Investigations on microstructure, mechanical, and ... · applications of AA 7075 Al alloy are ships and submarines, aircraft and space crafts, trucks and rail vehicles, automobiles

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Original Research Article

Investigations on microstructure, mechanical, andtribological behaviour of AA 7075–xwt.% TiCcomposites for aerospace applications

K.R. Ramkumar a, S. Sivasankaran b,*, Fahad A. Al-Mufadi b[1_TD$DIFF], S. Siddharth c,R. Raghu d

aCentre of Excellence in Corrosion and Surface Engineering, National Institute of Technology, Tiruchirappalli, TamilNadu, IndiabDepartment of Mechanical Engineering, College of Engineering, Qassim University, Buraidah 51452, Saudi ArabiacDepartment of Mechanical Engineering, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham,Amrita University, IndiadDepartment of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimbatore, Tamil Nadu, India

a r t i c l e i n f o

Article history:

Received 2 June 2018

Accepted 4 December 2018

Available online 3 January 2019

Keywords:

AA 7075 Al alloy

Metal matrix composite

Characterization

Mechanical properties

Wear

a b s t r a c t

This researchworkwas dedicated to prepare AA7075/(0, 2.5, 5 and 7.5 wt.%) TiCmetalmatrix

composites through stir casting route. The manufactured composites were effectively

characterized using various techniques such as X-ray diffraction, and advanced electron

microscopes. The mechanical properties by the flexural strength and hardness results had

performed and investigated elaborately. Further, the tribological properties in terms of the

wear resistance and the coefficient of friction was also done and demonstrated clearly. The

dispersion of TiC ceramic particles and its embedding over the ductile Al 7075 matrix was

successfully obtained which exhibited excellent mechanical and surface behaviour with the

function of TiC particles when compared tomonolithic Al 7075 alloy. These results were due

to the particulate strengthening of hard TiC ceramic particle over the soft ductile phase. In

addition, X-ray diffraction results ensured the manufacturing of Al 7075-x wt.% TiC metal

matrix composites successfully and no other inter-metallic phases were observed.

itechnika Wrocławska. Published by Elsevier B.V. All rights reserved.

© 2018 Pol

1. Introduction

The growing demand for novel lightweight materials withhigher strength and toughness has led to the development ofcompositematerials [1]. It is well known that the hard ceramic

* Corresponding author.E-mail addresses: [email protected] (K.R. Ramkumar), sivasank

[email protected] (F.A. Al-Mufadi), [email protected](S. Siddharth), [email protected] (R. Raghu).https://doi.org/10.1016/j.acme.2018.12.0031644-9665/© 2018 Politechnika Wrocławska. Published by Elsevier B.V

particles are usually having the higher value of hardness,Young's modulus value, and excellent creep resistance.However, the brittleness is themajor flaw of ceramic particles,which is being restricted for the applications of structural andaerospace parts [2]. However, the ductile metallic phases areusually having more value of toughness; but these ductile

[email protected], [email protected] (S. Sivasankaran),

. All rights reserved.

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[(Fig._1)TD$FIG]

Fig. 1 – (a) Schematic of stir casting of AA 7075–TiC composite preparation and (b) photograph of stir casting furnace.

Table 1 – Chemical composition of AA 7075 alloy.

Elements wt.%

Si 0.2Fe 0.23Cu 1.71Mg 2.46Zn 5.29Ti 0.54Cr 2.21Al Bal.

