Due to advantages of mechanical alloying in comparison with liquid state processes, this process has used 
a lot to synthesis nanostructured alloy. In the present study, aluminum and silicon elemental powders with 
composition Al-5wt % Si were synthesized by mechanical alloying in high energy planetary ball. X-ray diffractometer and scanning electron microscopic were used to study microstructural and morphological changes of 
powder particles and formation of solid solution of Al-Si during milling. Crystallite size, lattice strain and lattice parameter were determined by Scherer, Williamson–Hall and Nilson–Reley methods. Minimum crystallite size was 17.895 nm according to Scherer method and 32.644 nm according to Williamson-Hall. Solid solution of Al-Si was formed between 5 h and 30 h, due to crystallite size in nano scale and diffusion process in 
mechanical alloying. In addition lattice parameter changes and XRD results prove it.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3503

Dayani, D.

Shokuhfar, A.

Vaezi, M.R.

Zolriasatein, A.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 1, 01PCN38(4pp) (2012)   2304-1862/2012/1(1)01PCN38(4) 01PCN38-1  2012 Sumy State University Characterization and Formation Mechanism of Solid Solution in Nanocrystalline Al-5wt%Si Powders Produced by Mechanical Alloying  D. Dayani1,*, A. Shokuhfar1, M.R. Vaezi2, A. Zolriasatein3  1 Department of Engineering, Karaj branch, Islamic Azad University, Karaj, Iran 2 Division of Nanotechnology and Advanced Materials, Materials and Energy Research Center, Karaj, Iran 3 Advanced Materials and Nanotechnology Research Lab, Faculty of Mechanical Engineering,  K.N. Toosi University of Technology, Tehran, Iran  (Received 22 June 2012; published online30 August 2012)  Due to advantages of mechanical alloying in comparison with liquid state processes, this process has used a lot to synthesis nanostructured alloy. In the present study, aluminum and silicon elemental powders with composition Al-5wt % Si were synthesized by mechanical alloying in high energy planetary ball. X-ray diffrac-tometer and scanning electron microscopic were used to study microstructural and morphological changes of powder particles and formation of solid solution of Al-Si during milling. Crystallite size, lattice strain and lat-tice parameter were determined by Scherer, Williamson–Hall and Nilson–Reley methods. Minimum crystal-lite size was 17.895 nm according to Scherer method and 32.644 nm according to Williamson-Hall. Solid solu-tion of Al-Si was formed between 5 h and 30 h, due to crystallite size in nano scale and diffusion process in mechanical alloying. In addition lattice parameter changes and XRD results prove it.  Keywords: Mechanical alloying, Solid solution, Williamson-Hall, Crystallite size.   PACS number: 81.20.Ev                                                             * dayanidavood@gmail.com  1. INTERODUCTION  The solid state process of materials, mechanical al-loying (MA) has attracted lots of interests because of its capabilities to produce both equilibrium and non-equilibrium phases [1-4]. Mechanical alloying was devel-oped for the first time by Benjamin [5].This technique was the result of a long search to produce a nickel-base superalloy [2]. MA is explained as a high energy milling process in which powder particles are under the influ-ence of repeated cold welding- fracturing-welding [3]. The transfer of mechanical energy to the powder parti-cles results in introduction of strain into the powder through generation of dislocations and other defects which act as fast diffusion paths. Additionally, refine-ment of particle and grain sizes occurs, and consequently the diffusion distances are reduced. It is believe that solid solution can be synthesized easily and with less energy in compare to other methods. Generally, Not only mechanical alloying is able to synthesis solid solution during milling, but it also can lead to extension of the solid solubility limits which can be estimated by X-ray diffraction (XRD), generally from changes in the lattice parameter values calculated from shifts in peak posi-tions or even the absence of second phase peaks [2].  