Wear 253 (2002) 357–368
Two-body abrasive wear behaviour of aluminium alloy–sillimanite
particle reinforced composite
M. Singh∗ , D.P. Mondal, O.P. Modi, A.K. Jha
Regional Research Laboratory (CSIR), Hoshangabad Road, Near Habibganj Naka, Bhopal 462026, Madhya Pradesh, India
Received 3 May 2001; received in revised form 13 May 2002; accepted 27 May 2002
Abstract
In the present paper two-body abrasive wear behaviour of the cast aluminium alloy and aluminium alloy–10 wt.% sillimanite particle
composite has been studied at different applied loads and abrasive sizes for different sliding distances. It was noted that the wear rate
decreased with sliding distance and approached to a stable value and increased with increase in abrasive size and applied load irrespective
of the materials. It was interesting to note that at 25 ␮m abrasive size, composite showed superior wear resistance to that of alloy but
at 200 ␮m abrasive size, the former one suffered from inferior wear resistance than the later one irrespective of applied load. In the
intermediate abrasive size (100 ␮m) the composite exhibited superior wear resistance than that of alloy at lower applied load, whereas at
higher applied load the trend is reversed. These facts have been studied through wear surface, subsurface and wear debris analysis.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Two-body abrasive wear behaviour; Aluminium alloy; Sillimanite particle composite
1. Introduction
Metal matrix composites (MMCs) are gaining importance due to their properties like high specific strength, high
specific stiffness, improved high temperature performance,
superior wear and seizure resistance, etc. The properties
of these composite materials can be tailored by suitably
selecting the matrix alloy and the dispersoid phase. Due
to such versatile properties, these composite materials hold
potential for applications in automotive, aerospace, sporting
goods and in general engineering industries [1]. Different
ceramic materials such as silicon carbide, alumina, zircon,
etc. have been used as dispersoid for synthesising composites [2–8]. However, limited attempts have been made to
use natural minerals like granite, sillimanite, corundum, etc.
for synthesising aluminium alloy composites, even though
these natural minerals have great potential to be used as
reinforcement [9–13]. Because of superior wear resistance
in addition to higher strength and stiffness, the composites
have found wide applications in automobile components
like brake drum, piston, cylinder liners, etc. [1,14]. Out of
different wear processes, these components primarily suffer
either from abrasive or sliding wear.
∗ Corresponding author. Tel.: +91-755-587105/580836/782360;
fax: +91-755-587042.
E-mail address: [email protected] (M. Singh).
The abrasive wear of a material is defined as the progressive loss of material due to abrasive action of hard
particles present between the counter surfaces [15]. The
abrasive wear depends on various factors like abrasive size
[16–22], rake angle of abrasives [16,23,24], applied load
[16,21,22,25] and shape, size, volume fraction of the dispersoid phases [26–28]. In addition to these factors the
abrasive wear rate of a material also depends on the surface hardness [21,23,25,29] and materials properties like
fracture toughness [23,25,30–32].
The abrasive wear rate is correlated with hardness and
applied load by Hornbogen [25] by the following relation:
W =
K0 Edeff P
Ecoeff H
(1)
where K0 is the wear coefficient which is defined as the probability of formation of wear particles, P the applied load, H
the surface hardness of the material, Edeff the strain at asperities and Ecoeff is the strain associated with crack growth
within asperities. The term Ecoeff takes into account the
fracture toughness of a material which also dictates the wear
rate. Atkins [33] presented a criterion for removal of material during abrasive wear on the basis of fracture toughness,
plasticity and friction. Limited attempts have also been made
to assess qualitatively the effect of abrasive size on the wear
rate of materials [11,34,35]. Factorial design of experiment
by Mondal et al. demonstrated that wear rate of a material
0043-1648/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 3 - 1 6 4 8 ( 0 2 ) 0 0 1 5 3 - 9
358
M. Singh et al. / Wear 253 (2002) 357–368
increases more or less linearly with the abrasive size [34].
Das et al. [35] reported that especially at lower applied load
wear rate of SiC particle reinforced Al alloy composite remains invariant with abrasive size (when the abrasive size
is less than 50 ␮m). It is also reported by several investigators that relative size of wear grooves with respect to
ceramic reinforcement strongly governs the wear resistance
of composite [19,20]. According to these investigators, at
higher applied load and coarser abrasive sizes, the SiC or
Al2 O3 reinforced Al alloy composite suffers from higher
wear rate. This has been explained on the basis of greater
fracturing tendency, decohesion of ceramic reinforcements
due to combined effect of higher load and coarser abrasives
and wider and deeper wear groove formation.