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metallic phases have possessed the lower value of strength [3].In order to improve and achieve both the strength andtoughness of ductilemetallic phases,metalmatrix composites(MMCs) are being used currently. MMCs are one kind ofengineeringmaterials nowadayswhere hard ceramic particlesare dispersed with ductile metals [4]. Among various kinds ofMMCs, aluminium matrix composites (AMCs) are frequentlyused in most of the automotive and aerospace industries as ithas the lower value of density, and possesses excellentcastability [5]. Further, these AMCs have more attractive inhigh strength-to-weight ratio, high stiffness-to-weight ratio,high wear resistance, less cost, easily available one, more inthermal conductivity, good in thermal stability, and so on [6–8]. Several researchers have focused on and studied the Al-based MMCs reinforced with Al2O3, SiC, B4C, TiB2, ZrB2, andTiO2 [9–13]. Among the various second phase particles, TiCceramic particles are having the lower value of density, morein strength, excellent wettability with molten Al alloys, andpoor in chemical reactivitywith thematrix [14–16]. Further, AA7075 alloy has the characteristics of easy tomanufacture, goodabrasive resistance, excellent corrosion, good in wear resis-tance, higher in strength, and heat treatable alloy. Some of theapplications of AA 7075 Al alloy are ships and submarines,aircraft and space crafts, trucks and rail vehicles, automobilesand prosthetic device. Several manufacturing routes are thereto manufacture the MMCs in which the stir casting process ispreferred due to its simplicity, mass production, low cost, easeof applicability and flexibility [6,7]. However, there is no muchresearch work related to AA 7075 alloy reinforced withtitanium carbide (TiC) ceramic particles. In this investigation,an attemptwasmade to study the synthesis, characterization,

Table 2 – Properties of titanium carbide particles (TiC).

Density(g/cm3)

Meltingpoint (8C)

Vickershardness (GPa) mo

4.93 3067 24–32

mechanical, and wear properties of AA7075/TiC compositesthrough stir casting technique. The composites had reinforced0, 2.5, 5 and 7.5 wt% TiC. Themicrostructure of the compositescharacterized by X-ray diffraction and several electron micro-scopes by which the mechanical and were behaviour with thefunction of the reinforcement particles were investigated andreported.

2. Experimental procedure

This work encompasses the manufacturing of Al 7075–x wt.%TiC composites (x = 0, 2.5, 5, and 7.5 wt.%) by stir castingmethod (Fig. 1). The chemical composition of AA 7075 matrixalloy is illustrated in Table 1. In this technique, the Al 7075initially kept in a crucible furnace; heated to a temperature of800 8C. Simultaneously the ceramic particles of TiC preheatedto a temperature of 200 8C in a pre-heater which is availablewith the furnace. The properties of TiC are given in Table 2,

Elasticdulus (GPa)

Thermalconductivity (w/m/k)

Crystalstructure

400 17–32 Cubic

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Table 3 – The sample composition, weighing of AA 7075matrix and TiC particles.

% Al (7075) alloy (kg) TiC (g)

0 1 02.5 1 255 1 507.5 1 75

[(Fig._3)TD$FIG]

Fig. 3 – X-ray diffraction peak obtained on AA 7075–x wt.%TiC (x = 0, 2.5, 5, and 7.5) ex situ composites.

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which was supplied by Loba Chemie, India. Meanwhile, the Al7075 alloy had attained its liquid state and the stirring motorwas switched on. The stir casting set-up consisted of a blade,which wasmade of austenitic stainless steel. The speed of thestirrer was limited to 300 rpm. After reaching the vortex in themolten metal, the preheated TiC ceramic particles had mixedevenly. During mixing, the stirrer had started to rotate at aconstant speed. Then the mixed molten metal under vortexcondition was kept out for sometime (10 min) at hightemperature to have the uniform dispersion of the reinforce-mentwith thematrix. Prior tomixing the TiC particles, the slagwas removed from themoltenmatrix, which floated above themelt. The preheated ceramic TiC particles were then added tothe molten matrix by weight fraction starting from 2.5 wt.% to7.5 wt.% with the step size of 2.5. The reinforcement weightfractionwas restricted to 7.5 wt.% in the presentwork to retainconsiderable ductility with strength and to maintain thefluidity of the composite melt. Finally, the molten metal waspoured in the circular permanent metallic die of the size of30 mm diameter and 250 mm length. The various samplecomposition, the addition of matrix AA 7075 alloy in thefurnace and the TiC ceramic particles in mass basis are givenin Table 3. Fig. 1(a) shows the schematic of stir casting processused to manufacture the AA 7075–TiC composites. Fig. 1(b)shows the photograph of bottom pouring stir casting furnaceused in the present research work. Further, the time stepsinvolved in the manufacturing of AA 7075 alloy, and AA 7075–TiC composites were illustrated as a schematic in Fig. 2.

