- Email: [email protected]
Effect of ion bombardment on the crystallization kinetics of FeSiNbBCu amorphous alloys
Accepted Manuscript Effect of ion bombardment on the crystallization kinetics of FeSiNbBCu amorphous alloys Ling Tang, Kun Peng, Yingwei Wu, Wei Zhang PII:
S0925-8388(16)33524-1
DOI:
10.1016/j.jallcom.2016.11.057
Reference:
JALCOM 39552
To appear in:
Journal of Alloys and Compounds
Received Date: 30 September 2016 Revised Date:
1 November 2016
Accepted Date: 4 November 2016
Please cite this article as: L. Tang, K. Peng, Y. Wu, W. Zhang, Effect of ion bombardment on the crystallization kinetics of FeSiNbBCu amorphous alloys, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.11.057. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Effect of ion bombardment on the crystallization kinetics of FeSiNbBCu amorphous alloys Ling Tang1,2,
Kun Peng1,2*,
Yingwei Wu1,
Wei Zhang1
RI PT
1. College of Materials Science and Engineering, Hunan University, Changsha, China, 410082 2. Hunan province key laboratory for spray deposition technology and application, Hunan
SC
University, Changsha, China, 410082
Abstract
M AN U
Amorphous FeSiNbBCu alloy ribbons were bombarded by Ar ion with different time, the phase structure and crystallization kinetics of amorphous alloys after ion bombardment were evaluated by XRD and differential scanning calorimetry (DSC), respectively. The apparent activation energy of the first crystallization process
TE D
dropped from 378.6KJ/mol for the raw amorphous ribbon to 305.1KJ/mol for the sample after ion-bombardment, ion-bombardment has no obvious effect on the apparent activation energy of the second crystallization process. Ion-bombardment
EP
has an important effect on the crystallization mechanism of the first crystallization of amorphous alloys. Ion-bombardment will lead to the structure relaxation and induce
AC C
crystallization of amorphous alloys, which then has an important effect on the nucleation and growth mechanism of the initial stage of the first crystallization process.
Keywords:
amorphous
alloy,
non-isothermal
crystallization
kinetics,
bombardment, crystallization mechanism
---------------------------------------------*Corresponding author: Kun Peng, Tel.:+86-731-88822663, E-mail address: [email protected] 1
ion
ACCEPTED MANUSCRIPT 1.Introduction Finemet (Fe73.5Si13.5B9Nb3Cu1) amorphous/nanocrystalline alloys have drawn wide attention of the science community and industrial community for their excellent soft magnetic properties since its discovery in 1988 [1], and its magnetic properties
RI PT
are closely related to the microstructure [2-4], which are dependent on the control of crystallization process, therefore, the transformation of crystallization process is the fundament for regulation of performance. A great deal of effort has been devoted to
SC
the control of crystallization process of metallic glasses because the properties strongly depend on the finally microstructure [5-9]. Thermal annealing is the most
M AN U
used way for crystallization, in which the nanocrystalline structure can be obtained by a proper annealing treatment of amorphous alloys above the crystallization temperature. In order to improve the properties of nanocrystalline alloys, some other methods such as high external (electric, pressure) fields[10,11], mechanical
TE D
deformation[12], high current density electropulsing[13] were applied to induce the crystallization of amorphous alloys. Recently, Ion/electron irradiation has been reported for the crystallization of amorphous [5,9,14,15]. This method makes it
EP
possible that the crystallization occurs with a well controlled morphology and grain
AC C
dimension. Therefore, it is of great interest both for the fundamental research and potential technological applications. When the ion bombarding a target, their loss of kinetic energy can be partly
convert into heat energy result in the increase of temperature of the target, and momentum convert into force which will act on the target, therefore, the target will be acted by the combination of force and heat, which will induce the atomic diffusion and crystallization. This crystallization mechanism must be different from that of the thermal induced crystallization process, so far, the mechanism for such crystallization 2
ACCEPTED MANUSCRIPT still remains controversial. In this work, the influence of ion-bombardment on the structure of amorphous alloy was studied, and the crystallization thermodynamics and kinetics parameters of amorphous alloys after bombarded by Ar ion with different time were investigated. According the results, the influence of ion-bombardment on
RI PT
the crystallization mechanism of the first crystallization process was discussed.
2.Experimental
SC
Amorphous alloy ribbons with nominal composition of Fe73.5Si13.5B9Nb3Cu1 were prepared by the melt spinning technique. The thickness of the ribbon was
M AN U
approximately 25µm. The amorphous ribbons were bombarded by Ar ion beam for 0 min, 15 min and 20 min in the MIS800 multifunctional ion beam magnetron sputtering instrument (manufactured by Shenyang keyou Vacuum Technology Co., Ltd), respectively. The Ar ion energy and dose are 30 Kev and 4×1014 ion/cm2, these
TE D
samples after ion bombardment were used to investigate the structural transformation and crystallization process.
The structural transformations of the specimens were investigated by using X-ray
EP
diffraction (XRD, SIEMENS D5000) with Cu Kα radiation. The thermal behavior and
AC C
non-isothermal crystallization kinetic was evaluated with differential scanning calorimeter (DSC, NETZSCH STA449C) using varied heating rate of 5 K/min, 10 K/min, 15 K/min, 20 K/min under a flow of high purified argon.
3. Result and discussion 3.1 Structural transformation The XRD patterns of the Fe73.5Si13.5B9Nb3Cu1 amorphous ribbons bombarded by Ar ion with different time (0, 15 and 20 min) were presented in fig.1. It shows a broad 3
ACCEPTED MANUSCRIPT halo appears at about 2θ =45° and no other diffraction peaks of crystalline phases were detected for the raw amorphous ribbons and the sample be bombarded by Ar ion with 15 minutes. Therefore, the raw Fe73.5Si13.5B9Nb3Cu1 amorphous ribbons possess a typical characteristic of amorphous structure. The sample after 15 minutes ion
RI PT
bombardment also kept in amorphous state, but the symmetry of amorphous diffraction peak improved after ion-bombardment. There are many defects in the raw amorphous ribbons and these defects can be reduced through structural relaxation
SC
within amorphous phase caused by the ion bombardment, which will result in the improvement of symmetry of amorphous diffraction peak. When the bombardment
M AN U
time up to 20 minutes, three weak diffraction peaks corresponding to α-Fe(Si) phase can be found, which indicate that ion bombardment has induced the crystallization of the amorphous alloys, and the broad diffraction peaks of the α-Fe(Si) phase shows that the formed grains was in nanometer size. Ion bombardment will induce the
TE D
structural relaxation through the atom diffusion, and the diffusion distance increased with the increase of bombardment time, which will result in the crystallization.
