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Technical Report

Dry sliding wear behavior of heat treated hybrid metal matrix composite

using Taguchi techniques

T.S. Kiran a,⇑, M. Prasanna Kumar b, S. Basavarajappa c, B.M. Viswanatha a

a Department of Mechanical Engineering, Kalpataru Institute of Technology, BH Road, NH 206, Tiptur 572201, Karnataka, Indiab Department of Industrial Automation Engineering, PG Center, Visvesvaraya Technological University, Mysore, Indiac Department of Studies in Mechanical Engineering, University BDT College of Engineering, Davangere 577004, India

a r t i c l e i n f o

Article history:

Received 9 February 2014

Accepted 3 June 2014

Available online 17 June 2014

a b s t r a c t

Dry sliding wear behavior of zinc based alloy and composite reinforced with SiCp (9 wt%) and Gr (3 wt%)

fabricated by stir casting method was investigated. Heat treatment (HT) and aging of the specimen were

carried out, followed by water quenching. Wear behavior was evaluated using pin on disc apparatus.

Taguchi technique was used to estimate the parameters affecting the wear significantly. The effect of

HT was that it reduced the microcracks, residual stresses and improved the distribution of microconstit-

uents. The influence of various parameters like applied load, sliding speed and sliding distance on wear

behavior was investigated by means and analysis of variance (ANOVA). Further, correlation between the

parameters was determined by multiple linear regression equation for each response. It was observed

that the applied load significantly influenced the wear volume loss (WVL), followed by sliding speed

implying that increase in either applied load or sliding speed increases the WVL. Whereas for composites,

sliding distance showed a negative influence on wear indicating that increase in sliding distance reduces

WVL due to the presence of reinforcements. The wear mechanism of the worn out specimen was

analyzed using scanning electron microscopy. The analysis shows that the formation and retention of

ceramic mixed mechanical layer (CMML) plays a major role in the dry sliding wear resistance.

2014 Elsevier Ltd. All rights reserved.

1. Introduction

Life of machine component is an important design consider-

ation. Various parameters affect the life of components and the

selection of material directly influences the life significantly.

The choice of material for a particular application varies depend-

ing on the variables like cost, density, specific strength, modulus

and operating condition. The majority of engine components,

gear drives and so on in automotive and aerospace industries uti-

lizes metals and alloys. The sliding and rotating components

intended to work in lubricating conditions may eventually endup working in semi-lubricated or dry conditions. This will result

in higher operating temperature with increase in wear and lead

to quicker replacement of components. Hence, wear is one of

the major problems that need to be tackled in order to improve

the life of the component. Composite materials are the promising

alternate for alloys, specifically in dry operating conditions.

Current work concentrates on the development of a hybrid

reinforced composite material that can improve the wear resis-

tance in components. Historically addition of reinforcements

has shown significant improvement in tribological properties.

However in some instances it has shown deterioration in

mechanical properties.

Zinc–Aluminum (ZA) alloy is a competitive bearing alloy that

shows improvement in both mechanical and tribological proper-

ties compared with phosphor-bronze, SAE 73, SAE 660 and cast

iron. The density of the latter are much higher compared with

the former element [1,2]. ZA alloy exhibits superior wear resis-

tance at low speed-high load application even in the absence of lubricant, while there is a decline in wear resistance with increase

in speed and rise in temperature [3,4]. Seah et al. [5] and Babic

et al. [6] performed dry sliding wear behavior of ZA-27 alloy rein-

forced with Gr particles. These composite specimens exhibited

enhanced wear resistance than the alloy. The smeared Gr particles

formed a protective layer on the specimen. Applied load was

directly proportional to the wear rate for both alloy and composite

specimen [5,6], while variation in sliding speed showed contrast

results in composite specimen [6]. The hardness decreased with

the addition of graphite [5,6] as it is a soft inclusion.

Reinforcing hard SiCp into soft aluminum alloy improves the

wear resistance as well as hardness of the composite material

http://dx.doi.org/10.1016/j.matdes.2014.06.007

0261-3069/ 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Address: #133, Coronation Road, Tiptur 572201,

Karnataka, India. Tel.: +91 8134 252717, mobile: +91 98441 13298.

