Comparative processing-structure–property studies of Al–Cu matrix composites reinforced with TiC particulates

Composites: Part A 42 (2011) 812–824

Contents lists available at ScienceDirect

Composites: Part A journal homepage: www.elsevier.com/locate/compositesa

Comparative processing-structure–property studies of Al–Cu matrix composites reinforced with TiC particulates Hülya Kaftelen a,b,⇑, Necip Ünlü a, Gültekin Göller a, M. Lütfi Öveçog˘lu a, Hani Henein c a

Istanbul Technical University, Faculty of Chemistry and Metallurgy, Department of Metallurgical and Materials Engineering, 34469 Maslak, Istanbul, Turkey Mersin University, Engineering Faculty, Department of Metallurgical and Materials Engineering, 33343 Mersin, Turkey c University of Alberta, Department of Chemical and Materials Engineering, Edmonton, T6G 2G6 Alberta, Canada b

a r t i c l e

i n f o

Article history: Received 4 December 2009 Received in revised form 12 March 2011 Accepted 16 March 2011 Available online 23 March 2011 Keywords: A. Metal matrix composites (MMCs) E. Casting B. Microstructures B. Wear

a b s t r a c t Effects of TiC content and size on the microstructure, density, hardness and wear resistance of Al–4 wt.% Cu matrix composites were investigated. Al–4 wt.% Cu matrix composites were fabricated using two main processing routes of powder metallurgy (PM) and casting. In the PM process, Al–4 wt.% Cu matrix alloy reinforced with 10 wt.% TiC particulates of two different average sizes (13 lm and 93 lm) were mechanically alloyed and sintered. In the second process, Al–4 wt.% Cu–xTiC (x = 5, 10, 15 and 20 vol.%) composites were fabricated using a flux-assisted casting. Both the wear resistance and the hardness of cast composites improved with TiC content. The sintered composite containing smaller TiC particles (0.6– 3.5 lm) exhibited higher hardness than that reinforced with coarser TiC (0.8–5.6 lm) particles. However, the detachment of carbide particles from wear surfaces of the composite reinforced with TiC particles (0.6–3.5 lm) results in the deterioration of its wear resistance. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Metal matrix composites (MMCs) reinforced with discontinuous phases in the forms of short fibers, whiskers, and particulates exhibit considerably enhanced strength values at room temperature or at higher temperatures, low coefficient of thermal expansion, good wear resistance and stiffness compared to the corresponding unreinforced alloys [1]. The combination of abrasion and corrosion resistant ceramic reinforcement phases with the ductile and formable metals, i.e. Al, Cu have found many applications in tribology [2]. It is generally known that the Al composites containing hard particles exhibit high wear resistance depending on volume fraction, size and type of reinforcements compared to the matrix alloy [3–6]. Many researchers have reported that [4,5,7] the carbide reinforcement content has a significant effect in improving the wear resistance provided that good bonding between reinforcement particles and the matrix exists. For instance, Roy et al. [4] reported that type and size of reinforcement have a negligible effect on the sliding wear resistance of Al composites reinforced with TiC, TiB2, SiC and B4C; whereas volume fractions of reinforcement have significant influence on the wear resistance. Considering the commonly used carbide particles, TiC has attracted a growing interest due to its high hardness, elastic ⇑ Corresponding author at: Istanbul Technical University, Faculty of Chemistry and Metallurgy, Department of Metallurgical and Materials Engineering, 34469 Maslak, Istanbul, Turkey. Tel.: +90 212 285 30 90; fax: +90 212 285 34 27. E-mail address: [email protected] (H. Kaftelen). 1359-835X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesa.2011.03.016

modulus, low density, relatively high temperature stability and good wettability with molten Al [8]. Recently, due to their superior mechanical and physical properties, Al-based MMCs reinforced with TiC particles have been particularly attractive due to their superior mechanical and physical properties for aerospace, automotive, defense, and structural applications [2,8]. TiC particle reinforced Al matrix composites have been fabricated using the following techniques: self-propagating high temperature synthesis (SHS) [9], and powder metallurgy [10], infiltration [11] and casting [12,13]. Powder metallurgy (PM) involves the blending of pre-alloyed powders of the base metal and the reinforcement and then compaction of the powder mixture using hot isostatic pressing [14]. Although this process reduces the reaction interfaces between the carbide particles and the matrix material, high cost and large number of processing parameters such as milling time, speed and milling media, involved in the PM process restrict its application only to critical areas [15]. Liquid processing route is the most economically viable and attractive method to fabricated MMCs [16]. During the casting process, wetting properties of the reinforcement ceramics by molten metal is the most important aspect which affects the mechanical and physical properties of the MMCs. Therefore, many attempts for liquid state processing of Al–Cu/TiC composites have been undertaken regarding interfacial properties using sessile drop method [17,18]. Furthermore, a number of studies have been performed for Al MMCs to evaluate the relationships between the interface and mechanical properties in terms of manufacturing methods [19], types of reinforcement [12], chemical composition of the

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

matrix [20], and effect of heat treatment [21,22]. Within the liquid state systems, flux-assisted casting is an effective method in providing good interfacial bonding and thus in obtaining high strength composites without stirring [12]. It has been reported [12,23] that strength of composites produced using agent of flux is higher than those manufactured from metal powders. The use of K–Al–F based flux overcomes both thermodynamic (i.e. wettability of reinforcement) and mechanical barriers (i.e. surface oxide films) and improves the wetting properties of the melt during casting [23]. In this study, Al–4 wt.% Cu matrix composites were fabricated using PM (mechanical alloying and sintering) and flux-assisted casting processes. The main objective of this paper was to establish the structure and property relationships for Al–4 wt.% Cu matrix composites fabricated via these two different processes. Thus, the effects of both TiC particle size and volume fraction on the microstructure, hardness and sliding wear resistances of the Al–4 wt.% Cu matrix composites were evaluated and their properties were compared with those of the unreinforced Al–4 wt.% Cu alloy. Scanning electron microscopy (SEM), X-ray diffraction (XRD), density, hardness and wear tests were carried out in order to characterize Al–4 wt.% Cu matrix composites of the present investigation.

