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Technical Report

Investigations on dry sliding wear behavior of in situ casted AA7075TiC

metal matrix composites by using Taguchi technique

S. Baskaran, V. Anandakrishnan , Muthukannan Duraiselvam

Department of Production Engineering, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu, India

a r t i c l e i n f o

Article history:

Received 27 January 2014

Accepted 31 March 2014

Available online 12 April 2014

a b s t r a c t

High strength 7075 aluminum matrix composites with 4 and 8 wt.% of TiC particulate reinforcement was

synthesized by reactive in situ casting technique. X-ray diffraction analysis and scanning electron micros-

copy were used to confirm the presence of TiC particles and its uniform distribution over the aluminum

matrix. The dry sliding wear behavior of the as-casted composites was investigated based on Taguchi L27orthogonal array experimental design to examine the significance of reinforcement quantity, load, sliding

velocity and sliding distance on wear rate. The combination of 4 wt.% of TiC, 9.81 N load, 3 m/s sliding

velocity and 1500 m sliding distance was identified as the optimum blend for minimum wear rate using

the main effect plot. Load and sliding velocity were identified as the highly contributing significant

parameters on the wear rate using ANOVA analysis. Further a confirmation test was also conducted with

the optimum parameter combination for validation of the Taguchi results.

2014 Elsevier Ltd. All rights reserved.

1. Introduction

Light weight monolithic alloys are reinforced with hard second

phase particles to produce metal matrix composites, with

enhanced physical and mechanical properties, by suitable combi-

nations of matrix, reinforcements and processing routes, which

in turn increase their utilization in numerous applications. Partic-

ulate reinforced aluminum metal matrix composites, a class of

metal matrix composites takes ample attention in automobile

and aerospace industries due to their light weight, easy fabrication,

low cost, high wear resistance and isotropic properties [1]. The

production of composites are commonly done by various methods,

such as self-propagating high temperature synthesis[2], mechani-

cal alloying[3], reactive slag process[4], vacuum pressure infiltra-

tion[5], direct metal laser sintering [6], spray deposition[7], stir

casting (ex situ)[8] and reactive processing (in situ)[9]. However,in situ processing methods are prominent being economic, easy

and contributing several advantages over other methods like uni-

form distribution of very fine reinforcements, high interfacial

bonding strength between matrix and reinforcement, high degree

of thermodynamic stability and grain refinement [9,10]. The most

universally used particle reinforcements revealed by vast literature

are TiC, Al4C3, SiC, Al2O3, B4C, TiB2 and ZrB2, in which TiC has par-

ticular consideration due to its high hardness, high elastic modu-

lus, low density, low chemical reactivity, good wettability with

molten aluminum, thermodynamic stability and freedom from

observed gases[11].Discontinuously reinforced aluminum based metal matrix com-

posites generally posses superior tribological properties when

compared with unreinforced aluminum alloys[12]. To understand

the tribological behavior of composites, so far several investiga-

tions were attempted, including the study of dry sliding wear

behavior of as-casted SiC reinforced aluminum metal matrix com-

posites by Ma et al. [13]. The dry sliding wear behavior of alumi-

num and aluminum matrix composites reinforced with different

volume percentages of SiC was studied by Bauri and Surappa

[14]and Jha et al.[15]using pin-on-disc method. Tyagi[16]fabri-

cated the in situ AlTiC composites with different volume fractions

and investigated its dry sliding wear behavior. Kumar et al. [17]

studied the abrasive wear behavior of in situ formed Al4Cu/TiB 2

composite at normal load of 1050 N. Mandal et al. [18]fabricatedAl12Si/TiB2composite by reaction between K2TiF6and KBF4salts

and analyzed the role of TiB2content in dry sliding wear behavior.

Venkataraman and Sundararajan [19] studied the formation and

fracture of the mechanically mixed layer during dry sliding wear

analysis of AA7075/SiC composites.

Design of experiments (DOE) is a most useful statistical tool

employed in many areas including but not limited to: engineering,

medical, basic science, agriculture, management for design com-

parison, variable identification, design optimization, process con-

trol and product performance prediction. Taguchi technique a

well known DOE tool was used by Basavarajappa et al. [20] to

study the effect of applied load, sliding speed and sliding distance

http://dx.doi.org/10.1016/j.matdes.2014.03.074

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

Corresponding author. Tel.: +91 431 2503521; fax: +91 431 2500133.

