Wear Behavior of Dual Particle Size (DPS) Zircon Sand Reinforced Aluminum Alloy

ORIGINAL PAPER

Wear Behavior of Dual Particle Size (DPS) Zircon SandReinforced Aluminum Alloy

Suresh Kumar • Vipin Sharma • Ranvir Singh Panwar •

O. P. Pandey

Received: 1 July 2011 / Accepted: 11 May 2012 / Published online: 26 May 2012

� Springer Science+Business Media, LLC 2012

Abstract The present investigation aims to find the

combined effect of coarse and fine size particle reinforce-

ment of zircon sand in aluminum alloy LM13 on the wear

behavior. The composites are fabricated by varying the

reinforcement of fine and coarse size zircon sand particles

and compared with the single size reinforcement. Coarse

and fine particle zircon sand of 106–125 and 20–32-lm

size, respectively, are used in this study. The wear test was

carried out on pin-on-disc machine. Microhardness mea-

surement was done for developed composites. Wear track

and debris are analyzed by SEM to study the wear mech-

anism. Line profile and EDS analysis is also done to vali-

date the microstructural results. Study reveals that a

combination of 3 % fine and 12 % coarse particle rein-

forced composite exhibits better wear resistance while 3 %

coarse and 12 % fine particle reinforcement decreases the

wear resistance. It is also observed that zircon sand parti-

cles provide effective nucleation site for the eutectic sili-

con. Microstructural examination shows globular and

finely distributed eutectic silicon in the vicinity of the

reinforced particles.

Keywords Composite � Stir casting � Dual particle size �AMCs � Zircon sand

1 Introduction

Aluminum–silicon alloys find their application in different

engineering components because of their good castability,

high corrosion resistance, and low density. Wear resistance

of these alloys can be enhanced by incorporation of cera-

mic phase in the soft aluminum matrix [1]. Reinforcement

of hard ceramic particulates imparts a combination of

properties not achievable in either of the constituents

individually. In recent years, many processing techniques

have been developed to prepare particulate reinforced

aluminum matrix composites (AMCs). These techniques

are stir casting, liquid metal infiltration, squeeze casting,

spray co-deposition, powder metallurgy, etc. Among the

variety of processing techniques available for particulate or

discontinuous reinforced metal matrix composites, stir

casting is one of the methods accepted for the production of

large quantity composites. It is attractive because of sim-

plicity, flexibility, and is most economical for large size

components to be fabricated [1–5]. In recent years,

numerous research works have been reported on production

of AMCs by stir casting technique, but very limited

research work has been done on reinforcement of dual size

particles [6, 7]. Moreover, to the best of our knowledge no

work is reported on wear behavior of aluminum composites

reinforced with dual size zircon sand particles.

Prabhakar and co-workers [6] studied tribological

behavior of dual particle size (DPS) SiC particles rein-

forced composite and compared with single particle size

(SPS) reinforced composite. They found that the DPS

composite exhibited better wear resistance compared to

same volume fraction of SPS composite. Zhang et al. [7]

studied thermal conductivity of Al–12Si matrix composite

reinforced with 70 vol % SiC particles of two different

sizes and analyzed the effect of dual-sized particles on

structural and thermal conduction properties. The com-

posites fabricated with finer reinforcement particulates

exhibit greater strength as compared to coarser with the

same quantity of reinforcement. Ahmad et al. [8] studied

S. Kumar � V. Sharma � R. S. Panwar � O. P. Pandey (&)

School of Physics and Material Science, Thapar University,

Patiala 147004, Punjab, India

e-mail: [email protected]

123

Tribol Lett (2012) 47:231–251

DOI 10.1007/s11249-012-9983-y

the effect of particle size for Al2O3 reinforced AMCs and

reported that the fine particle reinforced composites have

higher hardness as compared to coarse particles. This is

because composites reinforced with the finer particle size

offer higher number of barriers per unit volume compared

with composites reinforced with larger particle size at the

same weight percentage. Small reinforcement particles

permit larger contact area with aluminum alloy matrix.

Ozdemir and Yakuphanoglu [9] have reported that the fine

particles reinforced composites also exhibit better thermal

conductivity as compared to composite reinforced with

larger particles. Das et al. [2] have compared the wear

properties of alumina and zircon sand reinforced AMCs

and reported that decrease in particle size improves wear

resistance. Roy et al. [3] have studied the effect of sub-

micron and micron size reinforcement of Al2O3 particles in

AMCs and concluded that submicron size particle rein-

forced composites offer lowest wear as compared to

Table 1 Composition of the LM13 alloy in wt%

LM13 alloy Si Fe Cu Mn Mg Zn Ti Ni Pb Sn Al

wt% 11.8 0.3 1.2 0.4 0.9 0.2 0.02 0.9 0.02 0.005 Balance

Table 2 Composition of the zircon sand (ZrSiO4)

Elements ZrO2 (?HfO2) SiO2 TiO2 Fe2O3

% in Bulk 65.30 32.80 0.27 0.12

Table 3 List of processing parameters

Melting temperature 750 �C

Total stirring time 22–25 min

Mixing time 8–10 min

Blade angle 45�No. of blades 3

Position of stirrer Up to 2/3 depth in the melt

Table 4 Reinforcement combination of composites

Composites Fine (wt%)

