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2016 J Phys.: Conf Ser 755 012025
(http://iopscience.iop.org/1742-6596/755/1/012025)
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Trang 2Temperature-time induced changes in magnetic properties of multi-component Fe78Si3.6C13.4Mn0.65B4.35 alloy
S N Kanea, S S Modakb, M Shaha, M Satalkara, K Gehlota, N Ghodkec,
J P Araujod and L K Vargae
a Magnetic Materials Laboratory, School of Physics, Devi Ahilya University, Khandwa Road Campus, Indore-452001, India
b Department of Physics, Jaypee University of Engineering and Technology, Guna-473226, India
c UGC-DAE-CSR, University campus, Khandwa Road, Indore-452001, India d
IFIMUP, Departmento de Fisica, Universidade de Porto, 4169-007 Porto, Portugal e
RISSPO, Hungarian Academy of Sciences, P.O Box, 49-125 Budapest, Hungary
Corresponding author: kane_sn@yahoo.com
Abstract Influence of thermal annealing as a function of temperature and time, on magnetic
and structural properties of Fe78Si3.6C13.4Mn0.65B4.35 (Fe78Si3.6C13.4Mn0.65 = Ci) alloy has been reported Information on structure, formed nano-crystalline phases and their correlation with magnetic properties has been studied using, magnetic measurements, differential scanning calorimetery (DSC) and x-ray diffraction (XRD) Thermal annealing treatment leads to rather coarse grain microstructure (~31 nm) accompanied by surface crystallization that appears to deteriorate the magnetic properties with annealing temperature
1 Introduction
Fabrication of Fe-based bulk metallic glasses using high purity raw elements and the strict processing under high vacuum results in high production cost That eventually restricts their industrial mass
production In this respect cast iron (Ci) based multi component bulk-type Fe-based amorphous alloys
emerged as suitable cheap magnetic alloys prepared with industrially available raw materials [1, 2] These alloys exhibit large glass forming region and good soft magnetic properties Depending upon the specific application requirement these cast iron based alloys can be prepared in the shape of ribbons, cylinders with transversal dimensions up to ~ 0.5 mm [3] and, their magnetic properties should also be optimized
In the present work we report the investigation of the effect of isochronal and isothermal annealing treatment on the structural and magnetic properties of cast iron based multi component
Fe78Si3.6C13.4Mn0.65B4.35 which is also represented as Ci 95.65B4.35 alloy
2 Experimental Details
Ribbons (about 16 m thick and 3.3 mm wide) of nominal composition Fe78Si3.6C13.4Mn0.65B4.35 were prepared using planar flow casting technique In order to determine the crystallization peak temperature differential scanning calirimetery (DSC) measurements were done at heating rate of 10
Trang 3C/min Utilizing DSC results, isochronal thermal annealing was done at 350, 380, 400, 425 and 450 o
C for 60 minutes Samples were also isothermally annealed at 380 0C for 15, 30 and 45 minutes X-ray diffraction (XRD) measurements on as-cast and annealed samples were carried out using Bruker D8 Advance X-ray diffractometer with Cu-K radiation (wavelength: = 0.154 nm) XRD patterns were analyzed by fitting a crystalline and an amorphous component using pseudo-Voigt line profiles
Crystalline volume fraction (V x) was obtained by integrating the main diffraction peak The average
grain size D is obtained by Scherrer’s formula using integral width of the (110) line and the lattice parameter a is calculated using Nelson-Taylor-Sinclair correction in order to take into account the peak shift due to sample offset For the amorphous phase, the first nearest neighbour distance X m is
calculated using the expression: X m = 1.227 / 2Sin Hysteresis loops of as cast and annealed samples were measured using a loop tracer at 50Hz using maximum applied magnetic field of ± 3000 A/m
Measured hysteresis loops were used to get information on coercive field (H c) and, saturation
induction (B 3000) values
3 Results and Discussion
Figure 1 depicts the DSC curve of as cast sample measured at 10 oC/min It can be seen that the studied alloy system exhibit a two step crystallization process with onset of the first peak at 4350C The crystallization temperatures corresponding to the two peaks are 463 and 524 oC respectively XRD patterns of as cast and annealed samples at various temperatures for 60 min are presented in figure 2 Perusal of figure 2 shows that the crystallization starts after annealing at 380 oC X-ray diffraction data was analyzed using a MATLAB based program that fits the data using pseudo Voigt line profiles Table 1 represents the annealing temperature evolution of various structural parameters obtained by analyzing the XRD data Effect of isothermal annealing at 380 oC for different time period on the structural properties of the studied alloy samples is shown in table 2 Perusal of tables 1 and 2 shows
that with increasing annealing temperature, although D increases but V x does not increase much, exhibiting that increase in annealing temperature results in grain coarsening Change of annealing time
does not have appreciable effect on, D and V x Obtained a values suggest that the precipitated
crystalline phase is bcc Fe (–Fe) Within the experimental errors the first nearest-neighbour distance
in the residual amorphous matrix (0.250 nm 0.001) almost remains constant for the studied specimens, showing that the studied samples have comparable mass densities
Effect of annealing temperature and time on the magnetic response of the studied alloy composition
is represented in the figure 3 Perusal of figure 3 (left panel) indicates that the flattening of hysteresis loops occur for the annealing temperature of 400 oC and above as also observed in case of other cast iron based samples ascribable to surface crystallization [4,5]
Temperature (oC)
Exo.
