UDK 544.022.51:669.017.13:621.762	ISSN 1580-2949
Original scientific article/Izvirni znanstveni članek	MTAEC9, 49(3)423(2015)
PROPERTIES AND STRUCTURE OF Cu-Ti-Zr-Ni AMORPHOUS POWDERS PREPARED BY MECHANICAL ALLOYING
LASTNOSTI IN STRUKTURA AMORFNIH PRAHOV Cu-Ti-Zr-Ni, PRIPRAVLJENIH Z MEHANSKIM LEGIRANJEM
Aleksandra Guwer, Ryszard Nowosielski, Anna Lebuda
Silesian University of Technology, Faculty of Mechanical Engineering, Institute of Engineering Materials and Biomaterials, Konarskiego Street
18A, 44-100 Gliwice, Poland aleksandra.guwer@polsl.pl
Prejem rokopisa - received: 2014-07-26; sprejem za objavo - accepted for publication: 2014-09-02
doi:10.17222/mit.2014.119
The method of fabrication, an investigation and a comparison of the structure, size and shape of grains of a quaternary Cu-Ti-Zr-Ni alloy were investigated. Cu-based amorphous alloys have a high strength, ductility, fracture toughness, fatigue strength and excellent corrosion resistance in solutions such as H2SO4, NaOH, NaCl and HNO3. Samples of powders were prepared by mechanical alloying in a high-energy ball mill SPEX 8000. To obtain the amorphous structure of the Cu47Ti34Zr11Ni8 powder, various milling times were used. Finally, four samples for testing were obtained with pure Cu, Ti, Ni, Zr (99.99 %). The structure of the Cu47Ti34Zr11Ni8 powders was examined by X-ray diffraction (XRD) after 7 h, 8 h, 9 h and 10 h of milling time. The chemical composition, particle size and shape of the prepared powders were investigated by scanning electron microscopy (SEM). The microhardness was measured by using a Vickers hardness-testing machine with automatic track measurement. The fully amorphous powders were obtained after 10 h of milling. The prolonged time of milling resulted in an increased particle size and a changed shape of the powders. The highest microhardness was obtained for the amorphous samples. In further work the studied amorphous powders will be consolidated using spark-plasma sintering, which is an innovative method for the production of amorphous alloys.
Keywords: mechanical alloying, Cu-based amorphous alloys, SEM, XRD, microhardness
Preiskovan je bil način izdelave, preiskava in primerjava strukture, velikosti in oblike zrn kvaternerne zlitine Cu-Ti-Zr-Ni. Amorfne zlitine na osnovi Cu imajo visoko trdnost, duktilnost, lomno žilavost, odpornost proti utrujanju in odlično odpornost proti koroziji v raztopinah H2SO4, NaOH, NaCl in HNO3. Vzorci prahov so bili pripravljeni z mehanskim legiranjem v visokoenergijskem krogličnem mlinu SPEX 8000. Za zagotovitev amorfne strukture prahu Cu47Ti34Zr11Ni8 so bili uporabljeni različni časi mletja. Iz čistega Cu, Ti, Ni, Zr (99,99 %) so bili izdelani štirje preizkušanci. Struktura prahov Cu47Ti34Zr11Ni8 je bila pregledana z rentgensko difrakcijo (XRD) po 7 h, 8 h, 9 h in 10 h mletja. Kemijska sestava, velikost in oblika delcev pripravljenih prahov je bila preiskana z vrstičnim elektronskim mikroskopom (SEM). Mikrotrdota je bila izmerjena z avtomatsko napravo za merjenje trdote po Vickersu. Popolnoma amorfni prahovi so bili dobljeni po 10 h mletja. Pri podaljšanju časa mletja je narasla velikost in spremenila se je oblika delcev prahov. Najvišjo mikrotrdoto so imeli amorfni vzorci. V nadaljevanju dela bodo preiskovani amorfni prahovi, sintrani z uporabo iskrilnega plazemskega sintranja, ki je inovativna metoda za izdelavo amorfnih zlitin.
Ključne besede: mehansko legiranje, amorfne zlitine na osnovi Cu, SEM, XRD, mikrotrdota
1 INTRODUCTION	subjected to multiple cold welding, cracking and
re-welding. With rapid cold deformation the specimen's
Bulk amorphous metallic alloys exhibit many supe-	temperature is increased because of the transformation of
rior properties compared to crystalline alloys. Lately, it	^he mechanical work into heat. The MA process allows
has been noted that rods and ribbons of Cu-based alloys	^he alloying of elements that are difficult or impossible
demonstrate a high tensile strength, fatigue strength,	to combine by conventional casting methods. The pro-fracture strength, ductility, relatively low cost of products of MA are advanced materials, including equili-
ducts, a good glass-forming ability and excellent corrosion resistance in solutions such as H2SO4, NaOH, NaCl	brium' non-equilibrium (amorphous, quasicrystals, nano-and HNO 1-5	crystalline) and composite materials. The final material
The n^ost. frequently encountered methods for the	properties depend on the MA process parameters (kind
preparation of amorphous materials are casting methods.	of mill' size and amount of grinding media' temperature
An alternative process to prepare amorphous alloys is	and atmosphere of milling, ratio of grinding media mass
mechanical alloying combined with the method of	to powder mass, etc.)8,9.
spark-plasma sintering. Using this production method	In this paper we report on the fabrication and an
Cu-based amorphous alloys were produced by, e.g., Kim	investigation of Cu47Ti34Zr11Ni8 alloy powder prepared
et al.6 and Chu et al.7	by mechanical alloying. The purpose of the present work
Mechanical alloying (MA) is defined as a high-	was to obtain amorphous powders that could be sintered
energy milling process during which the particles are	in the future.
