Fabrication and Characterizations of Mechanical Properties of Al-4.5%Cu/10TiC Composite by <i>In-situ</i> Method

Paper Menu >>

Journal Menu >>

Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 1075-1080

Published Online November 2012 (http://www.SciRP.org/journal/jmmce)

Fabrication and Characterizations of Mechanical

Properties of Al-4.5%Cu/10TiC Composite by

In-Situ Method

Anand Kumar*, Manas Mohan Mahapatra, Pradeep Kumar Jha

Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee, India

Email: *[email protected], [email protected]

Received July 5, 2012; revised August 7, 2012; accepted August 15, 2012

ABSTRACT

Addition of reinforcement such as TiC, SiC, Al2O3, TiO2, TiN, etc. to Aluminium matrix for enhancing the mechanical

properties has been a well established fact. In-situ method of reinforcement of the Aluminium matrix with ceramic

phase like Titanium Carbide (TiC) is well preferred over the Ex-situ method. In the present investigation, Al-Cu alloy

(series of 2014 Aluminiu m alloy) was used as matrix and reinforced with TiC using In-situ process. The Metal Matrix

Composite (MMC) material, Al-4.5%Cu/10%TiC developed exhibited higher yield strength, ultimate strength and hard-

ness as compared to Al-4.5%Cu alloy. Percentage increase in yield and ultimate tensile strengths were reported to be

about 15% and 24 % respectively whereas Vickers hardness increased by about 35%. The higher values in hardness in-

dicated that the TiC particles contributed to the increase of hardness of matrix. Fractured surface of the tensile specimen

of the composite material indicated presence of dimpled surface, indicating thereby a ductile type of fracture. During

the fabrication of composite, reaction products such as Al3Ti, Al2Cu and Al3C4 were identified with various morpho-

logies and sizes in metal matrix.

Keywords: In-situ; Metal Matrix Composites; TiC reinforcement; Mechanical Characterization

1. Introduction

Over the past few decades, researchers have emphasized

on production of light and strong materials. Aluminium

based metal matrix composite s are the advanced materials

with superior properties which are actively being sought

for engineering applications. In recent years, Al based

composite materials have gained significance in aero-

space, automotive and structural applications due to their

enhanced mechanical properties and good stability at

high temperature. The necessary characteristics of advan-

ced materials include high specific modulus, stiffness,

strength, hardness, ductility, corrosion resistance, low

heat expansion coefficient and so on [1].

The aim of designing the metal matrix composite ma-

terials is to combine the desirable properties of metal

(high strength and ductility) and ceramics (high modulus

and stiffness). In order to achieve the optimum mechani-

cal properties, it is essential to achieve the uniform dis-

tribution of reinforcement within the matrix. Aluminium,

Silicon, Copper, Titanium, Magnesium, and Nickel met-

als are widely used for preparation of metal matrix in

composites materials where as monofilaments, whiskers,

fibers or particulate types are widely used as reinforce-

ment phases in Metal Matrix Composites (MMCs). There

are many processing techniques which have been deve-

loped for fabricating Metal Matrix Composites (MMCs).

Such techniques are Powder Metallurgy (PM), liquid me-

tal infiltration, compocasting, squeeze casting method,

stir casting and spray decomposition metho d [2,3].

Among the fabrication techniques of MMC, stir cast-

ing (for particulate or discontinuous reinforced MMCs) is

generally preferred. Its advantages lie in its simplicity,

flexibility and applicability to large quantity of produc-

tion. It is also attractive because of minimized final cost

of the product. In the stir casting method, there are se-

veral factors that need considerable attention, including

the difficulty of achieving a uniform distribution of the

reinforcement. During these conventional processes, the

major difficulties are improper wetting due to oxidation

which exhibit interface binding between matrix and ce-

ramic phases. Improved wetting must be achieved to ob-

tain a good bond between the matrix and reinforcement.

Other limitations are the distributions of reinforcement,

interfacial reaction between the metal matrix and rein-

forcement, and control of volume fraction shape and size

of reinforcement, often encountered during the fabrica-

*Corresponding author.

A. KUMAR ET AL.

1076

tion of Metal Matrix Composites (MMCs). Therefore, all

such factors can affect the expected mechanical proper-

ties of MMCs [4-8].