Aluminum alloys with low melting temperature are the most widely used material for high specific strength structural applications in various fields like transportation industry. Common way to produce Alu-minum alloys is liquid state technique. According to advantages of mechanical alloying as a solid state technique in compare to liquid process which most im-portant of them is that problems associated with melt-ing and solidification are bypassed. So far research-ers’ve tried to assess effect of mechanical alloying on alloying behavior of aluminum with other elements such as Cu, Mg, Zn and Pb [1, 5-9]. The present study involves mechanical alloying of Al-5wt%Si high-energy ball mill. Scanning Electron Microscope (SEM) and X-ray diffractometer (XRD) were used as characterization techniques.  2. EXPERIMENTAL PROCEDURE  A mixture of commercial aluminum (99.9% purity and particle size of 75µm) and silicon powders (99.9% purity and particle size of < 20 µm) with composition Al – 5 wt% Si was milled in a planetary ball mill under argon at-mosphere. Fig. 1 shows the morphology of Al and Si pow-der particles. The following parameters were used ball-to-powder mass ratio of 12/1; ball diameter10 mm; speed, 250 rpm. Also 1.5wt% of stearic acid (CH3(CH2)16CO2H) was added as PCA. Mixture of powder was milled for 50hr. Samples of the milled powders were collected at different milling times:0,5, 20, 30 and 50 h. X-ray diffraction was performed on a wide angle dif-fractometer in the θ-2θ step scan mode by using Cu-Kα radiation. Scans were collected over a 2θ range of 20-90° with a step of 0.01°.The crystallite size (d) and the equivalent lattice strain (ε) were determined from the broadening ) of reflections shown in Fig. 1using the Williamson-Hall method (10):   cos   k /d + 2 sin , (1)  where  is the full-width at half-maximum (FWHM) of the diffraction peak, θ is the diffraction angle,  is the X-ray wavelength ( Cu  0.15406 nm, d is the crystallite size and   is the lattice strain.  Thus, it’s clear cut that when we plot cos   against  sin  we get a straight line with slope ( ) and intercept kλ/d The crystallite size (d) can be calculated from (K and  are determinate) and lattice strain( ) is slop line (11).  D.DAYANI, A.SHOKUHFAR, M.R. VAEZI, A.ZOLRIASATEIN PROC. NAP 1, 01PCN38 (2012)   01PCN38-2 Also scherer formola was used to determine crystal-lite size (2):   d  0.9 / cos , (2)  where  is the full-width at half-maximum (FWHM) of the diffraction peak, θ is the diffraction angle,  is the X-ray wavelength and d is the crystallite size (2). Furthermore the lattice parameter was obtained from a linear regression analysis of the measured lat-tice parameter, obtained from each peak, plotted against the Nilson–Reley function (12).   N – R  (cos2 /sin  + cos2 /  )/2.  (3)  Scanning electron microscope was used for evalua-tion of morphological changes.   a  b  Fig. 1 – Secondary electron SEM micrographs of Al and Si powder particles: (a) Al and (b) Si  3. RESULTS AND DISCUSSION  Fig.2 (a) shows XRD patterns of the Al–5 wt%Si powders milled for 0,5,20,30 and 50h. In general with increasing milling time due to variation of microstruc-ture [13], the peaks broaden which this event is shown in Fig. 1 (b). It is well known that the crystallite size and the lat-tice strain contributions to line broadening are inde-pendent of each other [14]. When goal is generally to estimate trend of crystal-lite size change with milling time, Scherer method can be acceptable [2]. Fig. 3 (a) shows variation of crystal-lite size achieved by scherer formula.   a    b  Fig. 2 –  (a) XRD pattern of Al-5wt%Si milled for different times and (b) changes of broadening of (111) Al peak during milling   a  b  Fig. 3 – (a) Crystallite size as a function of milling time, de-termined by Scherer method and (b)  shows changes of crystal-lite size and lattice strain which were determined from Wil-liamson-Hall method  CHARACTERIZATION AND FORMATION MECHANISM … PROC. NAP 1, 01PCN38 (2012)   01PCN38-3 Also Fig. 3 (b) shows changes of crystallite size and lattice strain which were determined from Williamson-Hall method.  