The standard metallographic procedure was used tocharacterize the manufactured ex situ MMCs samples. Thesmall specimen size of around 10 mm diameter with 10 mmheight was cold mounted using acrylic resin, polished withdifferent SiC grit papers, disc polishedwith 9 mmalumina, andlapped using 1 mm diamond suspension. Then, the samples[(Fig._2)TD$FIG]

Fig. 2 – Schematic of time steps involved during manufacturi

were chemically micro-etched using Keller's reagent (95 mldistilled water, 2.5 ml HNO3, 1.5 ml HCl, and 1.0 ml HF). Thescanning electron microscope of JEOL JSM6390, and thetransmission electron microscope (TEM) of JEOL JEM2100 wereused for effective characterization. The electron backscattereddiffraction (EBSD) of FEI Quanta FEG SEM equipped with TSL-OIM software was also performed to show the grain refine-ment occurred inAA7075matrix alloy by incorporating theTiCparticles. The X-ray diffractionmachine of Shimadzu XRD6000was used to have X-ray diffraction patterns using CuKaradiation, which was operated at 30 mA and 40 kV. During X-ray diffraction, 20–808 scanning rangewith the scanning rate of28/min was used. The flexural strength was obtained byconducting a three-point bending test. The flexural test wasconducted with 1 mm/min crosshead movement. The hard-ness was recorded using a Rockwell hardness tester at 150 kgfload of dwell time 20 s.

The dry sliding wear tests were conducted using thestandard Tribo Meter supplied by M/s. Ducom, Bangalore,India. Before thewear test, the sampleswith the dimensions of10 mm in diameter with the height of 15 mm were preparedusing the wire-cut electrical discharge machine (WEDM) and

ng of AA 7075 alloy and AA 7075 + wt.% TiC composites.

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then the samples were washed in acetone. The counterpartdisc made of high carbon high chromium steel with the outerdiameter of 70 mmwith 10 mm thickness was used. The inputparameters used were: the load of 40 N, the sliding velocity of1.5 m/s, the sliding distance of 500 m, and the disc speed of240 m. The wear test was conducted at room temperature andthe wear rate was calculated by weight loss basis which wasmeasured using the digital weighing balance of SartoriusCP423Swith 1 mg precision. Finally, the SEM investigationwascarried out on the worn samples to examine the various wearmechanism and worn surface morphology.

3. Results and discussions

3.1. XRD of AA7075/TiC AMCs

Fig. 3 shows the X-ray diffraction pattern obtained for AA 7075(JCPDS reference number 98-008-4180) alloy reinforced withdifferent weight percentage of TiC (JCPDS reference number 96-901-2565) ex situ particles (0, 2.5, 5 and 7.5 wt.%). It wasobserved that the intensity of peak corresponding to cubic TiCphase had started to increase with the increase of weightpercentage of TiC particles in the AMCs and simultaneously thematrix peak (a-Al) had started to decrease [17]. Further, it wasnoticed that the peak position of a-Al was incoherent which[(Fig._4)TD$FIG]

Fig. 4 – SEM images of Al 7075–composites of (a) Al 7075–0 wt.%7075–7.5 wt.% TiC composite and (e) EDX of (d).

was expected to the distortion of a-Al lattice produced by theincorporation of TiC ceramic particles. The manufacturedcomposites (all samples) exhibited well crystalline peaks andno other intermetallic phases were observed in XRD pattern,which demonstrated explicitly that there was no impurity.Further, these results had explained that there was no reactionbetween the a-Al matrix and cubic TiC phases [18,19].