2. Experimental procedure In the present study, two processes were utilized to fabricate Al–4 wt.% Cu matrix composites reinforced with TiC particles. In the first process, Al–4 wt.% Cu–xTiC (x = 5, 10, 15 and 20 vol.%) composites were fabricated using the K–Al–F flux-assisted casting method. TiC powders having 99.5% purity with an average particle size of 2.9 lm were supplied from Alfa AesarTM. Al ingots (99.8% purity) and copper wire (99.5% purity) were melted in graphite crucible using a lab-scale induction furnace heated to 800 °C. TiC powders were mixed with the K–Al–F-based flux using a ratio of 1:2 in a turbula mixer for 3 min and the resultant powder mixture was gently placed on the surface of the Al–4 wt.% Cu (hereafter termed as Al4Cu) molten alloy. The mixing ratio between the K–Al–F flux and TiC particles was chosen from a patent [24] to avoid the issue of penetrating an oxide layer and to minimize possible reactions between molten Al and TiC particles. The powder mixture was kept on the melt surface for 2 min without stirring. This flux comprises a mixture of KAlF4 and K3AlF6 corresponding to the 45 mol% AlF3 eutectic composition in the KF–AlF3 system [25]. After removing the liquid slag from the melt surface, Al4Cu alloy melt containing TiC particles was stirred briefly using a graphite rod. After this, the composite melt was cast into a cast iron mold. In the second fabrication process, elemental aluminum (Al), copper (Cu) and titanium carbide (TiC) powders having average particle sizes of 13 lm and 93 lm were mechanically alloyed and vacuum hot pressed. Three different batches of starting powders were prepared to constitute the following compositions: Al–4 wt.% Cu, Al–4 wt.% Cu–10 wt.% TiC (13 lm) and Al–4 wt.% Cu–10 wt.% TiC (93 lm), hereafter termed as the Al4Cu matrix alloy, Al4Cu/TiC-13 and Al4Cu/TiC-93 composites. These powder batches were mechanically alloyed (MA) in a Spex 8000DTM dual mill for 90, 120, 150, 180, and 210 min using 6.36 mm steel balls. To prevent excessive cold welding during the MA process, 3 wt.% of stearic acid was added as a process control agent (PCA). The powders and PCA were introduced into a hardened steel vial in a PlasLabsTM glove-box filled with high purity argon (99.995%) using ball-to-powder ratio (BPR) of 7:1. To evaluate the hardness properties of the MA’ed composite powders, the samples were cold mounted in plastic molds using epoxy resin and hardener. The mounted samples were polished metallographically and etched

813

with a 0.5 HF solution (200 parts distilled water, 1 part HF) for 30 s for microstructural characterization. Microhardness of the MA’ed powders was measured using a Shimadzu™ Vickers hardness tester under an indentation load of 10 g with 15 s dwell time. The MA’ed powders for 180 min were consolidated using a CentorrTM vacuum hot press (VHP) at 550 °C for 1 h under a constant pressure of 70 MPa. The resultant cross-sectional microstructures and reinforcement distributions were investigated using a field emission scanning electron microscope (FESEM) JEOLTM JSM 7000F operated at 10 kV. X-ray diffraction (XRD) investigations of both the Al4Cu matrix alloy and the Al4Cu/TiC composite samples were carried out in a BrukerTM D8 Advance powder diffractometer with a standard Cu Ka radiation source employing a step size of 0.02° in 2h. Vickers microhardness measurements were measured on the polished samples using a Schimadzu™ microhardness tester at a load of 200 g for a dwell time of 15 s. Average microhardness values with standard deviations were calculated from 25 impressions taken on both cast and sintered samples. Densities of composite samples were measured according to the Archimedes’ method [26] in ethanol as an immersion medium. Wear properties were examined using a TribotechnicTM dry sliding reciprocating wear instrument by rubbing 1.587 lm steel ball (100 CR6-62 HRC) on the surfaces of samples. A load of 3 N at normal atmospheric conditions (25 °C and at about 50% relative humidity), a sliding velocity of 10 mm/s, and a total sliding distance of 40 m were used. Before wear a test, each specimen was metallographically polished in order to make sure that the wear surface was in entire contact with the surface of the steel ball (ISO 3290). Each test was performed using a fresh steel ball. The worn surfaces were examined in a JEOLTM JSM-T330 scanning electron microscope to identify the wear mechanism. Results of the wear tests were evaluated on the basis of volume of the material loss measured by a profilometer (MahrTM Perhen S&P PerthometerTM). Grain size of samples were measured based on ASTM-E112 using polarized light in an optical microscope [27]. For this purpose, cast samples were polished using diamond suspensions (up to 1 lm) and then anodized in a diluted solution of HBF4 acid (3%) in distilled water. The carbon content of MA powders, sintered and cast samples were measured using EltraTM CS800 Carbon/Sulfur determinator. Samples were weighed directly into ceramic crucibles. Combustion was achieved in a stream of oxygen. Detection was done using an IR-cell. The TiC content was calculated based on the mass fraction of carbon in those composites.

3. Results 3.1. Characterization of cast samples: XRD analysis X-ray diffraction (XRD) investigations were carried out to identify the phases present in cast Al4Cu and Al4Cu/TiC samples. Fig. 1a–e shows a series of XRD patterns from the Al4Cu alloy and Al4Cu/TiC composites containing 5, 10, 15 and 20 vol.% TiC, respectively. Diffraction peaks belonging to the a-Al phase (face centered cubic Bravais lattice, space group: Fm3m, a = 0.40494 nm) [28], and Al2Cu phase (body centered tetragonal Bravais lattice, Space group:I4/mcm, a = b = 0.6063 nm and c = 0.4872 nm) [29] are present in all samples. Formation of the Al2Cu phase is expected according to the binary aluminum copper phase diagram [30]. Additionally, TiC peaks (face centered cubic Bravais lattice, Space Group: Fm3m, a = 0.43274 nm) [31] are identified in all composite samples containing various TiC contents (5–20 vol.%). Furthermore, as seen from Fig. 1b–e, XRD peak intensities of the TiC phase clearly increase with increasing volume fraction of TiC particles from 5 vol.% to 20 vol.%. In addition, KAlF4 phase (simple

814

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

Fig. 1. X-ray diffraction (XRD) patterns of the cast: (a) Al4Cu matrix alloy and the Al4Cu/TiC composite samples containing (b) 5, (c) 10, (d) 15, and (e) 20 vol.% TiC particles.

tetragonal Bravais lattice, Space Group: P4/mbm, a = 0.5024 nm and c = 0.6156 nm) [32] is present in the XRD reflections of the Al4Cu/20 vol.%TiC composite. This suggests that some of the protective flux got trapped in the cast ingots. 3.2. Characterization of cast samples: SEM investigations SEM images shown in Fig. 2 are representative microstructures of cast Al4Cu alloy and its composites containing 5 vol.% and 15 vol.% of TiC in Fig. 2a and b shows the representative SEM micrographs of cast Al4Cu alloy and corresponding EDS spectra taken from the intercellular region (indicated with an arrow), respectively. The microstructure of the cast Al4Cu alloy exhibited a cellular type a-Al matrix with an intercellular eutectic (indicated with an arrow). The eutectic phase was formed between a-Al and Al2Cu phases. Corresponding EDS analysis taken from intercellular region is given in Fig. 2b–d are the representative SEM micrographs taken from the Al4Cu/5 vol.% TiC and Al4Cu/15 vol.% TiC composites revealing that TiC particles are dispersed reasonably well in the Al matrix. However, a detailed examination shows a small-scale clustering of TiC particles in some local areas of the matrix. It has been reported that particle clustering occurred when the fine particle size and large volume fractions of reinforcement were introduced into matrix [33]. Kennedy et al. [12] reported the clustering phenomena in Al MMCs containing 10 vol.% of TiC (5 lm) and TiB2 (7 lm) for increased particle collisions due to greater numbers of particles present. Therefore, current findings verify the effect of both the particle size and the amount of reinforcement in Al matrix composites. Fig. 3a–d is the respective high magnification SEM micrographs of cast Al4Cu–10 vol.% TiC and Al4Cu–15 vol.% TiC composite samples and their corresponding EDS spectra taken from the matrix materials, revealing strongly bonded TiC particles existing in the matrix. The EDS results taken from the matrix of the composite samples (Fig. 3c and d) exhibit peak intensities of Ti and C increase with increasing TiC content. It is clear from the SEM/EDS investigations that no reaction products such as Al4C3, Al3Ti, as reported in other investigations [8,22], can be observed in the interface between Al and TiC particles or within the matrix at the present cast-