EP
3.2 Crystallization kinetics
Amorphous alloys were bombarded by Ar ion with 0, 15 and 20 minutes, then
AC C
their non-isothermal DSC curves were measured at heating rates of 5, 10, 15, and 20 K/min, the results are shown in fig.2(a), (b) and (c) respectively. The curves involve two exothermal peaks, the first peak corresponds to crystallization of α-Fe(Si) nano-crystalline and the second peak is the crystallization of iron-boron [16]. The crystallization temperature Tp1 and Tp2 are corresponding to the first crystallization peak temperature and the second crystallization peak temperature, respectively, all these characteristic temperature values are listed in table.1. These DSC traces manifested that all the characteristic temperatures (Tp1, Tp2) shift to higher 4
ACCEPTED MANUSCRIPT temperature side as the heating rate increases from 5 to 20 K/min, which indicating that the crystallization behaviors of amorphous alloys bombarded by Ar ion with different time have an obvious thermodynamic effect. It also can be seen from table.1, the first crystallization peak at the same heating rate shifts toward lower temperature
RI PT
side with the increase of ion-bombardment time. According Reisho Onodera’s research [10], the shift toward the lower temperature side indicating an acceleration of the crystallization, by contrast, the shift to higher temperature demonstrate a
SC
suppression of crystallization. The results suggested that ion-bombardment will induce and accelerate the formation α-Fe(Si) phase in finemet amorphous alloys.
M AN U
The activation energy is an essential parameter for transformation of amorphous structure to crystalline, the value of activation energy represents the difficulty of crystallization. According the value of characteristic temperature, the apparent activation energy E can be calculated. Based on the DSC data, Kissinger method is
TE D
used to determine the activation energy parameters corresponding to the characteristic temperature at a certain heating rate in non-isothermal conditions. The Kissinger
EP
equation can be expressed as follows [17]: ln(
β
T
2
)=−
E +C RT
AC C
Where β is the heating rate, T is the characteristic temperature and E is the corresponding activation energy, R is the universal gas constant, C is a constant. Therefore, the activation energy E could be calculated by -E/R which is the slope of the straight line obtained by plotting ln(β/T2) versus 1/T and ln(β) versus 1.052/T in Kissinger and Ozawa method, respectively. The calculated results are shown in fig.3 and table 2. For the first crystallization process, the activation energy decreased obviously with the increase of bombardment time. The activation energy for the sample 5
ACCEPTED MANUSCRIPT bombarded by Ar ion for 15 minutes is lower than that of the raw amorphous sample, this reduce maybe caused by the structural relaxation within amorphous phase. Ion-bombardment induced structure relaxation by atom diffusion in amorphous phase, which then influence significantly the subsequent crystallization process. Structure
RI PT
relaxation would not change the essential characters of amorphous alloy, but has an important role on the short range structure, such as the reduction of micro cavities, the redistribution of free volume, which are beneficial to subsequent crystallization
SC
process. The further decrease of activation energy for the sample bombarded for 20minuets is caused by the existence of nanocrystalline nucleus. The activation
M AN U
energy includes the energy used for the nucleation and grain growth. The sample after ion bombardment for 20 minutes has formed nanocrystalline in the amorphous phase, these nanograins will act as the nucleus for the subsequently crystallization of the residual amorphous phase, therefore, it has a lower activation energy for the formation
TE D
of α-Fe(Si) phase.
The activation energy of the second crystallization reaction has no obvious changes after ion bombardment. Ion bombardment will results in the structural
EP
relaxation or crystallization by atom diffusion, which then affect the first
AC C
crystallization process. Crystallization of amorphous alloy is achieved by atomic migration and diffusion, the motion of the atom in amorphous phase will be affected by the microstructure or the local environment around the atom. The difference of microstructure will lead to the difference in activation energy. Ion-bombardment cause the changes of amorphous microstructure then affect the activation energy, therefore, the activation energy for the first crystallization will be affected by the ion-bombardment. However, during the first crystallization process, Fe(Si) phase will Precipitate from the amorphous by atom migration which result in the rearrange of 6
ACCEPTED MANUSCRIPT atoms, and then obtain a similar microstructure composed of Fe(Si) nanocrystallites and residual amorphous phase. Therefore, the effect of ion-bombardment on the microstructure will be eliminated after the first crystallization. The second crystallization is corresponding to the formation of iron-boron compound from the
RI PT
residual amorphous phase, and it will not be affected obviously by the ion-bombardment on the raw amorphous phase.
SC
3.3 Crystallization mechanism
The volume fraction (α) of the crystalline phase during the non-isothermal
equation [18,19]:
=
M AN U
crystallization process can be calculated from the DSC curves by using the following
⁄
⁄
=
TE D
Where Tx and T∞ are the initial and final crystallization temperatures of amorphous ribbon alloys, respectively. dHc/dT is the heat capacity at constant pressure. A is the area between initial temperatures (Tx) and a given temperature (T), and A∞ is the area
EP
between initial temperatures (Tx) and final temperature (T∞) under the DSC curve. The
AC C
crystallized volume fraction α of the first exothermic event as a function of the temperature T at various heating rates is presented in Fig.4, fig.4 (a), (b) and (c) are the results of the sample bombarded by ion bombardment for 0 min, 15 min and 20 min. The variation trend of all these curves exhibits a typical sigmoid shape with temperature. The crystallized volume fraction slightly increased at the beginning and the end of the non-isothermal crystallization process (0.1<α<0.9), which suggest that the crystallization reaction proceeds slowly at these stages. Then at the stage of 0.1<α<0.9, α increases sharply, indicating that the crystallized reaction occurs quickly. 7
ACCEPTED MANUSCRIPT As these sigmoid curves shown, the crystallization reaction for the first exothermic event can be divided into three stages: at the first stage, nucleation precipitates from the amorphous matrix slowly and the bulk crystallization plays a dominant role; in the second stage, the increasing of the surface between nucleation and amorphous matrix
RI PT
results in the crystallized volume fraction increase sharply, the slope of the curves keep almost a constant, which means the crystallization reaction proceeds stably at this stage; at the third stage, the surface between crystallized phase and amorphous
SC
phase decrease as the result of grain coalesce [20].