(20–32 lm)

Coarse (wt%)

(106–125 lm)

SPS1 15 0

SPS2 0 15

DPS1 3 12

DPS2 12 3

LM-13 ALLOY (Al-Si alloy)

MOLTEN METAL

Melt at 800ºC

MELT + ZrO2

Stirring (630rpm) + Zircon sand

Held at 750ºC

CASTING

SAMPLE PREPERATION

CHARACTERIZATION TESTING

OPTICAL MICROSCOP

SEM WEAR HARDNESS

Fig. 1 Schematic diagram of experimental procedure

232 Tribol Lett (2012) 47:231–251

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micron size reinforcement. On the other hand, it is reported

that coarse particle reinforced composites exhibit better

wear resistance as compared to fine particle reinforced

composites [10, 11]. Yılmaz and Buytoz [10] have reported

that the wear rates decreased with increase in Al2O3 size

for the composites containing the same amount of Al2O3.

They have concluded that aluminum alloy composites

reinforced with larger Al2O3 particles are more effective

against abrasive wear than those reinforced with smaller

Al2O3 particles. Zou et al. [11] in their work depict that the

wear resistance of 38 vol% SiCp of average size 57-lm

reinforced composite is almost 10 times higher than that of

the SiCp of 5.5-lm reinforced composite having same

volume fraction. They also found that the depth of plastic

deformation zone in the subsurface decreases with

increasing volume fraction and average diameter of SiC

particles.

Considering all these parameters, this study is aimed to

analyze the combined effect of both coarse and fine size

particle reinforcement in aluminum alloy composite. Our

study is mainly focused on investigating the microstruc-

tural features and wear properties of DPS zircon sand

reinforced LM13 alloy which has not been studied so far.

The effect of dual size particles on the mechanical prop-

erties, microstructures, and wear resistance of the particu-

late reinforced composite at room temperature is reported

in this work.

2 Experimental

In this study, well-known piston alloy LM13 is used as

matrix material and high-purity zircon sand (ZrSiO4) as

reinforcement. LM13 alloy was obtained in the form of

ingots. The compositional analysis of the LM13 alloy was

done by wet chemical analysis which is given in Table 1.

Table 2 gives the composition of zircon sand used in the

present work.

The composite was made by stir casting route. The

detailed description of the process is similar to described in

other work [12–15]. Required quantity of LM13 alloy was

taken in a graphite crucible and melted in an electric fur-

nace. The temperature of melt was raised to 750 �C. This

molten metal was stirred using a graphite impeller at a

speed 630 rpm to create the vortex. The impeller blades

were designed in such way that it creates vortex. Different

Fig. 2 Optical micrograph of SPS1 composites containing 15 % fine

particles showing a uniform particle distribution, b showing dendritic

and fragmented dendritic growth in particle depleted region,

c eutectic silicon exhibiting globular morphology around particles,

and d SEM micrograph of SPS1 composite showing uniform

distribution of particles

Tribol Lett (2012) 47:231–251 233

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sizes of zircon sand were taken in defined proportion and

mixed properly and this mixed zircon sand (DPS) was

preheated at 450 �C to drive off the moisture. After the

formation of vortex in the melt, the sand particle was

charged inside the vortex at the rate of 20–25 g/min into

the melt during stirring with the help of funnel kept on top

of vortex. Zircon sand particle of fine grade (20–32 lm)

and coarse grade (106–125 lm) was selected for present

work. The stirring was continued for another 5 min even

after the completion of particle feeding to ensure homo-

geneous distribution of the sand particles. The vortex

method is one of the better known approaches used to

create and maintain a good distribution of the reinforce-

ment material in the matrix alloy. The molten mass was

finely poured into the metal mold and allowed to solidify at

room temperature. During production of composite, the

amount of LM13 alloy, stirring duration, and position of

stirrer in the crucible were kept constant to minimize the

contribution of variables related to stirring on distribution

of second phase particles. The other detail is given in

Table 3.

During fabrication of the DPS composite, zircon sand

particles of two sizes were chosen. In our earlier work on

spray forming, it was observed that 15 % reinforcement of

zircon sand reinforced composite has given better property,

so we have restricted the reinforcement up to 15 % only

[1]. In order to compare and correlate the effect of particle

size on mechanical and tribological properties, four dif-

ferent composites containing a total of 15 wt% reinforce-

ment were fabricated. In the first combination of DPS

(DPS1) there was 12 % coarse (106–125 lm) and 3 % fine

(20–32 lm) zircon sand particles, whereas, in the second

combination (DPS2) there was 3 % coarse and 12 % fine

zircon sand particles. The two composites were synthesized

by incorporation of only single size particle of fine (SPS1)

and coarse particles (SPS2) of 15 wt%. The reinforcement

combinations are also given in Table 4.