ing temperature of 800 °C. This can be explained by the short contacting time (3–5 min) and cooling rate leading to insufficient reaction time between the molten metal and the reinforcement. Although these intermetallic phases enhance wetting by reducing the contact angle between TiC particles and molten Al, they are undesirable for their brittleness in nature. The standard free energy change (DGo) for the reaction between Al and TiC was reported as +9.71 kJ [34] at 800 °C revealing that TiC formation is not favoured. The wettability of the reinforcement material with the liquid metal matrix is essential for good interfacial bonding and enhanced bond strengths [35]. Due to the strong metallic nature and closely matched crystal structure with Al, TiC particles are easily wetted by liquid Al [36,37] during solidification. For the Al–4 wt.% Cu/ TiC system, Contreras [38] reported the wetting angle as 86° at 800 °C using the sessile drop method. It is well known that second-phase particles retard the grain growth and hardens the matrix [20]. One of mechanisms proposed for grain refinement is based on the heterogeneous nucleation of the aluminum grains on the inoculants [39]. Studies in Al alloys indicate that TiC, Al3Ti, TiB2 and AlB2 are all effective heterogeneous nucleants in Al matrix and they are used to promote a uniform microstructure by suppressing the growth of columnar grains, hence act as grain refiners. It was reported that [39] heterogeneous nucleation on the substrate depends on compatibility between the crystal structures [40] and lattice parameters of the phases involved. In the present study, preliminary optical microscopy investigations conducted on both Al4Cu alloy and Al4Cu/TiC composite samples revealed that the increasing percentage of TiC particles leads to a finer grain size. The grain size of the primary a-phase in matrix Al4Cu alloy was measured as 80.9 ± 5.5 lm, whereas this value was measured as 22.62 ± 1.92 lm, 19.04 ± 1.97 lm, 17.67 ± 1.28 lm and 6.72 ± 0.99 lm for the Al4Cu/TiC composites containing 5, 10, 15 and 20 vol.% TiC, respectively. Obviously, the grain size values of the Al4Cu/TiC composites are smaller than that of the cast Al4Cu alloy and decrease further with TiC addition indicating that the addition of fine TiC particles effectively decreases the growth rate of the grains during the solidification process. An average grain size of 365 lm was reported for the cast Al ingot which decreased to 77 lm for that reinforced with

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

815

Fig. 2. SEM microstructures of cast: (a) Al4Cu matrix alloy, and its (b) corresponding EDS spectra taken from the intercellular region (indicated with an arrow). SEM micrographs taken from the cast (c) Al4Cu/5 vol.% TiC and (d) Al4Cu/15 vol.% TiC composites.

Fig. 3. SEM micrographs of the cast: (a) Al4Cu/10 vol.% TiC, (b) Al4Cu/15 vol.% TiC composites, and corresponding EDS spectra from overall area of (c) Al4Cu/10 vol.% TiC and (d) Al4Cu/15 vol.% TiC.

10 vol.% TiC particles having an average particle size of 10 lm [41]. However, Karantzalis et al. [36] stated that the addition of 3–

5 vol.% TiC into Al–Si–Cu alloy had almost no effect on a-Al grains and the average grain size was reported as 100 lm close to those of

816

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

the present composites. Several researchers reported that the TiC particles in Al matrix composites has a coherent interface with a-Al and thus these particles act as heterogeneous nucleation sites for the formation of a-Al crystals [42,43].

3.3. Density, hardness and wear results of cast samples The theoretical density of the composites was calculated by the rule of mixture (ROM) using the density of TiC as 4.93 g/cm3 [44]

Table 1 Measured density, estimated porosity values of the cast Al4Cu alloy and the Al4Cu/TiC (5–20 vol.%) composites. This table also shows hardness, relative wear resistance and average interparticle spacing values of cast samples. Samples

Al4Cu Al4Cu/TiC

a b

Nominal TiC content (vol.%)

Actual TiC content (vol.%)

Average particle size (lm)

Average interparticle spacing (lm)

qmeasureda

qtheoreticalb

(g/cm3)

(g/cm3)

Estimated porosity (%)

Hardness (GPa)

Relative wear resistance

0 5 10 15 20

0.0 4.0 8.1 11.5 18.5

– 2.9 2.9 2.9 2.9

– 9.56 6.48 5.31 3.98

2.767 ± 0.002 2.813 ± 0.005 2.928 ± 0.022 2.972 ± 0.061 3.081 ± 0.034

– 2.850 2.945 3.019 3.168

– 1 1 2 3

0.646 ± 0.111 0.856 ± 0.210 0.967 ± 0.229 1.111 ± 0.237 2.337 ± 0.300

1 1.82 2.42 13.66 56.63

Density values are measured using Archimedes’ method. Theoretical density values are calculated are based on the actual content of the TiC particles.

Fig. 4. Low magnification SEM images showing the worn surfaces of the cast: (a) Al4Cu matrix alloy and the Al4Cu/TiC composites reinforced with (b) 5, (c) 10, (d) 15, and (e) 20 vol.% TiC particles.

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

Al4Cu as 2.77 g/cm3. For theoretical density (qth), it was assumed that there were no voids after casting process. The ROM can be expressed by:

qth ¼ qc  V c þ qm  V m

ð1Þ

where Vm is the volume fraction of the matrix and Vc is the volume fraction of the carbides. The qc and qm are the density values of carbides and matrix, respectively. Actual volume fractions of carbide particles in sintered samples were calculated from weight percentage of carbon which was determined by the hot combustion method. The actual volume fraction values are used in the calculation of theoretical densities of cast samples. Table 1 lists the theoretical density, measured density and estimated porosity values of cast samples as a function of the volume fraction of TiC reinforcement. It can be seen that the density increases gradually from 2.77 g/cm3 for the as cast Al4Cu alloy to 3.08 g/cm3 for the Al4Cu/ 20 vol.% TiC alloy, as expected. This is attributed to the presence of TiC particles, which have a higher density (qTiC = 4.91 g/cm3) [44] than the density of Al (qAl = 2.71 g/cm3). It is also apparent that

817

the estimated porosity values of cast samples change from 1% to 3% depending on volume percent of TiC particles. Hardness is a property that is related to the material resistance against plastic deformation. Consequently, all factors that have an influence on dislocation mobility may affect the hardness of aluminum alloys. For particle-metal matrix composites, the hardness value depends primarily on the volume fraction and density of reinforcement phases [33]. For a given reinforcement particle size, increasing the volume content of reinforcements results in a small interparticle spacing and consequently leads to higher stresses [45].The interparticle spacing, k, can be expressed in terms of volume fraction (Vf) of dispersed particles and the average particle size by [46]:

 k¼D

p

6V f



2 3

12 ð2Þ

where D is average carbide particle size. In the present study, the results revealed that the interparticle spacing was reduced with increase in the volume fraction of TiC particles, as seen in Table 1. It is

Fig. 5. High magnification SEM micrographs showing the worn surface of the cast: (a) Al4Cu matrix alloy, and the composites reinforced with (b) 5, (c) 10, (d) 15, and (e) 20 vol.% TiC particles.