It is clear cut that, both Williamson-Hall and scher-er methods indicate that crystallite size decreases con-tinuously in nanometer scale. It is believed that the rea-son of this reduction during milling is due to the for-mation of new defects such as dislocations that could appear in different ways: formation of dense regions of these dislocations into the sub grains, pileup of the grain boundaries or untidy clusters within the crystallites. In general, reduction of crystallite size during milling can be contributed to dislocation generation caused by severe plastic deformation during mechanical alloying. Moreo-ver, it is seen that lattice strain generally increases with enhancement of milling time. It is found that the in-creased strains can be due to stress fields associated with the multiplication of the dislocations and the intro-duction of dislocations, vacancies, impurities and other lattice defects during milling [11, 14]. Decrease of crystallite size can provide suitable con-ditions to form solid solution of Al-Si. When crystallite size decreases to a nanometer scale makes grain bound-aries increase. This enhancement provide a connective network of short-circuit diffusion paths. An enhance-ment of self-diffusivity in comparison to boundary diffu-sion of a factor of about 100 has been reported. For this reason, alloying can be performance easily and by less energy [15, 16].  Furthermore, changes of lattice parameter and shifts of peaks also help to prove formation of solid so-lution of Al-Si. Fig. 4 and 5 show alterations of lattice parameter and the peaks shift, respectively.    Fig. 4 – Variation of lattice parameter as a function of milling time, determined by Nilson-Reley method    Fig. 5 – Displacement of (111) Al diffraction peak for different milling time: (a) 0 h, (b) 5 h, (c) 20 h, (d) 30 h and (e) 50 h According to famous Bragg’s law:   n   2dsin , (4)  where θ is the Bragg diffraction angle, d interplanar spacing and λ the wave length of the radiation used. In addition it is well known that there is a direct link be-tween d and a (lattice parameter). So if lattice parame-ter increased which means that interplanar spacing increases, thus θ must decreases until the Bragg’s law is valid [17]. It is clearly observed that after 5 h (111) Al peak moves toward higher angles while lattice pa-rameter faces a decline. Then (111) Al peak shifts to-ward lower angles up to 30 h which in this duration there is an increase in lattice parameter. Afterwards lattice parameter dramatically drops to a minimum value and it makes (111) Al peak shifts toward higher angels again. Generally, it can be ascribed displace-ment of (111) Al peak to lattice parameter changes [18]. Also according to Vegard’s law the lattice parameter of an alloy varies linearly with the solid solubility. The solid solubility increases with increasing lattice param-eter of aluminum (Al = 0.4049 nm) to the lattice pa-rameter of an diamond cubic silicon (Si = 0.543 nm) [19]. According to Fig. 4, it’s seen that lattice parame-ter increases from 5 h to 30 h increase.  In addition it is shown in Fig. 2 (a) that two peaks of Si ((400) and (331) peaks) disappear during mechan-ical alloying that this issue is a next reason to prove solid solution of Al-Si was formed.  Furthermore, solid solution of Al-Si is substitution-al solution which is dependence on a vacancy mecha-nism for diffusion and it is proved that during mechan-ical alloying formation of a large number of defects is unavoidable especially vacancies and because fracture of the powder particles and a lot of microcracks are generated by mechanical alloying process which these events lead to an increase in internal energy. That is why, activation energy needed for diffusion may be lowered by reducing the activation energy needed for the creation of vacancies. As a result, alloying can be performance easily [15, 16]. Fig. 6 shows SEM images of Al-5wt % Si powder par-ticles mechanical alloyed for different milling time. In the preliminary stage of milling (5h) particles are