The above calculation of activation energy usually shows the average value of
M AN U
crystallization process, but according the S-type curves in Fig.4, it is obvious that one crystallization proceeding is consist of different crystallization stages, thus, it is considerably to estimate the local activation energy at different transaction stage. In Kissinger function, the conversion rate at Tx is regarded as invariable, therefore, the
TE D
Ozawa-Flynn-Wall formula was applied to evaluating the local activation energy [21]: ln β = −1.052
E(α ) RT(α )
+C
EP
Where T(α) is a temperature corresponding to the certain crystallized volume fraction α at different heating rate, C is a constant, E(α) could be calculated by the slope of the
AC C
straight line obtained by plotting ln(β) versus 1.052/T in a certain crystallization fraction α.
For the first crystallization process, fig.5 illustrates the relationship between the
local activation energy E(α) and the crystallized volume fraction (α). For the sample without ion bombardment, the local activation energy has a maximum value and it decreases with the increase of the crystallized volume fraction, the energy used for nucleation plays a major role during the crystallization process. However, for the
8
ACCEPTED MANUSCRIPT sample after ion bombardment, the local activation energy at the first stage is much lower than that of the raw amorphous alloys. These results suggest that ion bombardment will lead to the structural changes in amorphous phase and then promote the crystallization of the amorphous alloys. The local activation energy at the
RI PT
same crystallized fraction has obvious difference for the same with different bombardment. It means that the crystallization need much lower activation energy during the ion-bombardment process.
SC
The local Avrami exponent is usually used to define the mechanism of nucleation and growth behavior during crystallization process. In order to analysis the
M AN U
mechanism of the crystallization process, the local Avrami exponent, n(α), was applied. For non-isothermal progress, the Avrami exponent n can be calculated by plotting ln(-ln(1-α)) versus ln(1/T) [22];
R∂ ln(− ln(1 − α)) Eα ∂ (1 / T )
TE D
n(α ) = −
The local Avrami exponent n(α) can be applied to characterize the nucleation and growth behavior with the increasing crystallized volume fraction α, by the following
EP
equation [23,24]:
n = a + bp
AC C
Where α is the nucleation index (a=0 for zero nucleation rate, 01 for increasing nucleation rate), b is the dimensionality of the growth (b=1, 2, 3 for one-dimensionality, twodimensionality, three-dimensionality growth respectively). And p is the growth index (p=0.5 for diffusion-controlled growth and p=1 for interface-controlled growth). It was reported that the crystallization of Fe-based amorphous alloys was controlled by diffusion, it means p=0.5. For diffused-controlled crystallization, n>2.5 indicates that the crystallization process is the different kinds of growth of small particles with an 9
ACCEPTED MANUSCRIPT increasing nucleation rate. 1.5
RI PT
different ion-bombardment time, the variation of the local Avrami exponent n(α) as a function of crystallized fraction α at a heating rate of 15K/min is shown in Fig.6. The local Avrami exponent at the first crystallization process of the sample after ion
SC
bombardment was higher than that of the raw amorphous alloys.
For the amorphous ribbons bombarded in 15min and the original ribbon, the
M AN U
main distinction of n(α) is in the stage of 0<α<0.3. In the stage of 0<α<0.3, the n(α) of original Finemet ribbon is range from 2.5 to 1.5, which indicates that the crystallization is dominated by one or two dimensional diffusion controlled grain growth with decreasing nucleation rate. When the ribbons bombarding in 15min,
TE D
n(α)>2.5 in the stage of α<0.1, indicating that the crystallization process is the different kinds of growth of small particles with an increasing nucleation rate. With the increase of crystallized volume fraction, n(α) is gradually consistent with the
EP
result of the raw amorphous sample. For the sample after 20 minutes bombarding,
AC C
When the 0<α<0.3, the value of n(α) is larger than 2.5, which means that the crystallization is dominated by the three dimensional growth of small particles with an increasing nucleation rate; when the 0.3<α<0.7, the value of n(α) is range from 1.5 to 2.5, indicate that the crystallization transformed into growth of precipitates with a decreasing nucleation rate; and in the stage of 0.7<α<0.9, the n(α) drops to less than 1.5, implying that the crystals grow upon without any nucleation; however, in the final stage of α>0.9, n(α) rise sharply, the anomalous n(α) mainly caused by the inhomogeneous nucleation on the pre-existing α-Fe(Si) grains and result in the 10
ACCEPTED MANUSCRIPT α-Fe(Si) grains growing up quickly. Ion bombardment mainly affect on the nucleation and growth mechanism of the initial stage of the crystallization process, which is caused by the structural relaxation and the formation of nano-grains in the amorphous.
RI PT
4. Conclusion The phase structure and non-isothermal crystallization kinetics of the Finemet amorphous alloys after Ar ion bombardment with different time were investigated by
SC
XRD and DSC. Ion-bombardment will cause the structure relaxation and induce the crystallization of amorphous alloys. Ion-bombardment will lead to an obvious
M AN U
decrease of apparent activation energy of the first crystallization process, but it has no obvious effect on the apparent activation energy of the second crystallization process. The local Avrami exponents at various heating rates indicated that the crystallization mechanism of α-Fe(Si) dominated by one or two dimensional growth with decreasing
TE D
nucleation rate transform to three dimensional growth in the stage of 0<α<0.3. Ion bombardment mainly affect on the nucleation and growth mechanism of the initial stage of the crystallization process, which is caused by the structural relaxation and
EP
the formation of nano-grains in the amorphous.
