Nanocrystalline Alloys - Features
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Transcript of Nanocrystalline Alloys - Features
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Nanocrystalline alloys:I. Crystallization
M. Miglierini et al.
Department of Nuclear Physics and Technology Slovak University of Technology
Ilkovicova 3,812 19 Bratislava, SlovakiaE-mail: [email protected]://www.nuc.elf.stuba.sk/bruno
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Nanocrystalline alloys prepared by controlled annealing from rapidly quenched amorphous ribbons exhibit an interesting class of materials from the point of view of their magnetic properties [1]. Resulting magnetic parameters, which are superior to those of conventional transformer steels and/or amorphous materials, are ensured by a presence of crystalline grains several nanometres in size embedded in the amorphous residual phase [2]. Magnetic parameters of amorphous alloys are frequently deteriorated in the process of their practical employment by elevated temperature especially during prolonged operational times. On the other hand, nanocrystalline alloys are in fact already partially crystallized and from this point of view their structure is more resistant to such external effects and that is why it is more stable. Nevertheless, because the excellent magnetic behaviour of nanocrystalline alloys depends strongly on the amount and size of the crystalline grains, the process of crystallization should be known.
[1] K. Suzuki, A. Makino, A. Inoue, T. Masumoto, J. Appl. Phys. 70 (1991) 6232.[2] G. Herzer, Phys. Scr. T49 (1993) 307.
The following slide shows a comparison of some magnetic parameters (magnetic permitivity e versus saturation magnetization Bs) for different types of magnetic materials used for, e.g. the production of cores of magnetic circuits. The main three types of compositions which yield nanocrystalline alloys are also listed.
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
• nanocrystalline alloys– good soft magnetic properties– thermal stabilization of the structure as
compared to amorphous alloys
• 1988: FINEMET: FeCuNbSiB• Yoshizawa Y, Oguma A, Yamauchi K
J Appl Phys 64 (1988) 6044
• 1988: NANOPERM: FeMB(Cu) where M = Zr, Mo, Ti, Nb, Hf, …
• Suzuki K, Kataoka N, Inoue A, et al.Mater Trans JIM 31 (1990) 743
• 1998: HITPERM: FeCoZrB(Cu)• Willard M A, Laughlin D E, McHenry M E, et al.
J Appl Phys 84 (1998) 6773
Nanocrystalline Alloys - Features
ferritesFe-Co
HITPERM
Si steel
Co-am
Fe-am
nc-FINEMET
NANOPERM
A. Makino, A. Inoue and T. MasumotoMater Trans JIM 36 (1995) 924
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Possible Applications of Nanocrystalline Alloys
magnetic shielding
transformersensors
ribbons
core
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Preparation of Nanocrystalline Alloys
• production of an amorphous precursor– mixing of appropriate amounts of pure elements
with subsequent melting– rapid quenching of the melt ( ~106 K/min)
method of planar flow casting– result: ribbon up to several cm wide
and typically about 20 m thick– check of composition (OES ICP)
and amorphicity (XRD)
• (nano)crystallization– check of crystallization behaviour by DSC (onset
of crystallization, first crystallization peak)– choice of temperature of annealing– annealing (in vacuum) for typically 1 hour
at the selected temperature– characterization of the resulting structural and magnetic properties
inductioncoil
melt
quenching wheel
melt-spunribbon
tube
planar flow
casting
amorphous ribbon
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Structures from a Melt
Starting material(melt)
quasicrystallinecrystalline amorphous
nanocrystalline
Conditions (quenching rate, composition, …)
• Ordered structure– periodicity– long range order
• Disordered structure– short range order– no translation symmetry
annealing
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
• structural characterization– DSC (differential scanning calorimetry)
• evolution of structure with temperature– XRD (X-ray diffraction)
• crystalline phases, relative fraction of crystallites and amorphous rest
– TEM (transmission electron microscopy)• including HREM (high resolution TEM)
and XTEM (cross-sectional TEM)• type and size of (nano)crystals
– STM (scanning tunnelling microscopy)• including AFM (atom force microscopy)• surface features
– ED (electron diffraction)• structural ordering of phases
• magnetic properties– magnetic measurements
• 57Fe Mössbauer spectroscopy (TMS + CEMS)– simultaneous information on both structural
arrangement and magnetic behaviour (hyperfine interactions)
Characterization of Nanocrystalline Alloys
200 250 3000
20
40
60
80
100
120ta =440o C
as-quenched
ta = 250o C
ta = 350o C
spec
ific
mag
netiz
atio
n (A
m2 /
kg)
temperature (K)
Miglierini M et al. J Appl Phys 85 (1999) 1014
ED
XTEM
TEM
STM
35 40 45 50 55
2 (o)
XRD
400 500 600 700 800
heat
flow
(a.u
.)
temperature (°C)
DSC
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Mössbauer spectrometry is a very sensitive tool for the study of both structural arrangement and hyperfine interactions (magnetic ordering) in nanocrystalline alloys [3]. Tthe FINEMET-type alloys, which are very frequently studied because their macroscopic properties are beneficial for practical applications [4] exhibit rather complicated Mössbauer spectra. They consist of several sextets of narrow lines ascribed to different crystallographic positions in the Fe-Si lattice which are superimposed upon a broadened signal which belongs to the amorphous rest of the original precursor [5]. Evaluation of such spectra is pretty complicated and, unfortunately, prevents from acquiring more detail information related to such phenomena as for example interfacial regions [6]. In order to benefit from its diagnostic potential, it is useful to investigate such materials whose Mössbauer spectra are reasonably simple. This is the situation for example in NANOPERM-type alloys which crystallize into bcc-Fe, the latter being a calibration material for Mössbauer spectrometry. Thus, here we concentrate on the Fe-Mo-Cu-B system which belongs to the NANOPERM family.
[3] H. Bremers, O. Hupe, C. E. Hofmeister, O. Michele and J. Hesse: J. Phys.: Condens. Matter 17 (2005) 3197.[4] T. Liu, Z. X. Xu and R. Z. Ma, J. Magn. Magn. Mat. 152 (1996) 365.[5] T. Pradell, N. Clavaguera, J. Zhu and M. T. Clavaguera-Mora: J. Phys.: Condens. Matter 7 (1995) 4129.[6] J. M. Grenèche and A. Slawska-Waniewska, J. Magn. Magn. Mat. 215-216 (2000) 264.
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
0 10 20 30
P(B
)
B (T)
0 1 2
P(
)
(mm/s)
Structural Arrangement and Mössbauer Spectra
crystalline(ordered structure)
hyperfine parameters
non-magnetic
magnetic
B
amorphous(disordered structure)
B
AM
AM CR
CR
Mössbauer spectra of an ordered structure (crystallites) exhibit narrow lines which lead to single values of the spectral parameters. Due to non-unique positions of resonant atoms in a disordered structure the spectral lines are broad and, consequently, distributions P() and P(B) of the spectral parameters must be considered.
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
-5 0 5
0.95
1.00
rela
tive
tran
smis
sion
velocity (mm/s)0 10 20 30
P(H)
H (T)
-5 0 5
0.95
1.00
rela
tive
tran
smis
sion
velocity (mm/s)0 10 20 30
P(H)
H (T)
FINEMETFe73.5Nb3Cu1Si13.5B
9
NANOPERMFe80Mo7Cu1B12
Fe-SiFe-Si
bcc- Febcc- Fe
Mössbauer Spectra of Nanocrystalline Alloys (295 K)
Fe on A site Fe on D site Si on D site
Miglierini M J Phys Condens Matter 6 (1994) 1431
Miglierini M and Grenèche J-M J Phys Condens Matter 9 (1997) 2303
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Annealing of the Amorphous Precursor• DSC continuous heating (temperature ramp of 10 K/min)• choice of annealing temperatures (B-M, A = as-quenched) => sample preparation• onset of crystallization identified at Tx1
diffusion-like precrystallization effects
normal grain-growth-like formation of-Fe nanocrystallites in amorphous matrix
diffusion controlled grain-growth ofalready created -Fe nanocrystallites
diffusion controlled nucleation and growth-like precipitation of -Fe(Mo)
structural relaxation
RT 300 400 500 600 700
A B C D E FG H
I
J K
L
M
heat
pow
er
Tx1
temperature ( oC)
Tx1 460oCMiglierini M et al. phys stat sol (b) 243 (2006) 57
Fe76Mo8Cu1B15
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
750 oC
550 oC
TEM and XRD
470 oC
100 200 300 400 500 600 700
heat
pow
er
temperature (o C)
650 oC
Tx1 450oC
• Tx1 = 450 oC
450 oC
Miglierini M et al. phys stat sol (b) 243 (2006) 57
Fe76Mo8Cu1B15
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Mössbauer Spectrometry
• evolution of Mössbauer spectra with temperature of annealing ta
• transmission Mössbauer spectra are plotted upside-down to enable 3D mapping• temperature of measurement 300 K and 77 K
Fe76Mo8Cu1B15
Miglierini M et al. phys stat sol (b) 243 (2006) 57
300 K 77 K
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Fitting Model
Fe80Mo7Cu1B12 440oC/1h
Miglierini M and Grenèche J-M J Phys Condens Matter 9 (1997) 2303, 2321Miglierini M and Grenèche J-M Hyperfine Interact 113 (1998) 375
crystalline
interface
amorphous
-5 0 5
0.95
1.00
rela
tive
tran
smis
sion
velocity (mm/s)
10nm
HREM
0 10 20 30 40
IF CRP(H
)
hyperfine field (T)
AM
295 K
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
100 200 300 400 500 600 700
heat
pow
er
temperature (o C)
Transmission Mössbauer Spectrometry (295 K)
600 oC
550 oC
510 oC
450 oC
• bulk• Tx1 = 450 oC (?)
Miglierini M et al. phys stat sol (b) 243 (2006) 57
410 oC
Fe76Mo8Cu1B15
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
600 oC
100 200 300 400 500 600 700
heat
pow
er
temperature (o C)
Conversion Electron Mössbauer Spectrometry (295 K)
550 oC
510 oC
450 oC
• surface• Tx1 = 450 oC
Miglierini M et al. Hyperfine Int 165 (2005) 75
410 oC
Fe76Mo8Cu1B15
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
40 45 50
(deg)
600 oC
XRD – Peak Decomposition
100 200 300 400 500 600 700
heat
pow
er
temperature (o C)
• Tx1 = 450 oC40 45 50
(deg)
550 oC
40 45 50
(deg)
510 oCMiglierini M et al. phys stat sol (b) 243 (2006) 57
40 45 50
(deg)
450 oC
40 45 50
(deg)
410 oC
Fe76Mo8Cu1B15
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Summary
• structure of nanocrystalline alloys– (nano)crystallites– residual amorphous matrix– interface = surface of crystalline grains + crystal-to-amorphous matrix region
• crystallization– first at the surface– progress of crystallization
is more rapid at the surface
• identification of crystallinephase
• amount of nanocrystals450 500 550 600
0
10
20
30
40
50
60
XRD TMS CEMS
A CR (%
)
temperature ( oC)
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
Mössbauer spectroscopy contributes to the study of nanocrystalline alloys from several viewpoints. First, it is possible to identify the structural arrangement from a very first look at a Mössbauer spectrum (e.g., onset and progress of crystallization). Crystalline phases are characterized by narrow and usually well separated lines whereas the amorphous residual phase exhibits broad patterns due to its disordered nature. Signal from resonant atoms located at the interfacial regions can be also distinguished. The latter two contributions are described by the help of distributions of hyperfine parameters through which information on both topological and chemical short-range order can be derived. The fraction (and/or type) of the crystalline phase(s) can be readily obtained from the spectral parameters.Second, magnetic order of the system under the study is also directly followed from changes of the spectral line shapes, viz. (broadened) doublet vs. sextet. This can be studied as a function of annealing temperature (i.e., crystalline contents), measuring temperature, and/or composition. More details can be found in another presentation.In this presentation, we have shown that the crystallization of amorphous precursors for the preparation of nanocrystalline alloys proceeds more rapidly on the surface of the rapidly quenched ribbons than in their bulk. In doing so, we have employed CEMS and TMS, respectively. The crystalline content was determined also from XRD and the results coincide well with those from TMS.The temperature of the onset of crystallization Tx1 determined from DSC is somewhat higher than that from XRD, TEM and MS due to different regime of annealing (continuous during DSC and isothermal during the preparation of the samples).