E-mail addresses: [email protected], [email protected]

(T.S. Kiran).

Materials and Design 63 (2014) 294–304

Contents lists available at 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

http://dx.doi.org/10.1016/j.matdes.2014.06.007mailto:[email protected]:[email protected]://dx.doi.org/10.1016/j.matdes.2014.06.007http://www.sciencedirect.com/science/journal/02613069http://www.elsevier.com/locate/matdeshttp://www.elsevier.com/locate/matdeshttp://www.sciencedirect.com/science/journal/02613069http://dx.doi.org/10.1016/j.matdes.2014.06.007mailto:[email protected]:[email protected]://dx.doi.org/10.1016/j.matdes.2014.06.007http://crossmark.crossref.org/dialog/?doi=10.1016/j.matdes.2014.06.007&domain=pdf

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[7–10]. Composites with increased volume fraction and larger rein-

forcement size increase the wear resistance. Particle pull out and

fracture was the mechanism observed for smaller and larger rein-

forcement size respectively [7]. A step by step increase in applied

load increased the wear rate, whereas a contrast result was

achieved in case of sliding speed by where the wear rate decreased

with increase in speed [8]. The increase in SiCp content improved

the hardness which reduced the wear rate significantly. Compos-

ites reinforced with SiCp exhibited superior wear resistance over

the alloy as fractured particles ensured the participation in wear

behavior avoiding the exposure of alloy [9]. Wilson and Alpas

[10] showed that incorporation of SiCp in Al alloy improves the

mild wear regime at higher load and speed compared to the unre-

inforced alloy. Prasanna kumar et al. [11] and Ranganath et al. [12]

evaluated the dry sliding wear behavior of ZA-27/garnet composite

and concluded that, increasing garnet content improved the wear

resistance. Meanwhile the wear resistance dropped with an

increase in applied load and sliding speed.

Inclusion of only graphite as reinforcement improved wear

behavior (as it is a solid lubricant), reducing hardness [5,6] (soft

inclusion) while SiCp inclusion showed improvement in both wear

and hardness [7–10]. The attempt to obtain the combined effect of

solid lubrication and improved hardness attributed to the creation

of hybrid composites. The effect of sliding speed in deciding the

wear behavior of hybrid composites was evaluated by Basavarajap-

pa et al. [13]. It was witnessed that, the specimen experienced

higher wear rate followed by seizure behavior at higher speeds

for alloy, while there was a minor effect of increase in speed for

hybrid composite reinforced with SiCp and Gr. On the contrary,

Suresha and Sridhara [14,15] evaluated that as sliding speed was

increased, wear loss was reduced for different combinations of

SiCp and Gr. Hardness reduces with inclusion of Gr particles in

Al-SiCp composite specimen.

Basavarajappa et al. [16] used Taguchi’s technique to identify

the influence of wear parameters and concluded that sliding

distance is the major contributor followed by applied load and

sliding speed. Graphite plays an important role in the formationof mechanical mixed layer (MML). Several researchers’ [17–19]

studied the heat treated ZA-27 alloy followed by water quenching

to investigate the hardness, tensile and wear behavior. Heat

treatment to ZA-27 alloy improved the distribution of microcon-

stituents. Heat treatment resulted in reduction of the hardness

and tensile properties but had a positive effect on the dry sliding

wear behavior [17–19]. The specimen heat treated for 5 h [18,19]

and aged for 8 h [17] showed superior wear behavior over other

heat treatment and aging conditions. The addition of solid lubri-

cant (Gr) with SiC particles in Al alloy proved to be positive on

the dry sliding wear behavior [20,21]. A detailed study on the for-

mation of mechanical mixed layer (MML) and its advantages on the

worn surface of the specimen were presented [22,23]. A statistical

approach was used to find out the significance of the factors affect-ing the wear behavior of hybrid MMCs [24–26].

The previous studies on ZA-27 alloy have concentrated on

utilization of SiCp and Gr particles separately. The current work

concentrates on the HT of ZA-27 alloy reinforced with SiCp and

Gr particles which were not investigated in earlier research works

to the best of author knowledge. The parameters that influence the

wear behavior of heat treated ZA-27 alloy and ZA-27/9SiC–3Gr are

evaluated by Taguchi technique in the present investigation.