However, very limited attempts have been made to characterise natural mineral reinforced composites in terms of
their abrasive wear characteristics [9–11]. It has been reported that granite particle reinforced composite exhibits
superior wear resistance than the unreinforced matrix alloy. No such attempts have been made to examine wear
behaviour of sillimanite particle reinforced Al alloy matrix
composite. The present paper aims to study the effect of
different factors like applied load, abrasive size and sliding
distance on the abrasive wear behaviour of sillimanite particle reinforced Al alloy composite. The wear mechanisms
under different experimental conditions have been studied
through examination of wear surface, subsurface and debris.
2. Experimental
2.1. Material preparation
Aluminium alloy (BS: LM6) nominally contains Si:
13 wt.%, Fe: 0.6 wt.%, Mn: 0.5 wt.%, Mg: 0.1 wt.%, Cu:
0.1 wt.% and Al: balance. It was selected as the matrix material. The ingots of aluminium alloy were cut into small
pieces and were melted in a graphite crucible using an oil
fired graphite furnace. After removing the dross, 10 wt.%
preheated sillimanite (Al2 SiO5 ) particles of size range
50–150 ␮m containing Al2 O3 : 55.0 wt.%, SiO2 : 37.04 wt.%,
TiO2 : 0.64 wt.%, Fe2 O3 : 0.35 wt.%, ZrO2 : 3.4 wt.%, CaO:
0.01 wt.% and MgO: 0.03 wt.% were incorporated in aluminium alloy melt by creating a vortex in the alloy melt
with the help of a mechanical stirrer. After thoroughly mixing the particles, composite samples were cast in permanent
Fig. 1. Schematic diagram of Suga abrasion tester.
M. Singh et al. / Wear 253 (2002) 357–368
359
disc mould of size 120 mm diameter and 6 mm thickness.
In order to compare the results with the matrix alloy, the
matrix alloy was also cast in a similar manner.
2.2. Microscopy
For microstructural study, samples of size 10 mm×10 mm
were cut from the composite samples and were cold mounted
in polyester resin. The cold mounted samples were polished
using standard metallographic procedure. The polished samples were etched in Keller’s etchant and then sputter coated
with thin layer of gold. The coated samples were examined in Joel JSM 5600 scanning electron microscope for microstructural study. The worn surface, subsurfaces and wear
debris were also studied in SEM.
2.3. Two-body abrasive wear test
Two-body abrasive wear tests were carried out on metallographically polished samples of size 40 mm×35 mm×4 mm
using a Suga make (Japan) abrasion tester (model: NUS-1).
The schematic diagram of test machine is shown in Fig. 1.
Emery papers of desired abrasive sizes were fixed on a wheel
(diameter 50 mm, thickness 12 mm) to serve as an abrasive
media. The samples were pressed against the abrasive media with the help of a cantilever mechanism. The specimens
were allowed to move to-and-fro against the abrasive media while the abrasive wheel also rotated slowly to enable
the samples to encounter fresh abrasive in each cycle prior
to traversing 26 m distance. Beyond this distance, degraded
abrasive is allowed to come back into contact with the specimen surface. The specimens were cleaned thoroughly before
and after wear tests and weight losses were measured using
the Mettler microbalance (upto 0.01 mg accuracy). The wear
rate was calculated from the weight loss data. The tests were
conducted at different abrasive sizes (25, 100 and 200 ␮m)
and applied loads (1, 3, 5 and 7 N) for siding distance upto
130 m in steps of 26 m.
3. Results
3.1. Microstructure
The microstructure of the composite showed dendritic
structure with reasonably uniform distribution of dispersoid
particles (Fig. 2a). A magnified view of the microstructure
(Fig. 2b) showed sound interfacial bonding of the dispersoid
particle with the matrix alloy. It is evident from this figure
that the eutectic silicon is of faceted needle shaped and the
concentration of eutectic silicon is more near the dispersoid
(sillimanite particles).