A new approach has been developed as In-situ pro-

cessing, including SHS (Self-Propagating High Tempera-

ture Synthesis), reactive gas infiltration, liquid-solid or

solid-gas-liquid reactions, XDTM, DIMOX, VLS,

PRIMEXTM [9-11]. In-situ process involve a chemical re-

action resulting in the formation of a very fine, thermo-

dynamically stable, clean surfaces of ceramic rein-

forcement within a metal matrix. The other advantages of

In-situ process are, isotropic in nature, strong chemical

bonding between th e matrix and reinforcement phase, th e

distribution of reinforcement particles within the metal

matrix is homogeneous [12-14]. Therefore, the produced

composite are of better mechanical properties as com-

pared to monolithic materials.

Various types and sizes of reinforcements are used in

matrix of Aluminium like SiC, TiC, Al2O3, B4C, TiB2,

TiN, etc. Among these, TiC is a relatively new reinforce-

ment in metal matrix composites an d has good properties

such as wettability, thermal stability and distribution in

Aluminium metal matrix [15-17].

Present work deals with In-situ fabr ication of Al-4.5%

Cu metal matrix composite with 10 wt% TiC as rein-

forcement by In-situ process. The interfacial reaction

between the elements in composite is very important,

because the load is transferred at the interface and can

affect the mechanical properties of composite. The pro-

duced MMC was evaluated in terms of microstructural

characterization and mechanical properties testing such

as hardness and tensile strength.

2. Experimental Procedure

The raw materials used for the present study for the

preparation of the metal matrix was commercial available

Aluminium ingot (97.95% pure) and Copper (99.98%

pure). The chemical composition of commercial Alu-

minium ingot is shown in Table 1.

The setup used for the In-situ preparation of MMC

through stir-casting route is shown in Figure 1. The high

temperature electric furnace was used for preparation of

Al-4.5%Cu matrix alloy and master alloy o f Al-10%Ti.

In order to produce the composite, both alloys were

melted in graphite crucible and stirred gently at 475 rpm

with mechanical stirrer at 1150˚C temperature with hold-

ing time of 90 minutes. Impurities from the Aluminium

melt or dross was then removed from the surface of mol-

ten metal. The melts were degassed by using hex-

achloroethane (C2Cl6) at 750˚C for removing dissolved

hydrogen gas. The required amount of activated charcoal

powder was weighed and then encapsulated in alu-

minium foil wrappings and added into the molten alloy.

Mechanical stirring was carried out for 2 - 3 minutes. KF

and NaF were added as flux on the surface of liquid me-

tal. The flux reacted with metal alloy and formed layer of

slag that dissolved the oxide film from the liquid surface.

Activated charcoal is assumed to react with Titanium and

formed Titanium carbide (TiC) at 1150˚C temperature

with holding time of 30 minutes. TiC particles were

reinforced into matrix materials by In-situ process. The

resultant slurry was stirred for 1 - 2 min and finally

poured into a metallic mould to get the solidified casting .

The Al-4.5%Cu/10TiC MMC samples for microscopic

examinations were prepared by adopting standard metal-

lographic procedure. Samples were polished using dif-

ferent size of SiC grit papers of 120, 220 , 400, 600, 800,

1000, and 1200, followed by velvet cloth with aluminium

paste. The Keller’s reagent was used for etching with

mixture of 0.5 ml HF, 0.75 ml HCl, 2.5 ml HNO3 and ba-

lance amount of distilled water. The microstructures of

the etched sample were examined using Scanning Elec-

tron Microscope (SEM) as shown in Figure 2. Composi-

tional test of the sample were carried out using En-

ergy-Dispersive X-ray spectroscopy (EDX) and phase

analysis was done using X-Ray Diffraction technique

(XRD).

3. Result and Discussions

3.1. Microstructural Analysis

Figure 2 Shows a typical SEM micrograph of cast In-situ

Table 1. Chemical compositions of commercial aluminium

ingot.

MaterialsCuFeSiTi Mg Mn Cr NiAl

Chemical

Compositions 0.70.580.010.04 0.28 0.35 0.04 0.05Balance

Figure 1. Schematic of experime ntal se tup.