818

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

obvious from this table that additions of TiC reinforcements in various amounts to the Al4Cu alloy lead to significant increases in the hardness of Al4Cu. Whereas the Al4Cu/20 vol.% TiC has a hardness value of approximately 2.33 GPa, that of the as cast Al4Cu alloy is 0.6 GPa. The hardness of conventional Al4Cu alloys, fabricated by the casting processes, has been reported to be in the range between 0.4 and 0.87 GPa [47–49]. It is obvious from Table 1 that the increase in volume percent of TiC led to a decrease in interparticle spacing. Thus, Al4Cu/20 vol.% TiC composite has more particle–matrix interfaces and smaller interparticle spacing than Al4Cu/5 vol.% TiC composite resulting in higher stresses for the passage of dislocations through the carbides [47,50]. According to Eq. (2), the interparticle spacing (k) value of Al4Cu/20 vol.% TiC is calculated as 3.98 lm, while this value is 9.56 lm for Al4Cu/5 vol.% TiC composite. Higher microhardness in the case of Al4Cu/20 vol.%TiC composites can be attributed to the presence of high content of TiC reinforcement with a much reduced interparticle spacing when compared to Al4Cu alloy. Contreras et al. [48] reported similar hardness values for cast Al–xCu/TiC (x = 1, 4, 8, 20 and 33 wt.%) composite sample containing TiC particles with the average size of 1.25 lm. In this study, relative wear resistance of the samples was quantified by dividing the wear track area of the Al4Cu alloy to that of composites. Thus, wear resistance of the unreinforced Al4Cu alloy was taken as 1. Relative wear resistance of the Al4Cu alloy and those of the Al4Cu/TiC composites containing various amount of TiC are also listed in Table 1. The wear resistance is observed to increase with increasing the volume fraction of TiC particles. For instance, when the nominal volume fraction of TiC increases from 10% to 20%, the relative wear resistance increases by approximately 23 times. Additionally, a trend of increase in the relative wear resistance with increasing hardness can be observed. Similar tendency between the wear response and hardness was reported by Venkataraman and Sundararajan [5] who studied Al matrix composites comprising 10–40 vol.% of SiC reinforcement particles, and Herbert [49] who investigated the wear behavior of the Al– 4.5Cu alloy and in situ the Al–4.5Cu–5TiB2 composite. Low magnification SEM images of wear tracks developed on the surfaces of the Al4Cu alloy and Al4Cu/TiC composites during dry sliding tests are presented in Fig. 4a–e. As seen in Fig. 4a–e, the

width of wear surfaces and the amount of ridges observed at the edges of the wear surfaces decrease with increasing TiC contents from 0 vol.% through 20 vol.%. Furthermore, the dry sliding wear generates wear tracks having the typical characteristics of adhesive wear surface appearance. Fig. 5a–e is the SEM images of wear surfaces generated during dry sliding wear tests on the Al4Cu alloy and Al4Cu/TiC composite samples. The wear surface of the Al4Cu matrix alloy in Fig. 5a presents significant deformation traces in the form of micro-ploughing and grooving compared to that of composite counterparts as seen in Fig. 5b–e. The SEM/EDS microstructures of the worn surfaces reveal that the wear mechanism appears to be adhesive associated with oxidative wear for the Al4Cu alloy and the Al4Cu/5 vol.% TiC composite (Fig. 5b). The EDS analysis taken from the area marked as A in Fig. 5a confirms the presence of the oxidative wear. In addition, the wear progressed by the formation and growth of adhered wear debris resulting in a delaminated surface with rough wear tracks. Formation of oxygen rich regions on the wear surfaces indicates the existence of frictional heating between the steel ball and the surface of sample. For the present applied sliding load of 3 N, this kind of wear regime is in good agreement with the empirical-wear mechanism map for the Al (6061)/SiCw composite proposed by Wang et al. [51]. Worn surface characteristics have also been reported by Shyu and Hoji [52] for the in situ Al–TiC composites using sliding wear tests, and Anasyida et al. [53] who investigated the dry sliding behavior of Al–12Si–4 Mg alloy with 1–5 wt.% cerium additions, similar to those observed in the present study. Wear surface topographies of the Al4Cu/10 vol.% TiC, Al4Cu/15 vol.%TiC and Al4Cu/20 vol.% TiC particles are represented in Fig 5c–e, respectively. It is evident from these figures that the wear tracks developed on the surface of the composites are much narrow and shallow than those of the Al4Cu alloy and the Al4Cu/5 vol.% TiC composite. Furthermore, the examination of the SEM micrograph in Fig. 5d indicates that TiC reinforcement particles (indicated by arrows) tend to align themselves in the sliding direction during the wear test. The presence of well bonded carbide particles with matrix continuously protect the contact surface of the Al4Cu/ 10 vol.%TiC, Al4Cu/15 vol.%TiC and Al4Cu/20 vol.%TiC composites against the destructive action of the steel ball. Although particle

Fig. 6. Hardness of Al4Cu matrix, Al4Cu/TiC-13 and Al4Cu/TiC-93 composite powders as a function of the MA time.

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

delamination in some local areas in the wear surface of these composites exist (Fig. 5c–e), the presence of TiC particles having high volume fraction (>5 vol.%) leads to a reduction in real area of contact between the matrix and the counterface. Thus these particles have dominant effect in preventing the plastic flow and the adhesion of matrix material by remaining on the worn surface. 3.4. Characterizations of mechanically alloyed (MA) powders In the present work, hardness behavior of the powders was evaluated to determine the optimum time for mechanical alloying (MA). Fig. 6 shows the changes in the hardness of Al4Cu, Al4Cu/ TiC-13 and Al4Cu/TiC-93 powders as a function of MA time in the range of 90 and 210 min. Increases in the hardness of composite powders for times up to 120 min is due to the fragmentation of TiC particles and the cold deformation of matrix powders. When the MA time increases from 120 min to 180 min, the powders exhibit a smaller but still increasing trend in hardness. After 180 min of MA time, it can be seen that the hardness value of Al4Cu/TiC-13 powders reaches a saturation condition indicating equilibrium between welding and fracture processes has been achieved [54,55]. This conforms with preliminary SEM investigations of the Al4Cu/TiC powders MA’ed for 180 min revealed uni-

Fig. 7. XRD patterns of: (a) Al4Cu matrix, (b) Al4Cu/TiC-13 and (c) Al4Cu/TiC-93 composite powders after MA for 180 min.