AC C
Acknowledgements
This research is supported by the National Natural Science Foundation of China
(Grant nos. 51571087).
References
[1] Y.Yoshizawa, S. Oguma, K.Yamauchi, J. Appl. Phys., 64(1988) 6044-6046. [2] A. Makino, H. Men, T. Kubota, et al. Mater. Trans., A50(2009) 204-209. [3] G. Herzer, Scripta Metallurgica & Materialia, 33(1995) 1741-1756. [4] T. Ohkubo, H. Kai, D.H. Ping, et al. Scripta Materialia, 44(2001) 971-976. 11
ACCEPTED MANUSCRIPT [5] W. Qin, T. Nagase, Y. Umakoshi, Acta Materialia, 57(2009) 1300-1307 [6] J.R. Sun, Z.G. Wang, Y.Y. Wang, etal., Nucl. Instr. Meth. Phys. Res., B307(2013) 486-490 [7] Z.J. Yan, Y. Hu, K.K. Song, et al. Appl.Phys.Lett., 106(2015) 101909 [8] S.R. Cheng, C.J. Wang, M.Z. Ma, et al. Thermochimica Acta, 587(2014) 11-17
RI PT
[9] T. Nagase, T. Hosokawa, Y. Umakoshi, Metall. Mater. Trans., 38A(2007) 223-225 [10] R. Onodera, S. Kimura, K. Watanabe, et al. J. Alloy. Compd., 604(2014) 8-11.
[11] R. Onodera, S. Kimura, K. Watanabe, et al. J. Alloy. Compd., 637(2015) 213-218. [12] G.J. Fan, M.X. Quan, Z.Q. Hu, et al. J. Mater. Res., 14(1999) 3765-3774.
SC
[13] K. Georgarakis, D. V.Dudina, V.I. Mali, et al. Appl. Phys. A, 120(2015) 1565-1572. [14] N. Mehta, K. Singh, N. S. Saxena, J.Phys.Chem.Solid., 70(2009) 811-815.
M AN U
[15] G. Rizza, A. Dunlop, G. Jaskierowicz, et al. J. Phys. Cond. Matter., 16(2004) 1547-1562. [16] V.A. Blagojevc, M. Vasic, B. David, et al. Thermochimica Acta, 95(2014) 11891-6. [17] H.E. Kissinger. J. Res. Nation. Bur. Stand., 57(1956) 217-221.
[18] K. Nakamura, T.Watanabe, K.Katayama, et al. J. Appl. Poly. Sci., 16(1972) 1077-1091. [19] K. Nakamura, K. Katayama, T. Amano, J. Appl. Poly. Sci., 17(1973) 1031-1041.
TE D
[20] Y.X. Zhang, T.F. Duan, H.Y. Shi, J. Alloys. Compd., 509(2011) 9019-9025 [21] J.H. Flynn, J. Therm. Analy., 27(1983) 95-102. [22] K. Majhi. K.B.R. Varma, J.Mater. Sci., 44(2009) 385-391
EP
[23] S. Ranganathan, M.V. Heimendahl, J. Mater. Sci., 16(1981) 2401-2404. [24] V. R.V. Ramanan, G.E. Fish, J. Appl. Phys., 1982, 53(3) 2273-2275.
AC C
[25] K.Matusita, T. Komatsu, R.Yokota, J.Mater.Sci., 19(1984),291-296
12
ACCEPTED MANUSCRIPT
Tables
Table 1 Temperature values of crystallization peaks obtained from DSC curves.
15K/min
Tp1( )
541.2
538.2
537.0
Tp2( )
671.4
671.7
Tp1( )
549.7
549.5
Tp2( )
683.5
684.8
Tp1( )
557.2
556.0
Tp2( )
691.4
Tp1( )
560.6
Tp2( )
694.2
670.7 547.2 680.5 554.2
691.5
687.5
560.0
562.5
695.8
693.2
TE D
20K/min
20
RI PT
10K/min
15
SC
5K/min
0
M AN U
Bombarding Time(min)
Table 2 The values of apparent activation energy calculated by Kissinger method
0 15
AC C
20
EP
Bombarding Time (min)
Activation energy E（KJ/mol） Ep1 Ep2 378.6 424.5 341.2
416.5
305.1
438.6
ACCEPTED MANUSCRIPT
Figure caption
Fig.1. XRD pattern of Finemet amorphous ribbons bombarded with different time
RI PT
Fig.2. DSC curves of the Finemet alloys at different heating rates for bombarding (a) 0 min, (b) 15 min, (c) 20 min
SC
Fig.3.Kissinger plot for calculation of activation energies in amorphous bombarded with different
M AN U
time, (a) the first crystallization peak, (b) the second crystallization peak.
Fig.4 Crystallized volume fraction (α) of Finemet amorphous samples bombarded with: (a) 0 min, (b)15 min and (c)20 min as a function of temperature at different heating rate
Fig.5 Dependence of local activation energy E(α) on the crystalline fraction α for the first
TE D
exothermic event of amorphous alloy after ion-bombardment for 0, 15 and 20 min
Fig.6 Local Avrami exponent n(x) versus crystallized volume fraction for the first crystallization
AC C
EP
process of the sample bombarded with different time
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Fig.1. XRD pattern of Finemet amorphous ribbons bombarded with different time
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
Fig.2. DSC curves of the Finemet alloys at different heating rates for bombarding (a) 0 min, (b) 15 min, (c) 20 min
AC C
EP
TE D
M AN U
(a)
SC
RI PT
ACCEPTED MANUSCRIPT
(b)
Fig.3.Kissinger plot for calculation of activation energies in amorphous bombarded with different time, (a) the first crystallization peak, (b) the second crystallization peak.
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.4 Crystallized volume fraction (α) of Finemet amorphous samples bombarded with: (a) 0 min, (b)15 min and (c)20 min as a function of temperature at different heating rate
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
EP
Fig.5 Dependence of local activation energy E(α) on the crystalline fraction α for the first
AC C
exothermic event of amorphous alloy after ion-bombardment for 0, 15 and 20 min
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.6 Local Avrami exponent n(x) versus crystallized volume fraction for the first crystallization
AC C
EP
process of the sample bombarded with different time
ACCEPTED MANUSCRIPT
Highlight Ion-bombardment induces structure relaxation and crystallization of amorphous alloys.