3.2. Wear behaviour
Abrasive wear rate of the composite and the matrix alloy
plotted as a function of sliding distance is shown in Fig. 3.
Fig. 2. Microstructure of the composite showing (a) uniform distribution
of sillimanite particles in the matrix and (b) sound interfacial bonding of
the dispersoid with the matrix alloy.
Fig. 3a represents the variation of wear rate with sliding
distance at a fixed load of 1 N for different abrasive sizes.
Similar plots for 3, 5 and 7 N loads are shown in Fig. 3b–d,
respectively. It is noted from these figures that the wear
rate decreased with increasing sliding distance and increased
with increasing abrasive size. For example, the wear rate of
the alloy at load 1 N for 25 ␮m abrasive size at a sliding
distance of 26 m is 5.3 × 10−11 m3 /m which is reduced to
3.9 × 10−11 m3 /m at a sliding distance of 130 m (Fig. 3a).
When the abrasive size increased from 25 to 200 ␮m the
wear rate of the alloy increased from 5.3 × 10−11 to 7.08 ×
10−11 m3 /m for a fixed sliding distance of 26 m at an applied
load of 1 N (Fig. 3a). Similarly the wear rate of the composite
at load of 1 N for 25 ␮m abrasive size at a sliding distance
of 26 m is 3.87 × 10−11 m3 /m which is reduced to 2.68 ×
10−11 m3 /m at sliding distance of 130 m. When the abrasive
size increased from 25 to 200 ␮m at an applied load of 1 N
and for a fixed sliding distance of 26 m the wear rate changed
from 3.87 × 10−11 to 7.8 × 10−11 m3 /m. It may also be
noted that at an applied load of 1 N, the wear rate of the
composite is less than that of the alloy for the abrasive size
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M. Singh et al. / Wear 253 (2002) 357–368
Fig. 3. Variation of wear rate with sliding distance at a load of (a) 1 N, (b) 3 N, (c) 5 N and (d) 7 N for different abrasive sizes for the matrix alloy and
composite.
M. Singh et al. / Wear 253 (2002) 357–368
of 25 and 100 ␮m. But at 200 ␮m abrasive size the trend is
reversed.
Fig. 3b represents the similar wear behaviour at an applied
load of 3 N with sliding distance for different abrasive sizes.
It may be noted that wear rate of the composite is higher
when the abrasive size becomes 200 ␮m like that observed in
Fig. 3a at 1 N load. On the other hand, when load increased
to 5 N, the composite showed higher wear rate than that
of the alloy at a sliding distance of 26 m even at abrasive
size of 100 ␮m as shown in Fig. 3c. However, at later stage
(i.e. at sliding distance greater than 54 m) the alloy showed
higher wear rate as compared to the composite. When the
abrasive size increased to 200 ␮m, the composite showed
higher wear rate than the alloy like that observed in Fig. 3a
and b. Fig. 3d also showed that wear rate of the materials
increased with increasing abrasive size. It is interesting to
note that the composite suffers from higher wear rate than the
alloy when the abrasive size ≥100 ␮m. However, at 25 ␮m
abrasive size, the composite showed less wear rate than the
361
alloy. Thus, it may be noted from these figures that the wear
rate of the materials, in general increased with increasing
abrasive size. But depending on the abrasive size and load
the relative wear rate of the composite with respect to the
alloy was varying.
Fig. 4 represents the variation of wear rate of the composite and the alloy as a function of applied load for a fixed
sliding distance of 26 m and for different abrasive sizes. It
may be noted that the wear rate of the alloy and the composite increased with increasing applied load. Also the wear
rate of the alloy and the composite depended on the abrasive size and the applied load. With fine abrasive size and
at low load, the wear rate of the alloy is more than the composite. However, the trend of the wear rate is reversed for
coarse size abrasives and at high load. It is evident from
this figure that the wear rate of the composite at 100 ␮m
abrasive size is even less than that of the alloy upto applied
load of 4.25 N, but beyond this load the composite suffers
from higher wear rate than that of the alloy. It signifies the
Fig. 4. Variation of wear rate with applied load for different abrasive sizes at a sliding distance of 26 m.
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M. Singh et al. / Wear 253 (2002) 357–368
dependence of load and abrasive size on the relative wear behaviour of the composite material over the alloy. At 200 ␮m
abrasive size the critical load (the load at which composite
showed higher wear rate than the alloy) was reduced to 1 N
as shown in figure.