2. Design of experiments (DOE)

DOE is an important and powerful statistical technique that

evaluates the effect of multiple parameters simultaneously. Exper-

iments have to be conducted in a sequence, with a series of steps,so that the process performance is better understood. A certain

combinations of factors and levels are considered and varied in a

strategic manner. The results obtained are observed and analyzed,

to find out the significant factors and preferred levels [27]. The data

can be acquired in an orderly way by DOE based on Taguchi

approach. There are three main phases in the Taguchi process: (i)

the planning phase (ii) the conducting phase and (iii) the analysis

phase. Among the three listed phases, planning phase is vital

where the factors and levels are decided. The results obtained from

experiments are analyzed for better understanding of the influen-

tial factors.

3. Experimental procedure

3.1. Specimen preparation and wear test

ZA-27 is identified as the matrix material and the reinforce-

ments used are 9 wt% of SiCp with 45 lm and 3 wt% of Gr with

25lm in size. The composite specimen was prepared by stir

casting method. The ZA-27 alloy was heated above its liquidus

temperature of 500 C. A aluminite coated stirrer was introduced

in the molten slurry to homogenize the temperature. The mixture

of reinforcements were preheated and poured into the rotatingmolten slurry. To improve the wettability of reinforcements,

1 wt% of magnesium was added along with the reinforcements.

The molten slurry was stirred for 10 min, so that the reinforce-

ments distribute uniformly in the alloy. The melt was later poured

into permanent castings. The alloy and composite specimen were

subjected to T6 type of heat treatment in four steps: first, the spec-

imen were heat treated at 370 C for 5 h; second, the heat treated

specimen were quenched in water at room temperature; third, the

quenched specimen were aged at 180 C for 8 h; fourth, the aged

specimen were quenched in water at room temperature.

The dry sliding wear behavior of specimen were evaluated with

pin-on-disc apparatus at room temperature. The specimen were

machined as per ASTM: G99-05(2010) standards, with a dimension

of 8 mm diameter and 30 mm height. The specimen was pressed

against the rotating EN32 steel disc of hardness 65HRc and load

was applied on the specimen by cantilever mechanism. The disc

and specimen surface were cleaned with acetone before each

experiment to remove any traces on the surface. The specimen

were weighed before and after wear test using an electronic

weighing machine which can measure up to 0.1 mg. The difference

in the weight was measured and volume loss was calculated. The

weight loss of the disc is not considered as the hardness of disc

was more compared to specimen.

3.2. Plan of experiments

Wear tests of the base alloy and composite specimen were

conducted under dry sliding conditions for three parameters:

Applied load, sliding speed and sliding distance with variation of

3 levels as shown in Table 1. The experiments were planned based

on standard L27 orthogonal array (OA), consisting of 27 rows and

13 columns. The 1st, 2nd and 5th columns were assigned to

applied load (L), sliding distance (D) and sliding speed (S ) respec-

tively in the Orthogonal Array, while the remaining columns were

assigned to their interactions. The present investigation is based on

the objective to study smaller – the-better wear response.

Table 1

Process parameters used in the experiment.

Level Load, L (N) Sliding distance, D (m) Sliding speed, S (m/s)

1 15 1000 0.63

2 45 3000 1.88

3 75 5000 3.14

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4. Results and discussion

4.1. Heat treatment

As the dendrites dissolve uniformly after HT, the microstructure

of as-cast specimen is shown in Fig. 1. In as-cast alloy (Fig. 1a), the

aluminumrich (A)a-phase and zinc rich (B) g-phase can be clearly

differentiated as white and black regions respectively. The

eutectoid (C) a + g phase is rarely visible which is the vital phase

for tribological applications [17–19]. The SiC and graphite particles

are shown in Fig. 1b. As the Heat treatment was carried out, the

microstructure was fully transformed into eutectoid phase, giving

added advantage to both alloy and composite specimen. Themicrocracks and residual stresses present in the as-cast specimen

were reduced by HT process facilitating improved wear resistance.