E-mail address:[email protected](V. Anandakrishnan).

Materials and Design 60 (2014) 184192

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


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on dry sliding wear behavior of SiC and graphite particles rein-

forced aluminum composites and identified that sliding distance

has the highest influence on their wear behavior. Using L27Taguchi

experimental design, Mahapatra and Patnaik [21] studied the

mechanical and erosion wear behavior of hybrid composites and

Sahoo [22] optimized the process parameters for wear behavior

of electroless NiP coatings against steel. Sahin [23]investigated

the abrasive wear behavior of AA201415 wt.%SiC composite byL9Taguchi design and used analysis of variance(ANOVA) to analyze

the wear parameters. Koksal et al.[24]studied the effect of sliding

velocity, normal load, sliding distance and reinforcement ratio on

dry sliding wear behavior Al/AlB2composites and optimized these

parameters to get minimum wear rate by using L9Taguchi orthog-

onal array. Owing to above all, in the present work, aluminum

7075 based TiC reinforced metal matrix composites with varying

TiC content were fabricated by in situ reactive process and their

tribological behavior is investigated in a pin-on-disc tribo-meter

using Taguchi technique. Further the effect of reinforcement per-

centage, sliding velocity and load on the dry sliding wear behavior

of the developed composites is analyzed using standard statistical

tools.

2. Experimental details

2.1. Synthesis of composite material and experimental design

Aluminum alloy 7075 used for fabrication of the composite was

analyzed for purity and original chemical composition

was obtained as shown in Table 1. Initially 1.5 kg of AA7075 was

allowed to melt in a graphite crucible inside an electrical resistance

furnace and the molten aluminum was maintained at a tempera-

ture of 900 C. In order to obtain composites having different

weight percentages of TiC reinforcement by in situ casting tech-

nique, the appropriate weight of halide salt K 2TiF6 and graphite

powder to be added are stoichiometrically calculated and the same

is given inTable 2. The carefully weighed halide and graphite pow-

ders are mixed, preheated at 250 C for 2 h to eliminate moisture

and gently introduced into the molten aluminum at 900 C to get

stable and fine TiC particles[25,26]. Once in every 10 min, the melt

was stirred by using a graphite stirrer for allowing formation of

uniformly distributed TiC in the matrix alloy. During the in situ

process, the process parameters such as melting temperature, time

allowed for reaction are strictly adhered to standards available in

various literatures[1,2,4,11]. During the time of stirring, the occur-

rence of exothermic chemical reaction between molten aluminum

and the powders was observed by the drastic raise in melt temper-

ature. Thus, the raise in temperature in turn increased the fluidity

of the melt and enhanced the formation of more amounts of

uniformly distributed fine TiC particles inside the melt. The

exothermic chemical reaction pertaining to the above process is

as follows[11]:

3K2TiF6 4Al ! 3Ti 3KAlF4 K3AlF6 1

Ti 3Al ! Al3Ti 2

Al3Ti C ! TiC 3Al 3

The byproducts of the chemical reaction escaped as gases and

remaining floated as slag because of its low density, as explained

elsewhere[1]. The reaction ended at around one hour which was

observed by the absence of escaping gases and reaction sparks

After removing the slag, the molten composite was poured into

the 250 C preheated permanent mould and allowed to get cooled

and solidified. Finally, the castings were removed from the mould

and cut into the desired shape and size. The same procedure was

followed to produce composites of different weight percentages o

reinforcement by adding the required amount of salt and graphite

powder as given inTable 2. In order to study the effect of addition

of TiC reinforcement in the AA7075, one set of casting was produced

without adding salt and graphite powder in the AA7075 melt which

is further referred as AA70750 wt.%TiC throughout this article. To

confirm the presence of various elements and TiC particles in thecastings, X-ray diffraction analysis was performed on the as-casted

Table 1

Chemical composition of AA7075 alloy (%).

Fe Si Mn Mg Zn Cu Ti Cr Al

0.215 0.0588 0.0524 2.06 5.52 1.56 0.0362 0.180 Remaining

Table 2

Quantity of halide salt and graphite powders added for obtaining various composi

tions of materials.

Material composition Quantity of powder added (g)

K2TiF6 Graphite

AA70750 wt.%TiC 0 0

AA70754 wt.%TiC 240.54 12.03

AA70758 wt.%TiC 481.08 24.06

Table 3

Control factors and their levels.

