The Activation energy plots, for both steps of crystallization according Ozawa

Phase Transformation of CoPhase Transformation of Co7070FeFe55SiSi1010BB1515 Amorphous Alloy Induced by Heating Amorphous Alloy Induced by Heating

D.M. MinićD.M. Minić11, A.M. Maričić, A.M. Maričić22, R.Z, R.Z.. Dimitrijevi Dimitrijevićć33, ,

11Faculty of PhysicFaculty of Physical Chemistry, University of Belgradeal Chemistry, University of Belgrade22Technical Faculty Technical Faculty ČačakČačak, University of Kragujevac, University of Kragujevac

33Faculty of Mining and Geology, Department of Crystallography, University of BelgradeFaculty of Mining and Geology, Department of Crystallography, University of Belgrade

According to DSC measurements, the alloy crystallizes step by step with two well formed According to DSC measurements, the alloy crystallizes step by step with two well formed exothermal maxima at temperatures at about T1=460exothermal maxima at temperatures at about T1=460C and T2=540C and T2=540C, respectively.C, respectively.

DSC curve of initial amorphous Co70Fe5Si10B15 alloy; heating rate10 DSC curve of initial amorphous Co70Fe5Si10B15 alloy; heating rate10 C/min.C/min.

0.00118 0.00120 0.00122 0.00124 0.00126

1.5

2.0

2.5

3.0

3.5

R = - 0,99859B = - 66745,30041Ea = 554920,4276

T2

T1

R = -0,99933B = - 53581,02102Ea = 445472,6088

ln

1/T

The thermal and kinetic values of the crystallization process The thermal and kinetic values of the crystallization process were determined by analyzing the shifts of exothermal maxima in were determined by analyzing the shifts of exothermal maxima in DSC thermograms depending on the heating rate.DSC thermograms depending on the heating rate.

The Activation energy plots, for both steps of crystallization according Ozawa

0.00118 0.00120 0.00122 0.00124 0.001269.5

10.0

10.5

11.0

11.5

12.0

R = 0,99786B = 65370,43863Ea =543489,8268

R = 0,9994B = 52096,13749Ea = 433127,2871

T1

T2

ln(T

2 /)

1/T

The Activation energy plots, for both steps of crystallization according Kissinger

StepStep EaEa

[kJ/mol][kJ/mol]

OzawaOzawa

EaEa

[kJ/mol][kJ/mol]

KissingerKissinger

kk

[1/s][1/s]

t1/2t1/2

[1/s][1/s]

11 445.5445.51111 433.1433.11111 0.0190.019 36.536.5

22 554.9554.91111 543.5543.51111 0.0230.023 30.130.1

The thermal and kinetic parameters process of crystallizationThe thermal and kinetic parameters process of crystallization

It is obvious that initial sample, a, pass through successive It is obvious that initial sample, a, pass through successive phase transformations during heating treatment. Between phase transformations during heating treatment. Between ambient temperature and 300ambient temperature and 300C, initial alloy retains C, initial alloy retains amorphous properties what is consistent with SEM amorphous properties what is consistent with SEM investigations. investigations.

Prolonged heating between 400 and 500Prolonged heating between 400 and 500C induces C induces amorphous alloy crystallization to, at least, two unidentified amorphous alloy crystallization to, at least, two unidentified intermediary crystalline phases, (curves b and c). One of intermediary crystalline phases, (curves b and c). One of these two phases with characteristic peak at 2these two phases with characteristic peak at 2=44.20=44.20, is , is more abundant and represent the (111) inter-planar distance more abundant and represent the (111) inter-planar distance of Co-rich FCC cubic crystal lattice. The phase is always of Co-rich FCC cubic crystal lattice. The phase is always present at 400present at 400C, b, which means that its crystallization from C, b, which means that its crystallization from amorphous matrix started earlier between 300 and 400amorphous matrix started earlier between 300 and 400. In . In other words, thermally induced elemental segregation in other words, thermally induced elemental segregation in amorphous ribbon always starts in aforementioned amorphous ribbon always starts in aforementioned temperature region. The alloy segregation/crystallization temperature region. The alloy segregation/crystallization processes induced by heating are monitored also by processes induced by heating are monitored also by appearance of dendritic forms in SEM micrographs taken appearance of dendritic forms in SEM micrographs taken between 400 and 500 between 400 and 500 C.C.

References[1] J.D. Bernal, Nature, 185 (1960) 68.[2] S. Takayma, J. Mater. Sci., 11 (1976) 164.[3] U. Köster and U. Herald, “Crystallization of metallic glasses”,

Springer, New York, 1981, p.225-259.[4]R.G. Garvey, Powder Diffr. 1(1986) 114.[5]. S. Krumm, Materials Science Forum, 228-231 (1996) 183.[6]. Joint Commity for Powder Diffraction Standards, file cards No.

15-0806 and 5-0727.

a)

c)a) b) c) d)

SEM micrographs of thermally induced phase evolution of amorphous Co70Fe5Si10B15 alloy: a) the initial non-heated alloy; b) the initial alloy heated at 400oC for 20 minutes; c) the initial alloy heated at 700oC for 20 minutes; d) the initial alloy heated at 1000oC for 20 minutes.

A whole range XRD powder pattern of Co70Fe5Si10B15 alloy after heating at 1000oC for 20 minutes.

Thermally induced phase evolution of a) the amorphous o70Fe5Si10B15 alloy with temperature increasing: a) the initial alloy at ambient temperature; b) the initial alloy heated at 400oC for 20 minutes; c) the initial alloy heated at 500oC for 20 minutes; d) the initial alloy heated at 600oC for 20 minutes; e) the initial alloy heated at 700oC for 20 minutes.