EDX of the base alloy and hybrid composite are shown in Fig. 1c

and d respectively, which confirms the presence of reinforcements

(Fig. 1d). Since, all the specimen considered were heat treated, the

advantage of HT on as-cast is not discussed in the present work.

4.2. Hardness

Vicker hardness test was performed on the heat treated alloy

and composite specimen. The results showed a slight increase in

hardness of composite (108 HV) compared with the alloy

(106 HV). The reason for the slight increase is due to the presence

of soft Gr particle that hindered the hardness value [14,15]. Onemore factor that influenced the reduction in hardness value is heat

treatment [17–19].

4.3. Wear test

The dry sliding wear experiments were conducted as per the OA

and the results are tabulated as shown in Table 2. For better under-

standing of the various factors considered L (applied load, in N ), D

(sliding distance, in m), S (sliding speed, in m/s) and their interac-

tions, it is required to develop an analysis of variance (ANOVA). The

experimental results were analyzed using commercial software

MINITAB, which is used in DOE applications. The effects and order

of significance of the design parameter with their interactions are

to be studied on the wear behavior. The analysis was carried outfor a confidence level of 1%.

Fig. 1. Microstructure of as-cast (a) alloy, (b) composite, (c) EDX of alloy and (d) EDX of hybrid composite.

Table 2

Experimental design using L27 OA.

Test Load L, (N) Distance D, (m) Speed S , (m/s) Wear volume loss in

mm3

Alloy Composite

1 15 1000 0.63 1.4 0.5

2 15 1000 1.88 1.6 0.8

3 15 1000 3.14 2.2 1.2

4 15 3000 0.63 1.5 0.7

5 15 3000 1.88 2.4 1.0

6 15 3000 3.14 3.2 1.6

7 15 5000 0.63 2.5 0.9

8 15 5000 1.88 3.3 1.2

9 15 5000 3.14 4.6 1.810 45 1000 0.63 1.7 0.9

11 45 1000 1.88 2.3 1.1

12 45 1000 3.14 2.7 1.5

13 45 3000 0.63 2.7 1.4

14 45 3000 1.88 2.7 1.7

15 45 3000 3.14 4.1 2.1

16 45 5000 0.63 3.8 1.3

17 45 5000 1.88 4.6 1.9

18 45 5000 3.14 6.1 2.6

19 75 1000 0.63 3.5 1.5

20 75 1000 1.88 4.6 2.1

21 75 1000 3.14 6.5 2.8

22 75 3000 0.63 4.7 1.9

23 75 3000 1.88 5.9 2.6

24 75 3000 3.14 7.7 3.2

25 75 5000 0.63 5.9 2.7

26 75 5000 1.88 7.9 3.8

27 75 5000 3.14 9.5 4.1

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Tables 3 and 4 shows the ANOVA results for the WVL of alloy

and composites respectively. It can be noted from column 7 of

Tables 3 and 4 that the p-value is zero for applied load, sliding

speed and sliding distance, which indicates that these play a major

role in the wear volume loss and have statistical significance.

Table 3 shows that applied load ( p = 55.86%) had a great influence

on wear loss of the alloy, while sliding distance ( p = 21.35%) and

speed ( p = 15.93%) showed less influence on the WVL. The interac-

tions (L * S) had a negligible influence ( p = 0.66%) on the WVL,

while the other two interactions (L * D and D * S ) had no effect on

the wear behavior. It can be observed from Table 4 that applied

load ( p = 56.67%) has highest influence followed by sliding distance

( p = 19.25%) and speed ( p = 14.22%). The influence of interaction

(L * D) is negligible ( p = 1.63%) on wear volume loss. Thus load is

an important factor that controls the WVL of both alloy and com-

posite materials.

4.4. Analysis of control factors

The response table for WVL of alloy and composite is presented

in Table5, to analyze the influence of the control factors. Analysis of

control factors will give the additional important information about

the nature of the process under consideration. The highest differ-

ence of control factors indicates the strongest influence on WVL.