Control factors Units Level

1 2 3

Reinforcement wt.% 0 4 8

Load N 9.81 19.62 29.43

Sliding velocity m/s 1 2 3

Sliding distance m 1000 1500 2000

Table 4

Experimental results for wear rate with calculated S/N ratios.

Expt.

no.

Reinforcement

(wt.%)

Load

(N)

Sliding

velocity

(m/s)

Sliding

distance

(m)

Wear rate

(mm3/m)

S/N

ratio

1 0 9.81 1 1000 0.00191 54.38

2 0 9.81 2 1500 0.00147 56.65

3 0 9.81 3 2000 0.00109 59.20

4 0 19.62 1 1500 0.00290 50.75

5 0 19.62 2 2000 0.00253 51.94

6 0 19.62 3 1000 0.00367 48.71

7 0 29.43 1 2000 0.00485 46.28

8 0 29.43 2 1000 0.00266 51.50

9 0 29.43 3 1500 0.00230 52.76

10 4 9.81 1 1000 0.00264 51.56

11 4 9.81 2 1500 0.00149 56.53

12 4 9.81 3 2000 0.00070 63.09

13 4 19.62 1 1500 0.00395 48.06

14 4 19.62 2 2000 0.00242 52.32

15 4 19.62 3 1000 0.00278 51.11

16 4 29.43 1 2000 0.00441 47.11

17 4 29.43 2 1000 0.00228 52.84

18 4 29.43 3 1500 0.00142 56.95

19 8 9.81 1 1000 0.00193 54.28

20 8 9.81 2 1500 0.00138 57.20

21 8 9.81 3 2000 0.00126 57.99

22 8 19.62 1 1500 0.00369 48.65

23 8 19.62 2 2000 0.00286 50.87

24 8 19.62 3 1000 0.00213 53.43

25 8 29.43 1 2000 0.00501 46.00

26 8 29.43 2 1000 0.00308 50.22

27 8 29.43 3 1500 0.00229 52.80

S. Baskaran et al./ Materials and Design 60 (2014) 184192 185


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material samples. Further, to see the size, distribution and morphol-

ogy of the in situ formed TiC particles and the grain structure of the

as-casted materials, microstructures were obtained by scanningelectron microscopy after etching with kellers etchant.

2.2. Wear test

The dry sliding wear tests were conducted as per ASTM: G99 to

evaluate the dry sliding wear behavior of the as-casted materials in

a DUCOM pin on disc wear testing machine. Based on the avail-

able literatures [1324], amount of reinforcement, applied load,

sliding velocity, and sliding distance were identified as the impor-

tant dry sliding wear testing parameters and they are varied in

three levels as shown in Table 3. In order to reduce the number

of experiments for the selected parameters and their levels, a stan-

dard Taguchi L27 orthogonal array was preferred to conduct the

experiments as shown inTable 4. Wear sample pins of 6 mm diam-

eter and 31 mm height prepared from the as-casted materials were

allowed to slide over hardened D3 steel counterpart disc having a

hardness of 63 HRC. In order to study the wear behavior of the pin,

keeping the counterpart without wear, the counterpart was chosen

to have hardness higher than that of the pin. The end faces of the

sample pins and contacting counterpart, polished to a surface

roughness close to 1 lm were kept perfectly flat in order to get

uniform contact between pin and disc during the wear test. Before

and after each experimental run, the pin and the disc were cleanedwith acetone, dried and their masses were measured using an elec-

tronic weighing machine with least count 0.0001 g. The mass of the

disc was carefully examined to confirm that there was no consid-

erable wear in the counterpart as the mass loss of pin alone was

taken as a measure of sliding wear. The wear rate of the sample

pin was calculated by using the standard formula for wear rate

(Eq.(4)) as used elsewhere[27], for each and every experimental

run and provided inTable 4.

Wear rate mm3=m Mass loss=density

Sliding distance

4

Fig. 1. X-ray diffraction results of as-casted AA7075 and composites.

(a) (b)

(c) (d)

TiC

TiC

Fig. 2. SEM image of the AA7075 matrix composites with TiC reinforcement: (a) 0 wt.%, (b) 4 wt.%, (c) 8 wt.% and (d) 4 wt.%.