still soft and cold welding is a predomination process. In ad-dition, in this stage particles shape has gotten flattened because of effects of cold working during milling (Fig. 6(a)). In middle stage (20 h) particles has become more work hardening. That is why, they are fractured and fracture predominates (Fig. 6(b)). Finally, Welding and fracture mechanisms then reach equilibrium (50 h), thus particles with randomly orientated interfacial boundaries is formed and the morphology and size of particles becomes more uniform (Fig. 6(c)). As shown in Fig. 6 (c), it is obvious that after 50h the morphology of the particles is globular and the distribution of particle morphology and particle size becomes narrower.  According to Fig. 6, it is completely obvious that during milling particles size decreases. This reduction in particles size reduces the diffusion distances be-tween particles and facilitates diffusion [11].   D.DAYANI, A.SHOKUHFAR, M.R. VAEZI, A.ZOLRIASATEIN PROC. NAP 1, 01PCN38 (2012)   01PCN38-4                       a                                      b       c  Fig. 6 – Backscatter SEM images of Al-5wt % Si powders milled for different times: (a) 5 h, (b) 20 h and (c) 50 h  The EDX analysis was performed in order to evaluate formation of solid solution. Fig. 7 shows that elemental distribution of Al and Si. It is seen that Si diffused into Al matrix, which confirms solid solution formation.   4. CONCLUSION  In the present study, nanocrystalline Al-5wt%Si has been successfully synthesized by mechanical alloying under argon atmosphere. It was seen that after 50h the crystallite size reached to 17.895 nm according to Scherer method and 32.644 nm with strain of 0.45 % according to W-H technique. Furthermore, XRD results, SEM images and lattice parameter changes have proved       Fig. 7 –  backscatter SEM image and according its elemental mapping analysis for 50 h mechanical alloyed specimen  solid solution of Al-Si was formed during milling. Also it has been mentioned several reason for produced solid solution of Al-Si which included formation of defects especially vacancies, reduction of crystallite size, changes of lattice parameter and decreased particle size during milling. Moreover, morphology changes of powders was evaluated. It was found that early milling welding was predominant mechanism after 20 h it was observed, fracture was major mechanism and after 50 h fracture and welding mechanisms then reached equi-librium. As a result the morphology of the particles became globular. In addition, it was determined that formation of sol-id solution had been in a particular period of mechani-cal alloying (between 5 h and 30 h).   REFERENCES  1. S. Scudino, M. Sakaliyska, K.B. Surreddi, J. Eckert, J. Alloy Compd. 483, 2 (2009). 2. C. Suryanarayana, Prog. Mater. Sci. 46, 1 (2001). 3. C. Suryanarayana, Rev. Adv. Mater. Sci. 18, 203 (2008). 4. E. Ma, M. Atzmon, Mater. Chem. Phys. 39, 249 (1995). 5. J.B. Fogagnolo, D. Amador, E.M. Ruiz-Navas, J.M. Torralba, Mat. Sci. Eng. A-Struc., 433, 45 (2006). 6. G. Ran, J-E. Zhou, S. Xi, P. Li, J. Alloy Compd. 419, 66 (2006). 7. M. Tavoosi, M.H. Enayati, F. Karimzadeh, J. Alloy Compd. 464, 107(2008). 8. M. Rafiei, S. Khademzadeh, N. Parvin, J. Alloy Compd. 489, 224(2010). 9. I. Manna, P. Nandi, B. Bandyopadhyay, K. Ghoshray,  A. Ghoshray, Acta Mater. 52, 4133 (2004). 10. G.K. Williamson, W.H. Hall, Acta Metall. Mater. 1, 22 (1953). 11. J. Safari, G.H. Akbari, A. Shahbazkhan, M.D. Chermahini, J. Alloy Compd. 509, 9419 (2011). 12. A. Korchef, Y. Champion, N. Njah, J. Alloy Compd. 427, 176 (2007). 13. M. Mhadhbi, M. Khitouni, M. Azabou, A. Kolsi, Mater. Charact. 59, 944 (2008). 14. S. Sivasankaran, K. Sivaprasad, R. Narayanasamy, P.V. Satyanarayana, Mater. Charact. 62, 661 (2011). 15. L. Lu, M.O. Lai, Mater. Design. 16, 33 (1995). 16. L. Lu, M.O. Lai, S. Zhang, J. Mater. Process. Tech. 67, 100 (1997). 17. Z.P. Xia, J.J. Shen, Y.Q. Shen, Z.Q. Li, J. Alloy Compd. 448, 210 (2008). 18. A.R. Abbasi, M. Shamanian, j. Alloy Compd. 508, 152 (2010). 19. J. Milligan, R. Vintila, M. Brochu, Mat. Sci. Eng. A-Struct. 508, 43 (2009).  