In order to understand the effect of abrasive size more
clearly, the wear rate at 26 m sliding distance was plotted
as a function of abrasive size at different applied loads in
Fig. 5. It may be noted from this figure that there exists
a critical abrasive size depending on applied load above
which the composite suffers from higher wear rate than the
alloy. It is also noted that the critical abrasive size decreased
with increasing applied load and remained almost constant
beyond the applied load of 5 N. It is also evident from the
figure that the effect of abrasive size on wear rate of the alloy
is relatively insignificant when the abrasive size is less or
equal to 100 ␮m. Similar observations may be true for the
composite when the applied load is less or equal to 5 N. But
at higher applied load (≥5 N), the wear rate of the composite
increases almost linearly with abrasive size. The effect of
abrasive size on wear rate becomes more pronounced when
it was greater than 100 ␮m.
3.3. Worn surface
The worn surfaces of the alloy and composite are shown
in Figs. 6 and 7, respectively. Fig. 6a shows the worn surface
of the alloy when abraded against 25 ␮m abrasive size at
1 N load. It shows continuous wear grooves and cracking of
flakes along the wear track (marked arrow). In some places
the diversions of wear grooves is also noted (marked A).
The wear surface also shows the removal of the material
by tearing mechanism. Fig. 6b represents the worn surface
of the alloy when abraded against 200 ␮m abrasive size at
Fig. 5. Wear rate as a function of abrasive size at different applied loads at a sliding distance of 26 m.
M. Singh et al. / Wear 253 (2002) 357–368
363
cles leading to cavities (marked A) is clearly evident from
the figure. This figure also shows surface cracking (marked
C), deformation of flakes (marked D) and removal of material due to delaminating mechanism. A magnified view of
Fig. 7c is shown in Fig. 7d. It is evident from this figure that
the sillimanite particles undergo severe fracturing into finer
particles which in due course scooped off from the wear surface. Severe surface cracking is clearly evident from figure.
3.4. Subsurface
Fig. 6. Worn surface of the matrix alloy: (a) abrasive size = 25 ␮m and
load = 1 N, showing cracking of flakes along the wear track (marked
arrow), diversion of wear grooves (marked A); (b) abrasive size = 25 ␮m
and load = 7 N, showing longer flakes (marked A), surface cracks (marked
arrow), material removal with delamination (marked C).
7 N load. It may be noted from the figure that the width
of the continuous wear grooves is significantly wider than
that observed in Fig. 6a. Longer flakes along the wear track
(marked A), subsurface cracks (marked arrow), removal of
material by delamination (marked C) and tearing of flakes
are evident from this figure. Fine secondary wear grooves
within the primary wear grooves are also clearly noted in
the figure.
Fig. 7a represents the worn surface of the composite
abraded against 25 ␮m abrasive at 1 N load. The figure shows
finer wear grooves, protruded dispersoid particles (marked
A) and pits (marked B). A higher magnification micrograph
of the worn surface is shown in Fig. 7b. It may be noted that
the sillimanite particles are getting fractured (marked A) into
finer pieces and the interface between the sillimanite particles and the matrix gets weakened (marked B). This figure
also shows removal of material due to tearing of flakes and
microdelaminating mechanism. Fig. 7c represents the worn
surface of the composite abraded against 200 ␮m abrasive
size at an applied load of 7 N. It shows severe damage than
that observed in Fig. 7a. Scooping-off of sillimanite parti-
The subsurface of the alloy at 1 N load and 25 ␮m abrasive size is shown in Fig. 8a. Very thin layer of subsurface
deformation is noted from the figure. In the deformed layer
the eutectic silicon is noted to be fragmented in finer ones.
The subsurface of the alloy at load 7 N and 200 ␮m abrasive
size is shown in Fig. 8b. The figure shows subsurface crack
along the sliding direction (marked arrow) and relatively
wider deformed regions attached to the bulk. The fracture
and delamination of flakes (marked B) is clearly evident
from this figure.