It can be seen from Table 5 that the strongest influence on WVL

was applied load, followed by sliding distance and sliding speedrespectively in case of alloy. In case of composite, applied load

was the most influential factor and sliding speed was the second

most influential factor followed by sliding distance. Fig. 2(a and

b) shows the interaction plot for alloy and composites. Three levels

(low, medium and high) are considered in the experimentation and

a straight line can be drawn for second and third column. In the

first column of Fig. 2(a and b), there is a sudden increase in the

slope after 45 N, which shows that increase of applied load will

affect the wear performance of the specimen (Fig. 2a). The increase

in sliding distance has positive effect on the composite as the line

shows a reduction in slope (Fig. 2b), while the alloy (Fig. 2a) shows

no change in the wear behavior. The reason for the reduction in

slope of composite specimen is the smearing of reinforcements

and formation of protective layer inhibiting the WVL. Hence, as

sliding distance is increased, the wear resistance improves margin-

ally for composite (Fig. 2b).

Fig. 3(a and b) shows the main effects plot for means of alloy

and composite respectively. The rise in slope of lines indicates

the increase in WVL due to increase in applied load from 45 to

75 N, which can be analyzed that the wear phenomenon has

entered severe wear from mild wear.

4.5. Regression analysis

To ascertain the correlation between the factors (applied load,

sliding speed and sliding distance) and responses (volume loss),

multiple linear regression equations were generated using

MINITAB software. The regression equations are as follows:

WearðalloyÞðmm3Þ ¼ 0:078þ 0:0266L þ 1:84e4D þ 0:020S

þ 0:5e5LD þ 0:0111LS þ 1:06e4DS

ðR-Sq ¼ 93:59% R-SqðadjÞ ¼ 91:66%Þ ð1Þ

WearðCompositeÞðmm3Þ ¼0:137þ0:00987L1:8e5Dþ0:154S

þ0:4e5LDþ0:00332LS þ3:3e5DS

ðR-Sq¼95:32% R-SqðadjÞ ¼93:92%Þ ð2Þ

Eqs. (1) and (2) refers to the linear regression equation for cal-

culating volume loss by substituting the values of variables of alloyand composite respectively. The positive sign of the co-efficients

Table 3

Analysis of variance for alloy.

Source Degrees of freedom Sum of squares Adjusted sum of squares Adjusted mean of Squares F -ratio P -value Percentage (%) of contribution

L 2 68.019 68.018 34.009 553.16 0.000 55.86

D 2 26.605 26.605 13.303 216.37 0.000 21.35

S 2 20.099 20.098 10.049 163.45 0.000 15.93

L * S 4 2.761 2.761 0.690 11.23 0.002 0.66

L * D 4 1.128 1.128 0.282 4.59 0.032 –

D * S 4 0.901 0.901 0.225 3.67 0.056 –Error 8 0.492 0.492 0.061 6.20

Total 26 120.005 ‘ 100

S = 0.620278, R-Sq = 93.6% and R-Sq(adj) = 91.7%.

Table 4

Analysis of variance for hybrid composite.

Source Degrees of freedom Sum of squares Adjusted sum of squares Adjusted mean of Squares F -ratio P -value Percentage (%) of contribution

L 2 13.040 13.040 6.520 397.83 0.000 56.67

S 2 4.602 4.602 2.301 140.41 0.000 19.25

D 2 3.469 3.469 1.734 105.83 0.000 14.22

L * D 4 0.891 0.891 0.223 13.59 0.001 1.63

L * S 4 0.304 0.304 0.076 4.64 0.031 –

D * S 4 0.109 0.109 0.027 1.66 0.251 –

Error 8 0.131 0.131 0.016 8.23Total 26 22.547 100

S = 0.229643, R-Sq = 95.3% and R-Sq(adj) = 93.9%.

Table 5

Response table for means: smaller is better.

Level Wear response of alloy Wear response of composite

L D S L D S

1 2.522 2.944 3.078 1.078 1.378 1.311

2 3.411 3.878 3.922 1.611 1.800 1.800

3 6.244 5.356 5.178 2.744 2.256 2.322

Delta 3.722 2.411 2.100 1.667 0.878 1.011

Rank 1 2 3 1 3 2


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refers to increase in the wear volume loss with increase in their

associated variables. While negative sign indicates that WVL

decreases with increase in the associated variables. The negative

sign in Eq. (2) indicates that as sliding distance is increased, wear

resistance is increased due to the smearing of reinforcements that

act as ceramic mixed mechanical layer (CMML). However, the

effects of interactions are relatively insignificant.