Dry sliding wear tests of the reinforced and unreinforced

alloys were performed under the ambient temperatures

between 25 and 30 �C and relative humidity between 22

and 35 %, using a pin-on-disc wear and friction monitor

(Model TR-20, Ducom, Bangalore). The cylindrical-

Fig. 3 Optical micrograph of SPS2 composites containing 15 %

coarse particles showing a uniformly arranged particles in the alloy

matrix, b consistent and better bonding between zircon sand particle

and alloy matrix and morphology of silicon at particle–matrix

interface, c long dendrite in particle depleted region and the presence

of silicon in between dendrite arm spacing, and d SEM micrograph of

SPS2 composite showing uniform distribution of fine particles with

clustering at some places

234 Tribol Lett (2012) 47:231–251

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shaped samples (30 9 9 mm) of composite were tested

against the hardened EN32 steel disc having chemical

composition (0.14 % C, 0.52 % Mn, 0.18 % Si, 0.13 % Ni,

0.05 % Cr, 0.06 % Mo, 0.019 % P, 0.015 % S, balance Fe)

and hardness 65 HRC. Before testing, each specimen was

ultrasonically cleaned in acetone.

The wear tests of specimen from each set of composite

have been conducted up to 2,880 m of sliding distance at a

constant sliding velocity of 1.6 m/s and under five different

loads 1, 2, 3, 4, and 5 kg. The microstructural analysis has

been done with the help of both optical (Eclipse MA-100,

Nikon) and scanning electron microscope (SEM, JEOL,

JSM-6510LV, Japan) with EDS attachment at various

magnifications. Before optical observation, the sample was

mechanically polished and etched by Keller’s reagent for

obtaining better contrast.

Microhardness of the different phases was measured

using microhardness tester (Mitutoyo, Japan). Microhard-

ness measurement was done on each set of sample by

taking minimum of five indentations per sample at 100 kgf

load. To understand the procedure in a better way, the

schematic diagram of the experimental procedure is shown

in Fig. 1.

3 Results and Discussion

3.1 Microstructural Analysis

The optical micrographs of SPS1 reinforced with 15 % fine

particles (20–32 lm) are shown in Fig. 2. Figure 2a shows

fairly uniform distribution of reinforced particles in alloy

matrix. Uniform distribution of second phase particles is

required for achieving better wear resistance and mechan-

ical properties. Fairly uniform distribution of particles in a

molten alloy is achieved due to the high shear rate during

stirring which also minimized the particle settling tendency

[14, 15]. However, agglomeration of particles is also

observed which is visible at certain places (Fig. 2a, b).

Figure 2b shows the micrograph of the composite where

fragmented dendrites in the alloy matrix can be seen,

though limited dendritic growth in the particle depleted

Fig. 4 Optical micrograph of DPS1 composites containing 12 %

coarse and 3 % fine particles showing a coarse and fine particles are

uniformly arranged in the alloy matrix, b eutectic silicon morphology

changes from acicular to globular in vicinity to particle, c densely

distributed globular silicon near the particle, and d SEM micrograph

of DPS1 composite showing distribution of fine and coarse particles

Tribol Lett (2012) 47:231–251 235

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region is also visible. This growth has occurred because of

clustering of zircon sand. Fine size zircon sand are pushed

or engulfed by advancing solid–liquid interface creating

sufficient space inside the matrix which leads to growth of

dendrite [14]. Dendritic fragmentation can be attributed to

the shearing of initial dendritic arms by the stirring action.

During particle addition, local solidification of the melt

occurs which is induced by the particles as there is a

temperature difference between the particle and the melt. It

was also found that the perturbation in the solute field due

to the presence of particles can change the dendrite tip

radius and the dendrite tip temperature. These effects give

rise to a dendrite–cell transition as the density of particles

is increased. Also the length of the dendrite is reduced in

the presence of the particles [14]. The higher magnification

micrograph (Fig. 2c) exhibits some what rounded mor-

phology of eutectic silicon having fine distribution as col-

onies around the reinforced particles. SEM micrograph of

SPS1 composite also exhibits homogeneous distribution of

particle whereas at some places particle clustering and

porosity due to entrapment of air during pouring are also

observed (Fig. 2d).

The optical micrographs of SPS2 reinforced with 15 %

coarse particles (106–125 lm) are shown in Fig. 3.

Fig. 5 Sequential growth of

solid in the composite showing

fragmentation of dendrite and

growth of rosette dendrite

having cellular morphology

236 Tribol Lett (2012) 47:231–251

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Figure 3a shows the homogeneous distribution of coarse

particles in the alloy matrix. The mechanical stirring not only

distributed the particles homogeneously but also delays the

particle settling prior to solidification [1]. Good bonding

between particle and alloy matrix is exhibited in Fig. 3b. The

smooth interface provides better mechanical and tribological

properties as transfer of load occurs through the interface [1,

2]. Figure 3c shows the presence of long dendrite in areas

where particle is not present. The second phase hard particle

restricts the growth of dendrite and modifies the matrix with

more refined structure leading to improvement in strength

[15–19]. It also contributes for refinement of silicon phase.