Fig. 9a represents the subsurface of the composite at load
of 7 N and 25 ␮m abrasive size. Delamination and fracture
of large flakes (marked A) from the bulk were noted. The sillimanite particle (marked B) is noted to be strongly bonded
at the subsurface with the bulk region but the particles get
fragmented (marked C) into finer ones due to wear. Which
are finally picked up in the wear track. The subsurface of
the composite at load of 7 N and abrasive size of 200 ␮m is
shown in Fig. 9b and c. The large crack at the interface between dispersoid particle and matrix is noted at Fig. 9b and
fracture of sillimanite particles is observed in Fig. 9c. Subsurface cracks (marked arrow), fracturing and delamination
of flakes (marked A) are evident from Fig. 9b and c.
3.5. Wear debris
The wear debris collected during two-body abrasive wear
of the alloy at load of 1 N and abrasive size of 25 ␮m is
shown in Fig. 10a. The debris is noted to be of flakes and
microcutting chips. Some fragmented pieces of abrasives
or dispersoids are also seen in the figure. The wear debris
of the alloy at load of 1 N and abrasive size of 200 ␮m is
shown in Fig. 10b. The debris is primarily noted to be long
continuous chips. The debris is associated with large number
of microcracks and the surface of this debris is of card deck
type in nature. The debris of the alloy at load of 7 N and
abrasive size of 25 ␮m. Fig. 10c is also noted to be almost
similar to that of the debris shown in Fig. 10b. The debris
also contains few abrasive particles (marked A).
The wear debris of the composite at load of 1 N and abrasive size of 25 ␮m is shown in Fig. 11a. The debris consists
of mircrocutting chips of matrix alloy and fragmented abrasive or dispersoid particles (marked A). The size of the debris is noted to be smaller than that of the alloy as shown in
Fig. 10a. When the abrasive size is increased to 200 ␮m and
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M. Singh et al. / Wear 253 (2002) 357–368
Fig. 7. Worn surface of the composite: (a) abrasive size = 25 ␮m and load = 1 N, showing protruded dispersoid particles (marked A), pits (marked B);
(b) a magnified view showing fractured sillimanite particles (marked A) and the weakened interface (marked B); (c) abrasive size = 200 ␮m and
load = 7 N, showing cavities (marked A), surface cracking (marked C), deformation of flakes (marked D); (d) a magnified view of part (c) showing
fracturing and fragmentation of sillimanite particles.
load is 1 N, the debris changed its morphology as shown in
Fig. 11b. The debris become relatively longer and associated
with more cracks. Fig. 11c shows the debris obtained when
composite specimen abraded at 7 N load and at abrasive
size of 200 ␮m. The nature of the debris was similar to that
obtained in Fig. 11b. But the debris in Fig. 11c are noted
to be longer than that of Fig. 11b. The debris in Fig. 11b
and c also shows fracture and fragmentation of abrasives or
dispersoids.
4. Discussion
One of the important parameters which greatly affects the
abrasive wear characteristics of the composites is the uniformity of the dispersoid particles in the matrix and the nature of interfacial bonding of the particles with the matrix
alloy. Good interfacial bonding and uniform distribution of
dispersoids help in retaining the particles in the matrix alloy
during abrasion and thus prevent the damages caused due
to abrasive particles. A poor dispersoid/matrix bonding and
agglomeration of dispersoids leads to easy removal of dispersoids from the matrix and thus causing higher wear rates
than the matrix alloy. The microstructure of the presently
developed composite (Fig. 2a and b) shows reasonably uniform distribution of particles and good interfacial bonding
between particle and matrix alloy.
Abrasive particles in two-body abrasion like that in the
present investigation behave as if they are a single body. This
is due to fact that they are embedded on emery paper/cloth
which in turn is rigidly fixed on a metallic wheel held against
the specimens. Because of this fact, they cannot freely move,
deflect or change their position on the paper in which they are
embedded. This results in transfer of total stress applied on
the particles to the specimen surface. As a consequence, high
stress condition is created in this mode of wear operation and
abrasive particles (embedded into emery paper) penetrate
into the specimen surface to a same depth irrespective of the
nature of microconstituents present in the material [27].