819

form and fine distribution of TiC particles within equaixed microstructure of Al4Cu matrix. However, Al4Cu/TiC-93 powders still exhibit a slight increase in their hardness values with further milling (210 min). The milling energy required for the fragmentation of large carbide particles (93 lm) is comparatively greater than that of the small carbide particles (13 lm) [56], therefore the saturation value of Al4Cu/TiC-13 powders is attained in a short time (180 min) compared to the Al4Cu/TiC-93. After 180 min, the saturation is almost achieved for the Al4Cu/TiC-13 composite, therefore, 180 min is considered as an optimum time for mechanical alloying and the powders MA’ed for 180 min are used for sintering. Fig. 7a–c is X-ray diffraction (XRD) patterns of Al4Cu matrix alloy, Al4Cu/TiC-13 and Al4Cu/TiC-93 composite powders MA’ed for 180 min, respectively. As expected, diffraction peaks belonging to Al (fcc Bravais lattice, Fm3m space group, a = 0.40494 nm) [28] and Cu (fcc Bravais lattice, Fm3m space group, a = 0.36150 nm) [57] are present in all samples. In addition to Al and Cu phases, the reflections arising from TiC (fcc Bravais lattice, Fm3m space group, a = 0.43274 nm) [31] can be identified in the Al4Cu/TiC-93 (Fig. 7c) and Al4Cu/TiC-13 (Fig. 7b) composite powders, indicating

Fig. 8. XRD patterns of the sintered: (a) Al4Cu matrix, (b) Al4Cu/TiC-13 and (c) Al4Cu/TiC-93 composite samples obtained after 180 min of MA time.

820

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

that no reaction took place to form any intermetallic phases (Al2Cu, Al3Ti, Al4C3) during MA process. 3.5. Characterizations of sintered Al4Cu/TiC composites: XRD analysis The XRD patterns of the sintered Al4Cu matrix alloy, Al4Cu/TiC13 and Al4Cu/TiC-93 composite samples are given in Fig. 8a–c, respectively. Fig. 8a is the XRD pattern of the Al4Cu matrix alloy sample exhibiting strong diffraction peaks belonging to the Al, Al2Cu phase (body centered tetragonal Bravais lattice, I4 space group, a = 0.5070 nm and c = 0.4890 nm) [29] and reflections arising from the Al7Cu2Fe phase (simple tetragonal Bravais lattice, P4/mnc space group, parameters a = 0.6336 nm and c = 1.487 nm) [58]. In addition to Al matrix and the Al2Cu phase, TiC phase [31] were identified from the XRD spectra of the Al4Cu/TiC-13 and Al4Cu/TiC-93 composite samples (Fig. 8b and c). Although iron impurities were not identified by X-ray diffraction analysis of MA’ed powders, after sintering, peaks belonging to the Al7Cu2Fe phase are present in the XRD patterns of all sintered samples. This observation suggests that the steel balls and vial utilized as the milling media during MA process wear out. The absence of iron peaks in the X-ray diffraction pattern of milled powders (Fig. 8) is presumably due to low volume fraction (<2 vol.%) of iron dissolved in the matrix during the MA process. This observation is in agreement with the atomic absorption analysis (AAS) results

indicating that the iron content of each sample was determined to be 0.077 wt.% for Al4Cu, 1.513 wt.% for Al4Cu/TiC-13 and 1.730 wt.% for Al4Cu/TiC-93 composite powders alloyed for 180 min. Similarly, recent work on Al4Cu/ZrC composites have shown that the iron contamination during MA process leads to formation of iron containing Al7Cu2Fe phase in the Al4Cu/ZrC composites after sintering [6].

3.6. Characterizations of sintered Al4Cu/TiC composites: SEM analysis Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) investigations were conducted to reveal the morphological features in the sintered samples. Fig. 9 shows the SEM microstructure and corresponding EDS spectra taken from the sintered Al4Cu matrix alloy. As seen in Fig. 9a, the microstructure of the Al4Cu matrix alloy comprise two kinds of intermetallic phases, one having flower-like (marked as F) and the other rod-like (marked as R) particles. On the basis of EDS analyses, flower-like particles and rod-like particles are suggested to be Al2Cu (Fig. 9b) and Al7Cu2Fe phases (Fig. 9c), respectively. In addition, small porosities (marked as P) are also observed in the microstructure of the Al4Cu matrix alloy (Fig. 9a). The SEM images depicting the microstructure of the sintered Al4Cu/TiC-13 and Al4Cu/TiC-93 composite samples are shown in Fig. 10. SEM results reveal that Al4Cu/TiC-13 (Fig. 10a) and

Fig. 9. (a) SEM micrograph of the sintered Al4Cu matrix alloy, (b and c) corresponding EDS spectra taken from the particles marked as F and R on the SEM micrographs, respectively (P denotes the porosity).

821

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

Fig. 10. SEM micrographs of the sintered (a) Al4Cu/TiC-13, (b) Al4Cu/TiC-93composites, (c) and (d) corresponding EDS spectra taken from the particles marked as C in (a), and marked as R in (b), respectively.

Al4Cu/TiC-93 composites (Fig. 10b) exhibit similar microstructural features in terms of homogeneous particle distributions associated with similar carbide particle sizes after MA process. It should be noted that the size of the carbides are remarkably smaller than their initial average size. The sizes of TiC particles are in the range between 0.6 and 3.5 lm for the Al4Cu/TiC-13 composite and 0.8– 5.6 lm for the Al4Cu/TiC-93 composite. On the basis of SEM studies accompanied with EDS analyses (Fig. 10c and d), it can be inferred that TiC particles (light appearing particles, marked as C) and fine rod-like Al7Cu2Fe intermetallics (marked as R) dispersed in Al matrix and the microstructural features of these composites are very similar. Although the Al2Cu phase is present, on the basis of XRD analysis results, this phase is not easily discernable from the complex microstructures of the composites. 3.7. Density, hardness and wear results of sintered samples Similar with the cast samples, the theoretical density values of sintered samples were calculated using the rule of mixtures. Note that the actual volume percentage of carbide particles has been used to calculate theoretical density values of sintered samples. Table 2 gives the theoretical and measured density values of sintered samples. Nominal wt.% and vol.% of carbide particles given

in Table 2 are obtained from the carbon analysis results of MA powders. The finer initial TiC (13 lm) powders appeared to have a beneficial effect on the densification of the Al4Cu/TiC-13 composite compared to the Al4Cu/TiC-93 composite including coarse initial TiC (93 lm) particles since relative density increased as starting particle size decreased. Under the indentation load of 200 g, the hardness of the sintered Al4Cu matrix alloy was measured as 0.90 ± 0.08 GPa, while the composites exhibited higher hardness values, which are listed in Table 2. The incorporation of TiC particles into the Al4Cu matrix alloy yielded further improvement in the hardness, because hard particulate reinforcements act as a barrier to the dislocation movement within the matrix and exhibit greater resistance to indentation of the hardness tester [59]. The hardness values of the Al4CuTiC-93, Al4Cu/TiC-13 composites and the Al4Cu matrix alloy correlate well with relative density values which are given in Table 2. It is evident from Eq. (2) that for a constant fraction (Vf) of carbide particles, the interparticle spacing (k) is directly proportional to the carbide particle size [45]. Thus, the expected increase of hardness with decreasing interparticle spacing can be confirmed with the results given in Table 2. The interparticle spacing values of each composite are also given in Table 2. Note that the interpar-