The silicon possessing accicular morphology in the matrix

acquires globular form in vicinity to the particles. Similar

modification in silicon morphology was reported in earlier

work by Kaur and Pandey [20] and attributed this morpho-

logical transformation to the localized rapid cooling effect

produced by zircon sand particle due to large temperature

difference in the melt around its vicinity. The SEM micro-

graph of this composite exhibits nearly uniform distribution

of zircon sand where clustering of particles at certain places

is also observed (Fig. 3d).

The optical micrographs of DPS1 containing 12 %

coarse and 3 % fine zircon sand particles are shown in

Fig. 4. It depicts the homogeneous distribution of coarse

and fine reinforced particles in the alloy matrix as shown in

Fig. 4a. The eutectic silicon becomes finer and nucleates

near zircon sand particle as colonies, which is seen in

Fig. 4b, c. During stirring, shearing force is applied on the

molten mass. As nucleation starts the dendrites get frag-

mented due to shearing action and solidifies as rosette type.

As the solid–liquid interface moves, the dendrite acquires

cellular type of features on small under cooling which

always exits ahead of solid–liquid interface. Second phase

particles present in the melt also provide nucleation center.

Since the system is continuously in the agitated state,

where second phase particles are fairly distributed

throughout the melt, it hinders the growth of long

dendrites. This results in cellular growth because of

interference offered by these particles, as shown in

Fig. 4a–c. SEM micrograph of DPS 1 depicts homoge-

neous distribution of particles which are arranged in ran-

dom fashion due to limited amount of coarse particle

reinforcement (Fig. 4d). However, fine particles have the

Fig. 6 Optical micrograph of DPS2 composites containing 12 % fine

and 3 % coarse particles showing a distribution of zircon sand

particle, b good bonding between zircon sand particle and alloy

matrix, c clustering of fine particles, and d SEM micrograph of DPS2

composite showing the particle distribution and porosity

Tribol Lett (2012) 47:231–251 237

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tendency of clustering though it is not much in this case as

compared to SPS1. This transition is schematically depicted

in Fig. 5 where fragmentation of primary dendrite and

growth of rosette dendrite having cellular structure is shown.

Optical micrograph of DPS2 composite containing 12 %

fine and 3 % coarse zircon sand particles is shown in

Fig. 6. Homogeneous distribution of particles can be seen

(Fig. 6a). Eutectic silicon morphology has changed from

acicular to globular which is uniformly distributed

throughout the matrix as is seen in Fig. 6b. However, the

fine particles and silicon form a network structure because

of pushing interface from different nucleation sites as is

seen in Fig. 6a–c which are taken from different areas. This

is clear in Fig. 6b, c where the network of silicon and fine

particles are observed. Moreover, the clustering of fine

particles at some places is also observed. SEM micro-

graph of DPS2 composite exhibits uniform distribution of

particles (Fig. 6d). However, porosity at certain places is

also observed. Overall analysis of structure indicates that

fine particles have tendency of clustering in the composite

because these are pushed to a greater extent by solidifi-

cation front as compared to coarse particles. Most of the

fine particles are placed at grain boundaries and very

limited particles are engulfed within the grains [16].

Particle pushing and engulfing phenomenon during

solidification is also correlated with the mutual wetting

behavior among the solid, liquid, and particle phases. If

the contact angle at a solid–liquid interface of a particle is

\90�, the particle can be engulfed into the solid, and if

the contact angle is [90�, the particle would be pushed

ahead [17]. Coarse particles have greater tendency to

settle as compared to fine particles. Composite reinforced

with coarse particles in majority exhibit clustering due to

settling of particles and fine particles form cluster by

pushing action of solidification front [16, 17]. Moreover,

most of these adverse phenomena are rectified in our

prepared composites.

Figure 7 represents the X-ray line profile of the DPS2

composite. It exhibits the presence of all the phases and

their distribution in the matrix. An important feature

observed in this analysis which is also clear in micro-

structural features as discussed earlier is that silicon finds

its path for nucleation near zircon sand particle. Moreover,

the interface is smooth as can be seen with sharp increase/

decrease of lines for different elements. Figure 8 presents

the EDS analysis of composite. The spot analysis done at

particle indicates the presence of oxygen, silicon, and zir-

con elements.

3.2 Microhardness Measurement

The microhardness measurement at different phases of

composites has been carried out to know the effect of

reinforced particulates on the alloy matrix, which is given

in Table 5.

Microhardness measurement has been carried out on

the embedded zircon sand particles as well as in the

vicinity of particles and matrix. Zircon sand particles

show high hardness which decreases as we move away

from particle. The high hardness at particle–matrix

interface indicates good bonding between particle and

alloy matrix. Fine particle zircon sand reinforced com-

posite shows better microhardness in comparison to coarse

particle zircon sand reinforced composite at interface and

matrix.

Fig. 7 Line profile analysis of SPS2 composite showing distribution

of different elements

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3.3 Wear Characteristics

3.3.1 Effect of Sliding Distance on Wear Rate

The variation of wear rate with sliding distance of the

composite has been investigated at five different loads

which are shown in Fig. 9. It is observed that wear rate of

the composites increases with the increase in applied load.

The curve reveals two different types of wear behavior

under an applied load. The steep rise in the initial stage

gives rise to greater wear corresponding to the run in wear.

However, steady state wear is obtained in the later stage.

Moreover, with increase in load the run-in and steady state

wear rate are also found to increase. These results are

analogous to results reported earlier under similar sliding

conditions by Kaur and Pandey [20] for spray-formed

zircon sand reinforced composite and Chaudhury et al. [21]

for stir cast Al–2Mg–11TiO2 composites.

The wear behavior of SPS1 shows that steady state wear

is approachable after 1,000-m sliding distance (Fig. 9a),

while in SPS2 as shown in Fig. 9b steady state wear is

delayed and occurs after sliding distance of 1,500 m at low

loads where as on high loads the steady state wear is

approachable at 2,000-m sliding distance. Run-in wear of

SPS2 is higher as compared to SPS1 composite as shown in

Fig. 9a, b. This indicates that fine particle reinforced

composite exhibits better wear resistance as compared to

coarse particle reinforced composites. These results are in

good agreement with the earlier reported results [22, 23].

To study the effect of inverse particle size addition, i.e.,

fine particle addition in coarse particle reinforced com-

posite and vice versa, the wear rate comparison of SPS2

and DPS1 as shown in Fig. 9c, d clearly shows that addi-

tion of 3 % fine particles to coarse particle exhibits better

wear properties as compared to only coarse particle rein-

forced composite. There is decrease in not only wear rate

but also in run-in wear which reduces to greater extent and

steady state wear approaches at earlier sliding distance. On

the other hand, comparing the coarse particle addition to

fine particle with fine particle reinforced composite, i.e.,

SPS1 and DPS2 gives different results, as shown in Fig. 9a,

d. The graphical presentation reveals that coarse particle

addition marginally increases the wear rate as compared to

single size fine particles reinforced composite, but run-in

wear is slightly lesser. It can be concluded after analyzing

the data that fine particle addition in coarse particle rein-

forced composites enhances the wear properties, while

coarse particle addition to fine particle reinforced com-

posite do not work well to enhance the wear properties. As

reported earlier, the coarser particles help to carry a greater

portion of the applied load, thereby reducing the load on

the finer particles as well as on the base metal. In addition

to this, the coarser particles in the DPS composites could

help to shield the finer particles from the plowing action of

the abrasive thus, helping the smaller particles to continue

performing their wear resisting function longer than in SPS

composites [6]. This can be attributed to the fact that, less

quantity of coarser particles is unable to shield the fine

particles and also chipping off of coarser particle during

adhesive wear pulls out the finer particles along with them

Fig. 8 Point analysis of SPS2 composite done at zircon sand particle showing the presence of O, Si, and Zr elements

Table 5 Variation of hardness at different phases in composites

Composites Microhardness (Hv)

At particle At interface At matrix

SPS1 709 123 88.6

SPS2 736 103 82.1

DPS1 716 102 79

DPS2 719 116 81

Tribol Lett (2012) 47:231–251 239

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at higher load. It is confirmed by the result as mentioned

earlier, in which 12 % coarse zircon sand particles with

3 % fine zircon sand particles gives better wear resistance.

3.3.2 Effect of Load on Wear Rate

The bar graph of wear rate comparison of composites with

different loads is presented in Fig. 10. In Fig. 10a, the

graphical representation clearly shows the wear rate of

coarse particle reinforced composite, i.e., SPS1 is higher as

compared to fine particles reinforced composite, i.e., SPS2

at all investigated loads. Further at low and high loads the

wear rate of SPS1 is nearly double as compared to SPS2

whereas wear rate difference is less between the compos-

ites at load range of 3–4 kg. This representation concludes

that fine particle reinforced composite exhibits better wear

resistance in comparison to coarse particles. Similar results

are reported earlier by other researchers [22, 23].

Figure 10b shows that the wear rate of DPS2 is higher

than SPS1 composite at all investigated loads. Graphical

study clearly depicts that the addition of coarse particle in

fine particle reinforced composites is not effective in

enhancing the wear resistance of the composite. It is not

the case in the composite with fine particle addition to the

coarse particle reinforced composite as presented in the

Fig. 10c. SPS2 containing 15 % coarse particle shows

higher wear rate in comparison to DPS1 reinforced with

12 % coarse and 3 % fine zircon sand particles. The fine

particle addition enhances the wear resistance of the coarse

particle composite at all the investigated loads. It is con-

cluded from Fig. 10b, c that the fine particle addition in

coarse particle reinforced enhances the wear resistance of

the composite, but the coarse particle addition to fine

particle reinforced composite increases the wear rate.

The graphical comparison of composites SPS1, SPS2,

DPS1, and DPS2 depicts that the composite reinforced with

15 % coarse particle, i.e., SPS2 exhibits higher wear rate at

all the investigated loads. At higher load, the difference

between wear rate of SPS2 as compared to other com-

posites is greater, which is lesser at low load.

0

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Fig. 9 Wear rate of composites against sliding distance at different

loads. a Wear rate of SPS1 LM13/15 % zircon sand fine particles

(20–32 lm), b wear rate of SPS2 LM13/15 % zircon sand coarse

particles (106–125 lm), c wear rate of DPS1 LM13/15 % zircon sand

(12 %C ? 3 %F), and d wear rate of DPS2 LM13/15 % zircon sand

(12 %F ? 3 %C)

240 Tribol Lett (2012) 47:231–251

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The wear rate of all the composites on different loads is

shown in Fig. 11 for comparison. It shows the wear rate of

SPS1, SPS2, DPS1, and DPS2 at different loads. The wear

follows a linear relationship with respect to increasing load

which portrays Archard’s law of adhesive wear for metals.

It clearly shows that SPS1 exhibits better wear resistance as

compared to all the composites under investigation.

The wear rate results of SPS1 show a change in slope of

wear curve from 2- to 3-kg load. This change in slope

corresponds to the change in wear behavior from mild to

severe behavior. On the other hand, the transition from

mild to severe behavior in SPS2 occurs from 3 to 4-kg load.

The severe wear manifested itself by massive surface

damage and large-scale matrix material transfer to the

counterface accompanied by the generation of coarse

debris particles, typically in the shape of plates with a shiny

metallic appearance. Kaur and Pandey [20] have also

reported similar behavior for spray-formed zircon sand

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SPS 1 SPS 2 DPS 1 DPS 2

d

Fig. 10 Bar graph of wear rate at different loads. Wear rate comparison of a SPS1 and SPS2, b SPS1 and DPS2, c SPS2 and DPS1, and d SPS1,

SPS2, DPS1, and DPS2

1 2 3 4 51

2

3

4

5

6

7

8

9

10

11

12

13

wea

r ra

te x

10-3

(mm

3/m

)

Load (Kg)

SPS 1 SPS 2 DPS 1 DPS 2

Fig. 11 Wear rate of composites at different loads

Tribol Lett (2012) 47:231–251 241

123

reinforced LM13 composite, i.e., same alloy and size of

reinforcement as used in this study.

To compare the effect of dual size particle on wear rate

against load, the graph shows that DPS1 exhibits better

wear resistance by only addition of 3 % fine particles as

compared to SPS2 composite, which contain only coarse

particle of single size. The fine particles work effectively

to resist wear and their shielding is done by the coarse

particles [6]. On comparing the results of SPS1 and DPS2

it is observed that addition of the coarse particle to fine

particles adversely affect the wear properties, as shown in

Fig. 11.

The wear mechanism can be further explained well by

analyzing the microstructural features of the worn surface

of pin and the wear debris.

3.3.3 Morphological Analysis of Worn Surface and Debris

The morphologies of worn out surface of pins and debris

offer clues to the wear mechanisms involved in sliding the

Fig. 12 SEM micrograph of worn out surface of SPS1 composite at different loads. a 1 kg, b 2 kg, c higher magnification at 2 kg, d 3 kg,

e 4 kg, and f 5 kg

242 Tribol Lett (2012) 47:231–251

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sample against load. The SEM micrographs of the single and

dual size zircon sand reinforced composites tested at loads of

1–5 kg at a speed of 1.6 m/s are presented in Fig. 12, which

show the wear track morphology of the specimens tested.

One of the common features observed in both lower and

higher loads is the formation of grooves and ridges running

parallel to the sliding direction in composites. On further

analyzing, it has been found that wear grooves are fine in

worn pin surface of composite subjected to low load as

compared to higher load. The depth of microplowing is

increased on increasing load to 5 kg where contact asper-

ities change the shape. Consequently, the size and the depth

of the grooves become greater at this stage. However, at

high loads the worn surfaces in some places reveal patches

from where the material was removed from the surface

during the course of wear [20, 24].

Figure 12a shows the SEM micrograph of worn pin

SPS1 composite reinforced with fine size zircon sand

particles at a load of 1 kg. The worn surfaces are smooth

and plowing strips are very shallow on the surface. At 2-kg

load, the plowing marks got deeper as shown in Fig. 12b

and damaged spots in the form of craters can be seen,

which grow further in size on increasing load. Particle

cracking and microcrack are observed at higher magnifi-

cation, as shown in Fig. 12c. These factor increases the

wear rate significantly. This behavior is characterized as

severe wear behavior, in which material removal is

accelerated.

Fig. 13 SEM micrograph of wear debris generated from SPS1 at different loads. a 3 kg, b 4 kg, and c 5 kg

Tribol Lett (2012) 47:231–251 243

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The material of the pin adheres along the flat running

surfaces causing adhesive sliding wear as shown in

Fig. 12d at 3-kg load. This wear behavior causes the

damage to parent material and wear rate increases signifi-

cantly. The crack running from the removed material is

also visible in the matrix and loosely held debris flakes,

which may detach further on higher load.

At 4 kg, the material removal increases significantly and

the cross section of the craters increases, as shown in

Fig. 12e. At 5-kg load material removal rate is significantly

higher. Adhesive wear is dominating at this stage. Micro-

cracks result in delamination, which in turn damage the

parent material by excessive material loss. The loose wear

debris and crushed zircon sand particles are seen on the

wear track, as shown in Fig. 12f.