Fig. 4(a and b) shows the normal probability plot for alloy and

composite. These probability plots clearly indicates that the

values lies closer to the normal probability line implying that

the errors are distributed normally and the model is adequate.

Thus the model formulated for prediction of volume loss of alloy

and composite which are represented by Eq. (1) and Eq. (2) is

adequate.

4.6. Response surface analysis

Response surface methodology (RSM) is a statistical method

that make use of quantitative data from suitable tests conducted

to determine and solve multi-variable equations. RSM, which is

used to analyze the results and surface plots for alloy and compos-

ites are shown in Figs. 5 and 6 respectively. WVL at any zone from

the tests conducted can be predicted from the surface plots. From

Figs. 5 and 6 it is clear that applied load has the most dominant

effect on WVL for both alloy and composite. The remaining factors,

sliding distance and sliding speed were less dominant compared to

load. In Fig. 5, the interactions L * D and L * S show that the slope of

load is more compared to the other two factors, clearly indicating

that applied load has more effect on the WVL.

Fig. 2. Interaction plots for wear volume loss (mm3) of (a) alloy and (b) composites.


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The magnitude of wear volume loss of alloy (Fig. 5), when com-

pared with composite (Fig. 6) is nearly double, which confirms the

wear resistance of composites and the presence of reinforcements

that inhibit the WVL. The smeared and adhered reinforcements actas a medium preventing the specimen from excessive wear.

4.7. Determination of accuracy of wear volume loss

For each experiment in the design matrix, the WVL model of

Eqs. (1) and (2) were used to calculate the theoretical wear volume

loss for alloy and composite. The results are summarized in

Table 6.

The experimental values were compared with the calculated

values and the comparison is shown in Fig. 7. It can be noticed that

the WVL values calculated from the multiple linear regression

model follows almost the similar trend as that of the experimental

values. The peaks of the alloy and composites reveal that the exces-

sive wear was inhibited due to the addition of reinforcements. Theslopes of the alloy are higher while that of composites are lower

signifying the importance of reinforcements. The variation may

be due to the irregularities in the experiment like environmental

condition, machine vibration or human errors.

4.8. Wear mechanism

Fig. 8(a and b) and Fig. 8(c–e) show the worn out surfaces of

alloy and composites respectively at a sliding speed of 1.88 m/s,

sliding distance of 3000 m and at different applied load. The single

arrow shows the sliding direction of worn surface. It is evident that

the surface of alloy (Fig. a and b) is rough with deep grooves com-

pared with the composite specimen (Fig. 8c–e) with fine grooves.

Fig. 8a and Fig. 8b shows the worn out surfaces of alloy at an

applied load of 15 and 75 N respectively. Due to the increase in

applied load, the morphology shows that the alloy (Fig. 8a and b)

has experienced severe wear under the absence of reinforcements.

The composites (Fig. 8c–e) show smooth surface in black region

(double arrow) due to the presence of graphite that smears outduring sliding and acts as a layer, protecting the specimen from

Fig. 3. Main effects plot for means (a) alloy and (b) composite.


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direct contact with the disc, thus enhancing wear resistance

[10,13–16]. The presence of SiCp and Gr are shown in Figs. 8e

and 9(a–c). These reinforcements participate in the wear process,

protecting the specimen from excessive wear.

During the wear process, the asperity on the surface of the

rotating steel disc comes in contact with the surface of the speci-

men (composite). Due to a large difference in the hardness of alloy

and reinforcement, the asperities in the counterface are pressedinto the specimen and the soft surface of composites is scratched.

Due to work-hardening of the surface layer of composite, the pro-

jected Fe asperity may detach from the counterface and adhere on

the composite surface. Due to severe scratching on the counterface,

large delamination cavities are formed as a result of fracture of the

surface material. The debris (Fig. 10) from both (specimen and

steel disc) materials are pushed down into the cavities and grooves

of specimen, until it becomes flat as the surrounding surface. The

formation of debris from the counterface may be by two ways.

