CC BY
8
УДК 537.622.4
Crystallization Kinetics and Magnetic Properties
of Fe80-xCoxP\4B6 Metallic Glasses
Darja A. Prahova* Alexander M. Grishin Vladimir S. Ignahin Lyubov A. Lugovskaya^ Roman N. Osaulenko*
Physical and Technical Institute Petrozavodsk State University Lenina, 33, Petrozavodsk, 185910
Russia
Received 30.10.2016, received in revised form 13.06.2017, accepted 06.09.2017 We report about formation mechanism, crystallization kinetics and magnetic properties observed in the series of rapidly solidified Fe80-xCoxPiAB6 metallic glasses with x = 25, 32, 35 and 40 at.%. Magnetic soft Fe8o-xCoxPl4Be metallic glasses have 15-25 ¡m thick and 2-8 mm wide. The ribbon samples were created to meltspun onto the massive copper wheel from the RF-melted superheated master ingots..
Keywords: meltspun ribbons, eutectic crystallization, phase analysis, magnetosoft properties. DOI: 10.17516/1997-1397-2018-11-1-117-123.
Introduction
The investigation and application metallic glasses are important and advanced problem for modern science, because metallic glasses have anisotropy as compared to crystal metal. The amorphous structure composition allows improving some the physical property, when a variation of stoichiometry determines limits to applicability of metallic glasses. Today a industry apply metal glass on based Fe — Ni — P — B, but replacement Ni to Co [1-3] lead to increased thermostability.
1. Experimental
The metallic glasses on based Fe — Co — P — B were created melt spun on fast-running disk of copper. Initially the preform with known stoichiometry parameters heated to temperatures greater the temperature of melting on 100 degrees (melting temperature is 1313 K), and then the liquid melt was press out on surface of disc by argon pressure through of nozzle ampoule. The growth of crystals was smaller due to the presence of P and B. And thus the metallic ribbons on based Fe — Co — P — B had amorphous state.
The metallic glasses have a glossy surface, width is few millimeters and thickness is 15-25 ^m. Except but the surface has grooves (they are distinguishable under a microscope). The grooves were born, because liquid melt interacted with surface of disc.
* prakhva.darja@rambler.ru t Liubov@mail.ru ^ roman@petrsu.ru © Siberian Federal University. All rights reserved
The crystallization kinetics was studied the differential scanning calorimetry (DSC) and x-ray diffraction. DSC was conduct on hardware and software system Hitachi ST A 7300. This complex is carried out thermogravimetric analysis to measure the crystallization temperature and the generated heat. X-ray diffraction was conduct in CuKa and MoKa radiations. The investigation of magnetic properties was produced in dynamic regime on difference frequency and maximum magnetic force value.
2. Results and discussion
X-ray diffraction pattern was record in CuKa reflection and MoKa transmission radiations. The x-ray pattern of as-cast ribbons was diffusely so it is characteristic for scattering noncrystalline object (red line in Fig. 1). The characteristic size of regions coherently scattering X-rays is small as 1.6 nm.
1 1 1 1 1 1 1 1 1 1 1 1 i 1 i
Fe^Co^P^B,
-45-35—14—6
• - a-FeCo
x - (Fe,Co)3(P,B) -
+ - FeCoP
1 *"Fe304
it • 1 873 K
JLJLJ Vlîirt*+X x ft x . xi X * . uwL^,-1L- XX x •
} L 714.5 K ■
NuL........v. ^—.....
30 40 50 60 70 80 90 100
20 [deg]
Fig. 1. XRD pattern of Fe45Co35P14B6 ribbon in as-cast (red line) condition and after annealing at 714.5 and 873 K
Finbak-Warren atomic pair distribution function (PDF) phase analysis revealed superposition of two main bcc a — FeCo and bct (Fe, Co)3(P, B) phases. Theoretical PDF for (Fe, Co)3(P, B) phase matches much better a fine structure of the second coordination sphere.
The temperature of crystallization and the generated heat were detected with help DSC. The estimation of crystallization temperature allows evaluating the industrial range of application metallic glasses on based Fe — Co — P — B in the form of functional material for magnetic screens and sensors feeble magnetic field.
The Fig. 2 show differential scanning calorimetry thermogram for Fe48Co32PuB6. As you can see by with decreasing the heating rate is decreased the values of crystallization temperature. This connected with different the heating rates of volumes of study samples.