Wear debris generated at higher load of SPS1 is pre-

sented in Fig. 13. Figure 13a shows wear debris obtained at

3-kg load in which plate-like debris of matrix alloy

and debonded zircon sand particles are observed. Wear

is governed by delamination which gives plate-like

Fig. 14 SEM micrograph of worn out pin surface of SPS2 composite at different loads. a 1 kg, b 2 kg, c 3 kg, d 4 kg, e 5 kg, and f higher

magnification at 5 kg

244 Tribol Lett (2012) 47:231–251

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morphology of debris with microcracks. The pull-out of

ductile aluminum having thread-type morphology is also

seen. Wear debris at 4-kg load as shown in Fig. 13b shows

the plate or flakes of alloy matrix and debonded zircon sand

particles which get spheroidized as they are trapped in the

track during sliding action. The debris particles are likely

to act as the third-body abrasive particles and could be

responsible for the higher wear rate. Loose debris particles

trapped between the specimen and the counterface causes a

microplowing on the contact surface of the composite.

Majority of flakes have number of cracks due to repetitive

stress occurred in sliding under high load. When the load is

increased, the dominant wear mechanism delaminates and

severe plastic deformation occurs. Wear debris generated at

5-kg load as shown in Fig. 13c is having long flakes gen-

erated by delamination along with small flakes. Small

flakes are generated by the crushing of the flakes at high

load. Debris having long flakes as compared to debris

generated at low load depicts the severe wear behavior.

Worn out pin surface micrographs of SPS2 are presented

in Fig. 14. Figure 14a shows worn surface at 1-kg load in

which grooves and ridges running parallel to the sliding

direction can be seen. Microplowing dominates the wear

mechanism although local damaged spots are also observed

on the surface. At 2-kg load, the grooves are distinct and

deeper, crater grow in size which exposes the reinforced

particles, as shown in Fig. 14b. As load increases the

adhesive wear mechanism operates and removes the ductile

matrix material. The particles are protruding in the matrix

depicting good bonding between particle and alloy matrix

as observed in Fig. 14c. At higher load, the material

removal is governed by adhesive wear and crack propa-

gation resulting in delamination of matrix material. The

protective layer of the reinforcing particles can no longer

remain stable under the plowing action at high load. The

material removal is enhanced by adhesive wear mechanism

and number of craters is increased between deep plowing

marks, as shown in Fig. 14d, e. Material removal during

the process is in the form of small pieces resulting in the

formation of flake-type debris. As shown in Fig. 14f, the

craters are so large and distinct that the surface underneath

is visible. The higher magnification SEM examination at

5-kg load of the subsurface clearly reveals cracks indicat-

ing delamination wear.

Wear debris of SPS2 composite is shown in Fig. 15. The

debris obtained at 1-kg load is of plate-like morphology

Fig. 15 SEM micrograph of wear debris generated from SPS2 at different loads. a 1 kg, b 3 kg, c 4 kg, and d 5 kg

Tribol Lett (2012) 47:231–251 245

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and zircon sand particle is not observed, which indicates

that the reinforced particles are bearing the load and plate-

like debris as shown in Fig. 15a is generated. As load

increases the debonding of zircon sand particles occurs and

long flakes of debris having different morphologies as

shown in Fig. 15b are observed. In the collected wear

debris, zircon is present in the form of mechanically mixed

layer. The particle itself has cracked into further smaller

fragments and after long run it makes an oxide-rich layer

on the worn surface by picking iron oxide from the coun-

terface which was confirmed by EDS analysis (discussed

later). Several microcracks are visible in debris indicating

delamination while zircon sand particle takes spherical

shape by trapping in during course of sliding. Twisted and

layered debris revealing the repetitive nature of stress

occurred at high load sliding condition. At 4-kg load, as

shown in Fig. 15c the debris having long flakes apart from

this small metallic debris is also observed, which get

Fig. 16 SEM micrograph of worn out pin surface of DPS 1 composite at different loads. a 1 kg, b 2 kg, c 3 kg, d 4 kg, e 5 kg, and f lower

magnification at 5 kg

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fragmented during sliding action. Debris at 5-kg load

shows mixed morphology with long flakes, small frag-

mented flakes, and layered flakes. Crack propagation leads

to delamination although some flakes depicting microcut-

ting behavior as shown in Fig. 15d can be seen.

Figure 16 shows the pin surface morphology of DPS1

composite. At 1-kg load, the grooves running all over the

pin surface along sliding direction are shown in Fig. 16a.

Load increment initiates the formation of cater and crack,

as shown in Fig. 16b. At 2-kg load, the crater formation

starts by the loss of parent material. The rupture of

mechanically mixed layer initiates the adhesive wear

mechanism and crater grows in size at 3 kg (Fig. 16c). At

4-kg load, the material removal shows the dimple-like

morphology as void nucleates around the particle in the

ductile matrix, as observed in Fig. 16d. At higher load, i.e.,

at 5 kg the cracks propagates and removal of material

occurs by delamination, as shown in Fig. 16e. A lower

magnification micrograph shows the dimple morphology

around the particle (Fig. 16f).