A. KUMAR ET AL. 1077

Figure 2. SEM micrograph of as cast composite.

Al-4.5%Cu-10%TiC composite. The presence of elements

in metal matrix composite can be observed as peaks of

Al, Cu, Ti and carbon by EDX spectrum shown in the in

Figure 3. The particles of TiC were formed by In-situ

reaction method and were found to be located at Alumi-

num grain boundaries or partly inside the Aluminum

grains. The microanalysis result exhibit the distribution

of TiC as reasonably uniform, though several small clus-

ters of particles are present along with some voids.

Figure 4 presents the XRD spectrums of the as cast

Al-4.5%Cu/10%TiC composite. The dominant phases

observed are Al3Ti, Al4C3, CuAl2 and TiC in the cast

composite. Among these phases, the binary compounds

Al3Ti and Al4C3 are mostly observed in first phase

chemical reactions at lower temperature in In-situ pro-

cess. The reason for synthesis of Al3Ti may be due to ex-

cessive titanium reaction with aluminium. At higher tem-

perature, theses compound react to each other and form

TiC particles in the composite [18]. The binary com-

pound Al4C3 was formed due to excess of carbon present

in molten aluminium. The compound Al4C3 is brittle in

nature and unstable at higher temperatures. Decrease in

retained carbon leads to increase in amount of TiC and

reduction in amount of impurities along the grain boun-

daries. Consequen tly, both tensile and ductility improved

in produced MMCs [19]. The phases identified have

clearly been labeled in Figure 5(a). The optimum molar

ratio of Ti and C is 1:1.3 in composite. Under such con-

dition these binary compound can be reduced to the pro-

duced composite. TiC particles form only when reaction

temperature was more than 1000˚C. TiC particles were

spherical, needle or block in shape with smooth and clear

surface [20-23]. Figure 5(b) shows that the size and

shape of TiC particles formed were from 0.1 µm to 0.8

µm with spherical shape.

3.2. Mechanical Testing

In order to investigate the hardness of as-cast matrix ma-

terials and composites, the samples were tested by using

a standard Vickers hardness testing machine with a py-

ramid indentor of load 5 kg. The load was applied for 15

sec and average of five readings was taken for each spe-

cimen at different locations to circumvent the possible

effects of particle segregation.

The average values of hardness of matrix material and

composite were 61 and 94 respectively as shown in the

Table 2. The TiC particles embedded with matrix mate-

rials affected 35.79% increase in the hardness.

The tensile specimens were prepared according to

ASTM E-8 as shown in the Figure 6. Yield strength and

ultimate strength of matrix and composite material was

tested with universal testing machine. The strain rate was

0.01s–1 during testing of the specimens. For each testing

condition, 3 specimens were subjected to tensile test and

the average of three values was noted. The yield strength

increases from 76 to 87 Mpa and ultimate strength in-

creases from 118 to 147 Mpa after 10% TiC reinforce-

ment in Al-4.5%Cu as shown in Table 2. The investiga-

tion of fracture surface morphology of matrix and com-

posite material specimens was observed by Scanning

Electron Microscope (SEM).

Figure 3. EDX results of Al-.45%Cu/10TiC.

Figure 4. XRD pattern of composite material.

A. KUMAR ET AL.

1078

(a)

(b)

Figure 5. (a) SEM micrograph of the Al-4.5%Cu/10TiC; (b)

SEM micrograph (at higher magnification) of Al-4.5%/

10%TiC.

Table 2. Average Hardness and Tensile value of matrix and

composite Materials.

Sl. No. Materials Vickers Hardness

(Hv5)

Yield

Stress

( σy (Mpa) )

Ultimate

Stress

( σu (Mpa))

1. Al-4.5%Cu 61 76 118

2. Al-4.5%Cu/10%TiC 94 87 147

2.5

GL=25

Figure 6. Schematic of tensile specimen (all dimension in

mm).