The depth of penetration of the abrasives into the specimen surface is a function of several factors like effective
stress level [21,22,25], abrasive size [16–22], rake angle of
M. Singh et al. / Wear 253 (2002) 357–368
365
Fig. 8. Subsurface of the alloy: (a) abrasive size = 25 ␮m and load = 1 N;
(b) abrasive size = 200 ␮m and load = 7 N, showing subsurface crack
along the sliding direction (marked arrow), and fracture and delamination
of flakes (marked B).
abrasive tips [16,23,24] and hardness [21,23,25,29] of the
specimen surface subjected to wear. The depth of penetration increases with increasing abrasive size, rake angles and
applied load while decreases with increasing the surface
hardness of the material. Greater depth of penetration of
the abrasives leads to increase in the wear rate. Because
of these facts the alloy as well as composite suffer from
higher wear rate at higher applied load and coarser abrasive
size (Figs. 3–5). At higher applied load and coarser abrasive size, subsurface deformation, generation and growth of
surface and subsurface cracks may be more (Figs. 6b and
7b–d). Accumulation of these cracks leads to fracture
and fragmentation of flakes and delamination of material
(Figs. 7c, d, 8b, 9a and c). Greater depth of penetration may
also be confirmed from wider and longer flakes, at higher
load and coarser abrasives (Figs. 10b, c, 11b and c).
It is interesting to note that the alloy exhibits more or less
same wear rate when the abrasive size is less than 100 ␮m
irrespective of applied load (Fig. 5). This may be attributed
to less depth of cut made by the finer abrasives and the wear
may be taking place primarily due to rubbing action of the
abrasives over the specimen surface. Under these circumstances, microploughing and delamination may be prevail-
Fig. 9. Subsurface of the composite at an applied load of 7 N: (a) abrasive
size = 25 ␮m, showing delamination and fracture of flakes (marked A),
sillimanite particles (marked B) and particle fragmentation (marked C);
(b) abrasive size = 200 ␮m, showing subsurface cracks (marked arrow);
(c) abrasive size = 200 ␮m, showing fracturing and delamination of flakes
(marked A) and ceramic dispersoids.
ing mechanisms of material removal and the extent of these
mechanisms may not be changing significantly with abrasive size. But at significantly coarser abrasive size, transition
of wear mechanism may happen. Under such conditions
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M. Singh et al. / Wear 253 (2002) 357–368
Fig. 10. Wear debris of the alloy: (a) abrasive size = 25 ␮m and
load = 1 N; (b) abrasive size = 200 ␮m and load = 7 N; (c) abrasive size = 25 ␮m and load = 7 N, showing dislodged abrasive particles
(marked A).
microcutting and accumulation of surface and subsurface
cracks may be the prevailing wear mechanisms. The extent
of microcutting (width and depth of wear grooves) and
surface and sub surface cracks increases with increase in
abrasive size when the abrasive size is greater than 100 ␮m.
But in case of composite this type of variation is noted only
Fig. 11. Wear debris of the composite: (a) abrasive size = 25 ␮m and
load = 1 N, showing microcutting chips and fragmented abrasive or dispersoid particles (marked A); (b) abrasive size = 200 ␮m and load = 1 N;
(c) abrasive size = 200 ␮m and load = 7 N.
at lower applied load (1 N). At higher applied load the wear
rate of the composite increases monotonically with increase
in abrasive size. This may be attributed to greater tendency
of fracture, fragmentation and subsequent removal of sillimanite particles from the matrix at coarser abrasive size and
higher applied load (Figs. 7b–d and 9a–c). Additionally,
M. Singh et al. / Wear 253 (2002) 357–368
the fragmented sillimanite particles cause further wear
of the material. The matrix alloy in composite is also plastically constrained and thus the flakes generated due to
microploughing action are not able to flow (deform) over
the wear surface rather they are removed in subsequent
process as relatively more equiaxed microcutting chips
(Fig. 11).
In a multiphase material like metal matrix composites containing hard phases like ceramic reinforcement and softer
metallic matrix, the harder one carries the major portion
of applied stress and protects the relatively soft alloy matrix. The hard dispersoid particles also remain present on
the specimen surface as protuberance and protect the abrasives to come in effective contact with the matrix surface.
Thus, the ceramic particles can protect the matrix more effectively at lower load and finer abrasives. It may also be
noted that the SiC abrasives are significantly harder (9 in
Moh scale) than that of the sillimanite particles used as reinforcement (6–7 in Moh scale). Thus, during abrasive wear
the SiC abrasives can generate fine sillimanite particles due
to cutting action. These fine sillimanite particles are easily
picked up at the wear surface and make the surface relatively harder. Because of interaction of these facts, at finer
abrasives and lower applied load, the composite exhibits less
wear rate than that of the alloy. However, this phase constitutes only a minor volume fraction of the area of the mating
surface in the specimen and thus they are highly stressed.
