior performance, mechanical
stability and failure tolerance such as excellent wear resistance,
high fracture toughness and high hardness [1-3]. IPCs have
attracted considerable attention as result of their unique
mechanical properties, which can be widely used in aerospace
and automotive industries and other structural applications [4].
Especially, aluminum matrix composites reinforced by Si3N4
have the potential for use in aerospace applications owing to
Si3N4 ceramics processing higher Young’s modulus, combined
with lower density, higher melting point and excellent
oxidation resistance. Moreover, metal-ceramic interpenetrating
composites have a large use in the occlusal contact area
accompanying with high forces, such as mechanical production
of oil pump, piston, die and bearing [5].
Tribology properties of IPCs can generally be enhanced by
introducing a secondary phase (s) as three dimensional network
structure into the metal matrix materials. There is a plethora of
papers by experimentalists who have studied the wear behavior
of metal composites reinforced by ceramics secondary phases
[6]. However, there has little work to study the abrasive
behavior of Si3N4/AlSi11 interpenetrating composites. The
abrasive wear resistance of Si3N4/AlSi11 interpenetrating
composites has been found to be significantly lower than that
of AlSi11 metal owing to the changes of microstructure, the
morphology, the volume fraction and mechanical properties of
three-dimensional network reinforcing phase, and interface
between matrix and reinforcement.
So, in present paper, an attempt has been made to evaluate
the dry sliding wear behavior of Si3N4/AlSi11 interpenetrating
composites over a range of loads and sliding speeds. The
microstructures of them are discussed. And, the sliding wear
mechanisms of them are studied.
2. Experimental Procedure
A reticulated polyurethane (PU) was chosen as a template
to prepare the porous perform (skeleton as the reinforcement of
IPCs) by the replica technology. The pore size of the PU was
about to 5-10 ppi (pores per inch). Si3N4 powder (Si3N4ı
97%, diameter İ100 ȝm) was used as starting material. The
sintering temperature is 1400°C at 200°C/h.
The composition of the alloys used in this study was
Al-11wt.%Si which chemical composition is shown in Table 1.
In order to eliminate the influence of impurities, the melt need
to be refined. Alloy was melted in a clay–graphite crucible
under Ar atmosphere. The liquid metal was infiltrated into the
preform skeleton by pressure infiltration technology.
Si3N4/AlSi11 interpenetrating metal-ceramic composites
reinforced by different volume fraction as 12, 20%,
respectively, were fabricated. The micro-structural
characterization of IPCs and porous perform were performed
on a scanning electron microscope (SEM. Hitachi, S-2500)
which was shown in Figure 1. Samples for making
micrographs were mounted in a holder and polished using SiC
papers (up to 2000 grit). The microstructures of matrix were
characterized using SEM equipped with an energy dispersive
spectroscopy (EDS) which was shown in Figure 2.
The specimens were subjected to wear test under dry
sliding condition. The tests were conducted on 6mm diameter,
35 mm long cylindrical specimens against a rotating steel disc
which is covered by corundum sand paper. A pin-on-disc wear
test machine was used for carrying out wear tests (Figure 3).
The tangential friction force and wear depth were monitored
with the help of electronic sensors. These two parameters were
measured as a function of load and sliding distance. For each
type of material, tests were conducted at four different nominal
loads (100, 150, 200 and 250 N) at different sliding speed as
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100, 200, 300 and 400 rpm. Wear tests were carried out at
temperature of 200°C without lubrication for 20 min.
Table 1 Chemical composites of metal matrix
Cu Mg Si Fe Mn
Zn Ti Al
4.7600 0.5900 17.0600 0.1890 0.0160 0.0060 0.0016
Bal.
Figure 1. 3-D network structure and interpenetrating composites:
(a)skeleton and (b) IPCs
(b)
Figure 2. Al matrix alloy and its EDS analysis: (a) SEM micrograph of Al
matrix alloy and (b) EDS analysis
Figure 3. Pin-on-disc wear test machine
3. Results and Discussion
Due to IPCs possessing a continuous metal network
with VAlSi11VSi3N4, it has a high toughness. Due to IPCs
possessing interpenetrating ceramic phase, it has a higher
Young’s modulus, hardness and load bearing capacity than
MMCs. Wear resistance properties research for IPCs is
interesting. There are many factors inÀuencing on wear
behavior, which make it difficult to compare results
from different laboratories or different testing
methods [7]. The friction coefficients were tested with different
time under different load which were shown in Figure 4 (a).
It is shown that under lower load, the friction coefficient curve
is not steady, while under higher load, it is steady. Under
higher load conditions, the friction coefficients are lower than
lower load conditions. Figure 4 (b) shows the friction
coefficients- time relations under different round speed. It is
shown that under lower round speeds, the friction coefficients
are higher than higher round speeds. The reason is that higher
load and round speeds causes soft matrix metal covering
with the wear surface. This effect would require more testing to
con¿rm and explain it. It is well known that the wear resistance
of the IPCs increases with increasing Si3N4 content. The width
and depth of the wear grooves of the Si3N4 12wt.% composites
are narrower and shallower than those of Si3N4 20wt.%
composites. The grooves become even more indistinct with the
increasing Si3N4 content.