3.2. Microstructures of AA7075/TiC AMCs

Fig. 4 shows the SEM images of AA 7075 reinforced with thedifferent weight percentage of TiC particles in which the a-Alphase and the second phase particles were clearly seen. Somecasting defects, namely, the porosity, the scratches, and theasperities were also observed in the unreinforced monolithicalloy (Fig. 4(a), [20]). However, the intentionally addedreinforcements particles were distributed uniformly/homo-geneously over the matrix (Fig. 4(b)–(d)). These homogeneousdistributions of TiC particles are necessary to enhance themechanical properties of materials. Further, Fig. 4(b)–(d) hadclearly shown the proper interface between the TiC particlesand the a-Al matrix which had indicated the good bonding ofsecond phase particles in thematrix. This could be expected toenhance the load bearing capacity of a-Al matrix. In addition,the observed clear interface between the TiC particles and a-Almatrix could be expected to increase the thermal stability. In

TiC, (b) Al 7075–2.5 wt.% TiC, (c) Al 7075–5 wt.% TiC, (d) Al

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[(Fig._5)TD$FIG]

Fig. 5 – TEM micrographs of Al 7075–7.5% TiC composites: (a), (b) particulates and (c), (d) dislocation density.

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general, the undesirable intermetallic compounds would formif there is no proper interface between the ceramic particlesand matrix which lead to having the thermodynamicallyunstable ceramic particles in the liquid matrix melt [21]. Theenergy dispersive diffraction (EDAX) pattern for AA 7075–7.5 wt.% TiC was also shown in Fig. 4(e) which confirmed thepresence of both a-Al and TiC particles and no intermetalliccompounds [17,19].

However, the proper interface between the ceramic particlesand matrix phase with the good bonding of TiC particles in thematrix was achieved in the present research work. In order toconfirm the proper interface between TiC and a-Al matrix, TEMinvestigation on AA 7075–7.5 TiC AMC was carried out which isshown in Fig. 5. TheTEM images of Fig. 5 revealed theTiCparticlemorphology, dislocations and interfacial properties in a-Almatrix phase. The measured TiC particle size was around250 nm (ultra-fine level) which was calculated from the averageof 125 TiC particles obtained from several TEM images. Further,proper interfacial characteristics could be observed clearly basedon Fig. 5(a) and (b). In addition, there was no reaction layeraround the TiC particles due to which the TiC particles could notable to change its shape from around spherical shape to needle-like shape. These results confirmed that the TiC particles hadattained the stability duringhigh-temperature casting processes.Moreover, more amounts of dislocations were also observed(Fig. 5(c) and (d)) which was due to the difference in the value ofthe coefficient of thermal expansion between the matrix phaseand TiC ceramic particles. In general, the a-Al matrix wouldexpand and contract at a faster rate when compared to the TiCceramic particles which were due to differences in the value ofthe coefficient of thermal expansion. Due to this, a considerableamount of dislocations had formed after solidification whichproduced more amount of strain fields [22].

Fig. 6 shows the grain size map obtained from EBSD for AA7075 alloy reinforced with different weight percentage of TiC

composites. Based on the grain size colour orientation map,it was very clear that the AA 7075 matrix grains were refinedwith the function of TiC ceramic particles. In general, thepresence of strain fields with more amounts of dislocationsis the major benefits to enhance the mechanical propertieswhich could be achieved by the grain refinement process.Based on EBSD colour map, the grain size of a-Al matrix wasdetermined and the grain size variation with the function ofTiC particles is shown in Fig. 7. The observed average grainsize of a-Al matrix had started to decrease by incorporatingthe TiC particles due to the pinning effect of TiC particles inthe matrix [23–25]. The calculated average grain size of AA7075 alloy, AA 7075–2.5 wt.% TiC, AA 7075–5.0 wt.% TiC, andAA 7075–7.5 wt.% TiC AMCs were 155 � 4 mm, 121 � 3, 89� 4.5 and 65 � 2.5 mm, respectively (Fig. 7). Further, thecrystallographic characteristics in terms of grain boundariesorientation angles, namely, low angle grain boundary(LAGBs, 0–158), high angle grain boundaries (HAGBs, >158)can also be used to examine the behaviour ofmaterials. Fig. 8shows the grain boundaries representations,misorientationangle, and the corresponding pole figure for AA 7075 alloyand AA 7075 reinforcedwith 7.5 wt.% TiC composite. In Fig. 8(a) and (d), the red colour grain boundaries were indicatedthe angle from 08 to 58, the green colour grain boundarieswere indicated the angle from 58 to 158, and the blue colourgrain boundaries were indicated the angle of more than 158.From Fig. 8, it was very clear that the AA 7075–7.5 wt.% TiCcomposites was produced more HAGBs (78.8%) whereas theAA 7075 alloy was exhibited the HAGBs of 41.8% only. Theseresults explained that more grain refinement was occurredin the composite. This grain refinement was expected tomake the changes in the solidification of matrix melt withthe function of TiC particles. The introduction of TiCparticles in a-Al matrix would lead to diminishing the a-Al grain growth [23,24]. This diminishing rate of grain grow