2 EXPERIMENTAL 2.1 Materials
Four samples with the composition Cu47Ti34Zr11Ni8 were prepared using elemental powders of copper, titanium, zirconium and nickel (99.99 % purity, < 325 mesh). Each sample was prepared with 8 g of properly weighed powders. The masses and melting points10 of the individual elements (Cu, Ti, Zr, Ni) are shown in Table 1. The powder composition was weighed on an analytical high-precision balance AS/X.
Table 1: Characteristics of used elements (Cu, Ti, Zr, Ni) Tabela 1: Zna~ilnosti uporabljenih elementov (Cu, Ti, Zr, Ni)
Powder	x/%	m(8 g)/g	TJ°C
Copper	47	3.9252	1085 10
Titanium	34	2.1389	1670 10
Zirconium	11	1.3187	1854 10
Nickel	8	0.6170	1453 10
x/% - amount fraction x/% - množinski delež
2.2 Research methodology
Four different milling times were applied: (7, 8, 9, 10) h. The process of mechanical alloying was interrupted every 30 min for 30 min to lower the temperature of the crucible and the powders. Cr steel balls of 13 mm diameter were used and the ball-to-powder weight ratio was 5:1. The powder mixture and the Cr steel balls were placed in an austenitic crucible in an argon atmosphere inside a glove bag, as shown in Figure 1.
Figure 1: Schematic illustration of the cylindrical steel vessel placed in the holder inside the SPEX 8000 mill
Slika 1: Shematski prikaz cilindri~ne jeklene posode, postavljene v mlin SPEX 8000
A high-energy ball mill SPEX 8000 CertiPrep Mixer/ Mill "shaker" type was used, which generated vibrations of the balls and the powder inside the container11,12.
An X-ray diffractometer X'Pert Pro Panalytical and radiation (A Co-Ka) of 0.178897 nm were used to study the structure of the obtained powders. The data of the diffraction lines were recorded using the "step-scanning" method in the 20 range from 30 ° to 70 ° and with a 0.013 ° step. The time of the step was 40 s and the scanning speed was 0.084 ° s-1.
The particles size and shape of the Cu47Ti34Zr11Ni8 powders were assessed using the microscope SEM SUPRA 25 ZEISS with a magnification up to 500-times
The chemical compositions of the samples were measured with energy-dispersive X-ray spectroscopy (EDS) with an EDS analyzer as part of the SEM. The values of the characteristic radiation energy allow a qualitative analysis in the test sample, and the intensity (peaks height) allows for a quantitative analysis.
The microhardnesses of the particles were measured by the Vickers tester with automatic track measurement using image analysis FUTURETECH FM-ARS 9000. The microhardness measurements were made under a load of 0.97 N. In each of the prepared samples, seven particles were tested.
3 RESULTS AND DISCUSSION
3.1	XRD analysis
Figure 2 demonstrates the XRD patterns of the Cu47Ti34Zr11Ni8 powders after different milling times (7 h, 8 h, 9 h, 10 h). After 7 h of mechanical alloying there is no significant change in the position of the diffraction peaks and the slightly diminished intensity of those peaks is observed. After 8 h and 9 h of processing the broadening and intensity reduction of the crystalline diffraction lines were observed and a maximum broad diffuse diffraction started to form, and after 10 h of milling the samples were amorphous. The diffraction pattern shows a single broad diffraction halo with the 20 range of 43-54 ° from the amorphous phase without simple peaks (Figure 2d).
The same alloy was tested by Shengzhong et al.13 The team of researchers used different process parameters for a QM-1SP planetary high-energy ball miller and pure elemental powders, i.e., 99.9 %. The process of mechanical alloying was interrupted every hour for 30 min. They obtained an amorphous phase after 8 h, 9 h, 10 h and 12.5 h of milling time.
The amorphous structure of the Cu50Ti50 powders was obtained after 8 h of mechanical alloying by using identical parameters to those indicated in this article14.
