j m a t e r r e s t e c h n o l . 2 0 1 5;4(4):411415

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Origina

Inves d mprope coprepa

Ehsan G ehAli Rahb

Ceramic Department, Materials and Energy Research Center, Tehran, Iran

a r t i c

Article histor

Received 31

Accepted 10

Available on

Keywords:

Aluminum

Boron carbid

Microwave s

Metal matri

1. Int

Among meposites areenhanced hard phaseand wear reimproved [nal properment and pcarbide is low density

CorresponE-mail: m

http://dx.do2238-7854/l e i n f o

y:

August 2014

February 2015

line 12 March 2015

e

intering

x composite

a b s t r a c t

B4C reinforced aluminum composites were fabricated by microwave heating of the mixture

of B4C (10, 15 and 20 wt%) and aluminum powders at 650, 750, 850 and 950 C. The effect of

different amounts of B4C on the microstructure and mechanical properties of aluminum

matrix was examined. The maximum bending (238 10 MPa) and compressive strength(330 10 MPa) values were measured for composites sintered at 950 and 750 C, respectively.The maximum hardness (112 Vickers) was measured for Al20 wt% B4C composite sintered

at 850 C. XRD investigations showed the decomposition of boron carbide and also the for-

mation of Al3BC by heating the composites at 850 C. SEM micrographs showed uniform

distribution of reinforcement particles in Al matrix.

2015 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier

Editora Ltda. All rights reserved.

roduction

tal matrix composites, aluminum alloy based com- known as very promising light materials withmechanical properties. In fact, by introducing a

either in particulate or ber form, the modulussistance of aluminum alloys could be signicantly13]. Among different parameters affected by theties of the composites, the nature of the reinforce-rocessing route play a paramount role [4,5]. Boronan interesting material for many reasons. It has

(2.51 g/cm3), excellent chemical resistance and is

ding author.-alizade@merc.ac.ir (M. Alizadeh).

extremely hard [6]. Additionally, boron carbide (B4C) has a highneutron absorption cross-section making it a valuable mate-rial for nuclear applications [6]. Despite these advantages, themonolithic B4C does not seem to be introducing well as anadvanced structural ceramic due to high brittle nature relatedto shock induction localized at high strain rates [7]. It is knownthat combining the B4C with a metal can mitigate the prob-lems associated with brittleness. By far, the most popularmetal used in joining B4C for this purpose is aluminum [812].Aluminum wets B4C well at elevated temperatures. Moltenaluminum has been shown to form a variety of binary andtertiary phases when in contact with B4C such as Al3BC, AlB10and Al4C3. Among these phases, Al3BC is the most commonly

i.org/10.1016/j.jmrt.2015.02.005 2015 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. All rights reserved.l Article

tigation on microstructural anrties of B4Caluminum matrixred by microwave sintering

hasali, Masoud Alizadeh , Touradj Ebadzadariechanicalmposites

, Amir hossein Pakseresht,

412 j m a t e r r e s t e c h n o l . 2 0 1 5;4(4):411415

observed phase [13,14]. The sintering of composite materialsby microwave processing has been known to reduce heatingtemperature and time and lead to ne microstructures andimproved mechanical properties [1522].

The boron carbides react strongly with liquid aluminum,resulting in a variety of compounds, including Al3BC, AlB24C4(AlB10), Al8B4C7, Al3B48C2 (b-AlB12), AlB2, AlB12C2, AlB48C2,Al4C3 and a-AlB12.7 [23]. Some studies have reported onthe reactivity of B4C in aluminum processed by inltrationand powder metallurgy techniques and on the formation ofdifferent compounds at different processing temperatures[14,24,25,26]. The main aims of the present work are the feasi-bility of themicrowavestructural p

2. Ex

B4C (Aldricwere used purity andtive. The Table 1.

The miried out usmixed powsamples w250 MPa ustest samplto obtain and heightout using amonitored RAYR312Msoaking timtered sampThe three pments wercompressivused, respediffractomeyses were AlB4C comtered samp(MKV-h21, ten successMicrostrucsamples wCambridge

Table 1

Composite

A B C D

3. Results and discussion

3.1. XRD analysis

For studying the effect of sintering temperature on the phasestructure and chemical compound of the composites, four Dcomposites (Table 1) were sintered at 650, 750, 850 and 950 C.As Fig. 1 shows, the identied phases were Al, B4C and Al3BC.It seems that the formation of Al3BC begins from the temper-ature of 850 C [13].

Density

be seen in Fig. 2, there are no sharp changes in den- different composites sintered at the same temperature.further reveals that composite A with no Co additivee minimum density, which implies that Co additive cana binder between Al and B4C particles. Meanwhile, it

be noted that the accurate calculation of relative den- samples is impossible due to partial decomposition of

AI :AI3BC :

B4C :

950C

850C

750C

10

650C

XRd at

600

Fig. formation of aluminumB4C composites by using heating and investigation of the mechanical androperties of these composites.

perimental procedures

h-378100) and aluminum (1056-merck) powdersas the starting materials and cobalt powder (99.8%

5 m mean particle size) was used as an addi-composition of composite samples is given in

xing of powders presented in Table 1 was car-ing the Spex instrument (8000D, Mixer mill). Theders were compacted to prepare the bar shapeith the dimension of 25 mm 5 mm 5 mm ating a uniaxial press. The compression strengthes were fabricated using a hydraulic press typecylindrical preforms with a diameter of 10 mm

of 8 mm. The sintering of samples was carried microwave furnace (900 W and 2.45 GHz), whichtemperature using an optical pyrometer (Model:SCL2G) at 650 C, 750 C, 850 C and 950 C without

e in a graphite bed. The bulk density of sin-les was measured using the Archimedes Principle.oint bending and compressive strength measure-e examined by Santam-STm 20. For bending ande strength tests, ve and three specimens werectively. X-ray diffraction (Philips (30 kV and 25 mA)ter system with CuK radiation ( = 1.5405 A)) anal-performed to identify the phases present in theposites. Vickers microhardness values of the sin-les were determined using a Microhardness TesterAkashi) under a load of 1 kgf for 15 s. At leastive indentations were performed for each sample.tural investigations and EDS analyses of sinteredere carried out using a SEM (Stereoscan 360, Leica).

Different compositions of composite samples.

Al (wt%) B4C (wt%) Co (wt%)

90 10 089 10 183.5 15 1.578 20 2

3.2.

As cansity ofFig. 2 has thact as shouldsity ofB4C.

Inte

nsity

5

Fig. 1 sintere

2.3

2.35

2.4

2.45

2.5

2.55

Den

sity

(gr

/Cm3

)2 theta(degree)15 20 30 40 50 60 70 807565554525 35

D patterns of composite containing 20 wt% B4C 650 C, 750 C, 850 C and 950 C.

1000950900850800750700650

TemperatureC

Al-10wt%B4CAl-10wt%B4C-1wt%CoAl-15wt%B4C-1.5wt%CoAl-20wt%B4C-2wt%Co

2 Density versus sintering temperature.

j m a t e r r e s t e c h n o l . 2 0 1 5;4(4):411415 413

Fig. 3 Bac (a) Al10 wt% B4C1 wt% Co and (b) Al15 wt%B4C1.5 wt

Fig. 4 Bac : (a) Al10 wt% B4C and (b) Al10 wt% B4C1 wt% Co.

3.3. Mi

Mechanicamicrostructhe SEM midistributionFig. 3. Fromin contrastreinforcemthe adhere

Fig. 5 shCo compossome spotsEDS analysments, the as a criterioture. In spopeak is seetion and fostronger peFinally, it sAl particlesinterface of

3.4. Ben

The matrixeffects: (1) alloy due tokscattered images of B and C composites sintered at 850 C:% Co.

kscattered images of A and B composites sintered at 750 C

crostructural analysisl and physical properties are highly affected by theture of sintered composites. Figs. 3 and 4 illustratecrographs of A, B and C composites. Homogeneous

of B4C reinforcements can be seen typically in Fig. 4(a) and (b), it is observed that A composite

to B composite has some porosity around the B4Cent particles. It seems that Co additive can improvence of Al matrix to B4C particles.ows SEM and EDS micrographs of Al20% B4C2%ite sintered at 850 C. Also, the EDS spectra, from

labeled 1 through 3, are shown in Fig. 5. Since theis is incapable of detection of carbon and boron ele-detection of Al peaks in the EDS spectra can be usedn for proong of B4C existence in the microstruc-t 1, there are not any peaks, while at spot 2, Al

n, which probably seems that the interfacial reac-rmation of Al3BC phase have occurred. In spot 3ak of Al is observed in the matrix of composite.eems that the dark and light regions are B4C and, respectively and Al3BC is probably formed at the

these particles.

ding strength

hardening is mainly the consequence of threesmaller grain sizes in the AMC matrix than in the

the reinforcement tangle. The hardening follows

Spot

10 m

0 Kev

Fig. 5 Baccomposite

the HallPeHigher dislbetween mbetween thhave a signhence on th1

12

3

10 0 Kev 10 0 Kev 10

Spot 2AIAI

Spot 3

kscattered image and EDS of Al20% B4C2% Cosintered at 850 C.

tch law: y 1/D, where D is the grain size. (2)ocation density generated by the CTE mismatchatrix and reinforcements. (3) Chemical reactione reinforcements particles and Al matrix, as it canicant effect on the interfacial characteristics ande mechanical properties of the composite [27,28].

414 j m a t e r r e s t e c h n o l . 2 0 1 5;4(4):411415

0

50

100

150

200

250

600 650 700 750 800 850 900 950 1000

Ben

ding

st

rengt

h(MPa

)

Al-10wt% B4CAl-10wt% B4C-1wt% CoAl-15 wt%B4C-1.5 wt%CoAl-20wt%B4C-2 wt%Co

TemperatureC

Fig. 6 A plot showing variation in bending strength ofcomposites with sintering temperature.

The bendinpresent wofor B4C werespectivelof composiFig. 6, comothers andB4C particl

The C cbending stbending strfacial reactbetween Asintering tecould be thobvious thaporosity, mproperties parameter

3.5. Com

The comprtemperaturB4C and sinpressive strsection, thearies, whicmotion, lea

150170190210230250270290310330350

600

Com

pre

ssive

stre

ngt

h (M

Pa)

Fig. 7 Thstrength.

40

50

60

70

80

90

100

110

120

600

hard

ness

theardn

perave

utionThis ng, wmall

and

Mi

l tesavedingss in

expl9]:

mFm

Hc, and

mat microhardness increased with increasing reinforce-since B4C is inherently harder than Al matrix and

irly well distribution of the reinforcements improvesility of the soft matrix to resist deformation. Sinteringg strength of B4CAl composites fabricated in therk was found to be in the range of 123238 MPaight percent fractions in the range of 1020%,

y. Fig. 6 illustrates the bending strength changestes versus sintering temperature. As it is clear inposites have the lowest bending strength among

Co additive might promote the adhesion of Al toes as observed in SEM micrographs (Fig. 4).omposites sintered at 650 and 750 C have higherrength; however, with the raising temperatureength of B composites increases (Fig. 6). The inter-ion and formation of Al3BC and also more cohesionl matrix and reinforcement as a result of highermperature which causes higher atomic diffusione possible reason for the above mentioned. It ist many parameters including interfacial reaction,icrocracks, grains size, etc. affect on mechanicalof composite; so the evaluation of each individualregardless of the impact of others is unreasonable.

pressive strength

essive strength results as a function of sinteringe (Fig. 7) show that an increase in the amount oftering temperature lead to an increase in the com-ength. As it was discussed in the bending strength

smaller grain size will lead to more grain bound-h can act as strong obstacles to the dislocationding to the increase of compressive strength.

Fig. 8 microh

Themicrowdistribfaces. sinteriwith sments

3.6.

For almicrowresponhardnecan betion [1

Hc = H

wherematrixtion of

Thement, the fathe ab1000950900850800750700650Tem pratu reC

Al-10%B4C

Al-10%B4C-1%Co

Al-15%B4C-1.5%Co

Al-20%B4C-2%Co

e effect of sintering temperature on compression

temperaturmicrohardnwith raisinness increaof interfacimicrohardnformation sintering te

4. Co

Microwavemetal matrand more, 1000950900850800750700650

TemperatureC

Al-10 wt%B4C

Al-10 wt%B4C-1 wt%Co

Al-15 wt%B4C-1.5 wt%Co

Al-20 wt%B4C-2 wt%Co

effect of sintering temperature oness on sintered samples.

formed studies on the composites fabricated by sintering revealed a narrow grain size with uniform

of the reinforcements, and well-bonded inter-may be correlated with the advantage of microwavehich have been proved to produce the compositesgrain size, homogeneous distribution of reinforce-

proper interfacial characteristic [29,30].

crohardness

ted samples, the average microhardness of the sintered composites was higher than the cor-

value for the reference 6061 Al alloy and thecreased with the increasing amount of B4C. Thisained by the law of mixtures in the following equa-

+ HrFrHm, and Hr are the hardness of the composite,

reinforcement, respectively, fm and fr are the frac-rix and reinforcement, respectively (Fig. 8).e is another parameter, which inuences on theess of the composite. In the Al/B4C composites,g sintering temperature to 850 C the microhard-sed due to decrease in porosity and enhancemental bonding. At sintering temperature of 950 C, theess of composites decreased probably due to the

of Al3BC and the grain coarsening with increasingmperature.

nclusions

sintering was used successfully to produce Al/B4Cix composite. At sintering temperature of 850 C

the interfacial reaction between Al and B4C causes

j m a t e r r e s t e c h n o l . 2 0 1 5;4(4):411415 415

the formation of Al3BC. 1 wt% cobalt could improve themicrostructural and mechanical properties of the compos-ites. In all composites, the microhardness and compressivestrength values increased with increasing the weight fractionof B4C. Microwave heating could produce Al/B4C compositesalong with saving energy and time.

Conicts of interest

The authors declare no conicts of interest.

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Investigation on microstructural and mechanical properties of B4Caluminum matrix composites prepared by microwave sintering1 Introduction2 Experimental procedures3 Results and discussion3.1 XRD analysis3.2 Density3.3 Microstructural analysis3.4 Bending strength3.5 Compressive strength3.6 Microhardness

4 ConclusionsConflicts of interestReferences