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Technical Report

Wear performance of AlSiCB4C hybrid composites under dry sliding conditions

M. Uthayakumar a,, S. Aravindan b, K. Rajkumar b

a Department of Mechanical Engineering, Kalasalingam University, Krishnankoil 626 126, Indiab Department of Mechanical Engineering, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, India

a r t i c l e i n f o

Article history:

Received 15 September 2012

Accepted 29 November 2012

Available online 8 December 2012

a b s t r a c t

Hybrid metal matrix composites consist of a metal or an alloy matrix with strongly embedded multiple

hard reinforcements to enhance the wear resistance properties. This research study emphasizes on the

dry sliding wear behavior of aluminum reinforced with 5% SiC and 5% B4C hybrid composite using a

pin on disc tribometer. Wear performance of the hybrid composites were evaluated over a load ranges

of 20100 N, at the sliding velocities from 1 to 5 m/s. Detailed metallurgical examination and energy dis-

persive analysis were carried out to assess the effect of SiC and B4C particles on the wear mechanisms.

The Focused Ion Beam (FIB) technique is used to characterize the tribo layers that have been formed at

the worn surfaces of composites. The experimental results show that the hybrid composites retain the

wear resistance properties up to 60 N load and sliding speed ranges 14 m/s. The enhancement of wear

resistance with small amount of SiC and B4C is achieved by the cooperating effect of reinforcement

particles.

2012 Elsevier Ltd. All rights reserved.

1. Introduction

The need for a new wear resistant material for high perfor-

mance tribological applications has been one of the major driving

forces for the tribological development of ceramic particulate rein-

forced aluminum alloy during the last decade [1]. Various forms of

reinforcements are used in aluminumalloy matrices such as silicon

carbide, alumina, and zirconia. in the form of fibers, whiskers or

particulate to enhance the wear performance and also properties

tailored to the suitable applications [2]. Moreover, B4C is under-

stood to have neutron absorbing capability [3], and hence, B4C

reinforced composite may well be suited for applications in nuclear

reactors. Many researchers exploited the different reinforcement

particles with different form to fabricate the aluminum composites

and used different fabrication routes for achieving the requiredproperties. SiC, TiB2 and B4C are the suitable reinforcement mate-

rials to improve the tribological properties of a matrix material

[4]. Bekir investigated the tribological and mechanical properties

of Al2O3SiC reinforced aluminum composites. The increase in

mono ceramic reinforcement in aluminum matrix increases the

wear resistance obviously. An alternative approach is to improve

the overall properties of composites by way of adding one or more

suitable (multiple) reinforcements to the virgin metal matrix. This

is called as the hybrid composite to exploit the properties of rein-

forcements [5].

Metal Matrix Composites (MMCs) also have excellent wear

properties. It is true that some MMCs have shown improved wear

resistance, for example graphite particle reinforced with aluminumalloy in sliding wear. Particle reinforcement of alumina in alumi-

num alloy increased the wear resistance [6]. Manish et al. have re-

ported that the introduction of reinforcing particle in an aluminum

matrix could reduce the wear rate with increased transition load

means the load at which transition occurs from mild to severe

wear [7]. Rao and Das have found that the wear coefficient of the

alloy was significantly higher than that of the AlSiC composite

and is suppressed further due to addition of silicon carbide parti-

cles and applied pressure [8]. According to Alahelisten et al., the

tribological behavior of a composite depends on the microstruc-

tural properties of the material, type of loading and sliding condi-

tion [9]. Coppergraphite (5 wt%) composite is a tribological

composite was fabricated through powder metallurgy (P/M) route

and can be used in sliding electrical contact applications requiringlow friction and wear in addition to high electrical conductivity

[10]. The influence of sliding speed on the friction and wear behav-

ior of the Al-13% SiC composite and Al-13% B4C composite sliding

against a commercial phenolic brake pad has been investigated un-

der dry condition by Shorowordi et al. [11]. It is observed that

higher sliding velocity leads to lower wear rate and friction coeffi-

cient for both the metal matrix composites. Formation of a com-

pact transfer layer has been identified at the worn surface of the

MMCs which enhances the tribological properties. According to

Topcu, increasing weight percent of B4C in aluminum matrix in-

creased the hardness of the composite [12]. Tang et al. demon-

strated the dry sliding friction and wear properties of 5 wt% and

10wt% B4C particulate reinforced aluminum metal matrix compos-

ites. According to the findings, the wear rate of 10 wt% was approx-

imately 40% lower than that of composite 5 wt% B4C particle

0261-3069/$ - see front matter 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.matdes.2012.11.059

Corresponding author. Tel.: +91 4563 289042, mobile: +91 9443918525.E-mail address: [email protected] (M. Uthayakumar).