Fe78Si3.6C13.4Mn0.65B4.35 sample measured at
10 oC/minute
Figure 2: XRD patterns of as cast and
annealed Fe78Si3.6C13.4Mn0.65B4.35 samples
at various temperatures for 60 minutes
As-cast
Ann 350 oC/1h Ann 380 oC/1h Ann 400 oC/1h Ann 425 oC/1h
Ann 450 oC/1h
2
Trang 4Table1: Temperature transformation of Table2: Time transformation of structural
structural parameters for samples annealed parameters for samples annealed at 380 oC for 60 minutes
In order to further optimize the magnetic properties of the studied alloy system, the annealing temperature of 380 oC was chosen, which shows partial crystallization with average grain diameter of
11 nm It is worth noting that XRD pattern of the specimen annealed at 380 oC, shows presence of small crystalline fraction ( 5 %) after annealing for 1 hour By choosing different annealing time would lead to various levels of structural relaxation and/or crystallization having different average grain diameter of the nano-grains, giving rise to the variation in magnetic properties Keeping the above mentioned reason in account, specimens were also annealed at 380 oC for different times e.g
15, 30, 45 and 60 min Time evolution of the hysteresis loops corresponding to annealing temperature
of 380 oC is presented in figure 3 (right panel)
Figure 4 represents the annealing temperature and time evolution of coercive field behaviour of the studied samples It shold be noted that insets in the figure 4 (both in left and right panel) exhibit the variation of saturation induction (B3000) values as a function of isochronal and isothermal annealing treatment respectively It can be seen in the figure 4 (left panel) that there is an initial decrement in the coercvity till annealing temperature of 350 oC, which may be due to relaxation of quenched in stresses Further coercive field values increases rather sharply with annealing temperature
Fe78Si3.6C13.4Mn0.65B4.35 alloy (left panel) Annealing time evolution of Fe78Si3.6C13.4Mn0.65B4.35 alloy samples annealed at 380 oC (right panel)
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
H (A/m)
As-q
350 oC
380 oC
400 oC
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
H (A/m)
15 min.
30 min.
45 min.
60 min.
Sample
details
<D>
(nm) ( 1 )
a
(nm) ( 0001)
V x (%) ( 1 )
380 oC 11.5 0.2849 5.5
400 oC 17.5 0.2848 10.5
425 oC 25 0.2849 19
450 oC 31.5 0.2848 30.5
Sample details
<D>
(nm) ( 1 )
a
(nm) (0.0001)
V x
(%) ( 1 )
15 min 11.0 0.2868 3.2
30 min 11.0 0.2869 3.9
45 min 11.5 0.2845 6.0
60 min 11.5 0.2849 5.5
Trang 5Figure 4: Annealing temperature evolution of coercivity and saturation induction values (inset) of
Fe78Si3.6C13.4Mn0.65B4.35 alloy (left panel) Annealing time evolution of coercivity and saturation induction (inset) of Fe78Si3.6C13.4Mn0.65B4.35 alloy samples annealed at 380 oC (right panel)
This behaviour indicates the presence of non-exchange coupled nanograins It can be seen in table 1
that grain coarsening (average grain diameter~31 nm and V x ~ 30%) is responsible for large distance between the grains and hence deteriorating the magnetic properties Coercive field values of the studied alloy system varies between 8 to 914 A/m The lowest value of coercivity (Hc ~ 8 A/m) is exhibited for the sample annealed at 3800C for 15 min It should also be noted that the saturation induction (B3000) values ranges between 1.28 to 1.54 Tesla Highest value (1.54 T) of B3000 corresponds to the annealing treatment at the temperature of 400 oC for 60 min
4 Summary
Changes in the structural and magnetic properties as a function of thermal annealing temperature and time for cast iron based multi component Fe78Si3.6C13.4Mn0.65B4.35 alloy in the form of ribbons have been studied using DSC, XRD and hysteresis measurements Studied alloy system exhibit two-step crystallization, exhibiting a pre-peak, before the main peak For the samples isochronally annealed at
various temperatures, coercive field values range between 8 – 914 A/m,whereas B3000 values vary between 1.28 - 1.54 Tesla The lowest Hc value of 8 A/m was obtained for the sample annealed at 380
o
C for 15 min Best B3000 value of 1.54 Tesla was obtained for the one annealed at 400 oC for 1 hr Obtained lattice parameter values suggest that the precipitated crystalline phase is bcc Fe (–Fe) Thermal annealing leads to rather coarse grains ~ 31 nm, but low crystalline fraction ~ 30% This appears to reduce the ferromagnetic exchange interaction between –Fe nano-crystals, thereby deteriorating the magnetic properties Thermal annealing leads to the flattening of the hysteresis loop that ascribed to surface crystallization
Acknowledgement
S N Kane acknowledges gratefully the financial support from Indo Portuguese joint project No.IND/Portugal/P-07/2013 and, also by the project CSR-IC-IC-BL-25/CRS-122-2014-15/218
References
[1] Inoue A, Shen B L, Koshiba H, Kato H and Yavari A R 2004 Acta Mater 52 1631
[2] Qin C, Zhang W, Asami K, Ohtsu N and Inoue A 2005 Acta Mater 53 3903
[3] Inoue A and Wang X M 2000 Acta Mater 48 1383
[4] Kane S N, Lee H J, Kim S B, Jeong Y H, Hyun S W, Kim C S and Varga L K
2009 J Physics: Conference series 144 012040
[5] Herzer G and Hilzinger H R 1986 J Magn Magn Mater 62 143
10
100
1000
0 100 200 300 400 500 1.1
1.2
1.3
1.4
1.5
1.6
Ci95.65B4.35
Ann Temp ( o C)
8 10 12
1.25 1.30 1.35 1.40 1.45
1.50
Ci95.65B4.35
Ann Time (Min.)
Ann Time (Min.)
4