RI PT
Ion-bombardment will decrease activation energy of the first crystallization process.
AC C
EP
TE D
M AN U
SC
Ion-bombardment mainly affect on the crystallization mechanism of initial stage.
S0925-8388(16)33524-1
DOI:
10.1016/j.jallcom.2016.11.057
Reference:
JALCOM 39552
To appear in:
Journal of Alloys and Compounds
Received Date: 30 September 2016 Revised Date:
1 November 2016
Accepted Date: 4 November 2016
Please cite this article as: L. Tang, K. Peng, Y. Wu, W. Zhang, Effect of ion bombardment on the crystallization kinetics of FeSiNbBCu amorphous alloys, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.11.057. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Effect of ion bombardment on the crystallization kinetics of FeSiNbBCu amorphous alloys Ling Tang1,2,
Kun Peng1,2*,
Yingwei Wu1,
Wei Zhang1
RI PT
1. College of Materials Science and Engineering, Hunan University, Changsha, China, 410082 2. Hunan province key laboratory for spray deposition technology and application, Hunan
SC
University, Changsha, China, 410082
Abstract
M AN U
Amorphous FeSiNbBCu alloy ribbons were bombarded by Ar ion with different time, the phase structure and crystallization kinetics of amorphous alloys after ion bombardment were evaluated by XRD and differential scanning calorimetry (DSC), respectively. The apparent activation energy of the first crystallization process
TE D
dropped from 378.6KJ/mol for the raw amorphous ribbon to 305.1KJ/mol for the sample after ion-bombardment, ion-bombardment has no obvious effect on the apparent activation energy of the second crystallization process. Ion-bombardment
EP
has an important effect on the crystallization mechanism of the first crystallization of amorphous alloys. Ion-bombardment will lead to the structure relaxation and induce
AC C
crystallization of amorphous alloys, which then has an important effect on the nucleation and growth mechanism of the initial stage of the first crystallization process.
Keywords:
amorphous
alloy,
non-isothermal
crystallization
kinetics,
bombardment, crystallization mechanism
---------------------------------------------*Corresponding author: Kun Peng, Tel.:+86-731-88822663, E-mail address: [email protected] 1
ion
ACCEPTED MANUSCRIPT 1.Introduction Finemet (Fe73.5Si13.5B9Nb3Cu1) amorphous/nanocrystalline alloys have drawn wide attention of the science community and industrial community for their excellent soft magnetic properties since its discovery in 1988 [1], and its magnetic properties
RI PT
are closely related to the microstructure [2-4], which are dependent on the control of crystallization process, therefore, the transformation of crystallization process is the fundament for regulation of performance. A great deal of effort has been devoted to
SC
the control of crystallization process of metallic glasses because the properties strongly depend on the finally microstructure [5-9]. Thermal annealing is the most
M AN U
used way for crystallization, in which the nanocrystalline structure can be obtained by a proper annealing treatment of amorphous alloys above the crystallization temperature. In order to improve the properties of nanocrystalline alloys, some other methods such as high external (electric, pressure) fields[10,11], mechanical
TE D
deformation[12], high current density electropulsing[13] were applied to induce the crystallization of amorphous alloys. Recently, Ion/electron irradiation has been reported for the crystallization of amorphous [5,9,14,15]. This method makes it
EP
possible that the crystallization occurs with a well controlled morphology and grain
AC C
dimension. Therefore, it is of great interest both for the fundamental research and potential technological applications. When the ion bombarding a target, their loss of kinetic energy can be partly
convert into heat energy result in the increase of temperature of the target, and momentum convert into force which will act on the target, therefore, the target will be acted by the combination of force and heat, which will induce the atomic diffusion and crystallization. This crystallization mechanism must be different from that of the thermal induced crystallization process, so far, the mechanism for such crystallization 2
ACCEPTED MANUSCRIPT still remains controversial. In this work, the influence of ion-bombardment on the structure of amorphous alloy was studied, and the crystallization thermodynamics and kinetics parameters of amorphous alloys after bombarded by Ar ion with different time were investigated. According the results, the influence of ion-bombardment on
RI PT
the crystallization mechanism of the first crystallization process was discussed.
2.Experimental
SC
Amorphous alloy ribbons with nominal composition of Fe73.5Si13.5B9Nb3Cu1 were prepared by the melt spinning technique. The thickness of the ribbon was
M AN U
approximately 25µm. The amorphous ribbons were bombarded by Ar ion beam for 0 min, 15 min and 20 min in the MIS800 multifunctional ion beam magnetron sputtering instrument (manufactured by Shenyang keyou Vacuum Technology Co., Ltd), respectively. The Ar ion energy and dose are 30 Kev and 4×1014 ion/cm2, these
TE D
samples after ion bombardment were used to investigate the structural transformation and crystallization process.
The structural transformations of the specimens were investigated by using X-ray
EP
diffraction (XRD, SIEMENS D5000) with Cu Kα radiation. The thermal behavior and
AC C
non-isothermal crystallization kinetic was evaluated with differential scanning calorimeter (DSC, NETZSCH STA449C) using varied heating rate of 5 K/min, 10 K/min, 15 K/min, 20 K/min under a flow of high purified argon.
3. Result and discussion 3.1 Structural transformation The XRD patterns of the Fe73.5Si13.5B9Nb3Cu1 amorphous ribbons bombarded by Ar ion with different time (0, 15 and 20 min) were presented in fig.1. It shows a broad 3
ACCEPTED MANUSCRIPT halo appears at about 2θ =45° and no other diffraction peaks of crystalline phases were detected for the raw amorphous ribbons and the sample be bombarded by Ar ion with 15 minutes. Therefore, the raw Fe73.5Si13.5B9Nb3Cu1 amorphous ribbons possess a typical characteristic of amorphous structure. The sample after 15 minutes ion
RI PT
bombardment also kept in amorphous state, but the symmetry of amorphous diffraction peak improved after ion-bombardment. There are many defects in the raw amorphous ribbons and these defects can be reduced through structural relaxation
SC
within amorphous phase caused by the ion bombardment, which will result in the improvement of symmetry of amorphous diffraction peak. When the bombardment
M AN U
time up to 20 minutes, three weak diffraction peaks corresponding to α-Fe(Si) phase can be found, which indicate that ion bombardment has induced the crystallization of the amorphous alloys, and the broad diffraction peaks of the α-Fe(Si) phase shows that the formed grains was in nanometer size. Ion bombardment will induce the
TE D
structural relaxation through the atom diffusion, and the diffusion distance increased with the increase of bombardment time, which will result in the crystallization.