Characterization and Formation Mechanism of Solid Solution in Nanocrystalline Al-5wt%Si  Powders Produced by Mechanical Alloying

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 1, 01PCN38(4pp) (2012) 
 
 
2304-1862/2012/1(1)01PCN38(4) 01PCN38-1  2012 Sumy State University 
Characterization and Formation Mechanism of Solid Solution in Nanocrystalline Al-5wt%Si 
Powders Produced by Mechanical Alloying 
 
D. Dayani1,*, A. Shokuhfar1, M.R. Vaezi2, A. Zolriasatein3 
 
1 Department of Engineering, Karaj branch, Islamic Azad University, Karaj, Iran 
2 Division of Nanotechnology and Advanced Materials, Materials and Energy Research Center, Karaj, Iran 
3 Advanced Materials and Nanotechnology Research Lab, Faculty of Mechanical Engineering,  
K.N. Toosi University of Technology, Tehran, Iran 
 
(Received 22 June 2012; published online30 August 2012) 
 
Due to advantages of mechanical alloying in comparison with liquid state processes, this process has used 
a lot to synthesis nanostructured alloy. In the present study, aluminum and silicon elemental powders with 
composition Al-5wt % Si were synthesized by mechanical alloying in high energy planetary ball. X-ray diffrac-
tometer and scanning electron microscopic were used to study microstructural and morphological changes of 
powder particles and formation of solid solution of Al-Si during milling. Crystallite size, lattice strain and lat-
tice parameter were determined by Scherer, Williamson–Hall and Nilson–Reley methods. Minimum crystal-
lite size was 17.895 nm according to Scherer method and 32.644 nm according to Williamson-Hall. Solid solu-
tion of Al-Si was formed between 5 h and 30 h, due to crystallite size in nano scale and diffusion process in 
mechanical alloying. In addition lattice parameter changes and XRD results prove it. 
 
Keywords: Mechanical alloying, Solid solution, Williamson-Hall, Crystallite size. 
 
 PACS number: 81.20.Ev 
 
 
                                                          
* dayanidavood@gmail.com  
1. INTERODUCTION 
 
The solid state process of materials, mechanical al-
loying (MA) has attracted lots of interests because of its 
capabilities to produce both equilibrium and non-
equilibrium phases [1-4]. Mechanical alloying was devel-
oped for the first time by Benjamin [5].This technique 
was the result of a long search to produce a nickel-base 
superalloy [2]. MA is explained as a high energy milling 
process in which powder particles are under the influ-
ence of repeated cold welding- fracturing-welding [3]. 
The transfer of mechanical energy to the powder parti-
cles results in introduction of strain into the powder 
through generation of dislocations and other defects 
which act as fast diffusion paths. Additionally, refine-
ment of particle and grain sizes occurs, and consequently 
the diffusion distances are reduced. It is believe that 
solid solution can be synthesized easily and with less 
energy in compare to other methods. Generally, Not only 
mechanical alloying is able to synthesis solid solution 
during milling, but it also can lead to extension of the 
solid solubility limits which can be estimated by X-ray 
diffraction (XRD), generally from changes in the lattice 
parameter values calculated from shifts in peak posi-
tions or even the absence of second phase peaks [2].  
Aluminum alloys with low melting temperature are 
the most widely used material for high specific 
strength structural applications in various fields like 
transportation industry. Common way to produce Alu-
minum alloys is liquid state technique. According to 
advantages of mechanical alloying as a solid state 
technique in compare to liquid process which most im-
portant of them is that problems associated with melt-
ing and solidification are bypassed. So far research-
ers’ve tried to assess effect of mechanical alloying on 
alloying behavior of aluminum with other elements 
such as Cu, Mg, Zn and Pb [1, 5-9]. 
The present study involves mechanical alloying of 
Al-5wt%Si high-energy ball mill. Scanning Electron 
Microscope (SEM) and X-ray diffractometer (XRD) 
were used as characterization techniques. 
 
2. EXPERIMENTAL PROCEDURE 
 
A mixture of commercial aluminum (99.9% purity and 
particle size of 75µm) and silicon powders (99.9% purity 
and particle size of < 20 µm) with composition Al – 5 wt% 
Si was milled in a planetary ball mill under argon at-
mosphere. Fig. 1 shows the morphology of Al and Si pow-
der particles. The following parameters were used ball-to-
powder mass ratio of 12/1; ball diameter10 mm; speed, 
250 rpm. Also 1.5wt% of stearic acid (CH3(CH2)16CO2H) 
was added as PCA. Mixture of powder was milled for 
50hr. Samples of the milled powders were collected at 
different milling times:0,5, 20, 30 and 50 h. 
X-ray diffraction was performed on a wide angle dif-
fractometer in the θ-2θ step scan mode by using Cu-Kα 
radiation. Scans were collected over a 2θ range of 20-
90° with a step of 0.01°.The crystallite size (d) and the 
equivalent lattice strain (ε) were determined from the 
broadening ) of reflections shown in Fig. 1using the 
Williamson-Hall method (10): 
 
 cos   k /d + 2 sin , (1) 
 
where  is the full-width at half-maximum (FWHM) of 
the diffraction peak, θ is the diffraction angle,  is the 
X-ray wavelength ( Cu  0.15406 nm, d is the crystallite 
size and   is the lattice strain.  
Thus, it’s clear cut that when we plot cos   against  
sin  we get a straight line with slope ( ) and intercept kλ/d 
The crystallite size (d) can be calculated from (K and  are 
determinate) and lattice strain( ) is slop line (11). 
 D.DAYANI, A.SHOKUHFAR, M.R. VAEZI, A.ZOLRIASATEIN PROC. NAP 1, 01PCN38 (2012) 
 
 
01PCN38-2 
Also scherer formola was used to determine crystal-
lite size (2): 
 
 d  0.9 / cos , (2) 
 
where  is the full-width at half-maximum (FWHM) of 
the diffraction peak, θ is the diffraction angle,  is the 
X-ray wavelength and d is the crystallite size (2). 
Furthermore the lattice parameter was obtained 
from a linear regression analysis of the measured lat-
tice parameter, obtained from each peak, plotted 
against the Nilson–Reley function (12). 
 
 N – R  (cos2 /sin  + cos2 /  )/2.  (3) 
 
Scanning electron microscope was used for evalua-
tion of morphological changes. 
 
 
a 
 
b 
 
Fig. 1 – Secondary electron SEM micrographs of Al and Si 
powder particles: (a) Al and (b) Si 
 
3. RESULTS AND DISCUSSION 
 
Fig.2 (a) shows XRD patterns of the Al–5 wt%Si 
powders milled for 0,5,20,30 and 50h. In general with 
increasing milling time due to variation of microstruc-
ture [13], the peaks broaden which this event is shown 
in Fig. 1 (b). 
It is well known that the crystallite size and the lat-
tice strain contributions to line broadening are inde-
pendent of each other [14]. 
When goal is generally to estimate trend of crystal-
lite size change with milling time, Scherer method can 
be acceptable [2]. Fig. 3 (a) shows variation of crystal-
lite size achieved by scherer formula. 
 
 
a 
 
 
 
b 
 
Fig. 2 –  (a) XRD pattern of Al-5wt%Si milled for different times 
and (b) changes of broadening of (111) Al peak during milling 
 
 
a 
 
b 
 
Fig. 3 – (a) Crystallite size as a function of milling time, de-
termined by Scherer method and (b)  shows changes of crystal-
lite size and lattice strain which were determined from Wil-
liamson-Hall method 
 CHARACTERIZATION AND FORMATION MECHANISM … PROC. NAP 1, 01PCN38 (2012) 
 
 
01PCN38-3 
Also Fig. 3 (b) shows changes of crystallite size and 
lattice strain which were determined from Williamson-
Hall method.  
It is clear cut that, both Williamson-Hall and scher-
er methods indicate that crystallite size decreases con-
tinuously in nanometer scale. It is believed that the rea-
son of this reduction during milling is due to the for-
mation of new defects such as dislocations that could 
appear in different ways: formation of dense regions of 
these dislocations into the sub grains, pileup of the grain 
boundaries or untidy clusters within the crystallites. In 
general, reduction of crystallite size during milling can 
be contributed to dislocation generation caused by severe 
plastic deformation during mechanical alloying. Moreo-
ver, it is seen that lattice strain generally increases with 
enhancement of milling time. It is found that the in-
creased strains can be due to stress fields associated 
with the multiplication of the dislocations and the intro-
duction of dislocations, vacancies, impurities and other 
lattice defects during milling [11, 14]. 
Decrease of crystallite size can provide suitable con-
ditions to form solid solution of Al-Si. When crystallite 
size decreases to a nanometer scale makes grain bound-
aries increase. This enhancement provide a connective 
network of short-circuit diffusion paths. An enhance-
ment of self-diffusivity in comparison to boundary diffu-
sion of a factor of about 100 has been reported. For this 
reason, alloying can be performance easily and by less 
energy [15, 16].  
Furthermore, changes of lattice parameter and 
shifts of peaks also help to prove formation of solid so-
lution of Al-Si. Fig. 4 and 5 show alterations of lattice 
parameter and the peaks shift, respectively. 
 
 
 
Fig. 4 – Variation of lattice parameter as a function of milling 
time, determined by Nilson-Reley method 
 
 
 
Fig. 5 – Displacement of (111) Al diffraction peak for different 
milling time: (a) 0 h, (b) 5 h, (c) 20 h, (d) 30 h and (e) 50 h 
According to famous Bragg’s law: 
 
 n   2dsin , (4) 
 