Table 5

Response table for S/N ratios (smaller is better).

Level Reinforcement Load Sliding velocity Sliding distance

1 52.47 56.77 49.68 52.01

2 53.29 50.65 53.34 53.38

3 52.39 50.72 55.12 52.76

Delta 0.90 6.12 5.44 1.37

Rank 4 1 2 3

186 S. Baskaran et al. / Materials and Design 60 (2014) 184192


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3. Results and discussion

3.1. X-ray diffraction analysis

X-ray diffraction (XRD) patterns of the as-casted AA70750 wt.%TiC and the composites with different weight percentages

of TiC reinforcement are shown inFig. 1. It is observed that, peaks

corresponding to aluminum are present in all the three materials,

whereas TiC peaks are present in AA70754 wt.%TiC and AA7075

8 wt.%TiC composites and no other reaction product peaks are seen.

Comparing the XRD peaks of composites, it is observed that the

intensity of the peaks corresponding to TiC is found to be higher

with increased amount of TiC in the materials.

3.2. Scanning electron microscopy

The scanning electron microscopy images of AA70750 wt.%TiC,

AA70754 wt.%TiC and AA70758 wt.%TiC are shown in Fig. 2(ad).

Veryclear grainboundaries with the presence of precipitates homo-geneously distributed along the grain boundaries are observed in

Fig. 2(a) corresponding to AA70750 wt.%TiC. FromFig. 2(b and c),

thegrain sizes areobservedto be relatively reduced with increasing

amount of TiC particles. The formed TiC particles are found to be

segregated along the grain boundaries homogeneously as seen in

Fig. 2(bd). The appearance of TiC particles which is observed by

thick grain boundaries is found to be more in AA70754 wt.%TiC

(Fig. 2(b)) and further more in AA70758 wt.%TiC (Fig. 2(c)) corre-

sponding to theamount of halidesalt andgraphitepowder addition,

which is also evident by the intensity of corresponding peaks in

their respective XRD patterns (Fig. 1). At higher magnification as

shown in Fig. 2(d), the interfaces between the aluminum matrix

and TiCparticles areclearlyobserved, andalso theuniformdistribu-

tion of TiC particles is observed along the grain boundaries with theappearance of some TiC particles dispersed inside the aluminum

matrix grains. The individual TiC particle measuring around 2 lm

could be seen visibly with its clear boundary and the interfaces

between the TiC particlesare also observed in higher magnification.

All these observations are in good agreement with earlier litera-

tures, which states that the uniform distribution of reinforcement

particles, strong and clear interface between matrix and reinforce-

mentparticles, formation of reinforcement with size in few microns,

etc. are the possible advantages of in situ formation of reinforce-

ment over ex situ processes[1,4,9].

3.3. Statistical analysis

In Taguchi method, the objective function is converted to Signalto Noise (S/N) ratio which is treated as the quality characteristic. In

the present work, wear rate is taken as the objective function and

Taguchis Lower the Better quality characteristic is chosen to

minimize the objective function (i.e. wear rate).

3.3.1. Analysis of factors

To analyze the effect of factors influencing wear rate, the S/N

ratio values for all the experimental trials as shown in Table 4

are calculated using the statistical tool Minitab 16. The delta values

for individual factors are derived from the S/N ratio values as

shown inTable 5, using which the order of influencing factors on

wear rate from high to low is identified as load, sliding velocity

sliding distance and reinforcement respectively. From the maineffect plot as shown in Fig. 3, it is observed that in order to get

840

0.0035

0.0030

0.0025

0.0020

0.0015

29.4319.629.81

321

0.0035

0.0030

0.0025

0.0020

0.0015

200015001000

Reinforcement (wt.%)

M

ean

Load (N)

Sliding velocity (m/s) Sliding distance (m)

Fig. 3. Main effect plot for wear rate in mm3/m.

Fig. 4. Depth of wear of AA70758 wt.%TiC composite with respect to sliding

distance (up to 1000 m) at sliding velocity: (a) 1 m/s, (b) 2 m/s and (c) 3 m/s.