Materials and Design 47 (2013) 456464

Contents lists available at SciVerse ScienceDirect

Materials and Design

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m a t d e s

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reinforced composites. These experimental results indicate the sig-

nificant effect of B4C particle on enhancing wear resistance of com-

posites. It is understood that instead of increasing mono SiC

reinforcement particles in aluminum composites, adding smaller

amount of B4C can drastically improve the tribological properties

and also positive impact on the fracture toughness. Due to increas-ing the mono reinforcement particles in metal matrix apparently

affect the fracture toughness which is also one of the wear control

parameter [13]. Addition of B4C particles with bigger particle size

results in more homogeneous composite microstructure compared

to the composite with smaller B4C particle size due to agglomera-

tion [14]. Addition of B4C to the powder mixture resulted in a dras-

tic decrease in infiltration temperature and fully infiltrated

composites [15]. Aluminum reinforced with SiC has been prepared

by various researchers in order to understand the effect of various

factors such as the particle size [16], the load [17] and the sliding

speed [18]. In this work, a detailed examination of the dry sliding

wear on the aluminummatrix with 5%wt B4C and 5%wt SiC as rein-

forcements with varying sliding velocity from 1 m/s to 5 m/s over a

load range of 20100 N.

2. Experimental procedure

2.1. Preparation of composite

Hybrid composite comprises 1100 aluminum alloy as matrix

and SiC and B4C as reinforcements. Samples of the composites

were prepared by stir casting route. The melting was carried out

in a resistance furnace. Scraps of 1100 aluminum were preheated

at 450 C for 34 h before melting. Chemical composition of the

matrix material is shown in Table 1.

The SiC and B4C particles were also preheated at 1000 C to

make their surfaces oxidized to improve the wetting property with

aluminum melt. The average particle size of the SiC (5 wt%) parti-cles was 10 lm, and the average particle size of B4C (5 wt%) was

65lm. The preheated aluminum scraps were first heated above

the liquidus temperature to melt it completely. Then it is slightly

cooled below the liquidus to maintain the slurry in the semisolid

state.

The preheated reinforcements were added to aluminum semi

solid melt and mixed manually. Manual mixing was used because

it was very difficult to mix using automatic device when the alloy

was in a semisolid state. The composite slurry was then reheated

to a fully liquid state, and mechanical mixing was carried out for

about 1015 min at an average mixing speed of 150300 rpm.

The final temperature was controlled to be within 750 C 1 0 C,

and pouring temperature was controlled to be around 720 C. After

thorough stirring, the melt was poured into steel molds of 20 mm

diameter and 300 mm in length and allowed to cool to obtain cast

rods. Developed composites were tested for their physical and

mechanical properties. The tensile properties of composite were

carried out in an Instron tensile tester, the sample preparation

was based on the ASTM D3552 96(2007). The property of the

composite is listed in Table 2.

2.2. Tribology test

Dry sliding wear tests were carried out using a pin on disc ma-chine. Pins were machined from the 1100 aluminum alloys and

also from cylindrical castings of the hybrid composites for tribol-

ogy tests based on the ASTM G99 05(2010). Cylindrical pins of

dimensions 11 mm diameter and 25 mm height were machined.

Typical specimen is presented in Fig. 1.

Pins were tested against an EN30 steel disc having the hardness

62 HRC, ground to a surface finish (Ra) of 2.54lm. The tribological

tests were carried out in the ranges of applied normal loads of 20

100 N instep of20 N and at a sliding speed range from1 to 5 m/sin

steps of 1 m/s with a constant sliding distance of 4000 m. Prior to

the tests, the pins were polished with a SiC-1200 grit polishing pa-

per and cleaned with acetone. The friction forces were recorded

during the entire wear test and average value was taken. The

weight of the pin was measured before and after each wear testusing an electronic digital weight balance with an accuracy of

0.1 mg. The temperature rise of pin during wear testing was mea-

sured using K type thermocouple. The thermocouple is embedded

in the pin at a distance of 2 mm from the contact surface. The

experimental setup is shown in Fig. 2.