3.3. Fractography

The fracture surface of dog-bone tensile specimens of

matrix material and TiC reinforced material were ana-

lyzed under Scanning Electron Microscope (SEM) to de-

termine the mode of failure of the material. Typically, all

the specimens exhibited cup-and-cone failure mode which

indicates a ductile fracture mode. The presence of dim-

ples on fracture surface clearly indicates that necking had

occurred prior to matrix fracture. The fractograph of

Al-4.5% Cu matrix material shows a large deep dimple

in fracture surface which exhibited ductile failure as

shown in the Figure 7(a). Al-4.5%Cu/10%TiC compo-

site material observed small dimples on the fracture sur-

face which also revealed the presence of fracture mode to

be ductile one, as shown in Figure 7(b). Some de-

bonded particles are also seen on fracture surface which

proves that relatively strong bonding is present in be-

tween the matrix material and reinforced particles. Fig-

ure 7(c) shows a higher magnified fractograph of Al-

4.5%Cu/10%TiC composite material which observed crack

propagation on fracture surfaces, though this propagation

could no longer propagate and were arrested by rein-

forced particles. The transfer of loads form metal matrix

to particles clearly understands to successfully synthesize

hard TiC particles through In-situ pr ocessing.

(a)

(b)

Figure 7(a) SEM micrograph of fractured specimen of

Al-4.5%Cu; (b) SEM micrograph of fractured specimen of

Al-4.5%Cu/10%TiC.

A. KUMAR ET AL. 1079

4. Conclusion

In-situ Al-4.5%Cu/10%TiC metal matrix composite was

successfully fabricated using stir casting route. Ti was

added in elemental form and activated charcoal powder

was added in the melt which resulted into the formation

of Titanium Carbide as reinforcement. As the reinforce-

ment phase was formed inside the melt (In-situ process),

the distribution of Titanium Carbide was seen to be more

uniform. The yield, ultimate tensile strength and hardness

were seen to increase by 12.64%, 19.72%, and 35.79%

respectively in the composite material with TiC as rein-

forcement. The fracture surface of tensile sample shows

small dimples indicates ductile fractures. Tensile strength,

fracture surface and hardness of Al-4.5%Cu/10%TiC

MMC fabricated in the present investigation indicated

improvements of material properties.

5. Acknowledgements

The authors would like to thank the Department of Me-

chanical and Industrial Engineering. Indian Institute of

Technology, Roorkee for providing the necessary facili-

ties and fund for experiment an d tests

REFERENCES

[1] P. K. Rohtagi, “Metal Matrix Composites,” Journal of

Defence Science, Vol. 43, No. 4, 1993, pp. 323-349.

[2] D. B. Miracle, “Metal Matrix Composites from Science to

Technological Significance,” Composites Science and Tech-

nology, Vol. 65, No. 15-16, 2005, pp. 2526-2540.

doi:10.1016/j.compscitech.2005.05.027

[3] M. K. Surappa and P. K. Rohatgi, “Preparation and Prop-

erties of Cast Aluminium-Ceramic Particle Composites,”

Journal of Materials Science, Vol. 16, No. 4, 1981, pp. 883-

993.

[4] A. Sato and R. Mehrabian, “Aluminium Matrix Compo-

sites: Fabrication and Properties,” Metallurgical Transac-

tions B, Vol. 7, No. 3, 1976, pp. 443-451.

[5] J. Hashim “The Production of Cast Metal Matrix Com-

posite by a Modified Stir Casting Method,” Journal Tek-

nologi, Vol. 35, No. 35A, 2001, pp. 9-20.

[6] S. M. L. Nai and M. Gupta, “Influence of Stirring Speed

in the Synthesis of Al/SiC Based Functionally Gradient

Materials,” Composite Structures, Vol. 57, No. 1-4, 2002,

pp. 227-233.

[7] J. Hashim, L. Looney and M. S. J. Hashmi, “Metal Ma-

trix Composites: Production by the Stir Casting Method,”

Journal of Materials Processing Technology, Vol. 92-93,

1999, pp 1-7.

[8] S. P. Balasivanandha, L. Karunamoorthy, S. Kathiresan

and B. Mohan. “Influence of Stirring Speed and Stirring

Time on Distribution of Particles in Cast Metal Matrix

Composite,” Journal of Materials Processing Technology,

Vol. 171, No. 2, 2006, pp. 268-273.