5/9

minimum wear rate, the optimal process parameters should be in

middle level for reinforcement (4 wt.%TiC), low level for load

(9.81 N), high level for sliding velocity (3 m/s) and middle level

for sliding distance (1500 m). Further it is also observed from the

main effect plot that load has the strongest influence on wear ratefollowed by sliding velocity and amount of reinforcement. The

load, being the predominating factor on wear rate, when increased

from 9.81 N to 29.43 N for AA70758 wt.%TiC composite, for all the

sliding velocities tested, the depth of wear is highly responsive and

found increasing as observed from Fig. 4(ac). This shows that,

when the load increases, the hard asperity of the counterface mate-rial ploughs the softer surface of the pin deeper which is

Fig. 5. (a) Worn surface of AA70758 wt.%TiC composite for 29.43 N load at 1 m/s sliding velocity and (b) magnified view of zone A.

Element Weight (%) Atomic (%)

O K 33.04 48.07

Al K 53.72 46.34

Ti K 3.89 1.89

Fe K 6.22 2.59

Zn L 3.13 1.11

Totals 100.00

Fig. 6. Energy dispersive spectroscopy of worn surface of AA70754 wt.%TiC composite after sliding 2000 m with 3 m/s sliding velocity at 9.81 N load.



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apparently seen in the worn surface of AA70758 wt.%TiC compos-

ite for highest load at 1 m/s sliding velocity as shown in Fig. 5(a

and b). Further, along the sliding direction, the worn surface is

observed with severe plastic deformation leading to formation of

parallel deep grooves with wear debris spread all over. The trend

of higher depth of wear at higher load as observed is similar to

the findings reported by several investigators [3,5,8,13,14,16,18].

The stress concentration during sliding at higher load is more

at the sharp edges of the TiC particles which initiate cracks in

the matrix adjacent to the TiC particles which further propagates

parallel to the sliding direction and thereby gets segmented and

forms debris[28]. Thus, the debris formed in between the sliding

surfaces further plough the pin surfaces creating parallel and dee-

per ploughs all along the sliding surface as shown in Fig. 5(a). All

these mechanisms contribute severe plastic deformation or severewear on pin surface while sliding in dry environment at higher

loads. When the sliding velocity increases generally the amount

of heat generation elevates because of increased friction between

the sliding surfaces[29]. At this elevated temperature, the soft alu-

minum matrix on the pin gets severe plastic deformation and leads

to formation of mixture of the oxide surface known as mechani-

cally mixed layer (MML) which allows smooth sliding of the mat-

ing surface thereby reducing the wear rate[28]as observed in the

main effect plot for higher velocity. The formation of oxide in the

worn surface of AA70754 wt.%TiC composite after sliding

2000 m with higher sliding velocity (3 m/s) at low load (9.81 N)

condition is evidenced by the identification of O, Al, Ti, Fe and Zn

peaks in the selected zone (spectrum 2) by the energy dispersive

spectroscopic analysis as shown inFig. 6. This behavior of low wearrate for higher sliding velocity was obtained in C/ZrO2 composites

and reported by Jha et al. [15]and Zhu et al. [30]in their earlier

research work.

In any interaction graph, the parallel lines indicate the absence

and non parallel lines indicate significant presence of interaction

effect of factors on the response. From the interaction plot for wear

rate as shown inFig. 7, it is observed that the interactions of rein-

forcement with load is insignificant for lower loads and significant

at higher load, the reason is at higher loads and large amount of

reinforcement, the ploughs formed are deeper, wider and more

in numbers which in-turn increases the wear rate. The interaction

of load with sliding distance is significant for highest load after

sliding long distance is contrary to that of the other two low load

conditions because of the formation of more amount of larger deb-ris which in-turn increases the wear rate. The interaction of sliding

velocity with sliding distance for lowest and highest velocities is

observed to be converse because of the softening of matrix mate-

rial at higher velocity which provides smooth sliding with lower

wear rate. The interaction of reinforcement with sliding velocity

and sliding distance and also the interaction between load and

sliding velocity are observed to be insignificant as the lines o

interaction are almost parallel.