2.3. Worn surface analysis

The worn surfaces of wear tested samples were examined using

Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray

Table 1

Chemical composition of aluminum alloy.

Element Si Cu Mn Zn Others Al

Wt (%) 0.95 0.050.2 0.05 0.1 0.050.15max 99

Table 2

Properties of hybrid composite.

Sample Yield strength

(N/mm2)

Tensile strength

(N/mm2)

Elongation

(%)

Hardness

Al 5%SiC5%B4C 81.37 134.62 2.2 116 (HV)

Fig. 1. Typical composite specimen.

Fig. 2. Typical experimental facility.

M. Uthayakumar et al./ Materials and Design 47 (2013) 456464 457

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Spectroscopy (EDAX). Wear debris was also analyzed using SEM

with EDAX. Tribo film and sub surface deformation of worn surface

is studied using a dual beam FIB.

3. Results and discussion

3.1. Effect of load on coefficient of friction

The variation of coefficient of friction of composite and unrein-

forced aluminum alloy with normal load is shown in Fig. 3. The

coefficient of friction is high for aluminum when compared with

the hybrid composite. The reduction of friction coefficient is due

to the major role played by the formation of boron oxide layer

(B2O3) at the contact zone. The pulled out B4C particles were react-

ing with environment readily to form the B2O3 oxide layer. The for-

mation of boron oxide layer is influenced by the generated heat. It

is observed that coefficient of friction is decreased up to 60 N load

and after that it is increased drastically with load. This may be re-

lated to the formation and tearing of oxide layer and tribo layer at

the contact surfaces respectively. Similar observation is made onaluminumgranite composites when wear tested under different

pressure i.e. coefficient of friction is decreased with applied pres-

sure up to 0.8 MPa and then coefficient of friction is increased with

applied pressure [2].The tribo layer formation and its stability at

the contact surface are influenced by the normal load and sliding

velocity. The stable tribo layer is formed at the contact surfaces un-

der the condition of load from 20 N to 60 N and sliding velocity

from1 m/s to 4 m/s. The state at velocity 4 m/s gives better result

among other conditions. However, these oxide films may break

down during dry sliding at high load beyond 60 N. The tempera-

ture and wear volume of the alloy are observed to be increased

continuously with increasing pressure; however, the increase in

the wear volume is consistent with one of the Archids laws which

states that the volume of wear material is proportional to the nor-mal load or pressure between the contacting surfaces.

3.2. Effect of sliding velocity on coefficient of friction

The coefficient of friction of composite with sliding speed is

shown in Fig. 4a. The trend of the coefficient of friction is similar

to that of wear rate. Similar results is reported on aluminumgran-

ite composites when dry wear tested under different sliding speed,

the coefficient of friction is decreased up to 3.96 m/s and then coef-

ficient of friction is increased with increasing sliding speed beyond

3.96 m/s [2]. The SEM micrograph of the surface tested at 2 m/s

and 20 N normal load is presented in Fig. 4b. Very narrow groove

line and thin tribo layer covered at the worn surface are observed.

The EDAX profile of worn surface at 20 N and 2 m/s is shown in

Fig. 4c. The predominant peaks of aluminum alloy and reinforce-

ment particles with Fe and O peak are observed. Fe peaks indicat-

ing the reinforcement particles abrade the counter steel surfacematerial. SEM image of worn surface at 3 m/s and 20 N is shown

in Fig. 4d. It shows the thick tribo layer presence in worn surface

and plastically formed grooves. The SEM worn surface at 5 m/s

and 20 N is shown in Fig. 4e. The higher sliding speed produced

rough worn surface and completely torn out tribo layer. It is under-

stood that irrespective of load, the higher speed causes the worn

surface to get completely damaged. The corresponding EDAX at

5 m/s and 20 N is shown in Fig. 4f where the high intensity peak

of Fe is observed. From all this EDAX profiles, presence of O peak

confirms the oxidative driven wear in all cases.