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[(Fig._6)TD$FIG]

Fig. 6 – Grain size colour orientation map obtained by EBSD for (a) AA 7075 alloy, (b) AA 7075–2.5 wt.% TiC, (c) AA 7075–5 wt.%TiC and (d) AA 7075–7.5 wt.% TiC.

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had started to increase with the percentage of TiC particleswhichwas themain reason to have afine graina-Almatrix atthe higher amount of TiC particulate composite.

3.3. Mechanical properties of AA7075/TiC AMCs

The mechanical behaviour in terms of Rockwell hardness andbending stress for the manufactured AA 7075/TiC AMCs areshown in Figs. 7 and 9, respectively. The measured averagehardness of around 109 HRC was obtained in 0 wt.%monolithic alloy whereas around 248 HRC was obtained in7.5 wt.% TiC reinforced composite. The improved hardness ofaround 2.3 times was obtained in the higher reinforcedcomposite. This huge enhancement in hardness value wasdue to the presence of more dislocations, grain refinement,and effective bonding between a-Al matrix and TiC particles(Figs. 4–6 and 8). The induced bending stress (sb) of eachspecimen from the three-point bending test was determinedusing the formula [26]:

sb ¼ 3WL2

2bt2(1)

whereW is the appliedflexural load in 'N', L the span of the twosupport in 'mm', b the width of the specimen in 'mm', and t isthe thickness of the specimen in 'mm'. Further, the corre-sponding induced bending strain (eb) on the tested sample wasalso calculated using:

eb ¼ dt

L2(2)

where d is the deflectionmeasured in 'mm' at the centre of thespecimen. The variation of bending stress and bending straincurves of AA7075/TiC composites are shown in Fig. 9. Theobserved bending stress had started to increase with thefunction of the percentage of TiC particles steadily. Thiswas attributed to the presence of hard TiC ceramic particles,its uniform distribution, grain refinement, and proper embed-ding of TiC particles with a-Al matrix (Figs. 4–6 and 8) [14].

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[(Fig._7)TD$FIG]

Fig. 7 – Effect of TiC content on the average grain size (mm) and the Rockwell hardness number (HRC) of Al 7075–xwt.% TiCcomposites (x = 0, 2.5, 5.0 and 7.5 wt.%).

[(Fig._8)TD$FIG]

Fig. 8 – EBSD results of AA 7075 alloy: (a) LAGBs and HAGBs representation, (b) misorientation angle and (c) pole figure; EBSDresults of AA 7075–7.5 wt.% TiC composite: (d) LAGBs and HAGBs representation, (e) misorientation angle and (f) pole figure.

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Based on the rule of mixture, the presence of hard TiC particlewould impart hard nature in the composites and hence theAMCs possessed more bending stress. Further, the effectiveinterfacial bonds (Fig. 4) between the a-Al matrix and TiCceramic particles, and the grain refinement occurred in the

matrix (Fig. 6) had expected to assist the effective load carryingcapacity of the matrix. In addition, the incorporation andgetting of uniform distribution of TiC particles (Fig. 4) in thematrix would enhance the strength in the composites due toOrowan strengthening mechanism. Moreover, the associated

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[(Fig._9)TD$FIG]

Fig. 9 – Bending stress–strain curves of Al 7075–xwt.% TiCcomposites (x = 0, 2.5, 5.0 and 7.5 wt.%).