As a result, the possibility of fracture or fragmentation of
sillimanite particles increases with increase in applied load
and abrasive size (Figs. 7d, 9a and c). These fragmented particles are relatively coarser in size and thus are not picked
up into the wear surface. The abrasive particles also experience similar type of fracture or fragmentation and decohesion from abrasive media due to their interaction with hard
ceramic particles in the composite. The coarser abrasive particles and fragmented sillimanite particles are not picked up
into the wear track. Rather these particles create a three-body
type of wear condition in addition to the two-body abrasive
wear and lead to deep and random scratches (grooves) on
the wear surface (Fig. 7b). This results in additional wear of
composite material.
The above discussion suggests that there may be a critical
applied load and abrasive size beyond which the sillimanite
particles may be fractured or fragmented and finally scooped
off from the wear surface and thus composite may suffer
from higher wear rate than that of the alloy. The critical
applied load and the critical abrasive size are interdependent,
i.e. one increases with decrease of the other. This is exactly
examined in Figs. 4 and 5.
In the regime where composite exhibits less wear as
compared to the alloy, the improvement in wear resistance
of the composite over the base alloy increases with increase
in load (Figs. 4 and 5). This signifies that at finer abrasives
and higher applied load, the composite shows significantly
higher wear resistance than that of the base alloy. This may
be due to increased protection offered by dispersoid parti-
367
cles to the matrix from the abrasive action of the abrasive
particles. But at lower applied load, the depth of cut may
be very fine and the wear may be taking place primarily
due to rubbing action and delamination mechanism. Thus,
the effect of sillimanite particles towards the protection of
the matrix may not result significantly to reduce the wear
rate especially at lower applied load and finer abrasive
size.
In general, the wear rate of the materials decreased with
increase in sliding distance. This was due to decreasing
cutting efficiency of abrasive particles [36–39] due to blunting, etc. as the same abrasives were used for all sliding
distances. This may be also due to increase in wear induced
work hardening of the matrix part of the composite [40,41].
Work hardening of the surface may be evident from the subsurface observations which depicts that eutectic silicons are
fragmented into finer silicon particles and get redistributed
into the subsurface (Figs. 8a and 9b). After several passes,
these parts are removed as flakes or cutting chips (Figs. 10
and 11) due to interaction of cutting action of the abrasives
and formation and growth of subsurface cracks. The cutting
efficiency of abrasive particles also deteriorates due to clogging, attrition and shelling [40,41] of the abrasive media.
Because of these facts, rubbing action also takes place which
causes tearing or delamination of flakes rather than cutting
of the material. These factors become more pronounced as
the number of passes on the same abrasive media increases
with increase in sliding distance and thus leading to stable
wear rate at larger sliding distances (Fig. 3).
5. Conclusions
(a) The microstructure of aluminium alloy sillimanite particle composite showed reasonably uniform distribution
of sillimanite particles in the matrix alloy and good interfacial bonding of dispersoid particles with the matrix
alloy.
(b) Wear rate of the composite and the matrix alloy increased with increase in applied load and abrasive size.
(c) Wear resistance (inverse of wear rate) of the composite was superior to that of matrix alloy for finer size
abrasives, whereas the trend reversed for coarser size
abrasives. At coarser abrasives, composite suffers from
higher wear rate than the alloy beyond a critical applied
load.
(d) Wear rate decreased with increase of sliding distance.
This may be due to work hardening of wear surface,
clogging, attrition and shelling of abrasive particles.
Acknowledgements
The authors are thankful to the Director, Regional
Research Laboratory, Bhopal for constant encouragement
and permission to publish the results.
368
M. Singh et al. / Wear 253 (2002) 357–368
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
A.I. Nuss Baum, Light Met. Age 55 (2) (1997) 54.
M.K. Surappa, P.K. Rohatgi, J. Mater. Sci. 16 (1981) 983.
D.M. Schuster, M. Skibo, F. Yep, J. Met. 39 (1987) 60.
R. Mehrabian, R.G. Riek, M.C. Fleming, Metall. Trans. 5 (1974)
1899.