3.3. Effect of load on wear rate

The variation of wear rate of composite and unreinforced alumi-num alloy with normal load is shown in Fig. 5a. It is observed that

the wear rate of the composite is lower when compared to unrein-

forced aluminum. Similar results were reported by many investiga-

tors for the AlSiC and AlAl203 composites [46]. The aluminum

pin is showing the continuously increasing trend of wear with

increasing normal load due to direct metal to metal contact. As a

result of large scale plastic deformation during dry sliding, larger

sized wear debris is formed. For the composite at a given normal

load, the wear rate increased mildly up to the load 60 N and there-

after the wear rate increased rapidly. Tang et al. [13] also reported

that AlB4C composites exhibited mild wear rate up to 65 N.

Embedded ceramic particles reduced the plastic deformation of

composite by impeding the dislocation. During sliding the lower

order of pull out particles is observed from the composite pin up

to 60 N. These pull out particles can act as a third body between tri-

bo couple resulting in a third body abrasion. With continuous slid-

ing, these pull out particles were compacted between the sliding

surfaces. Consequently it is increased the compaction of the pull

out particles between the tribo couple with increasing normal load.

The pull-out particles are mixed with oxide of both composite pin

and counter surface materials which are generated during the slid-

ing. It is well known that aluminum readily reacts with environ-

ment and forms the aluminum oxide. Singh et al. [2] observed

formation of aluminumoxide film at the contact surface when slid-

ing against the steel counter surface. The pull out particles and pro-

truded reinforcement particles in composite are abrading the

counter surface material. These pin and counter surface material

and their oxide which are combined during sliding, form the low

shear strength tribo layer. This low shear strength tribo layer con-

sists of mixture of all the constituents of the composite, counter

surface and oxide products. This tribo layer reduces the plastic

deformation of the composite pin to certain extent by way of

reducing the direct contact between the tribo surfaces. Similar

observation is reported by Alpas and Zhang [1] for the AlSiC com-

posites under the mild wear regime. Fig. 5b revealed (tested at

40 N and 4 m/s sliding condition) the Mechanically Mixed Layer

(MML) completely covered by tribo layer and slim grooves. EDAX

of worn surface of 40 N and 4 m/s is shown in Fig. 5c, almost all

peaks of aluminum alloy and reinforcement particles are observed.

In addition, O and Fe peaks are also observed. These peaks are

attributed to formation of oxide at the worn surface and abrasion

of counter surface material. The SEM image of worn surface at

60 N and 4 m/s is presented in Fig. 5d. The tribo layer has coveredthe worn surface which resulted due to lower order pulling out of

particles. Further these particles are mechanically comminuted be-

tween the tribo surfaces producing the fine particles and due to

20 40 60 80 100

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

coefficientoffriction

Load N

Alcomposite @ 1m/scomposite @ 2m/scomposite @ 3m/scomposite @ 4m/scomposite @ 5m/s

Fig. 3. Effect of load on coefficient of friction.

458 M. Uthayakumar et al./ Materials and Design 47 (2013) 456464

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this low order of wear rate is observed. Increasing the load beyond

60 N, the tribo characteristics is changed by protruded reinforce-

ment particles predominately leads to tearing the formed tribo

layer. Increased local stress results in larger wear debris formation

which gives an indication of severe plastic deformation of the com-

posite. Sannino and Rack [4] reported severe plastic deformation of

aluminumSiC composites when tested with high order of normal

load and sliding speed due to plastic flow attributed by instabilityof aluminum matrix. matrix More pull out reinforcements parti-

cles are observed when loading beyond the normal load of 60 N

which means that considerable plastic deformation of composite

has occurred. Pulled out particles can also form a third body abra-

sion condition. However the higher amount of presence of ceramic

particles in tribo layer results in tearing of the formed tribo layer.