EP
3.2 Crystallization kinetics
Amorphous alloys were bombarded by Ar ion with 0, 15 and 20 minutes, then
AC C
their non-isothermal DSC curves were measured at heating rates of 5, 10, 15, and 20 K/min, the results are shown in fig.2(a), (b) and (c) respectively. The curves involve two exothermal peaks, the first peak corresponds to crystallization of α-Fe(Si) nano-crystalline and the second peak is the crystallization of iron-boron [16]. The crystallization temperature Tp1 and Tp2 are corresponding to the first crystallization peak temperature and the second crystallization peak temperature, respectively, all these characteristic temperature values are listed in table.1. These DSC traces manifested that all the characteristic temperatures (Tp1, Tp2) shift to higher 4
ACCEPTED MANUSCRIPT temperature side as the heating rate increases from 5 to 20 K/min, which indicating that the crystallization behaviors of amorphous alloys bombarded by Ar ion with different time have an obvious thermodynamic effect. It also can be seen from table.1, the first crystallization peak at the same heating rate shifts toward lower temperature
RI PT
side with the increase of ion-bombardment time. According Reisho Onodera’s research [10], the shift toward the lower temperature side indicating an acceleration of the crystallization, by contrast, the shift to higher temperature demonstrate a
SC
suppression of crystallization. The results suggested that ion-bombardment will induce and accelerate the formation α-Fe(Si) phase in finemet amorphous alloys.
M AN U
The activation energy is an essential parameter for transformation of amorphous structure to crystalline, the value of activation energy represents the difficulty of crystallization. According the value of characteristic temperature, the apparent activation energy E can be calculated. Based on the DSC data, Kissinger method is
TE D
used to determine the activation energy parameters corresponding to the characteristic temperature at a certain heating rate in non-isothermal conditions. The Kissinger
EP
equation can be expressed as follows [17]: ln(
β
T
2
)=−
E +C RT
AC C
Where β is the heating rate, T is the characteristic temperature and E is the corresponding activation energy, R is the universal gas constant, C is a constant. Therefore, the activation energy E could be calculated by -E/R which is the slope of the straight line obtained by plotting ln(β/T2) versus 1/T and ln(β) versus 1.052/T in Kissinger and Ozawa method, respectively. The calculated results are shown in fig.3 and table 2. For the first crystallization process, the activation energy decreased obviously with the increase of bombardment time. The activation energy for the sample 5
ACCEPTED MANUSCRIPT bombarded by Ar ion for 15 minutes is lower than that of the raw amorphous sample, this reduce maybe caused by the structural relaxation within amorphous phase. Ion-bombardment induced structure relaxation by atom diffusion in amorphous phase, which then influence significantly the subsequent crystallization process. Structure
RI PT
relaxation would not change the essential characters of amorphous alloy, but has an important role on the short range structure, such as the reduction of micro cavities, the redistribution of free volume, which are beneficial to subsequent crystallization
SC
process. The further decrease of activation energy for the sample bombarded for 20minuets is caused by the existence of nanocrystalline nucleus. The activation
M AN U
energy includes the energy used for the nucleation and grain growth. The sample after ion bombardment for 20 minutes has formed nanocrystalline in the amorphous phase, these nanograins will act as the nucleus for the subsequently crystallization of the residual amorphous phase, therefore, it has a lower activation energy for the formation
TE D
of α-Fe(Si) phase.
The activation energy of the second crystallization reaction has no obvious changes after ion bombardment. Ion bombardment will results in the structural
EP
relaxation or crystallization by atom diffusion, which then affect the first
AC C
crystallization process. Crystallization of amorphous alloy is achieved by atomic migration and diffusion, the motion of the atom in amorphous phase will be affected by the microstructure or the local environment around the atom. The difference of microstructure will lead to the difference in activation energy. Ion-bombardment cause the changes of amorphous microstructure then affect the activation energy, therefore, the activation energy for the first crystallization will be affected by the ion-bombardment. However, during the first crystallization process, Fe(Si) phase will Precipitate from the amorphous by atom migration which result in the rearrange of 6
ACCEPTED MANUSCRIPT atoms, and then obtain a similar microstructure composed of Fe(Si) nanocrystallites and residual amorphous phase. Therefore, the effect of ion-bombardment on the microstructure will be eliminated after the first crystallization. The second crystallization is corresponding to the formation of iron-boron compound from the
RI PT
residual amorphous phase, and it will not be affected obviously by the ion-bombardment on the raw amorphous phase.
SC
3.3 Crystallization mechanism
The volume fraction (α) of the crystalline phase during the non-isothermal
equation [18,19]:
=
M AN U
crystallization process can be calculated from the DSC curves by using the following
⁄
⁄
=
TE D
Where Tx and T∞ are the initial and final crystallization temperatures of amorphous ribbon alloys, respectively. dHc/dT is the heat capacity at constant pressure. A is the area between initial temperatures (Tx) and a given temperature (T), and A∞ is the area
EP
between initial temperatures (Tx) and final temperature (T∞) under the DSC curve. The
AC C
crystallized volume fraction α of the first exothermic event as a function of the temperature T at various heating rates is presented in Fig.4, fig.4 (a), (b) and (c) are the results of the sample bombarded by ion bombardment for 0 min, 15 min and 20 min. The variation trend of all these curves exhibits a typical sigmoid shape with temperature. The crystallized volume fraction slightly increased at the beginning and the end of the non-isothermal crystallization process (0.1<α<0.9), which suggest that the crystallization reaction proceeds slowly at these stages. Then at the stage of 0.1<α<0.9, α increases sharply, indicating that the crystallized reaction occurs quickly. 7
ACCEPTED MANUSCRIPT As these sigmoid curves shown, the crystallization reaction for the first exothermic event can be divided into three stages: at the first stage, nucleation precipitates from the amorphous matrix slowly and the bulk crystallization plays a dominant role; in the second stage, the increasing of the surface between nucleation and amorphous matrix
RI PT
results in the crystallized volume fraction increase sharply, the slope of the curves keep almost a constant, which means the crystallization reaction proceeds stably at this stage; at the third stage, the surface between crystallized phase and amorphous
SC
phase decrease as the result of grain coalesce [20].