Contour bands indicating ranges of wear rate against (a) rein-

forcement, load; (b) reinforcement, sliding velocity; (c) reinforce-

ment, sliding distance; (d) load, sliding velocity; (e) load, sliding

distance; and (f) sliding velocity, sliding distance are shown in

Fig. 8(af). From the contours shown inFig. 8(a), it is observed that

for all the materials tested the wear rate is less than 0.002 mm 3/m

when the load is lower than 12 N, 0.0020.003 mm3/m when the

load is 1219 N and 0.0030.004 mm3/m when the load is higherthan 19 N. Whereas, when the load is above 26 N, an exceptiona

wear rate of less than 0.003 mm3/m is observed only for AA7075

4 wt.%TiC composite which shows that theAA70754 wt.%TiC com-

posite is having better wear resistance than AA7075 alloy and

AA70758 wt.%TiC composite at higher load. When the sliding

velocity is higher than 2 m/s, a better wear range of 0.001

0.002 mm3/m is observed irrespective of the amount of reinforce-

ment as shown in Fig. 8(b). But for lower sliding velocity (1 m/s)

the wear rate is observed to be higher than 0.003 mm 3/m for al

the materials tested. From Fig. 8(c) it is observed that, the wear rate

for AA70754 wt.%TiC composite is less than 0.0025 mm3/m for a

wider range of sliding distance from 1100 m to 2000 m, whereas

for AA70758 wt.%TiC composite the wear rate is more than

0.0025 mm3/m above the sliding distance of 1550 m. From theabove inferences, it is apparent that AA70754 wt.%TiC composite

exhibits superior wear resistance than AA7075 alloy and AA7075

8 wt.%TiC composite. From the contour bands observed in

Fig. 8(d) it is apparent that the wear rate is high in the range o

0.0040.005 mm3/m for low sliding velocity and high load combi-

nation. Whereas, a better wear range of 0.0010.002 mm3/m is

observed for the combination of low load and high sliding velocity

A moderate wear range of 0.00200.0025 mm3/m is observed for

high load at higher sliding velocity. The wear rate is high and above

0.004 mm3/m for higher sliding distance at higher load as shown in

Fig. 8(e). Whereas, the wear rate is less than 0.0020 mm3/m for a

wide range of sliding distance from 1100 m to 2000 m at low load

condition. It is evident fromFig. 8(f) that the wear rate is minimum

when the sliding velocity is higher than 2 m/s for a wider range ofsliding distance from 1150 m to 2000 m.

Fig. 7. Interaction plot for wear rate in mm3/m.



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3.3.2. ANOVA analysisANOVA, a statistical tool is used to find out the significance of

the parameters on the wear rate. From the analysis of variance

for S/N ratios of the wear rate shown in Table 6 with computed

R-Sq value of 92.66%, load and sliding velocity are identified as

the significant parameters with 50.09% and 31.26% contribution

respectively. The effect of reinforcement and sliding distance on

the wear rate is found to be insignificant with very low percentage

contributions.

3.3.3. Regression analysis

To predict the wear rate within the specified level values of

parameters, using regression analysis, a second order polynomial

regression equation for wear rate with significant parameters is

derived withR-Sq value of 91.48% and given as Eq. (5)

Wear rate mm3=m

0:0000178 0:000265 B 0:000182 C

0:0000048 B B

0:0000464 B C 0:0000000513 B D

0:000352 C C

0:000000735 C D 0:000000751 A B

0:0000516 A C

0:0000000618 A D

8>>>>>>>>>>>>>>>>>>>>>:

9>>>>>>>>>>>=>>>>>>>>>>>;

5

whereAis Reinforcement in wt.%, Bis Load in N, Cis Sliding velocity

in m/s and D is Sliding distance in m. The residuals (errors) are

found to be normally distributed along the straight line in the

normal probability plot for wear rate as shown in Fig. 9.

(a)

(b)

0.0030

0.0030

0.0025

0.0020


Load(N)

28

26

24

22

20

18

16

14

12

10

0.0020

0.0025

0.0030

Wear rate

0.0040

0.0020

0.0035

0.0030

0.0025

0.0020


Slidingvelocity(m/s)

8763210 54

3.0

2.5

2.0

1.5

1.0

0.0020

0.0025

0.0030

0.0035

Wear rate0.0010

8763210 54

(c)

0.0025

0.0025


Slidingdistance(m)

2000

1800

1600

1400

1200

1000

0.0020

0.0025

0.0030

Wear rate

0.0020

0.0030

0.0030

8763210 54

(d)

0.00400.00350.0030

0.0025 0.00250.0020

Load (N)

Slidingvelocity(m/s)

01 21 41 61 81 02 22 42 62 82

3.0

2.5

2.0

1.5

1.0

0.0020

0.0025

0.0030

0.0035

0.0040

0.0050

Wear rate

0.0050

0.0010

0.0020

(e)