Ultimately it leads to the exposure of the virgin composite material

at the contact zone which results in increased wear rate. The

unstable formation of tribo layer is attributed to the considerable

plastic deformation of composite pin. SEM image of worn surface

at 100 N and 4 m/s is shown in Fig. 5e. It is observed that thereis a severe distortion of worn surface and no presence of tribo

layer. The worn surface seems to be mostly torn out of formed

layer. EDAX profile of worn surface at 100 N and 4 m/s is shown

0 1 2 3 4 5 6

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

coefficientoffriction

Sliding velocity m/s

composite @ 20N

composite @ 60N

composite @ 80N

2 4 6 8 10

keV

0

2

4

6

8

10cps/eV

O FeFe

CuCu ZnZn

SiBAlC

(a)

(b)

(c)

2 4 6 8 10

keV

0.0

0.5

1.0

1.5

2.0

2.5

3.0

cps/eV

O FeFe

CuCu ZnZn

SiB

(d)

(e)

(f)

Fig. 4. (a) Effect of sliding velocityon coefficient of friction. (b) SEM micrograph at20 N and 2 m/s. (c) EDAXat 20 N and 2 m/s. (d) SEM micrographat 20 N and 3 m/s. (e) SEM

micrograph at 20 N and 5 m/s. (f) EDAX at 20 N and 5 m/s.


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in Fig. 5f. Comparing to 40 N and 4 m/s EDAX profile, similar peaks

are observed however there is a distinct difference in the intensity

of Fe peak. It is attributed to large scale third body abrasion of pull

out particles and protruded reinforcement particles.

3.4. Effect of sliding velocity on wear rate

The effect of sliding velocity on wear rate is shown in Fig. 6. It is

observed that the wear rate is reduced up to 4 m/s and then begins

to increase. Increase in sliding velocity increases the steady forma-

tion of tribo layer at the contact surface. Though heat generation is

increased with increase of sliding velocity, the generated heat is inone way helpful in the formation of boron oxide- rich tribo layer

which would affect the compact layer formation at the contact sur-

face. However when the sliding speed increased beyond the 4 m/s,

high heat is generated results in the occurrence of the softening of

composite pin. In addition to that, peeling off and thrown out of

formed layer are also observed. It results in increased wear rate

of the composite pin.

3.5. Bulk temperature rise

The temperature was measured from 1 mm underneath of com-

posite while sliding, The temperature is continuously monitored

with the help of K type thermo couple. The temperature rise re-

ported at end of wear test is reported in Fig. 7. Temperature is

increasing with increase of load. The trend shown by the 1 and2 m/s for temperature rise is similar. Beyond 3 m/s the visible in-

crease of temperature rise is observed. The temperature increases

with increase in sliding velocity. The temperature rise with sliding

20 40 60 80 100

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

WearrateX10-5m

m3/m

Load N

Alcomposite @ 1m/scomposite @ 2m/scomposite @ 3m/scomposite @ 4m/scomposite @ 5m/s

2 4 6 8 10

keV

0

1

2

3

4

5

6

cps/eV

O FeFe

CuCu ZnZn

SiBC Al

(a)

(b)

(c)

2 4 6 8 10

keV

0

2

4

6

8

10cps/eV

O FeFe

CuCu ZnZn

SiBC Al

(d)

(e)

(f)

Fig. 5. (a) Effect of load and wear rate. (b) MML at 40 N. (c) EDAX at 40 N. (d) MML at 60 N. (e) MML at 100N. (f) EDAX at 100 N.


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velocity within constant duration of test is due to more asperity

contact between the composite and counter surface. However

there is no steep temperature rise up to 60 N because formed tribo

layer reduce the metal to metal contact, thereby reducing frictional

heat between the tribo couple. The rapid temperature rise is ob-

served beyond the 60 N wherein more metallic contact results asa result of scarcity in tribo layer at the tribo surface.

Typical graph for temperature rise at 60 N load with 1 m/s slid-

ing velocity is presented in Fig. 8 with the temperature rise contin-

uously monitored, and the temperature rise is stabilized after

1000 m sliding distance due to steady and stable tribo layer forma-

tion. The compacted tribo layer between the tribo surface leads to

maintain the steady value of temperature rise after 1000 m.

4. Wear mechanism

Examination of the worn surfaces of the composite pin showed

many slim grooves and scratch marks along the sliding direction as

explained in the previous section. However to augment the wear

mechanism, study the worn surfaces at different load and slidingvelocity are necessary and the results are presented in this section.

The typical worn surface of hybrid composites is shown in Fig. 9. At

lower load (60 N) worn surfaces revealed that coverage of tribolay-

er and narrow grooved lines are observed from 1 to 3 m/s. The

worn surfaces are covered with smooth tribo layer up to 60 N with

range of sliding velocity 14 m/s. Wider Grooves and scratching

becomes more severe at the higher speeds of 15 m/s and 100 N.

Such wear features are the characteristics of severe abrasion, in

which hard asperities on the steel counter face, or pulled out hard

particles in between the contacting surfaces, plough or microcut

into the composite pin, causing wear debris. This suggests that

mixed mode of (two body and third body) abrasion occurred

mainly through ploughing which has resulted in wider abrasion

groove. It has been noted that abrasion is severe in AlB4CSiC

composite due to the presence of dislodged and fractured SiC that

becomes entrapped between the sliding surfaces or embedded into

soft aluminummatrix. SiC particles have a modulus lower than B4C

reinforcement particles. At 60 N and 5 m/s, the worn surfaces re-

vealed many plastically deformed into wider grooves. At 100 N

and 5 m/s, the worn surface shows localized metal matrix melting

layer. In aluminum hybrid composites it has been found that mild

abrasion is dominant under a load range of 2060 N and speed

range of 14 m/s whereas severe abrasion is seen under a load of

100 N, sliding velocity range of 14 m/s and melting wear is at high

load and high sliding speed.

When carefully examined at a higher magnification, the worn

surface showed three main features: (i) polished ceramic reinforc-

ing particles, (ii) matrix region around the ceramic particles, and

(iii) bright debris particles scattered on the surface. The bright

particles were particularly visible on the worn surface examined.

In this study a new technique of FIB milling is implemented for

measuring the tribolayer thickness and subsurface structure. FIB-

quanta 3D FEG-dual beam was used for this purpose. Rectangular

patterns of size 2 lm 2 lm with a depth of 4 lm were cut in

the sample using an ion beamwith a current of 5 nAunder vacuum.

FIB is used to cut the rectangular trench on wear track in the direc-

tion perpendicular to the sliding direction until a certain depth into

the substrate and the thickness is measured through the cross-

sectional analysis of the cut obtained through this milling. The

walls of the cut were viewed under SEM in a tilted position at 52

to clearly see the cross-section of the tribo layer, the substrate

and the interface and the thickness of the tribo film was measured.

Sliding contact between the metallic surfaces is accompaniedby plastic deformation. This deformation is localized within a small

volume of material adjacent to contact surfaces and this is known

as sub-surface deformation. The depth of subsurface deformation

0 1 2 3 4 5 6

2

4

6

8

10

12

14

16

18

20

wearrateX10-5m

m3/m

Sliding velocity m/s

composite @ 20N

composite @ 60N

composite @ 80N

Fig. 6. Effect of sliding velocity on wear rate.

20 40 60 80 100

40

50

60

70

80

90

100

110

Te

mperatureriseC

load N

composite @ 1 m/s

composite @ 2 m/s

composite @ 3 m/s

composite @ 4 m/s

composite @ 5 m/s

Fig. 7. Effect of temperature rise.

0 500 1000 1500 2000 2500 3000 3500 4000

34

36

38

40

42

44

46

48

TemperatureriseC

sliding distance m

composite @ 60N&1m/s

Fig. 8. Typical temperature rise of composite.


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is influenced by the sliding parameter. The process of wear debris

formation is closely related to the magnitude of the strain

gradients within the subsurface deformed layer. Typical FIB milled

trench of worn surface is shown in Fig. 10.

It is clearly visible of abrasion mark along the sliding direction.

Tribolayer is loosely interfaced with composite matrix and also

loose wear debris of the composite materials embedded on the sur-

face. FIB-FESEM image at 20 N and 4 m/s is shown in Fig. 11a. Itcomprises of the tribolayer and deformed sub structure immedi-

ately underneath of tribo layer. An interaction of boron carbides

against steel irrespective of the composition of the B4C, a dark-grey

film was formed on the steel surface. It also shows the considerable

thickness of tribo layer and thin layer of sub surface deformation.