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strain fields with the function of TiC particles (Fig. 5(b) and (c))in a-Al matrix had promoted more strength and hence themechanical properties had improved in the present researchwork. Baradeswaran and Elaya Perumal [27] had achieved theimproved bending strength of 435 MPa for AA 7075 alloy rein-forced with Al2O3 and Gr hybrid composite.

The fractured surfaces after bending under SEM images areshown in Fig. 10. From Fig. 10(a), it was clearly observed thatlower amount of dimples, the large size of cleavage fracture[(Fig._10)TD$FIG]

Fig. 10 – Fracture surface morphology of SEM images of Al 7075–c(c) Al 7075–5 wt.% TiC and (d) Al 7075–7.5 wt.% TiC composite.

surfaces and more amounts of porosities due to shrinkageswas observed in unreinforced AA 7075 alloy. However, theobserved size of voids near the TiC particles had started todecrease with the function of reinforcement which indicatedthe achievement of good bonding that might have expected todecrease the shrinkages. The decrease in the size of void ordimples had expected to grain refinement engendered by theTiC particles in thematrix. Further, therewere no voids aroundthe TiC particles which also confirmed the effective bonding inthe composites. In addition, the observed flattened fracturesurfaces with the function of TiC particles had again indicatedthe effective bonding occurrence [28].

3.4. Dry sliding wear behaviour of AA7075/TiC AMCs

The variation of wear rate, wear resistance and the coefficientof friction of AA 7075 alloy reinforcedwith the different weightpercentage of TiC particles is shown in Fig. 11. FromFig. 11(a), itwas observed that the wear rate had started to decrease withthe increase of the hard TiC ceramic particles in the a-Almatrix. These results were attributed to the improvement ofhardness, outstanding interfacial bonding between thematrixand ceramic particles, embedding of hard TiC particles, andgrain refinement in the structure [25,29]. The increase in wearresistance with the incorporation of TiC second phaseparticles in a-Al matrix is also shown in Fig. 11(a). Theaddition of TiC particles in the matrix was expected to have ahomogeneous cast structure that might have reduced theisolation of matrix. Further, the differences in the value of the

omposites of (a) Al 7075–0 wt.% TiC, (b) Al 7075–2.5 wt.% TiC,

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[(Fig._11)TD$FIG]

Fig. 11 – Wear behaviour of Al 7075–x wt.% TiC (x = 0, 2.5, 5 and 7.5) composites: (a) variation of wear rate, and wear resistanceand (b) variation of coefficient of friction.[(Fig._12)TD$FIG]

Fig. 12 –Worn surface morphology SEM images of Al 7075–composites of (a) Al 7075–0 wt.% TiC, (b) Al 7075–2.5 wt.% TiC, (c) Al7075–5 wt.% TiC, (d) Al 7075–7.5 wt.% TiC composite and (e) EDX of (d) showing the Fe elements present in the material.

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coefficient of thermal expansion between the TiC particle anda-Al matrix had expected to develop more amount of strainfields consequently it led to enhance the dislocation density.Due to this, the wear rate had started to decrease with thefunction of TiC particles. The variation of coefficient of frictionwith the function of TiC particle is also shown in Fig. 11(b) inwhich the value of the coefficient of friction had started todecrease considerably when the amount of TiC particlesincreased. The unreinforced monolithic AA 7075 alloy hadpossessedmore value of the coefficient of friction andhence, it

had the lower value of wear resistance (Fig. 11(a)). The severewear occurred in unreinforced alloy was attributed to thepresence of coarse grain matrix which had poor resistanceagainst deformation. However, the observed coefficient offriction value had started to decreasewith the incorporation ofTiC particles (Fig. 11(b)) which was due to more in strength,uniform distribution of TiC particles, grain refinement, wellbonding, and embedding of TiC particles (Figs. 4–6 and 8). Ingeneral, the a-Al matrix embedded with hard TiC particleswould offer more resistance against wear as the hard TiC

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particle would never allow the matrix to shear deformation.Due to this, it was expected that the contact had occurredbetween the reinforcement particles and the steel counterfaceinwhich the hard TiC particle would act as third body abrasion[27,30]. This could minimize the coefficient of friction andhence, the coefficient of friction had started to decrease withthe function of TiC particles (Fig. 11(b)).