where θ is the Bragg diffraction angle, d interplanar 
spacing and λ the wave length of the radiation used. In 
addition it is well known that there is a direct link be-
tween d and a (lattice parameter). So if lattice parame-
ter increased which means that interplanar spacing 
increases, thus θ must decreases until the Bragg’s law 
is valid [17]. It is clearly observed that after 5 h (111) 
Al peak moves toward higher angles while lattice pa-
rameter faces a decline. Then (111) Al peak shifts to-
ward lower angles up to 30 h which in this duration 
there is an increase in lattice parameter. Afterwards 
lattice parameter dramatically drops to a minimum 
value and it makes (111) Al peak shifts toward higher 
angels again. Generally, it can be ascribed displace-
ment of (111) Al peak to lattice parameter changes [18]. 
Also according to Vegard’s law the lattice parameter of 
an alloy varies linearly with the solid solubility. The 
solid solubility increases with increasing lattice param-
eter of aluminum (Al = 0.4049 nm) to the lattice pa-
rameter of an diamond cubic silicon (Si = 0.543 nm) 
[19]. According to Fig. 4, it’s seen that lattice parame-
ter increases from 5 h to 30 h increase.  
In addition it is shown in Fig. 2 (a) that two peaks 
of Si ((400) and (331) peaks) disappear during mechan-
ical alloying that this issue is a next reason to prove 
solid solution of Al-Si was formed.  
Furthermore, solid solution of Al-Si is substitution-
al solution which is dependence on a vacancy mecha-
nism for diffusion and it is proved that during mechan-
ical alloying formation of a large number of defects is 
unavoidable especially vacancies and because fracture 
of the powder particles and a lot of microcracks are 
generated by mechanical alloying process which these 
events lead to an increase in internal energy. That is 
why, activation energy needed for diffusion may be 
lowered by reducing the activation energy needed for 
the creation of vacancies. As a result, alloying can be 
performance easily [15, 16]. 
Fig. 6 shows SEM images of Al-5wt % Si powder par-
ticles mechanical alloyed for different milling time. In 
the preliminary stage of milling (5h) particles are still 
soft and cold welding is a predomination process. In ad-
dition, in this stage particles shape has gotten flattened 
because of effects of cold working during milling 
(Fig. 6(a)). In middle stage (20 h) particles has become 
more work hardening. That is why, they are fractured 
and fracture predominates (Fig. 6(b)). Finally, Welding 
and fracture mechanisms then reach equilibrium (50 h), 
thus particles with randomly orientated interfacial 
boundaries is formed and the morphology and size of 
particles becomes more uniform (Fig. 6(c)). As shown in 
Fig. 6 (c), it is obvious that after 50h the morphology of 
the particles is globular and the distribution of particle 
morphology and particle size becomes narrower.  
According to Fig. 6, it is completely obvious that 
during milling particles size decreases. This reduction 
in particles size reduces the diffusion distances be-
tween particles and facilitates diffusion [11]. 
 
 D.DAYANI, A.SHOKUHFAR, M.R. VAEZI, A.ZOLRIASATEIN PROC. NAP 1, 01PCN38 (2012) 
 
 
01PCN38-4 
  
                    a                                      b     
 
 
c 
 
Fig. 6 – Backscatter SEM images of Al-5wt % Si powders 
milled for different times: (a) 5 h, (b) 20 h and (c) 50 h 
 
The EDX analysis was performed in order to evaluate 
formation of solid solution. Fig. 7 shows that elemental 
distribution of Al and Si. It is seen that Si diffused into Al 
matrix, which confirms solid solution formation.  
 
4. CONCLUSION 
 
In the present study, nanocrystalline Al-5wt%Si has 
been successfully synthesized by mechanical alloying 
under argon atmosphere. It was seen that after 50h the 
crystallite size reached to 17.895 nm according to 
Scherer method and 32.644 nm with strain of 0.45 % 
according to W-H technique. Furthermore, XRD results, 
SEM images and lattice parameter changes have proved  
  
 
 
 
Fig. 7 –  backscatter SEM image and according its elemental 
mapping analysis for 50 h mechanical alloyed specimen 
 
solid solution of Al-Si was formed during milling. Also it 
has been mentioned several reason for produced solid 
solution of Al-Si which included formation of defects 
especially vacancies, reduction of crystallite size, 
changes of lattice parameter and decreased particle 
size during milling. Moreover, morphology changes of 
powders was evaluated. It was found that early milling 
welding was predominant mechanism after 20 h it was 
observed, fracture was major mechanism and after 50 h 
fracture and welding mechanisms then reached equi-
librium. As a result the morphology of the particles 
became globular. 
In addition, it was determined that formation of sol-
id solution had been in a particular period of mechani-
cal alloying (between 5 h and 30 h). 
 
 
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Characterization and Formation Mechanism of Solid Solution in Nanocrystalline Al-5wt%Si Powders Produced by Mechanical Alloying

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