The formed tribo layer reduced the transference shear force to

underneath of contact surface, resulted in low order of sub surface

layer. The low order of sub surface deformation resulted in fine

equi-axed wear debris, as shown in Fig. 11b. The magnitude of

sub surface deformation is increased with increase in normal load,

as evident from Fig. 12a. At higher load and the generated larger

shear force which produced larger strain gradient between the

contact surface and weaker section at interface of reinforced parti-

cles and matrix, as elucidated in the previous section, wear rate issubstantially higher at 100 N. This higher order of sub surface

deformation produces the larger equiaxed fragmentation of wear

debris, as shown in Fig. 12b.

It is clearly understood from the results of dry sliding wear of

AlB4CSiC composites that hybrid composites can withstand high

load.

When wear rate of the unreinforced alloy accelerated abruptly,the wear rate of the composite is, at 80 N load the SiC particle se-

vere to suppress the transition to a severe wear rate regime and

impede the transition to load higher than 80 N. But during the

Fig. 9. Typical worn surface of AlSiCB4C composite at different loads and sliding speeds.

Fig. 10. FIB-milled trench on the wear track of worn surface.


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lower load region there is no severe wear rate found. At lower end

the load spectrum load about 20 N SiC reinforcement also has a

beneficial effect on wear resistance. Low loads composite rein-

forced with SiC particles shows better wear resistance than unrein-

forced alloys, The increase in wear rate is due to increase in

hardness, higher hardness of SiC and B4C and pinning of dislocation

by these hard particles. The composite also impede the transition

to a higher wear rate regime observed in the matrix alloy above

80 N.

Sliding wear takes place due to relative sliding of two surfacesin contact with each other under the influence of applied load. Sur-

face and sub surface deformation along with material transition

between the two contour surfaces leads to the formation of MML

of the test specimen. Some amount of material may be oxidized

due to high localized heating under oxidizing atmosphere. As a re-

sult the surface of the specimen consists of oxide layer or mixed

layer of oxides and surface and counter surface material. The de-

gree of oxide layer/MML depends on the applied load. The MML

layer protects the surface effectively from wear. Singh et al. [2] also

reported that the steady formation of MML is completely protect-

ing the contact zone under the mild wear regime. The sliding wear

greatly influenced by the subsurface deformation and cracks. As a

result at high load and high speed material exhibits severe wear

(seizure). This was exactly observed in the present study. Up to60 N there is an oxide formation; tribo layer formation is attributed

mild wear rate. From 60 N to 100 N plastic deformation occurs

which leads to fracture of SiC and B4C.

The wear rate of the composite is less than the alloy due to the

resistance offered by the dispersed particle during sliding. In addi-

tion, the dispersion phase improves high temperature strength of

the matrix alloy. Under the transition load, for severe wear under

such circumstances the mechanically mixed layer gets removed

due to high order of sub surface cracking.

At the stage B4C particle protruded from the sliding surface, the

load on the composite surface would be borne mainly by B4C par-

ticle. It is known that the coefficient of friction between steel and

B4C is lower than that between steel and aluminum alloy [13].Hence B4C reinforcement in the AlSiC composites is improved

the wear performance.

5. Conclusion

Aluminum matrix reinforced with 5 wt% SiC and 5 wt% B4C par-

ticles were prepared by stir casting route and the friction and wear

behavior of the composites with different normal load and sliding

speed were investigated using pin-on-disc machine. From the

experimental results the following conclusions can be drawn:

1. The two step stir casting has produced uniformly distributed

reinforcement particles in aluminum matrix. The small addition

of 5% B4C has considerable effect on the wear resistance of thehybrid composites.

2. The experimental results show that the hybrid composites

retain the wear resistance properties up to 60 N and sliding

Fig. 11. (a) AlB4CSiC 20 N and 4 m/s. (b) Wear debris morphology at 20 N and 4 m/s.

Fig. 12. (a) AlB4CSiC 100 N and 4 m/s. (b) Wear debris at 100 N and 4 m/s.


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speed ranges 14 m/s. The enhancement of wear resistance

with small amount of SiC and B4C is achieved by the cooperat-

ing effect of reinforcement particles. B4C particles possibly pro-

duce boron oxide rich tribo layer which has reduced the

progress of wear and coefficient of friction.

3. This hybrid composites show that, it could not perform better athigher load and higher sliding speed. The wear rate and coeffi-

cient of friction are decreased with increasing sliding speed up

to 4 m/s and as a result, rate formation of tribo layer is higher

than tearing of formed tribo layer, whereas the trend is reversed

in higher sliding speed.