Wear debris of DPS1 composite is presented in Fig. 17.

The long flakes with microcracks along with debonded

zircon sand particle are observed in debris collected at 3-kg

load as shown in Fig. 17a. At higher load, i.e., 5-kg load,

the flakes having number of microcracks along the edges

reveals that cracks are responsible for their delamination

from the parent material. Some flakes having embedded

particles which are pulled out with the parent material due

to excessive plastic deformation as shown in Fig. 17b are

observed. Wear debris generated at 3-kg load shows cor-

rugated and layered structure, as shown in Fig. 17c. The

steps or layered structure observed could be due to rubbing

Fig. 17 SEM micrograph of wear debris generated from DPS 1 at different loads. a 4 kg, b 5 kg, and c 3 kg

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caused by constant sliding between the pin material and the

counterface. Each of the steps could then be caused by the

deforming force subjected in one rotation. Similar mor-

phology of wear debris is earlier reported by Bakshi et al.

[25] for aluminum–silicon composite coatings prepared by

cold spraying.

Worn surface of DPS2 is examined under SEM is

presented in Fig. 18. Figure 18a shows the worn surface

at 1-kg load. The excessive plowing action is observed

as the grooves are deeper at low load as compared to

other composite in this study. Crater also originated on

the surface having several microcracks at the edge per-

pendicular to the sliding direction. At 2-kg load, the

particles are exposed as parent material is removed by

adhesive wear mechanism, as shown in Fig. 18b. The

excessive deformation causes the crater to grow in size

and the edge having cracks causes delamination. Some

loosely held debris originated by the cracks can be

clearly seen in the micrograph (Fig. 18c). At 4-kg load,

the material removal is excessive. Figure 18d shows that

material along with particles is removed by delamination.

The grooves are again formed on the worn surface as

Fig. 18 SEM micrograph of worn out pin surface of DPS 2 composite at different loads. a 1 kg, b 2 kg, c 3 kg, d 4 kg, and e 5 kg

248 Tribol Lett (2012) 47:231–251

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seen in the micrograph. At 5-kg load, the crack propa-

gation lead to excessive removal of parent material

although some island-type parent material remains there,

as they bypass the crack growth, as shown in Fig. 18e.

Wear debris of DPS2 is presented in Fig. 19. The flake-

like morphology observed at 1-kg load is similar to other

composites debris. Zircon sand particles are also there in

debris, which are debonded from the alloy matrix, as

shown in Fig. 19a, b. A long flake with embedded zircon

sand particles is observed, which is pull-out from the alloy

matrix by excessive plastic deformation, as shown in

Fig. 19b. Coarse particle of zircon sand showing debond-

ing at low loads itself causes the decrease in wear resis-

tance of the composite. At 2-kg load, as shown in Fig. 19c

reveals the microlevel delamination on a flake itself, which

occurs due to number of microcracks. The long flakes with

microcracks and flakes with embedded zircon sand particle

are observed in wear debris generated at 3-kg load, as

shown in Fig. 19d. Flakes with embedded zircon sand

particle can be attributed to the fact that coarse zircon sand

particles provide hindrance for crack nucleation in the alloy

matrix containing majority of fine particles. The

Fig. 19 SEM micrograph of wear debris generated from DPS 2 at different loads. a 1 kg, b 1 kg, c 2 kg, d 3 kg, e 4 kg, and f 5 kg

Tribol Lett (2012) 47:231–251 249

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deformation observed is also not homogeneous due to the

presence of coarse particles in fine particle reinforced alloy

matrix. At 4-kg load, the wear debris having flakes along

with fragmented flakes as shown in Fig. 19e are seen. On

higher load, i.e., at 5 kg, flakes showing extensive micro-

cracks and small thin debris show microcutting behavior,

as shown in Fig. 19f.

EDS analysis of wear debris is shown in Fig. 20. The EDS

results indicate the presence of Fe on wear debris which

corresponds to the transfer of material from the counterpart

disc to composite material. This also indicates that debris is

generated by the rupture of mechanically mixed layer.

4 Conclusion

This study is carried out to determine the influence of DPS

zircon sand reinforcement on wear behavior of stir cast

Al–Si alloy LM13. The wear study was carried out at five

different loads at constant sliding distance and speed. From

this study following conclusion can be made:

1. Zircon sand particle provides nucleation site for silicon

during solidification which is confirmed by micro-

structure, EDS, and line profile analysis.

2. Fine size zircon sand particle reinforced composite

exhibits better wear resistance than coarse particle at

same weight percentage of reinforcement.

3. Limited amount of fine particle size addition to coarse

particle enhances the wear resistance as compared to

single size coarse particle at same weight percentage

of reinforcement.

4. Coarse particle addition to fine particle reinforced

composite adversely affects the wear properties of the

composite as compared to single size fine particle

composite.

Acknowledgments The authors are thankful to Armament Research

Board (ARMREB), Defence Research and Development Organization

(DRDO), India for providing financial support under the letter no.

ARMREB/MAA/2008/105 for this study.

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