[9] I. Gotman and M. J. Koczak, “Fabrication of Al Matrix In-

situ Composites via Self Propagating Synthesis,” Mate-

rials Science and Engineering, Vol. 187, No. A187, 1994,

pp. 189-199.

[10] S. Sheivani and M. F. Nazafabadi, “In-situ Fabrication of

Al-TiC Metal Matrix Composites by Reactive Slag Pro-

cess,” Material and Design, Vol. 28, No. 8, 2007, pp.

2373-2378.

[11] B. P. Khrishnan, M. K. Surappa and P. K. Rohatgi, “A

Direct Method to Prepare Cast Aluminium Alloy-Gra-

phite Particle Composite,” Journal of Material Science,

Vol. 16, No. 5, 1981, pp. 1209-1216.

[12] L. Peijie, E. G. Kandalova and V. I. Nikitin, “In-situ Syn-

thesis of Al-TiC in Aluminium Melt,” Materials Letters,

Vol. 59, No. 19-20, 2005, pp. 2545-2548.

[13] T. V. Christry, N. Murugan and S. Kumar, “A Compara-

tive Study on the Microstructures and Mechanical Proper-

ties of Al 6061 Alloy and the MMC Al6061/TiB2/12p,”

Journal of Minerals and Materials Characterization and

Engineering, Vol. 9, No. 1, 2010, pp. 57-65.

[14] C. Chunxiang, S. Yutian and M. Fanbin, “Review on Fa-

brication Method of In-situ Metal Matrix Composites,”

Journal of Material Science and Technology, Vol. 16, No.

6, 2000, pp. 619-626.

[15] M. Singla, D. D. Dwivedi, L. Singh and V. Chawla, “De-

velopment of Aluminium Based Silicon Carbide Particu-

late Metal Matrix Composite,” Journal of Minerals and

Materials Characterization and Engineering, Vol. 8, No.

6, 2009, pp. 455-467.

[16] S. B. Boppana and K. Chennakeshavalu, “Preparation of

Al-5Ti Mater Alloys for the In-situ Processing of Al-TiC

Metal Matrix Composites”. Journal of Minerals and Ma-

terials Characterization and Engineering, Vol. 8, No. 7,

2009, pp. 563-568.

[17] A. Albiter, C. A. Leon, R. A. L. Drew and E. Bedolla, “Mi-

crostructure and Heat-treatment Response of Al2024/TiC

Composites,” Materials Science and Engineering: A, Vol.

289, No. 1-2, 2000, pp. 109-115.

[18] P. Sahoo and M. J. Koczak, “Microstructure-Property

Relationships of In-situ Reacted TiC/Al-Cu Metal Matrix

Composites,” Material Science Engineering, Vol. 131,

No. 1, 1991, pp. 69-76.

[19] L. Lu, M. O. Lai and J. L. Yeo, “In-situ Synthesis of TiC

Composite for Structural Application,” Composite Struc-

ture, Vol. 47, No. 1, 1999, pp. 613-618.

[20] K. B. Lee, H. S. Sim and H. Kwon, “Reaction Products of

Al/TiC Composites Fabricated by the Pressureless Infil-

tration Technique,” Metallurgical and Materials Trans-

actions A, Vol. 36, No. 9, 2005, pp. 2517-2527.

doi:10.1007/s11661-005-0125-0

[21] R. F. Shyu and C. T. Ho, “In-situ Reacted Titanium Car-

bide Reinforced Aluminium Alloys Composite,” Journal

of Material Processing Technology, Vol. 171, No. 3, 2006,

pp. 211-216.

[22] B. Ranjit, “Synthesis of Al-TiC In-situ Composite: Effect

of Processing Temperature and Ti:C Ratio,” Transaction

of the Indian Institute of Metals, Vol. 62, No. 4-5, 2009,

pp. 391-395.

A. KUMAR ET AL.

1080

[23] B. Yang, F. Wang and J. S. Zhang, “Microstructure and

Characterization of in Situ Al/TiC and Al/TiC-20Si- 5Fe-3Cu-1Mg Composite Prepared by Spray Depo sit i on,”

Acta Materialia, Vol. 51, No. 17, 2003, pp. 4977-4989.