The worn surface morphology observed from SEM of AA7075–xwt.% TiC (x = 0, 2.5, 5 and 7.5) AMCs is shown in Figs. 12(a)–(d). The abrasion and delamination mechanisms are thecommon twowearmechanismswhichwould occur during thesliding wear test [23,24]. From Fig. 12(a) and (b), it wasobviously explained that severe delamination, more grooves,rigorous surface failure, matrix peeling, more scratches, andmore ploughing had occurred in AA 7075 monolithic alloy andAA 7075–2.5 wt.% TiC AMCs. Further, the adhesive wearmechanism was expected to be the dominant one as thesesamples was poor in strength and lower value of hardness.Some wear debris with white particles was also observedwhich was expected to oxidization. The formed debris wasattributed to poor in adhesive. However, fewer defects hadobserved in AA 7075–5 wt.% TiC AMCs and AA 7075–7.5 wt.%TiC AMCs. Further, wear tracks with good tribo-film had alsoobserved in these AMCs (5 and 7.5 wt.% TiC) samples. Due tothis, the value of the coefficient of friction had started todecrease with the function of reinforcement consequently thegood tribo film could decrease the adhesive wear. In addition,the higher reinforced sample had exhibited less wear track,fewer damages, and no oxidization layer. This was expected topossess higher amount of resistances, uniform distribution ofreinforcements, more in strength, and effective interfacialstrength between TiC particles [31] and a-Al matrix. Based onthese results, it could be concluded that admirable improvedtribological properties could be achieved in the manufacturedAMCs and hence, the parts made of these materials areexpected to run in long life which is the major expectations inthe aerospace industries.

4. Conclusion

The influence of TiC particles added to the Al 7075 alloy, themicrostructural characterizations, mechanical properties, andwear behaviour were investigated and reported. Based on theresults, the following conclusions are drawn from this study:

� A

ltered TiC wt.% of reinforcement particles had successfullyincorporated into the matrix through stir casting technique.

� C

onsecutively, the produced composites had the uniformdistribution of second phase particles (TiC) in the Al alloy.

� T

he grain size measured by EBSDmap for AA 7075 alloy andAA 7075 + 7.5 wt.% TiC ex situ composite were achieved155 mm and 65 mm, respectively which explained clearly thegrain refinement occurred by incorporating the TiC particles.

� W

ith the addition of ceramic content, the bending strengthof AA 7075–7.5 wt.% TiC composites had significantlyincreased by 5.8 times when compared to monolithic AA7075 alloy which attributed to the grain refinement, uniformdistribution, embedding of reinforcement particles with thematrix.

� T

he absence of voids, cracks and other defects near thematrix and reinforcement interface provided theway for theoccurrence of effective load transfer from Al 7075 matrix toTiC reinforcement, which results in the enhancement offlexural strength.

� T

he increasing of reinforcement in thematrix had exhibitedimproved wear resistance due to increase in strength in thematrix, dispersion strengthening, and effective bonding.

Data availability statement

The experimental datasets obtained from this research workand then the analyzed results during the current study areavailable from the corresponding author on reasonablerequest.

Authors' contributions

Dr. S. Sivasankaran has framed the idea of this work anddesigned the experiments. Mr. K.R. Ramkumar and Mr. S.Siddharth have carried out the experimental part of this work.Mr. R. Raghu has done the characterization studies using SEMand TEM. Dr. Fahad Al-Mufadi has contributed to materialsand tools. Dr. S. Sivasankaran has written this paper andfinally Dr. Fahad Al-Mufadi has fine tuned the article.

Acknowledgments

On behalf of all teamwork of this research, the correspondingauthor wishes to thank the Qassim University for all thefunding and support required to carry out this research.

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