400ȝm
400ȝm
(a)
(b)
matrix
reinforcement
(a)
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0200 400 600 8001000
0.30
0.32
0.34
0.36
0.38
0.40
0.42
0.44
0.46
0.48
0.50
0.52
0.54
0.56
0.58
0.60
friction coefficient
time/s
100N
150N
200N
250N
(a) Friction coefficient-time curve under different load
100 200 300 400 500
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
friction coefficient
time/s
100rpm
200rpm
300rpm
400rpm
(b) Friction coefficient-time curve under different speed
Figure 4. Friction coefficient-time curve under different wear conditions
Figure 5 shows the worn surface of IPCs and its metal
matrix. It is shown that with an increase in test time, the
morphology of the worn surface changes from fine scratches to
distinct grooves. The worn surfaces of the metal matrix and the
ceramic skeleton are different significantly. There is light and
shallow scratch on the surface of ceramic reinforcement which
is shown in Figure 5 (a). The surface exhibits a fractured and
broken characterization. It is shown that ceramic skeleton is
undergone abrasive wear. There are smooth and rough areas
to be seen. The smooth areas are due to the
polishing effect at the start of the wear test. The
damaged layer formed during this polishing stage is fatigued
with further sliding distance. The revealing angular ceramic
grains cause microcracks forming and result in the damaged
spall. There is a severe surface damage on the surface of metal
matrix which is shown in Figure 5 (b). Some deep and
symmetrical furrows on the worn surface of metal matrix are
observed which are described as local damage and even
fractured flakes. The metal matrix showed adhesive wear with
extensive plastic deformation, evidenced by smearing at the
edge of the wear track.
Figure 5. The worn surface of : (a) ceramic reinforcement and (b) metal
matrix
This cyclic wear process is illustrated schematically in
Figure 6. The overall wear processes divided into four stage as
initial stage (I), continual stage (II), middle stage (III) and final
stage (IV). Each individual stage is not steady state process. In
initial abrasive wear process (Figure 6a), the wear surface is
surrounded by matrix material that is subjected to compressive
loading. Owing to relatively soft and ductile performance of
the matrix, this stage is relatively short and considered as the
conventional wear mechanism. On the other words, metal
matrix alloy was cut by the counter as plates, which was either
removed out of the cells or smeared along the sliding direction.
With the continuing abrasive wear, the reinforcement phase is
gradually exposed and the compressive load is carried by
matrix and reinforcement together (Figure 6b). Owing to the
high modulus of ceramic reinforcement relative to the matrix,
however, this stage is hold for long time. With the wear
processes going on, the soft and ductile matrix gradually
recedes away and the compressive load is carried primarily by
reinforcement phase (Figure 6c). In the finial stage, the
exposed reinforcement phase finally failed by fracture due to
its brittleness (Figure 6d). Then the wear surface turn flat and
the first stage repeat again. This cyclic processes result in the
removal of materials and occurrence of abrasive wear. The four
stage wear behavior has also been observed by other
researchers [8-10]. The AlSi11/Si3N4 interpenetrating
composites showed a similar transition processing as initial
adhesive wear (I), mixed adhesive and abrasive wear (II),
adhesive wear (III) and final abrasive wear (IV).
80ȝm
100ȝm
(a)
(b)
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4. Conclusions
A AlSi11/Si3N4 interpenetrating composites (IPCs) were
fabricated by infiltrating technique. The friction coefficient
related to wear load, wear speed and wear time were discussed.
The worn surface damage of IPCs is studied based on the lower
and upper extreme cyclic wear behavior. Owing to the special
topology structure characteristic, aluminum alloy reinforced
with ceramic network structure can improve dry sliding wear
resistance. Reinforcements inhibit plastic flow and restrict
propagation of wear cracks. Increase in the volume fraction of
reinforcement leads to improvement in the wear resistance.
Reinforcements are crushed into small pieces regardless of the
morphology of original reinforcement present in the composite,
hence wear resistance of composite is marginally affected by
the reinforcement volume fraction. The wear mechanisms in
IPCs could be classified into four modes as initial adhesive
wear (I), mixed adhesive and abrasive wear (II), adhesive wear
(III) and final abrasive wear (IV).
Ceramic skeleton
Metal matrix
(a) initial stage
Ceramic skeleton
Metal matrix
5. Acknowledgment
This work was supported by the National Natural Science
Foundation of China (Grant No. U1134101) and the Natural
Science Foundation of Shandong Province (ZR2011EMM003)
and science technology development project of ministry of
education of Shandong (J10LD19).
(b) continual stage
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