First, the asperities on the surface of counterface break off and

are pressed against the composite surface during sliding, but are

obstructed by the surface material of composite. Secondly, the hard

reinforcements that bear the load on the composite surface will

certainly scratch heavily the counterface surface. These resultsare in agreement with Basavarajappa et al. [30].

Due to friction between the specimen and rotating disc during

dry sliding, temperature rises leading the specimen to lower its

mechanical property [1,2]. Due to rise in temperature, the alloy

loses its property of bonding with neighboring elements, resulting

in thin plate like wear debris (Fig. 10a). Even though zinc rich (g)

phase contributes in wear resistance, it is unable to withstand the

higher temperature due to higher applied load. The rise in the tem-

perature was noticeable as the applied load was increased, whichcauses a negative effect on the performance of specimen. As the

temperature rises, the bonding within the matrix begins to fail,

leading to severe wear and further changing to delamination with

further increase in applied load [25,26,28–30]. For composite

specimen, the rise in temperature was negligible as the formation

of protective layer secludedfurther exposureof newlayer inhibiting

the severe wear at lower load (15 and 45 N). At higher load (75 N),

the protective layer of composite specimen gradually exposed

newmaterial that were unableto retain and leading to severe wear.

In composites, due to rise in temperature, reinforcements gradually

start separating from the alloy, resulting in the direct exposure to

the rotating disc. The presence of microcracks (Fig. 8e) on the worn

out surfaces were observed. The effect of HT is that the residual

stress and microcrack is greatly reduced which affects the wearbehavior positively [17–19]. The reinforcements that smear out

Fig. 4. Normal probability plot of residuals of WVL (mm3) of (a) alloy and (b) composite.


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during the lower applied load and sliding speed get retained on the

specimen. As the applied load and sliding speed increases the

particles projected will brake and act as third body and startsremoving the matrix material. The metal oxides are formed because

of the rise in temperature, the crushed SiCp particles, the smeared

graphite along with a matrix material crush between the pin and

disc forming a ceramic mixed mechanical layer (CMML) preventingthe specimen from excessive wear (Fig. 8e). As the applied load is

Fig. 5. Response surface plot for alloy.

Fig. 6. Response surface plot for hybrid composite.


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increasedfurther, the layer formed will be destroyed at a faster rate

leading to direct contact between the new surface of specimen and

disc resulting in higher WVL. The similar results were observed by

other researchers [10,21,22,26,30].

The presence of Fe in Fig. 9(b and c) clearly shows that, there

was a formation of CMML on the surface on the specimen. But as

the applied load increased, there was a progressive increase in

the WVL. At lower load (15 N), the transfer of the disc material

onto the specimen surface was observed and the intensity of Fe

peak was higher experiencing mild wear. As the applied load was

increased (75 N), CMML formed on the specimen surface was

eroded. The formation and removal of the CMML at lower applied

load is slow, hence retaining the protective layer. At higher applied

load, the removal rate of the protective layer is at a faster rate than

the layer formation, leading to severe wear [22]. The study has

Table 6

Experimental and calculated values of alloy and composites.