Table 2 Measured relative density values of the sintered Al4Cu alloy and the Al4Cu/TiC-13 and Al4Cu/TiC-93 composites. This table also shows hardness, relative wear resistance and average interparticle spacing values of sintered samples. Samples

Al4Cu Al4Cu/TiC-13 Al4Cu/TiC-93 a b

Nominal TiC content (vol.%)

Actual TiC content (vol.%)

Average particle size (lm)

Average interparticle spacing (lm)

qmeasureda

qtheoreticalb

(g/cm3)

(g/cm3)

Relative density (%)

Hardness (GPa)

Relative wear resistance

0 10.3 10.9

0.0 9.7 9.7

– 1.5 2.5

– 3.26 5.45

2.690 ± 0.050 2.842 ± 0.009 2.779 ± 0.018

– 2.979 2.978

– 95.4 93.3

0.90 ± 0.08 1.854 ± 0.07 1.726 ± 0.04

1 7.6 9.1

Density values are measured using Archimedes’ method. Theoretical density values are calculated are based on the actual content of the TiC particles.

822

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

ticle spacing for each composite was estimated from the average particle sizes (i.e., 2.58 lm for the Al4Cu/TiC-93 and 1.50 lm for the Al4Cu/TiC-13 composite samples, as measured by an image analyzer). It can be noted from Table 2 that the actual volume fractions of TiC particles for the Al4Cu/TiC-13 and Al4Cu/TiC-93 composites are the same value of 9.7. Calculations show that the average interparticle spacing between the TiC particles is 3.26 lm for the Al4Cu/TiC-13 and 5.45 lm for the Al4Cu/TiC-93 composites. Therefore, the differences in average interparticle spacing values for the Al4Cu/TiC-13 and Al4Cu/TiC-93 composites depend directly on the mean TiC particle size. This explains the hardness differences between the Al4Cu/TiC-13 and Al4Cu/TiC-93 composite samples, as mentioned above. The relative wear resistance values of sintered Al4Cu matrix alloy, Al4Cu/TiC-13 and Al4Cu/TiC-93 composites calculated from the 2-D profile images of the wear tracks are also given in Table 2. The wear resistance results from this table revealed that the incorporation of carbide particles into the Al4Cu matrix alloy increases its wear resistance. Al4Cu/TiC-13 and Al4Cu/TiC-93 composites exhibit eight and nine times higher wear resistances, respectively, compared to the Al4Cu matrix alloy. In order to understand effective wear mechanisms for sliding wear resistance of composites, the worn surface appearances were examined in Fig. 11. The topography of the wear tracks developed on the composites is quite different than that of the Al4Cu matrix alloy (Fig. 11a), which exhibits typical surface damage like grooves aligned in the sliding direction. As can be seen in the SEM micrographs (Fig. 11b and c), the presence of TiC particles in the microstructure led the composites to resist destructive action of the counterface (steel ball) by reducing the size of the grooves. It is evident from the worn surface micrograph of the Al4Cu/TiC-13 composite that the wear surfaces become much rougher with signs of

local TiC particle detachment than that of the Al4Cu/TiC-93 composite (Fig. 11c). It can be suggested that TiC particles (0.8– 5.6 lm) in the Al4CuTiC-93 composite provided better interfacial bonding with the matrix than the carbide particles (0.6–3.5 lm) which were pulled out of the matrix in the Al4Cu/TiC-13 composite sample, hence continuously protecting the composite by remaining on the contact surface. Additionally, series of fine cracks perpendicular to the sliding direction on steel ball exist in worn surface of the Al4Cu/TiC-13 composite sample (Fig. 11b), these are generally associated with delamination. 4. Discussion The intrinsic material factors such as reinforcement type, size, shape, size distribution and reinforcement volume fraction have significant effect on the sliding wear rate of Al composites [3,60]. In order to understand the role of volume fraction of carbide particles and their size effects on the sliding wear properties of Al4Cu matrix composites fabricated by different processes, hardness-carbide content-wear resistance relations values are plotted in Fig. 12. In this figure, relative wear resistances and hardness values of all samples are presented using open and filled symbols, respectively. The results given in Tables 1 and 2 have been used in Fig. 12. The best results were obtained for the cast Al4Cu/TiC (2.9 lm) composite which contains 20 vol.% of TiC particles. This composite has higher hardness and better wear resistance than the other composites of the present investigation. The wear resistance of the sintered Al4Cu/TiC-93 composite is comparable with the wear resistance of the cast Al4Cu/TiC composite containing 8.1 and 11.5 vol.% of TiC particles (see Table 1), since average carbide particle sizes of the Al4Cu/TiC-93 (average 2.5 lm) and Al4Cu/TiC (2.9 lm) composites are close with each

Fig. 11. Worn surface appearances of sintered: (a) Al4Cu alloy, (b) Al4Cu/TiC-13, (c) Al4Cu/TiC-93 composites, and (d) corresponding EDS spectra from the particles marked as C in (c).

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

823

directly proportional with both the hardness and the relative wear resistance of the composites. 5. Conclusions

Fig. 12. Hardness and relative wear resistance of the Al4Cu alloy and Al4Cu/TiC composites as a function of carbide particle content. (hardness values are shown as filled symbols, whereas relative wear resistance values are shown as open symbols).

other. The Al4Cu/TiC-93 composite has a relative wear resistance value of 9.1 (Table 2). This value is 2.42 for the cast Al4Cu/TiC composite containing 8.1 vol.% of TiC and 13.6 for the cast Al4Cu/TiC containing 11.5 vol.% of TiC particles (see Table 1). Considering close carbide particle sizes for these composites, it can be concluded that volume fraction of carbide particles play significant roles in the improvement of wear resistances of composites. Fig. 13 shows the variation of hardness and wear resistance values of both sintered and cast Al4Cu matrix composites as a function of the interparticle spacing. Note that the data from Table 1 and 2 were used for plotting Fig. 13. For the cast Al4Cu/TiC (2.9 lm) composites, hardness and wear resistance values increase as the interparticle spacing decrease because of greater numbers of carbide particles present. The sintered Al4Cu/TiC-13 and Al4Cu/ TiC-93 composites contain same volume fraction (9.7 vol.%) of carbide particles, hence the interparticle spacing values of both composites are influenced only by the differences in particle size. Although the sintered Al4Cu/TiC-13 composite has lower interparticle spacing value than that of sintered Al4Cu/TiC-93 composite, it is obvious that wear resistance of the sintered Al4Cu/TiC-13 composite does not strongly depend on the carbide particle size. For constant volume fractions (9.7 vol.%), the sintered Al4Cu/TiC-93 composite exhibit greater wear resistance than the sintered Al4Cu/TiC-13 composite containing smaller carbide particles which were pulled out during wear test (Fig. 11b). However, in case of the cast Al4Cu/TiC (2.9 lm) composites, interparticle spacing values strongly depend on the carbide fraction content which is