The temperature of crystallization was detected as maximum value on differential scanning calorimetry thermogram (Fig. 2). Whereas crystallization temperature Tx depends on the heating rate a and follows Kissinger law governed by a modified Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory:
ln (T2) = Q + ln {T°g [2f (Tx)F-3(Tx)]-1/4} ■ (1)
Time f [min]
11 12 13
700 720 740 760 780
Temperature T [K]
Fig. 2. Differential scanning calorimetry traces for the Fe48Co32P14B6 ribbons heated at five different heating rates a = 2.5, 5, 10, 20 and 40 K/min
Activation energy Q and crystal/glass interfacial energy a were obtained as fitting parameters (Tab. 1).
Table 1
Specimen Tx for 40 K/min, K Q, k a, J/m2
Fe4oCo4oPi4B6 749.6 41021 0.230
Fe45 C035P14B6 754.5 46431 0.239
Fe4SCo32Pi4B6 753.5 46651 0.239
Fe55Co25Pi4B6 758.9 51846 0.248
The isothermal annealing — a heating under constancy the heat rates to assign temperature, which low of the temperature crystallization and kept there for a long time — allowed detecting living times of amorphous state the metallic glasses on based Fe — Co — P — B.
Isothermal annealing made it possible to detect the lifetime of the amorphous state of metallic glasses.
KJMA theory derived exponential temperature dependences of incubation time and the peak value of heat release tinc(T) = rexp (Q/T), $max(T) to 1/tinc(T) nicely accord the experimental data in Fig. 3. There activation energy Q exactly coincides with the one obtained at the process of isochronal annealing.
Comparing XRD spectra recorded for isochronal and isothermal heating regimes we arrived to rather unexpected conclusion. Isothermal annealing always results in the formation of nano-sized nuclei within the amorphous metallic matrix, whereas rapid isochronal heating to high temperatures leads to the formation of crystallites much bigger in size. This conclusion holds even more since isothermally annealed specimens remain in the cooling oven for much longer than incubation time.
For purpose of technology and applications important to conduct calculate by temperature 400 K and 500 K. The relaxation to the crystallization state less than 400 K happens through ~ 1019 years, 500 K ~ 109 years.
The investigation of magnetic properties was produced in dynamic regime by change frequency f = 20 + 610 Hz and 210 + 1010 Hz and maximum magnetic force Hmax = 100 A/m
and 1500 A/m (Fig. 4). The hysteresis M — H loops characterized by a rectangular view, small values the coercive force and relatively small hysteresis loss. This all indicate, that metallic glasses on based Fe — Co — P — B is magnetic soft materials.
Fig. 3. Differential isothermal calorimetry (DIC) scans of Fe45Co35P\4B6 ribbons annealed at seven different temperatures T below the crystallization temperature Tx = 754.5 K
Magnetic field H [A/m]
1500 -1000 -500 0 500 1000 1500
J_I_I_I_I_I__I_I_I_I_I_L.
0 100 200 300 400 500 600
Frequency f [Hz]
Fig. 4. Hysteresis M — H loops of as-quenched Fe55Co25Pi4B6 ribbon recorded at different frequencies of sinusoidal exciting field. Inset shows frequency dependence of hysteresis loss
The values of a coercive force was identify from hysteresis M — H loops subject to M/Mmax = 0. For metallic glasses on based Fe — Co — P — B usual with increase the frequency of the external field increases the coercive force. The coercive force growth comes the power function (inclusion of Fig. 4).
Hysteresis M — H loops were recorded to differentiate magnetic hysteresis losses proportional to the first power of the frequency f and eddy-current power loss proportional to f2. Hysteresis losses in saturated regime P(f) = (f /d) § M(H)dH at 60 Hz were estimated to be 0.56 W/kg while the maximum differential permeability was found to be about 110000. Bias magnetic field dependence of incremental magnetic permeability was acquired from the slope of minor loops recorded in superimposed weak ac- and slowly swept dc-magnetic fields.
Also the basic magnetization curves were obtained (Fig. 5). The Fig. 5 shows that basic magnetization curves growing rapidly and view complies curve for ferromagnetic material. The fact characterized by magnetic soft materials.
400
IF
& 300
'¡i> jj 200
100
0
Fig. 5. The basic magnetization curves of melt-spun material on based Fe — Co — P — B
The basic magnetization curves can be divided into two areas:
1. The areas have the sharp increase the magnetization of a small change in the magnetic field. This area called site Barkhausen jumps [4]. The sharp increase observable before a value magnetic field 650 A/m.
2. The areas have the stickle increase the magnetization of a small change in the magnetic field. As the case stands magnetization is due to the rotation vectors Ms processes in the direction of the external field [5].
The Fig. 5 show that magnetization curves do not cross in area of saturation, because vector Ms orientation effects are present.
The investigation of Curie temperature carried out on Hitachi ST A 7300, which was fit up constant magnet. We made isochronal annealing in constant magnetic field. During phase transition of the second order was change first weight derivative on 730 K (Fig. 6 red line).
For metallic glasses on based Fe—Co—P — B a difference between the temperature crystallization and Curie temperature is small value. It means than metallic glasses on based Fe—Co—P—B is not impossible annealing in paramagnetic state. Interested that, the magnetic state is changed with the condition structure modification. The phase transition of the first and second order was close together, because we conducted isothermal annealing with a constant magnetic field for better visibility of the metallic glasses condition change (Fig. 7). We observed that crystallization impacted on change a magnetization state, as so as during isothermal annealing the change magnetic and structure state was one by 718 K.
500 550 600 650 700 750 800 Temperature T, K
Fig. 6. The curves heat flow (green line) and derivative of weight (red line) vs. temperature for as-cast Fe48Co32P14Be, a regime of annealing is isochronal
Fig. 7. The curves heat flow (green line) and derivative of weight (blue line) vs. time of annealing for as-cast Fe48Co32Pi4Be, a regime of annealing is isothermal. Yellow line is a temperature vs. time of annealing
The Tab. 2 shows values the temperature crystallization and Curie temperature in constancy magnetic field for three different samples of metallic glasses on bases Fe — Co — P — B, the rate of heat is 10 K/min.
Table 2
Sample The temperature of The Curie temperature TC, K
crystallization Tmax, K
Fe45 Co35 PuBe 741 731
Feis Co32 P14B6 738 730
Fe55 Co25 P14B6 745 703
Conclusions
In summary, we created metallic glasses on based bases Fe — Co — P — B melt-spun. The metallic ribbons have x-ray amorphous condition with the characteristic size of regions coherently scattering is 1.6 nm. The crystal kinetics was defined DSC. The annealing was conducted in two regimes: isothermal and isochronal. The interesting that a isothermal annealing always results in the formation of nano-sized nuclei within the amorphous metallic matrix, whereas rapid isochronal heating to high temperatures leads to the formation of crystallites much bigger in size. The isochronal regime of annealing has allowed to establishing a temperature of crystallization and the industrial range of application metallic glasses on based Fe — Co — P — B. The crystallization temperature of metallic glasses on based Fe — Co — P — B has a value over than industrial samples. The investigation of magnetic properties shows that metallic glasses are not impossible annealing in paramagnetic state. The coercive force was detected, and it change with increase a frequency through a power function.
References
[1] M.Hollmark, V.I.Tkatch, A.Grishin, S.I.Khartsev, Processing and properties of soft magnetic Fe40Co40P14Be, amorphous alloys, IEEE transaction of magnetics, 37(2001), 2278-2280.
[2] V.I.Tkatch, A.Grishin, S.I.Khartsev, Delayed nucleation in Fe40Co40P14Be metallic glass, Materials science and engineering, A337(2002), 187-193.
[3] V.V.Popov, V.I.Tkatch, S.G.Rassolov, A.S.Aronin, Effect of replacement of Ni by Co on thermal stability of Fe40Co40Pi4B6 metallic glass, Journal of Non-Crystalline Solids, 356(2010), 1344—1348.
[4] H.Barkhausen, Zwei mit Hilfe der neuen Verstarker entdeckte Erscheinunften, hysische Zeitschrift, 1919.
[5] A.A.Preobrazhensky, E.G.Bishard, Magnetic materials and elements, Moscow, 1986.
Кинетика кристаллизации и магнитные свойства металлических стекол Fe80—xCoxP14B6
Дарья А. Прахова Александр М. Гришин Владимир С. Игнахин Любовь А. Луговская Роман Н. Осауленко
Петрозаводский государственный университет Ленина, 33, Петрозаводск, 185910
Россия
В настоящей 'работе показаны основы механизма кинетики кристаллизации быстрозакаленных металлических стекол на основе Feso-xCoxP-i4B6 при x = 25, 32, 35 и 40 at.%. В ходе работы была получены магнитомягкие металлические стекла медотом быстрой закалки на диске из жидкого состояния. Полученные ленты обладают толщиной порядка 15-25 цш и шириной около 2-8 mm.
Ключевые слова: быстрозакаленные ленты, эвтетическая кристаллизация, фазовый анализ, маг-нитомягкие свойства.