Test Load L, (N) Distance D, (m) Speed S , (m/s) Wear volume loss in mm3

Alloy Composite

Experimental Calculated Experimental Calculated

1 15 1000 0.63 1.4 0.93 0.5 0.48

2 15 1000 1.88 1.6 1.29 0.8 0.77

3 15 1000 3.14 2.2 1.66 1.2 1.074 15 3000 0.63 1.5 1.57 0.7 0.60

5 15 3000 1.88 2.4 2.21 1.0 0.98

6 15 3000 3.14 3.2 2.84 1.6 1.36

7 15 5000 0.63 2.5 2.22 0.9 0.73

8 15 5000 1.88 3.3 3.12 1.2 1.19

9 15 5000 3.14 4.6 4.03 1.8 1.65

10 45 1000 0.63 1.7 2.08 0.9 0.96

11 45 1000 1.88 2.3 2.86 1.1 1.38

12 45 1000 3.14 2.7 3.65 1.5 1.80

13 45 3000 0.63 2.7 3.03 1.4 1.32

14 45 3000 1.88 2.7 4.08 1.7 1.82

15 45 3000 3.14 4.1 5.13 2.1 2.33

16 45 5000 0.63 3.8 3.98 1.3 1.69

17 45 5000 1.88 4.6 5.29 1.9 2.27

18 45 5000 3.14 6.1 6.62 2.6 2.86

19 75 1000 0.63 3.5 3.23 1.5 1.43

20 75 1000 1.88 4.6 4.43 2.1 1.9821 75 1000 3.14 6.5 5.64 2.8 2.53

22 75 3000 0.63 4.7 4.48 1.9 2.04

23 75 3000 1.88 5.9 5.95 2.6 2.67

24 75 3000 3.14 7.7 7.42 3.2 3.30

25 75 5000 0.63 5.9 5.73 2.7 2.65

26 75 5000 1.88 7.9 7.46 3.8 3.36

27 75 5000 3.14 9.5 9.21 4.1 4.07

Fig. 7. Experimental and calculated values of alloy and composites.

Fig. 8. SEM of worn surfaces of Alloy (a) 15 N, (b) 75 N, hybrid composite (c) 15 N, (d) 45 N and (e) 75 N.


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clearly indicated the instability and the consequent removal of

CMML resulting in high WVL and further causing transition frommild to severe wear.

The wear debris thrown out from the rotating disc is been pre-

sented in Fig. 10 which shows the size of wear debris of alloy(Fig. 10a) and composite (Fig. 10b) at applied load of 75 N, sliding

Fig. 9. EDX of worn surfaces of hybrid composite at load (a) 15 N, (b) 45 N and (c) 75 N.

Fig. 10. Wear debris at 75 N (a) alloy and (b) hybrid composite.


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speed of 1.88 m/s and sliding distance of 3000 m. The size of the

wear debris proves that the extent of wear of alloy (Fig. 10a) expe-

riencing delamination wear. The mechanical layer formed on the

alloy surface were incapable of withstanding the higher load

(75 N) and the layer were detached and thrown away as thin plate

like particles (Fig. 10a). Whereas for composite specimen, the

smeared reinforcements were fragmented and crushed between

the specimen and rotating disc, forming a protective layer. The

wear debris of composites (Fig. 10b) exhibits mild wear with small

particles thrown out from the rotating disc. The debris emerged

out of the alloy measures up to 500 lm (Fig. 10a) and the average

size of debris are nearly 200 lm. In case of composite specimen,

the debris measured are below 100 lm (Fig. 10b). The size of

debris explains the extent of wear in alloy (delamination) in

comparison with the composite specimen.

5. Conclusions

The following conclusions were drawn:

(1) The microconstituents of heat treated materials are well dis-

tributed and gets dissolved providing wear resistance by the

zinc rich (g) constituent. The effort to reduce the residual

stresses is attained by heat treatment. The microcracks pres-

ent in the as-cast specimen which causes excessive wear are

reduced by heat treatment resulting in superior wear

resistance.

(2) The significant parameters in the wear analysis were found

from ANOVA. Applied load is the most significant factor fol-

lowed by sliding distance and sliding speed in causing wear

in case of the alloy. Similarly the contributions for compos-

ites are applied load, sliding speed and sliding distance.

The interactions show negligible contribution for both alloy

and composite specimen.

(3) The metal oxides are formed because of the rise in tempera-

ture, the crushed SiCp particles, the smeared graphite parti-

cles along with a matrix material crush between the pin and

disc forming a ceramic mixed mechanical layer (CMML).

(4) The addition of solid lubricant (Gr) as secondary reinforce-

ment along with SiCp improves the wear resistance by form-

ing a CMML on the contact geometry. The formation and

retention of CMML acts as a protective layer, thereby reduc-

ing the wear volume loss in case of composites.

(5) The size of wear debris that emerged out of wear specimen

demarcated the severity of wear in alloy while fine wear

debris showed mild wear in composites.

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