The above calculation of activation energy usually shows the average value of
M AN U
crystallization process, but according the S-type curves in Fig.4, it is obvious that one crystallization proceeding is consist of different crystallization stages, thus, it is considerably to estimate the local activation energy at different transaction stage. In Kissinger function, the conversion rate at Tx is regarded as invariable, therefore, the
TE D
Ozawa-Flynn-Wall formula was applied to evaluating the local activation energy [21]: ln β = −1.052
E(α ) RT(α )
+C
EP
Where T(α) is a temperature corresponding to the certain crystallized volume fraction α at different heating rate, C is a constant, E(α) could be calculated by the slope of the
AC C
straight line obtained by plotting ln(β) versus 1.052/T in a certain crystallization fraction α.
For the first crystallization process, fig.5 illustrates the relationship between the
local activation energy E(α) and the crystallized volume fraction (α). For the sample without ion bombardment, the local activation energy has a maximum value and it decreases with the increase of the crystallized volume fraction, the energy used for nucleation plays a major role during the crystallization process. However, for the
8
ACCEPTED MANUSCRIPT sample after ion bombardment, the local activation energy at the first stage is much lower than that of the raw amorphous alloys. These results suggest that ion bombardment will lead to the structural changes in amorphous phase and then promote the crystallization of the amorphous alloys. The local activation energy at the
RI PT
same crystallized fraction has obvious difference for the same with different bombardment. It means that the crystallization need much lower activation energy during the ion-bombardment process.
SC
The local Avrami exponent is usually used to define the mechanism of nucleation and growth behavior during crystallization process. In order to analysis the
M AN U
mechanism of the crystallization process, the local Avrami exponent, n(α), was applied. For non-isothermal progress, the Avrami exponent n can be calculated by plotting ln(-ln(1-α)) versus ln(1/T) [22];
R∂ ln(− ln(1 − α)) Eα ∂ (1 / T )
TE D
n(α ) = −
The local Avrami exponent n(α) can be applied to characterize the nucleation and growth behavior with the increasing crystallized volume fraction α, by the following
EP
equation [23,24]:
n = a + bp
AC C
Where α is the nucleation index (a=0 for zero nucleation rate, 0
ACCEPTED MANUSCRIPT increasing nucleation rate. 1.5
RI PT
different ion-bombardment time, the variation of the local Avrami exponent n(α) as a function of crystallized fraction α at a heating rate of 15K/min is shown in Fig.6. The local Avrami exponent at the first crystallization process of the sample after ion
SC
bombardment was higher than that of the raw amorphous alloys.
For the amorphous ribbons bombarded in 15min and the original ribbon, the
M AN U
main distinction of n(α) is in the stage of 0<α<0.3. In the stage of 0<α<0.3, the n(α) of original Finemet ribbon is range from 2.5 to 1.5, which indicates that the crystallization is dominated by one or two dimensional diffusion controlled grain growth with decreasing nucleation rate. When the ribbons bombarding in 15min,
TE D
n(α)>2.5 in the stage of α<0.1, indicating that the crystallization process is the different kinds of growth of small particles with an increasing nucleation rate. With the increase of crystallized volume fraction, n(α) is gradually consistent with the
EP
result of the raw amorphous sample. For the sample after 20 minutes bombarding,
AC C
When the 0<α<0.3, the value of n(α) is larger than 2.5, which means that the crystallization is dominated by the three dimensional growth of small particles with an increasing nucleation rate; when the 0.3<α<0.7, the value of n(α) is range from 1.5 to 2.5, indicate that the crystallization transformed into growth of precipitates with a decreasing nucleation rate; and in the stage of 0.7<α<0.9, the n(α) drops to less than 1.5, implying that the crystals grow upon without any nucleation; however, in the final stage of α>0.9, n(α) rise sharply, the anomalous n(α) mainly caused by the inhomogeneous nucleation on the pre-existing α-Fe(Si) grains and result in the 10
ACCEPTED MANUSCRIPT α-Fe(Si) grains growing up quickly. Ion bombardment mainly affect on the nucleation and growth mechanism of the initial stage of the crystallization process, which is caused by the structural relaxation and the formation of nano-grains in the amorphous.
RI PT
4. Conclusion The phase structure and non-isothermal crystallization kinetics of the Finemet amorphous alloys after Ar ion bombardment with different time were investigated by
SC
XRD and DSC. Ion-bombardment will cause the structure relaxation and induce the crystallization of amorphous alloys. Ion-bombardment will lead to an obvious
M AN U
decrease of apparent activation energy of the first crystallization process, but it has no obvious effect on the apparent activation energy of the second crystallization process. The local Avrami exponents at various heating rates indicated that the crystallization mechanism of α-Fe(Si) dominated by one or two dimensional growth with decreasing
TE D
nucleation rate transform to three dimensional growth in the stage of 0<α<0.3. Ion bombardment mainly affect on the nucleation and growth mechanism of the initial stage of the crystallization process, which is caused by the structural relaxation and
EP
the formation of nano-grains in the amorphous.
AC C
Acknowledgements
This research is supported by the National Natural Science Foundation of China
(Grant nos. 51571087).