(f)

0.0035

0.0030

0.00250.0020

Load (N)

Slidingdistance(m)

01 21 41 61 81 02 22 42 62 82

2000

1800

1600

1400

1200

1000

0.0020

0.0025

0.0030

0.0035

0.0040

Wear rate 0.0040

0.0035

0.0020

0.0040

0.0035

0.0030

0.0025

0.0025

0.0020

Sliding velocity (m/s)

Slidingdistance(m)

3.02.52.01.51.0

2000

1800

1600

1400

1200

1000

0.0020

0.0025

0.0030

0.0035

0.0040

Wear rate0.0050

0.0010

0.0030

Fig. 8. Contour plot for wear rate with respect to: (a) load, reinforcement, (b) sliding velocity, reinforcement, (c) sliding distance, reinforcement, (d) sliding velocity, load, (e)

sliding distance, load and (f) sliding distance, sliding velocity.



8/9

4. Confirmation test

A confirmation test was conducted based on the combination of

optimal level (i.e. A2B1C3D2) of each parameter obtained from

main effect plot and response table of wear rate. A very low per-

centage error of 3.75% is obtained between the predicted and

experimental value showing a very good correlation as shown in

Table 7.

5. Conclusions

The dry sliding wear tests were conducted by pin-on-disc wear

tester on the in situ fabricated AA7075 and AA7075 metal matrix

composites containing 4 and 8 weight percentages of TiC reinforce-

ment using a Taguchi L27 orthogonal array design. The followingconclusions are made from this study.

(1) The AA7075 matrix TiC reinforced composites were success-

fully fabricated through in situ casting technique.

(2) The XRD analysis confirmed the presence of TiC particles in

the composites.

(3) SEM analysis showed that TiC particles were uniformly dis-

tributed along the grain boundaries and the average size of

in situ formed TiC particles was found to be less than 2 lm

(4) From the main effect plot, the optimal level combination for

minimum wear rate was identified as 4 wt.%TiC reinforce-

ment, 9.81 N load, 3 m/s sliding velocity and 1500 m sliding

distance (i.e. A2B1C3D2).(5) From the ANOVA analysis, the significant parameters were

identified as load and sliding velocity with percentage con-

tribution of 50.09% and 31.26% respectively withR-Sq value

of 92.66%.

(6) Finally from the confirmation test conducted based on the

optimal level combination, the obtained wear rate wa

found to be very close to predicted value with a minor error

of 3.75%.

References

[1] Tjong SC, Ma ZY. Microstructural and mechanical characteristics of in situmetal matrix composites. Mater Sci Eng 2000;R29:49113.

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Table 6

Analysis of variance for S/N ratios of wear rate.

Source Df a Seq SSb Adj SSc Adj MSd F Pe P(%)

Reinforcement 2 4.516 4.516 2.258 0.42 0.677 1.02

Load 2 221.990 221.990 110.995 20.48 0.002 50.09

Sliding velocity 2 138.537 138.537 69.268 12.78 0.007 31.26

Sliding distance 2 8.470 8.470 4.235 0.78 0.499 1.91

Reinforcement load 4 8.114 8.114 2.028 0.37 0.820 1.83

Reinforcement sliding velocity 4 20.040 20.040 5.010 0.92 0.508 4.52Reinforcement sliding distance 4 9.037 9.037 2.259 0.42 0.792 2.04

Error 6 32.513 32.513 5.419 7.33

Total 26 443.21 100.00

S= 2.32784; R-Sq = 92.66%; and R-Sq(adj) = 68.21%.a Degrees of freedom.b Sequential sums of squares.c Adjusted sums of squares.d Adjusted mean squares.e Probability.

0.00

6

0.005

0.00

4

0.00

3

0.00

2

0.00

1

0.00

0

-0.001

99

95

90

80

70

60

50

40

30

20

10

5

1

Wear rate

Percent

M ea n 0 .00 25 59

StDev 0.001130

N 27

AD 0.420

P-Value 0.302

Normal - 95% CI

Fig. 9. Normal probability plot for wear rate.

Table 7

Confirmation experiment result.

Op timal c ontrol p arameters Error (%)

Predicted Experimental

Level A2B1C3D2 A2B1C3D2 3.75

Wear rate (mm3/m) 0.0006211 0.0005978



9/9

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