4. FIB study on the subsurface deformation shows that deforma-

tion is increasedwith increasing the normal load. The wear deb-

ris formation is largely influenced by the tribo layer thickness

and subsurface deformation, and wear debris become smaller

and eqaxied when the subsurface deformation is smaller.

5. The operating wear mechanisms are plastic deformation driven

by mild abrasion and severe abrasion at normal load ranges 20

60 N and 80100 N and sliding velocity ranges 14 m/s

respectively.6. The melt wear is also observed at higher load and high sliding

speed due to high order of local stress prevailing at the

condition.

Acknowledgement

The corresponding author submits his thanks to Tamil Nadu

State Council for Science and Technology for the support to carry-

out this work in Indian Institute of Technology, New Delhi, under

Young Scientist Fellowship Scheme (YSFS).

References

[1] Alpas AT, Zhang J. Effect of particulate reinforcement on the dry sliding wear

behavior of aluminumsilicon alloys (A356). Wear 1992;155:83104.

[2] Singh M, Prasad BK, Mondal DP, Jha AK. Dry sliding wear behavior of

aluminium alloy granite particle composite. Tribol Int 2001;34:55767.

[3] Miracle DB. Metal matrix composites from science to technological

significance. Compos Sci Technol 2005;65:252640.

[4] Sannino AP, Rack HJ. Dry sliding wear of discontinuously reinforced aluminum

composites: review and discussion. Wear 1995;189:119.

[5] Sadik Bekir. Investigation of tribological and mechanical properties Al2O3SiC

reinforced Al composites manufactured by casting or P/M method. Mater Des2008;29:20028.

[6] Uyyuru RK, Surappa MK, Brusethaug S. Effect of reinforcement volume fraction

and size distribution on the tribological behavior of Al-composite/brake pad

tribocouple. Wear 2006;260:124855.

[7] Roy Manish, Venkatraman B, Bhanuprasad VV, Mahajan YR, Sundararajan G.

The effect of particulate reinforcement on the sliding wear behavior of

aluminum matrix composites. Metall Trans 1992;23A:283347.

[8] Rao RN, Das S. Wear coefficient and reliability of sliding wear test proce-

dure for high strength aluminum alloy and composite. Mater Des 2010;31:

322733.

[9] Alahelisten A, Bergman F, Olsson M, Hogmark S. On the wear of aluminum and

magnesium metal matrix composites. Wear 1993;165:2216.

[10] Chandrakanth RG, Rajkumar K, Aravindan S. Fabrication of copperTiC

graphite hybrid metal matrix composites through microwave processing. Int

J Adv Manuf Technol 2010;48:64553.

[11] Shorowordi KM, Haseeb ASMA, Celis JP. Tribosurface characteristics of AlB4C

and AlSiC composites worn under different contact pressures. Wear

2006;261:63441.

[12] Topcu I, Gulsoy HO, Kadioglu N, Gulluoglu AN. Processing and mechanical

properties of B4C reinforced Al matrix composites. J Alloy Compd

2009;482:51621.

[13] Tang Feng, Wu Xiaoling, Ge Shirong, Ye Jichun, Zhu Hua, Hagiwara Masuo,

et al. Dry sliding friction and wear properties of B 4C particulate reinforced

Al-5083 matrix composites. Wear 2008;264:55561.

[14] Kertti Isil, Toptan Fatih. Microstructural variation in cast B4C reinforced

aluminum matrix composites. Mater Lett 2008;62:12158.

[15] Arslan Gursoy, Kalematas Ayse. Processing of silicon carbideboron carbide

aluminum composites. J Eur ceram soc 2009;29:47380.

[16] Chung S, Hwang BH. A microstructural study of the wear behavior of SiCp/Al

composites. Tribol Int 1994;27:30714.

[17] Kwok JKM, Lim SC. High speed tribological properties of some Al/SiCp

composites: 1, frictional and wear rate characteristics. Compos Sci Technol

1999;59:5563.

[18] Ravikiran A, Surappa MK. Effect of sliding speed on wear behavior of A356 Al-

30 wt% SiCp MMC. Wear 1997;206:5563.


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