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M.C. Ri et al. / Journal of Alloys and Compounds 781 (2019) 357e361
Thermomechanical Analysis (DMA) [27,28], Differential Thermal
Analysis (DTA) [29], Differential Scanning Calorimeter (DSC)
[11,28], and, of course, the X-ray Diffraction (XRD). Although XRD is
commonly used in detecting the crystallinity of an MG alloy, people
seldomly analyze the lattice parameters of these nanocrystals and
use that as a sign of structural change in response to thermo-
mechanical treatments. These partially crystallized MGs are good
candidates for CTC due to their heterogeneous combination of both
amorphous and crystalline phases and hence making XRD a useful
technique to monitor the change of lattice parameters. In fact, Fe-
based, partially crystallized alloys are widely used as soft mag-
nets [6,30] so a knowledge of the structural changes after CTC is
useful. More importantly since the treated specimens are un-
stressed, by monitoring the changes of the crystals we could also
work out the change of their neighbouring glassy matrix that is
uneasy to be resolved directly by any techniques. Therefore, in this
work we applied XRD crystallography to systematically investigate
the effect of CTC on the lattice parameters of Fe-based partially-
crystallized alloys.
0
@
1
n
X
A
Wa
¼
1 ꢁ
WjðCorrÞ ꢀ 100ð%Þ
(3)
morphous
j¼1
WstdðKnownÞ
WstdðKnownÞ
WaðCorrÞ ¼ Wa
(4)
(5)
SaðZMVÞa
Wa
¼
n
P
SkðZMVÞk
kꢁ1
Here WaðCorrÞ stands for the corrected weight fraction of a standard
material, WstdðKnownÞ the weight fraction of the known standard
material, WstdðMeasÞ- the relative fraction of the standard material,
Wa-the weight fraction of phase
is the Rietveld scale factor, Z the number of the unit cell for
chemical formula, M the molecular mass and V the molar volume.
a in an n phase mixture. Besides, S
2. Experimental methods
3. Results
Commercially available, FINEMET-type amorphous ribbons of
Fe73.5Si13.5B9Nb3Cu1 (supplied by Ningbo Zhongke B Plus New Ma-
terials Technology Co. Ltd.) and Fe50Co10Ni15.5Si12B8.5Nb3Cu1 (sup-
plied by An Tai Inc. of China Iron & Steel Group) alloys were selected
as the raw materials. Both ribbons were made via melt-spinning
Annealing induces crystallization in the MG samples. By
increasing the annealing temperature, the glassy samples were
partially crystallized and made heterogeneous as they contained
both glassy and crystalline phases [6,35]. The diffraction peaks
(Fig. 1a &b) of both series of the annealed alloys, heat-treated at
813 K for 1 h, could be indexed as Fe3Si (~98% in vol. %) and Si
(~2 vol %). Since Fe3Si is the major crystalline phase, we only
consider its contribution to the structural change hereafter. In both
alloys, the Fe3Si were face-centered cubic structures and at the Fm-
3m point group. The effects of annealing temperature on the lattice
parameters are presented in Fig. 1c and d. The initial lattice pa-
rameters were taken from the samples annealed at 733 K for 1 h.
With the increase of the annealing temperature, the lattice pa-
rameters were reduced from 5.7169 Å to 5.6735 Å in Fe73.5S-
and acquired a uniform thickness of 25 mm and a width of 25 mm
(the former) or 6 mm (the latter) respectively. Thermal properties
of the two MGs were measured by a DSC (NETZSCH DSC404 F3)
under a flow of purified argon atmosphere at a heating rate of 20 K/
min. To make partially-crystallized alloys, thermal annealing were
performed at a temperature between the primary (Tx1) and the
secondary (Tx2) crystallization temperature [6,30]. For Fe73.5S-
i13.5B9Nb3Cu1, Tx1 and Tx2 are 804 K and 930 K respectively and for
Fe50Co10Ni15.5Si12B8.5Nb3Cu1, Tx1 and Tx2 are 729 K and 844 K
respectively but there is a ternary crystalline peak with the
exothermic peak maximized at 937 K. Therefore, we annealed both
ribbons at 733 K, 753 K, 773 K, 793 K and 813 K for 1 hour before
subjecting them to CTC [3]. The procedure of CTC follows that of
Ketov et al. [1,2] with one cycle immerging the sample into liquid
nitrogen for 1 min and blowing the specimen in air at 320 K for
1 min with a hair dryer. The XRD (Bruker D8 Advance with typical
Cu-Ka radiation) is applied on all samples to check the
crystallinities.
The exact composition, lattice parameters and the volume
fraction of the crystals were analyzed by commercial softwares
“Bruker AXS DIFFRAC.EVA V4.2” and “Bruker AXS DIFFRAC TOPAS
V5.0” respectively. The lattice parameters of the crystals are ob-
tained from the Bragg equation as,
i13.5B9Nb3Cu1
and
from
5.7291 Å
to
5.6904 Å
in
Fe50Co10Ni15.5Si12B8.5Nb3Cu1 alloys. The relative changes in lattice
parameters were ꢁ0.76% and ꢁ0.71%, equivalent to a density
reduction of ꢁ2.3% and ꢁ2.1% respectively. Fig. 1e and f exhibit the
evolution of the weight fractions of the crystalline and glassy
phases. At the highest annealing temperature, e.g. 813 K, the
remaining phases are 65 w.t.% crystals, with a typical size of 18 nm,
and 35 w.t.% glasses in Fe73.5Si13.5B9Nb3Cu1 and 55 w.t.% crystals,
with a typical size of 25 nm, and 45 w.t.% glasses in Fe50Co10
-
Ni15.5Si12B8.5Nb3Cu1. We then took these 813 K, 1 h annealed spec-
imens as Sample A and Sample B and continued to study the effects
of CTC.
Fig. 2 showed that the lattice parameters were altered in the two
samples by CTC but the responses were serrations and the trends
are different in Sample A and Sample B. In comparison with the
initial lattice parameter of Sample A, lattice parameter went up
after 5, 15 and 20 cycles and went down after 10, 25 and 30 cycles.
On the other hand, in Sample B the 5, 10, 15 cycles increased the
lattice parameter whereas 20, 25 and 30 cycles decreased it. The
biggest extents of change were 0.0015 Å (5.6767 Åꢁ5.6752 Å) and
0.004 Å (5.6927 Åꢁ5.6887 Å) respectively, leaving volumetric re-
sidual strains (εv, re.) of 0.08% (3 ꢀ 0.0015 Å/5.6759 Å) and 0.21%
(3 ꢀ 0.004 Å/5.6904 Å).
2d sinQB ¼ n
l
(1)
where d is the atomic spacing, qB the incident angle (Bragg angle),
l
the X-ray wavelength (1.54056 Å). For a cubic structure, the lattice
parameter (a) is,
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
a ¼ dhkl
ꢀ
h2 þ k2 þ l2
(2)
where (hkl) are the Miller indexes. To confirm the reproducibility,
all the samples were measured at least three times.
The CTC needs to be performed at low temperature, and it is
important to know how much changes in lattice parameters are
affected by the low temperature itself. Fig. 3a and b shows the
changes of the lattice parameter when the temperature was
increased from 93 K to 298 K. At 93 K, the lattice parameters were
In particular, the volume fraction of crystallization was deter-
mined via the Rietveld refinement method [31]. The weight fraction
of crystallinities and the corresponding weight fraction of the
glasses are calculated as follows [32e34]: