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DOI: 10.1002/adem.201000339Analysis of Ball-Milled ZrAlNiCu Bulk MetallicGlass Powders**
By Jiang Wu,* Samuel Margueron, Nathalie Allain-Bonasso, Patrice Bourson, Eric Gaffet,Chuang Dong and Thierry Grosdidier*
This manuscript gives the first results of an ongoing research project focusing on the crystallizationprocesses of Zr65Al7.5Ni10Cu17.5 (Z1) and Zr58Al16Ni11Cu15 (Z2) bulk metallic glasses. Crystal-lization, induced by ball-milling and thermal annealing, has been observed and compared usingdifferential scanning calorimetry, X-ray diffraction and Raman spectroscopy. The thermal crystal-lization end-products obtained for the two alloys were different: tetragonal Zr2Cu and hexagonalZr6Al2Ni for Z1, while Z2 contained hexagonal Zr2Al, big cubic Zr2Ni and some a-Zr solid solution.For both alloys, the thermal crystallization products were different from those obtained after ball-milling. Interestingly, however, the stable phase obtained after sufficient mechanical milling was anFCC phase for both alloys. Raman spectroscopy suggests that nitrogen has an effect on the formation ofthis stable final product.
Over the last two decades, particular interest has been paid
to the preparation of bulk metallic glasses (BMGs) due to their
unique and original properties.[1,2] Ball-milling (BM) of
blended pure elements or pre-alloyed compounds is an
efficient technique for producing glassy powders.[3] Com-
bined with the powder consolidation within the supercooled
liquid region, bulk samples with amorphous structures can be
easily formed.[4,5]
[*] Dr. J. Wu, Dr. N. Allain-Bonasso, Prof. T. GrosdidierLaboratoire d’Etude des Microstructure et de Mecanique desMateriaux (LEM3, UMR CNRS 7239), Universite PaulVerlaine-Metz, Ile du Saulcy, F57045 Metz, (France)E-mail: [email protected]; [email protected]
Dr. S. Margueron, Prof. P. BoursonLaboratoire Materiaux Optiques, Photonique et Systemes(LMOPS),Universite Paul Verlaine-Metz, 2 Rue EdouardBelin, F57070 Metz, (France)
Dr. E. GaffetNanomaterials Research Group (NRG, UMR CNRS 5060),Site de Sevenans (UTBM), F90010 Belfort Cedex, (France)
Dr. J. Wu, Prof. C. DongKey Laboratory of Materials Modification (Ministry ofEducation), Dalian University of Technology, Dalian116024, (PR China)
[**] The authors gratefully acknowledge financial support fromthe National Basic Research Program of China (No.2007CB613902) and help from the China Scholarship Council.
616 wileyonlinelibrary.com � 2011 WILEY-VCH Verlag GmbH & Co
However, the crystallization of amorphous alloys under
ball-milling, which is considered as mechanically induced
crystallization (MIC), has been observed extensively in a
number of alloy systems, i.e., Al-, Fe-, Ti- and Zr-based
ones.[6–14] In particular, a cyclic crystalline–glassy–crystalline
phase transformation induced by BM has been reported in
Co�Ti, Zr�Ni, Zr�Al�Ni and Zr�Al�Ni�Cu�Pd sys-
tems.[12–15] These previous works have shown that the
crystallization process and the corresponding procedures
under ball-milling are significantly different from those
obtained under conventional thermal crystallization, indicat-
ing that the MIC cannot be attributed only to the local
temperature rise.[8,9] The exact mechanisms of MIC are not
fully understood but have been suggested to be related to the
effects – possibly combined – of pressure and mechanically
induced defects.[7–11,16]
This manuscript gives the first results of an on-going
research project set up to improve the understanding of MIC
in Zr-based BMGs. To this end, the crystallization behaviors of
Zr65Al7.5Ni10Cu17.5 (Z1) and Zr58Al16Ni11Cu15 (Z2) BMGs
under ball-milling and thermal cycles are here compared.
Experimental
BMG Preparation
Master ingots with nominal compositions Zr65Al7.5-Ni10Cu17.5 and Zr58Al16Ni11Cu15 (at-%) were prepared by
arc melting under an argon atmosphere. The levels of purity
for the different constituting elements are 99.9 wt-% for Zr,
99.999 wt-% for Al, and 99.99 wt-% for Cu and Ni. From these
. KGaA, Weinheim ADVANCED ENGINEERING MATERIALS 2011, 13, No. 7
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20 40 60 80 100
Inte
rnsi
ty (a
.u.)
2 Theta (degree)
Z2
Z1
Tg Tx
500 600 700 800
Exot
herm
ic
Temp.(K)
Z1
Z2
Fig. 1. XRD traces of the initial BMG blocks and the corresponding DSC scans (inset).
? ◊?
Z2
∇•
• •• •
•◊
◊◊ ∇∇∇∇∇
∇∇
∇
∇∇
∇ Zr2Ni
?
? unknow
• Zr2Al
◊ Zr
♦
Z1
♦
♦♦
♦♦♦♦♦
♦
Zr2Cu
♦Inte
nsity
(a.u
.)
20 30 40 50 60 70
2 Theta (degree)
♦Zr6Al2Ni
Fig. 2. XRD patterns of Z1 and Z2 samples annealed up to 873 K at a heating rate of20 K �min�1.
constituting elements, master alloys were melted and
re-melted four times to improve homogeneity. Rods with a
diameter of 3mm were then produced by copper mould
suction casting from themaster ingots. The amorphous nature
of these materials was examined bymeans of X-ray diffraction
(XRD) and differential scanning calorimetry (DSC) before
annealing and ball-milling.
Annealing and Ball-Milling
Thermal crystallization was performed in a Netzsch-409
DSC apparatus based on the isochronal and isothermal modes
under a continuous flow of high purity argon. The samples
under the isochronal measurements were continuously
heated from room temperature to 873K at a heating rate of
20 K �min�1. Isothermal annealingwas performed for a certain
period of time (1, 5, 10, 25 or 50min) at the set temperature of
753K.
The mechanically induced crystallization was carried out
using a planetary ball-mill, Pulverisette 4 system manufac-
tured by Fritsch. The starting materials were 3mm long
blocks crushed from the as-cast BMG rods. 10 g of such
blocks together with five stainless balls were sealed into a
stainless steel vial (125mL in volume) in air and milled at
room temperature. In this machine, the shock energy and the
shock frequency can be independently selected and con-
trolled. The effects of the milling parameters have been
discussed in detail in the literature [17–19]. Here, the absolute
rotation speeds of the disk (V) and vials (v) were set,
respectively, at 350 and �200 rpm.
Microstructure Characterization
The structural changes in the annealed and the milled
powders were characterized by XRD and Raman spectro-
scopy. The X-ray system, equipped with a RU300 rotating
anode and an INEL CPS120 position sensitive detector, was
operated with the Cu-Ka radiation. For the Raman measure-
ments, an excitation line of 514 nm (Arþ laser) with a�50 long
working distance objective was used in back scattering with a
LabRam, Horiba, Jobin-Yvon spectrometer. In order to limit
heating and oxidation or reaction induced by the laser, the
Raman measurements were performed at the liquid nitrogen
temperature (77K) in a close finger LINKAM cryostat with an
incident power of about 3mW for 360 s.
Results and Discussion
Thermal Crystallization
Figure 1 shows typical XRD patterns obtained from the
initial as-cast Z1 and Z2 BMG rods. Both traces exhibit the
typical features of amorphous structures, and no obvious
sharp peaks corresponding to crystals are visible. The DSC
scans are shown in the insert image in Figure 1, in which a
distinct glass transition followed by a sharp crystallization
event is observed, confirming the glassy nature of the initial
materials again. The glass transition temperature Tg and the
onset crystallization temperature Tx for Z1 are about 643 and
ADVANCED ENGINEERING MATERIALS 2011, 13, No. 7 � 2011 WILEY-VCH Verl
742K, respectively, while the corresponding values for Z2 are
732 and 809K. These results indicate that the Z2 BMG has a
higher thermal stability than the Z1 one.
To examine the changes in the microstructure of the
starting BMGs after annealing, the completely crystallized
samples which were heated up to 873K at a heating rate of 20
K �min�1 were analyzed by XRD. The results are shown in
Figure 2. The XRD pattern of the Z1 sample is similar to those
recorded by other researchers from the annealed Zr65Al7.5-Ni10Cu17.5 metallic glasses.[20–22] It can be indexed as amixture
of tetragonal Zr2Cu and hexagonal Zr6Al2Ni phases. The
isothermal crystallization procedure of the Z1 BMGs has been
investigated extensively by other authors. In general,
ag GmbH & Co. KGaA, Weinheim http://www.aem-journal.com 617
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∇∇
∗(42
2)
∗(42
0)∗(
331)
∗(40
0)
∗(22
2)∗ (
311)
∗(22
0)∗(20
0)
12h
4h
2h
1h
Inte
nsity
(a.u
.)
∗(11
1)
initial
(a) Z1
∗ FCC
∇ Cubic Zr2Ni
20 40 60 80 100 120
Tetragonal Zr2Cu
2 Theta (degree)
20 40 60 80 100 120
∗ (4
22)
∗ (4
20)
∗ (3
31)
∗ (2
22)
∗ (3
11)
∗ (2
20) ∗
(200
)
∗ (1
11)
12h
2hInte
nsity
(a.u
.)
2Theta (degree)
initial
1h
4h
∗ FCC (b) Z2
Fig. 3. XRD traces of a) Z1, and, b) Z2 powders showing the transformation afterdifferent milling durations.
Fig. 4. Brightfield TEM image and corresponding diffraction pattern of Z1 powder after12 h of milling.
quasicrystals, big cubic Zr2Ni, and tetragonal Zr2Cu phases
are the phases that precipitate at the first stage of isothermal
crystallization for Z1 BMGs. Correspondingly, the tetragonal
Zr2Cu and the hexagonal Zr6Al2Ni phases were also the final
stable products for Z1 BMGs on high temperature anneal-
ing.[20–22] For the Z2 sample, the analysis of the XRD traces in
Figure 2 shows that the peaks are associated with the big cubic
Zr2Ni and hexagonal Zr2Al compounds together with a-Zr
solid solution, while a few unidentified lines still exist. A
detailed analysis has revealed that the primary phase
precipitating from the amorphous matrix was a cubic phase
with a lattice parameter of about 0.360 nm. Subsequently, new
crystalline phases including big cubic Zr2Ni and hexagonal
Zr2Al compounds together with a-Zr were observed, while
the intensity of the initial cubic phase decreased. Such
evolution implies that the primary phase probably served
as the nucleation core for the formation of new phases. No
new phases appeared under further annealing and the XRD
pattern of the completely crystallized sample for the high
temperature isothermal annealing was very similar to the one
obtained in Figure 2 for continuous heating. The most
interesting point revealed in this section is that the thermal
crystallization processes for these two alloys are different.
Milling-Induced Crystallization
Figure 3 shows the XRD traces obtained on the powder
after ball-milling for different times. The initial as-cast
amorphous rod is also shown for comparison. Sharp
diffraction peaks corresponding to crystalline phases appear
after milling. For the Z1 alloy (Fig. 3a), the analysis reveals that
a big cubic Zr2Ni phase and a tetragonal Zr2Cu phase, together
with a phase having FCC features, form from the metallic
glass matrix at the early stage of milling (from 1 to 4 h of
milling). However, only the FCC-type phase remains after 12 h
of milling. This observation indicates that the big cubic Zr2Ni
and tetragonal Zr2Cu phase are metastable and transform into
the FCC phase during the milling. Comparatively, in the case
of the Z2 alloy (Fig. 3b), only the FCC phase is detected by
XRD over the entire range of milling time (1 to 12 h). Figure 4
shows a TEM brightfield image of the Z1 alloy after milling for
12 h. Nanocrystals formed in the milled powders and most of
the crystals have a size below 20 nm. The selected area
diffraction pattern, as shown in the insert image of Figure 4
and consistently with results from XRD, confirmed the
presence of a FCC structure. This implies that the amorphous
phase has almost entirely changed to the FCC phase. It was
also established in a previous DSC and TEM study that some
residual amorphous phase remained at the early stage of
milling but that the Z1 and Z2 alloys almost completely
crystallized after 12 h of milling.[23]
It is interesting to notice here that the FCC phase is always
the final crystallization product under the present milling
conditions and that it is completely different from the phases
found under thermal crystallization by annealing. The lattice
constants of the FCC phase were calculated to be 0.453 and
0.456 nm, respectively, from the XRD traces of Z1 and Z2
618 http://www.aem-journal.com � 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ADVANCED ENGINEERING MATERIALS 2011, 13, No. 7
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0 300 600 900 1200 1500 1800
1000
2000
3000
4000
5000
Inte
nsity
(a.u
.)
Wavenumber (cm-1)
Z1-12h
Z2-12h
165 220 500
Spectra of ZrN(FCC+defects)
Fig. 5. Raman spectra of Z1 and Z2 powders milled for 12 h.
powders. Such values compare very well the lattice parameter
of several reported Zr-based phases having FCC structures.
They are for example: Zr2Ni (0.451 nm),[12] Zr2Cu
(0.468 nm),[22] Zr3Al (0.438 nm, JCPDS 49-1316), ZrN
(0.458 nm, JCPDS 65-9413) and ZrO (0.462 nm, JCPDS
22-1058). In addition, FCC phases were also obtained after
milling of more complex Zr-based chemistry.[14,15,23]
A question then rises as to the exact nature of the FCC
phases that formed in these more complex alloys, as well as to
the small deviation of the lattice constant (< 3%) calculated
between the different reported FCC phases. To gain further
insights into the nature of the milled powders, Raman
spectroscopy was used. Raman spectroscopy is a technique
that can be sensitive to the formation of oxide and nitride but
not metallic compounds. Figure 5 shows the Raman spectra
for the Z1 and Z2 powders after 12 h of milling. Three
dominating peaks are found around 165, 220, and 500 cm�1.
These Raman spectra can be compared to those obtained by
Moura et al., who systemically investigated the ZrN and
ZrOxNy compounds having FCC structures.[24] They are very
similar to the Raman spectrum corresponding to the FCC ZrN
phase containing a little oxygen.[24] Also, according to their
results, the shifts of the peak positions towards the high
frequency region that we observed in our spectra can
correspond to structural defects.[24]
According to our Raman analysis, it can be suggested that
the contamination of nitrogen plays an important role in the
stabilization of the FCC phase during milling. Zr is a very
reactivemetal and can form easily interstitial compoundswith
oxygen, carbon or nitrogen. It is interesting to notice here that
the stabilization of a TiN-type of phase having an FCC
structure was also reported in TiAl-based alloys.[10] Guo et al.
reported that their powder milled for 30 h contained as much
as 32.6 at-% N.[25] The amount of N was still very high when
themillingwas done in the controlled argon atmosphere glove
box. Also, Goodwin and Ward-Close reported 6.8 to 7.8 wt-%
N when their vials were loaded in a glove box containing
99.995% pure argon.[26] Thus, it can be suggested that the FCC
ADVANCED ENGINEERING MATERIALS 2011, 13, No. 7 � 2011 WILEY-VCH Verl
phase that has formed after milling in both the Z1 and Z2
alloys has been stabilized by the presence of N. Further work
is now underway to completely clarify this issue and
quantitatively determine the exact amount of N in the milled
powders.
Conclusions
The structure changes of Zr65Al7.5Ni10Cu17.5 (Z1) and
Zr58Al16Ni11Cu15 (Z2) bulk metallic glasses under annealing
and ball-milling were studied. The thermal crystallization
processes of the two alloys were different. The tetragonal
Zr2Cu and hexagonal Zr6Al2Ni were the stable end-products
for the Z1 alloy. Comparatively, the Z2 alloy contained the
hexagonal Zr2Al, big cubic Zr2Ni and some a-Zr solid solution
after complete crystallization.
Interestingly, while the thermal crystallization products as
well as the sequences of phase changes involved during
milling were different for the two alloys, the same type of
stable phase was obtained after sufficient mechanical milling
in both cases. It was a FCC phase with lattice constant of the
FCC phase being 0.453 and 0.456 nm for the milled Z1 and Z2
powders, respectively. Raman spectroscopy results suggest
that the stabilization of this phase is related to some nitrogen
contamination coupled with the presence of structural defects
in the powders.
Received: November 16, 2010
Final Version: April 6, 2011
Published online: June 3, 2011
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