Metal matrix composites composed of Al–4 wt.% Cu (Al4Cu) as the matrix and 5–20 vol.% of TiC particulates with mean size of 2.9 lm were fabricated successfully by the K–Al–F type flux-assisted casting method. Additionally, Al–4 wt.% Cu matrix composites containing TiC particulates with average sizes of 13 lm and 93 lm were fabricated using mechanical alloying and hot pressing processing routes. Microstructural and phase characterizations of both sintered and cast samples were carried out using SEM and XRD analyses. The sliding wear properties of samples were also determined and their results were compared with those of unreinforced counterparts. On the basis of the results of the present investigation, the following conclusions can be drawn:  SEM investigations on the sintered Al4Cu/TiC composites showed that reasonably uniform distributions of the reinforcement TiC particles in the both cast Al4Cu/TiC (2.9 lm) and the sintered Al4Cu/TiC-13, Al4Cu/TiC-93 composites were observed. The XRD patterns of the sintered Al4Cu matrix alloy revealed the presence of the matrix a-Al and Al2Cu phases, whereas Al7Cu2Fe intermetallics existed after sintering in the Al4Cu/TiC-13 and Al4Cu/TiC-93 composites in addition to a-Al and Al2Cu phases. Except for the Al2Cu phase in both sintered and cast Al4Cu/TiC composites, there is no evidence of any interfacial reaction products between Al and TiC reinforcements.  The hardness and wear resistance of the cast and sintered composites were improved significantly as compared with those of the Al4Cu matrix alloys. On the basis of SEM observations of worn surfaces, the wear behaviors of the cast Al4Cu matrix alloy and the cast Al4Cu/5 vol.% TiC composite are characterized by deep ploughing grooves, adhesion and oxidation, whereas the cast Al4Cu/10 vol.%TiC, Al4Cu/15 vol.%TiC and Al4Cu/20 vol.%TiC composites exhibit narrow and shallow wear tracks associated with slight adhesion. Furthermore, when the well bonded TiC particles exist in the cast Al4Cu matrix, the improvement in wear resistance and hardness values of cast composites can be explained by high volume fraction and low interparticle spacing. In the case of sintered Al4Cu/TiC-13 and Al4Cu/TiC93 composites, hardness values are related to the interparticle spacings of composites. However, the wear resistance of the sintered Al4Cu/TiC-13 composite does not depend on the interparticle spacing since weakly bonded TiC particles pull out from the matrix during the wear test. Furthermore, on the basis of hardness and relative wear resistances of all composites fabricated by casting and sintering processes, it can be stated that these properties depend more on the volume fractions of the carbide particles than their sizes. Acknowledgements

Fig. 13. Variation of hardness and relative wear resistance values of samples as a function of interparticle spacing (here the hardness values are shown as filled symbols, whereas relative wear resistance values are shown as open symbols).

This research has been supported by Istanbul Technical University, Research Fund under the Project Title ‘‘Investigation of Production, Microstructural and Physical Properties of AlCu Alloys Reinforced with TiC and ZrC’’ with the Project No. 32838. The authors wish to thank London and Scandinavian Metallurgical Co. Ltd. for supplying flux material. The authors are also grateful to Mrs. Çig˘dem Çakır Konak for her help in the SEM investigations and research assistant Mert Günyüz for his help during the wear experiments. Further, we would like to express our gratitude to State Planning Organization (DPT) for funding the project entitled ‘‘Advanced Technologies in Engineering’’ with the project number

824

H. Kaftelen et al. / Composites: Part A 42 (2011) 812–824

001K120750 out of which the main infrastructure of the Particulate Materials Laboratories was founded. One of the authors (H. Kaftelen) gratefully acknowledges the Scientific and Technological Research Council of Turkey (TUBITAK) for the financial support through the International Research Fellowship Fund. References [1] Koczak MJ, Khatri SC, Allison JE, Bader MG. Metal matrix composites for ground vehicle, aerospace, and industrial applications. In: Suresh S, Mortensen A, Needleman A, editors. Fundamentals of metal matrix composites. Amsterdam: Elsevier; 1993. p. 297–312. [2] Wang W, Shi P, Qi M, Xu JJ, Chen FX, Yang DZ. Dry sliding wear of a Ti50Ni25Cu25 particulate-reinforced aluminum matrix composite. Metall Mater Trans A 1998;29A:1741–7. [3] Chung S, Hwang BH. A microstructural study of the wear behavior of SiC/Al composites. Tribol Int 1994;27:307–14. [4] Roy M, Venkataraman B, Bhanuprasad VV, Mahajan YR, Sundararajan G. The effect of particulate reinforcement on the sliding wear behavior of aluminum. Metall Trans A 1992;23:2833–47. [5] Venkataraman B, Sundararajan G. The sliding wear behaviour of Al–SiC particulate composites I macrobehavior. Acta Mater 1996;44(2):451–60. [6] Kaftelen H, Öveçog˘lu ML, Henein H, Çimenog˘lu H. ZrC particle reinforced Al– 4 wt.%Cu alloy composites fabricated by mechanical alloying and vacuum hot pressing microstructural evaluation and mechanical properties. Mater Sci Eng A 2010;527:5930–8. [7] Mandal A, Chakraborty M, Murty BS. Effect of TiB2 particles on sliding wear behavior of Al4Cu alloy. Wear 2007;262:160–6. [8] Lee KB, Kim HS, Kwon H. Reaction products of Al/TiC composites fabricated by the pressureless infiltration technique. Metal Mater Trans A 2005;36(A):2517–27. [9] Wei YY, Yi FZ, Zhang YR. The combustion synthesis process of AlTiC system in an elevated-temperature Al-melt. Chem Mater Sci 2002;17:13–6. [10] Gotman I, Koczak MJ, Shtessel E. Fabrication of Al matrix in situ composites via self-propagating synthesis. Mater Sci Eng A 1994;187:189–99. [11] Albiter A, Contreras A, Salazar M, Gonzales-Rodriguez JG. Corrosion behavior of aluminium metal matrix composites reinforced with TiC processed by pressureless melt infiltration. J Appl Electrochem 2006;36:303–8. [12] Kennedy AR, Karantzalis AE, Wyatt SM. The microstructure and mechanical properties of TiC and TiB2-reinforced cast metal matrix composites. J Mater Sci 1999;34:933–40. [13] Lopez VH, Scoles A, Kennedy AR. The thermal stability of TiC particles in an Al7 wt.%Si alloy. Mater Sci Eng A 2003;356:316–25. [14] Lloyd DJ. Particle-reinforced aluminum and magnesium matrix composites. Int Mater Rev 1994;39(1):1–23. [15] Lavernia EJ, Srivastava TS. The rapid solidification processing of materials science, principles, technology, advances and applications. Mater Sci 2010;45:287–325. [16] Rogathi PK, Asthana R, Das S. Solidification, structures, and properties of cast metal–ceramic particle composites. Int Metal Rev 1986;31:115–39. [17] Feest EA. Interfacial phenomena in metal matrix composites. Composites 1994;25(2):75–86. [18] Clyne TW. Physical metallurgy. In: Cahn RW, Haasen P, editors. Metallic composite materials. Amsterdam: Elsevier; 1996. p. 568–625. [19] Kennedy AR, Wyatt SM. Characterizing particle–matrix interfacial bonding in particulate Al–TiC MMCs produced by different methods. Composites A 2001;32:555–9. [20] Lee HS, Yeo JS, Hong SH, Yoon DJ, Na KH. The fabrication process and mechanical properties of SiCp/Al–Si metal matrix composites for automobile air-conditioner compressor pistons. J Mater Proc Technol 2001;113:202–8. [21] Vedani M, Gariboldi E, Silva G, Di Gregorio C. Influence of interface properties on mechanical behavior of particle reinforced metal matrix composites. Mater Sci Technol 1994;10:132–40. [22] Kennedy AR, Weston DP, Jones MI. Reaction in Al–TiC metal matrix composites. Mater Sci Eng A 2001;316:32–8. [23] Kennedy AR, Wyatt SM. The effect of processing on the mechanical properties and interfacial strength of aluminium/TiC MMCs. Compos Sci Technol 2000;60:307–14. [24] Ellis JD, Kelie JLF, Karantzalis A, Kennedy AR, Wood JV. Metal matrix composites. Patent no: WO 98/06880; 1998. [25] Kennedy AR, Karantzalis AE. The incorporation of ceramic particles in molten aluminum and the relationship to contact angle data. Mater Sci Eng 1999;A264:122–9. [26] ASTM international standard test method for water absorption, bulk density, apparent porosity, and apparent specific gravity of fired whiteware products. Test method designation C-373; 2006.

[27] ASTM international standard test methods for standard test methods for determining average grain size E-112-96; 2004. [28] International Center for Diffraction Data (ICDD): card no. 4-0787, database ed. Joint Committee on Powder Diffraction Standards (JCPDS). Germany; 2006. [29] International Center for Diffraction Data (ICDD): card no. 71-5027, database ed. Joint Committee on Powder Diffraction Standards (JCPDS). Germany; 2006. [30] Lyman T. Metallography, structures and phase diagrams. Metals handbook, vol. 8. Metals Park, OH: American Society for Metals; 1973. p. 259. [31] International Center for Diffraction Data (ICDD): card no. 32-1383, database ed. Joint Committee on Powder Diffraction Standards (JCPDS). Germany; 2006. [32] International Center for Diffraction Data (ICDD): card no. 1-84-1009, database ed. Joint Committee on Powder Diffraction Standards (JCPDS). Germany; 2006. [33] Asthana R. Processing effects on the engineering properties of cast metalmatrix composites. Adv Perform Mater 1998;5:213–55. [34] Contreras A, Angeles-Chavez C, Flores O, Perez R. Structural, morphological and interfacial characterization of Al–Mg/TiC composites. Mater Charact 2007;58:685–93. [35] Lloyd DJ. The solidification microstructure of particulate reinforced aluminium SiC composites. Compos Sci Technol 1989;35:159. [36] Karantzalis AE, Lekatou A, Georgatis E, Paulas V, Mavros H. Microstructural observations in as cast Al–Si–Cu/TiC composite. J Mater Eng Perform 2010;19:585–90. [37] Kaptay G. Interfacial criterion of spontaneous and forced engulfment of reinforcing particles by an advancing solid/liquid interface. Metall Mater Trans A 2001;32A:993–1005. [38] Contreras AJ. Wetting of TiC by Al–Cu alloys and interfacial characterization. Colloid Int Sci 2007;311:159–70. [39] Ramachandran TR, Sharma PK, Balasubramanian K. 68th WFC – world foundry congress, India, February, 2008. p. 189–93. [40] Mitra R, Chiou WA, Fine ME. Interfaces in as-extruded XD Al–TiC and Al/TiB2 metal matrix composites. J Mater Res 1993;8:2380–92. [41] Kennedy AR, Wyatt SM. The effect of processing on the mechanical properties and interfacial strength of aluminium/TiC MMCs – a quantitative study. Compos Sci Technol 2000;60:307–14. [42] Tone XC. Fabrication of in situ TiC reinforced aluminum matrix composites part I: Microstructural characterization. J Mater Sci 1998;33:5365–74. [43] Sato K, Flemings MC. Grain refining of Al–4 5Cu alloy by adding an Al–30TiC master alloy.. Metall Mater Trans A 1998;29A:1707–10. [44] Brook RJ. Concise encyclopedia of advanced ceramic materials. 1st ed. Elsevier Science; 1991. p. 393. [45] Karnesky RA, Meng L, Dunand DC. Strengthening mechanisms in aluminium containing coherent Al3Sc precipitates and incoherent Al2o3 dispersoids. Acta Mater 2007;55:1299–308. [46] Barbacki A, Frackowiak W. Z Metallkd 1988;79:410. [47] Kouzeli M, Mortensen A. Size dependent strengthening in particle reinforced aluminium. Acta Mater 2002;50:39–51. [48] Contreras A, Albiter A, Bedolla E, Perez R. Processing and characterization of Al–Cu and Al–Mg base composites reinforced with TiC. Adv Eng Mater 2004;6(9):767–75. [49] Herbert MA, Mitra R, Chakraborty M. Wear behaviour of cast and mushy state rolled Al–4.5Cu alloy and in-situ Al4.5Cu–5TiB2composite. Wear 2008;265:1606–18. [50] Wong WLE, Gupta M. Development of Mg/Cu nanocomposites using microwave assisted rapid sintering. Compos Sci Technol 2007;67:1541–52. [51] Wang Z, Peng HX, Liu J, Yao CK. Wear behaviour and microstructural changes of SiCw–Al composite under unlubricated sliding friction. Wear 1995;184:187–92. [52] Shyu RF, Hoji CT. In-situ reacted titanium carbide reinforced Al alloys composites. J Mater Proc Technol 2006;171:411–6. [53] Anasyida AS, Daud AR, Ghazali MJ. Dry sliding wear behaviour of Al–12Si–4Mg alloy with cerium addition. Mater Des 2010;31:365–74. [54] Suryanarayana C. Mechanical alloying and milling. Prog Mater Sci 2001;46:1–184. [55] Öveçoglu ML, Nix WD. Characterization of rapidly solidified and mechanically alloyed Al–Fe–Ce powders. Int J Powder Metall 1986;22:17–30. [56] Bhaduri A, Gopinathan V, Ramakrishnan P, Miodownik AP. Microstructural changes in a mechanically alloyed Al–6.2Zn–2.5Mg–1.7Cu alloy (7010) with and without particulate SiC reinforcement. Metal Mater Trans A 1996;27A:3718–26. [57] International Center for Diffraction Data (ICDD): card no. 085-1326, database ed. Joint Committee on Powder Diffraction Standards (JCPDS). Germany; 2006. [58] International Center for Diffraction Data (ICDD): card no. 25–1121, database ed. Joint Committee on Powder Diffraction Standards (JCPDS). Germany; 2006. [59] Sharma SC, Ramesh A. Effect of heat treatment on mechanical properties of particulate reinforced Al6061 composites. J Mater Eng Perform 2000;9:557–61. [60] Pai BC, Rohatgi PK. Production of cast aluminium–graphite particle composites using a pellet method.. J Mater Sci 1978;13:329.