F.M. Hosking, F.F. Portillo, W. Wunderlin, R. Mehrabian, J. Mater.
Sci. 17 (1982) 477.
K.J. Bhansali, R. Mehrabian, J. Met. 34 (9) (1982) 30.
A. Banerji, M.K. Surappa, P.K. Rohatgi, Metall. Trans. 14B (1983)
273.
A. Banerji, S.V. Prasad, M.K. Surappa, P.K. Rohatgi, Wear 82 (1982)
141.
M. Singh, O.P. Modi, R. Dasgupta, A.K. Jha, Wear 233–235 (1999)
455.
M. Singh, A.K. Jha, S. Das, A.H. Yegneswaran, J. Mater. Sci. 35
(2000) 4421.
M. Singh, D.P. Mondal, R. Dasgupta, A.K. Jha, Aluminium Trans.
3 (1) (2000) 7.
M. Singh, D.P. Mondal, A.K. Jha, S. Das, A.H. Yegneswaran,
Composites: Part A 32 (2001) 787.
K. Anand, Kishor, Wear 85 (1983) 163.
O. Vingsbo, in: Proceedings of the Conference on Wear of Materials,
ASME, New York, USA, 1979, p. 620.
Standard terminology relating to erosion and wear, in: Annual Book
of ASTM Standards, 1994, ASTM, p. 40.
B.K. Prasad, S. Das, A.K. Jha, O.P. Modi, R. Dasgupta, A.H.
Yegneswaran, Composites A 28A (1997) 301.
H. Sin, N. Saka, N.P. Suh, Wear 55 (1979) 163.
E. Rabinowicz, A. Mutis, Wear 8 (1965) 381.
N. Axen, K.H. Zum Gahr, Wear 157 (1992) 189.
A. Wang, H.J. Rack, Wear 146 (1991) 337.
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
M.A. Moore, R.M. Douthwaite, Metall. Trans. 7A (1976) 1833.
L.J. Badse, Wear 11 (1968) 213.
I.M. Hutchings, Chem. Eng. Sci. 42 (40) (1987) 869.
M.J. Murray, P.J. Mutton, J.D. Watson, J. Lubr. Technol. Trans.
ASME Tribol. 104 (1982) 9.
E. Hornbogen, Wear 33 (1975) 251.
B.K. Prasad, A.K. Jha, O.P. Modi, S. Das, A.H. Yegneswaran, Met.
Trans. JIM 36 (1995) 1048.
T. Kulik, T.H. Kosel, V. Xu, in: K.C. Ludema (Ed.), Proceedings
of the International Conference on Wear of Materials, Vol. 1, April
1973, ASME, Denver, USA, 1989, p. 23.
T. Jain-Main, S. Ye-Ying, Z. Hua-Ji, Z. Chingan, K. Zianwu, Tribol.
Int. 18 (1985) 101.
K.H. Zum Gahr, Met. Prog. 116 (1979) 46.
M.A. Moore, F.S. King, in: Proceedings of the Conference on Wear
of Materials, ASME, New York, USA, 1979, p. 275.
I.M. Hutching, in: Proceedings of the Conference on Advanced
Materials and Processes, University of Cambridge, 22–24 July 1991,
p. 56.
K.H. Zum Gahr, Z. Metallkde 69 (1978) 312.
A.G. Atkins, in: Proceedings of the Fourth Tewsbury Symposium of
Fracture, Melbourne University, February 1979, p. 171.
D.P. Mondal, S. Das, A.K. Jha, A.H. Yegneswaran, Wear 223 (1998)
131.
S. Das, S. Gupta, D.P. Mondal, B.K. Prasad, Aluminium Trans. 2 (1)
(2000) 27.
T. Hasakado, H. Suda, T. Trukui, Wear 155 (1992) 297.
A.P. Mercer, I.M. Hutchings, Wear 132 (1989) 77.
T.H. Kosel, N.F. Firore, J. Mater. Eng. Syst. 3 (1981) 7.
A. Misra, I. Finnie, Wear 65 (1980) 359.
B.K. Prasad, S.V. Prasad, A.A. Das, J. Mater. Sci. 27 (1992) 4489.
B.K. Prasad, S.V. Prasad, A.A. Das, Mater. Sci. Eng. 156A (1992)
205.