References
[1] Y.Yoshizawa, S. Oguma, K.Yamauchi, J. Appl. Phys., 64(1988) 6044-6046. [2] A. Makino, H. Men, T. Kubota, et al. Mater. Trans., A50(2009) 204-209. [3] G. Herzer, Scripta Metallurgica & Materialia, 33(1995) 1741-1756. [4] T. Ohkubo, H. Kai, D.H. Ping, et al. Scripta Materialia, 44(2001) 971-976. 11
ACCEPTED MANUSCRIPT [5] W. Qin, T. Nagase, Y. Umakoshi, Acta Materialia, 57(2009) 1300-1307 [6] J.R. Sun, Z.G. Wang, Y.Y. Wang, etal., Nucl. Instr. Meth. Phys. Res., B307(2013) 486-490 [7] Z.J. Yan, Y. Hu, K.K. Song, et al. Appl.Phys.Lett., 106(2015) 101909 [8] S.R. Cheng, C.J. Wang, M.Z. Ma, et al. Thermochimica Acta, 587(2014) 11-17
RI PT
[9] T. Nagase, T. Hosokawa, Y. Umakoshi, Metall. Mater. Trans., 38A(2007) 223-225 [10] R. Onodera, S. Kimura, K. Watanabe, et al. J. Alloy. Compd., 604(2014) 8-11.
[11] R. Onodera, S. Kimura, K. Watanabe, et al. J. Alloy. Compd., 637(2015) 213-218. [12] G.J. Fan, M.X. Quan, Z.Q. Hu, et al. J. Mater. Res., 14(1999) 3765-3774.
SC
[13] K. Georgarakis, D. V.Dudina, V.I. Mali, et al. Appl. Phys. A, 120(2015) 1565-1572. [14] N. Mehta, K. Singh, N. S. Saxena, J.Phys.Chem.Solid., 70(2009) 811-815.
M AN U
[15] G. Rizza, A. Dunlop, G. Jaskierowicz, et al. J. Phys. Cond. Matter., 16(2004) 1547-1562. [16] V.A. Blagojevc, M. Vasic, B. David, et al. Thermochimica Acta, 95(2014) 11891-6. [17] H.E. Kissinger. J. Res. Nation. Bur. Stand., 57(1956) 217-221.
[18] K. Nakamura, T.Watanabe, K.Katayama, et al. J. Appl. Poly. Sci., 16(1972) 1077-1091. [19] K. Nakamura, K. Katayama, T. Amano, J. Appl. Poly. Sci., 17(1973) 1031-1041.
TE D
[20] Y.X. Zhang, T.F. Duan, H.Y. Shi, J. Alloys. Compd., 509(2011) 9019-9025 [21] J.H. Flynn, J. Therm. Analy., 27(1983) 95-102. [22] K. Majhi. K.B.R. Varma, J.Mater. Sci., 44(2009) 385-391
EP
[23] S. Ranganathan, M.V. Heimendahl, J. Mater. Sci., 16(1981) 2401-2404. [24] V. R.V. Ramanan, G.E. Fish, J. Appl. Phys., 1982, 53(3) 2273-2275.
AC C
[25] K.Matusita, T. Komatsu, R.Yokota, J.Mater.Sci., 19(1984),291-296
12
ACCEPTED MANUSCRIPT
Tables
Table 1 Temperature values of crystallization peaks obtained from DSC curves.
15K/min
Tp1( )
541.2
538.2
537.0
Tp2( )
671.4
671.7
Tp1( )
549.7
549.5
Tp2( )
683.5
684.8
Tp1( )
557.2
556.0
Tp2( )
691.4
Tp1( )
560.6
Tp2( )
694.2
670.7 547.2 680.5 554.2
691.5
687.5
560.0
562.5
695.8
693.2
TE D
20K/min
20
RI PT
10K/min
15
SC
5K/min
0
M AN U
Bombarding Time(min)
Table 2 The values of apparent activation energy calculated by Kissinger method
0 15
AC C
20
EP
Bombarding Time (min)
Activation energy E（KJ/mol） Ep1 Ep2 378.6 424.5 341.2
416.5
305.1
438.6
ACCEPTED MANUSCRIPT
Figure caption
Fig.1. XRD pattern of Finemet amorphous ribbons bombarded with different time
RI PT
Fig.2. DSC curves of the Finemet alloys at different heating rates for bombarding (a) 0 min, (b) 15 min, (c) 20 min
SC
Fig.3.Kissinger plot for calculation of activation energies in amorphous bombarded with different
M AN U
time, (a) the first crystallization peak, (b) the second crystallization peak.
Fig.4 Crystallized volume fraction (α) of Finemet amorphous samples bombarded with: (a) 0 min, (b)15 min and (c)20 min as a function of temperature at different heating rate
Fig.5 Dependence of local activation energy E(α) on the crystalline fraction α for the first
TE D
exothermic event of amorphous alloy after ion-bombardment for 0, 15 and 20 min
Fig.6 Local Avrami exponent n(x) versus crystallized volume fraction for the first crystallization
AC C
EP
process of the sample bombarded with different time
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Fig.1. XRD pattern of Finemet amorphous ribbons bombarded with different time
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
Fig.2. DSC curves of the Finemet alloys at different heating rates for bombarding (a) 0 min, (b) 15 min, (c) 20 min
AC C
EP
TE D
M AN U
(a)
SC
RI PT
ACCEPTED MANUSCRIPT
(b)
Fig.3.Kissinger plot for calculation of activation energies in amorphous bombarded with different time, (a) the first crystallization peak, (b) the second crystallization peak.
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.4 Crystallized volume fraction (α) of Finemet amorphous samples bombarded with: (a) 0 min, (b)15 min and (c)20 min as a function of temperature at different heating rate
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
EP
Fig.5 Dependence of local activation energy E(α) on the crystalline fraction α for the first
AC C
exothermic event of amorphous alloy after ion-bombardment for 0, 15 and 20 min
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.6 Local Avrami exponent n(x) versus crystallized volume fraction for the first crystallization
AC C
EP
process of the sample bombarded with different time
ACCEPTED MANUSCRIPT
Highlight Ion-bombardment induces structure relaxation and crystallization of amorphous alloys.
RI PT
Ion-bombardment will decrease activation energy of the first crystallization process.
AC C
EP
TE D
M AN U
SC
Ion-bombardment mainly affect on the crystallization mechanism of initial stage.