3.2	Microstructure
Figure 3 shows the powders after: a) 7 h, b) 8 h, c) 9 h, d) 10 h of milling time. The initial size of the powders
Figure 2: X-ray diffraction pattern of Cu47Ti34Zr11Ni8 powders after: a) 7 h, b) 8 h, c) 9 h, d) 10 h of mechanical alloying Slika 2: Posnetek rentgenske difrakcije prahov Cu47Ti34Zr11Ni8 po: a) 7 h, b) 8 h, c) 9 h, d) 10 h mehanskega legiranja
Figure 3: Shape and size of Cu47Ti34Zr11Ni8 powder after: a) 7 h, b) 8 h, c) 9 h, d) 10 h of mechanical alloying, (SEM, magnifications 500-times)
Slika 3: Oblika in velikost prahu Cu47Ti34Zr11Ni8 po: a) 7 h, b) 8 h, c) 9 h, d) 10 h mehanskega legiranja, (SEM, pove~ava 500-kratna)
was about 44 ^m. As a result of the mechanical synthesis the powders changed their size and shape. The largest particles were found after 7 h of milling time (238 ^m x 143 ^m). During this milling time, the particles were stuck to large agglomerates, then after 8 h of milling time the particles disintegrated, because after 8 h of milling the particles were crushed to a smaller average of 47 ^m x 25 ^m. By using longer milling times (9 h, 10 h), the particles size was increased and their shape became more homogeneous and spherical. However, their size was below that after 7 h of milling time. The average size of the particles after the milling time is listed in Table 2.
Table 2: Average particle size (^m) of the MA powders Tabela 2: Povpre~na velikost delcev (um) MA-prahov
Time of mechanical alloying (h)
Average particle size (um)
238 x 143
47 x 25
63 x 41
10
87 x 62
Figure 4: a) EDS spectrum with marked EDS X-ray lines and b) SEM micrographs of Cu47Ti34Zr11Ni8 powders after 10 h of mechanical alloying with 30 min interruption
Slika 4: a) EDS-spekter z ozna~enimi EDS rentgenskimi linijami in b) SEM-posnetek prahov Cu47Ti34Zr11Ni8 po 10 h mehanskega legiranja s prekinitvijo 30 min
Figure 4 depicts the XRD spectrum and the analyzed area of the Cu47Ti34Zr11Ni8 powder after 10 h of milling. Energy-dispersive X-ray analysis (EDS) shows the X-ray lines of copper, titanium, zirconium and nickel elements in the sample. The amount of Cu, Zr, Ni and Ti depends on the time of milling. Table 3 presents the detailed results of the chemical analysis for every sample. The particles contain the basic components (Ti, Cu, Zr and Ni). The initial atomic percentage of Cu equals 47 %, for Ti it is 34 %, for Zr it is 11 % and for Ni it is 8 %. The results indicate that the obtained powder particles after the alloying process have a very similar atomic composition compared to the initial weighed composition. The chemical composition of the milled powders confirms the existence of the metals identified from the XRD spectra.
Table 3: Chemical composition of the powders surface Tabela 3: Kemijska analiza povr{ine prahov
Samples	Cu47Ti34Zr11Ni8 (7 h)	Cu47Ti34Zr11Ni8 (8 h)	Cu47Ti34Zr11Ni8 (9 h)	Cu47Ti34Zr11Ni8 (10 h)
The average microhardness (HV)	428	496	545	553
Milling Time (h)
10
Element
Cu
Ti
Zr
Ti
Zr
Ni
Cu
Ti
Zr
Ni
Cu
Ti
Zr
Ni
Cu
Ti
Zr
Ni
x/%
47
34
11
32.89
09.23
07.27
49..58
33.02
9.82
7..58
8.73
33.43
10.02
7.82
51.50
30.94
08.98
08.57
3.3 Microhardness
The microhardness was measured on pressed powders with ten indentations for each sample and are shown in Figure 5. The deduced average microhardness after milling times (7 h, 8 h, 9 h, 10 h) is shown in Table 4. The highest average microhardness was obtained for the powders after 10 h of milling time (553 HV), i.e., for the powders with the fully amorphous structure. The average microhardness increases with the milling time. The difference between the lowest 334 HV, after 7 h of
Figure 5: Powders microhardness after different milling times Slika 5: Mikrotrdote prahov po razli~nih ~asih mletja
milling, and the highest (518 HV), after 10 h of milling, was 184 HV. This indicates the great heterogeneity of the obtained particles. The average microhardness of the amorphous powder Cu47Ti34Zr11Ni8 (553 HV) is higher than that of the amorphous powders Cu50Ti50(542 HV).14
4 CONCLUSIONS
The result of the tests and the examination of the Cu47Ti34Zr11Ni8 powders lead to the following conclusions:
•	It is possible to obtain an amorphous structure for a four-component alloy Cu47Ti34Zr11Ni8 by using mechanical synthesis in a SPEX 8000 mill.
•	An amorphous structure was obtained for the 10 h milling-time sample.
•	The largest particles are obtained after 7 h milling and the smallest after 8 h milling. The largest shape and the best size regularity were obtained for the amorphous powders.
•	The presence of the initial elements Cu, Ti, Zr, Ni in the milled particles was confirmed. The content of elements in the milled powders corresponds to the initial weighed composition.
•	The average microhardness value increases with the milling time and the highest hardness is achieved in the amorphous sample (553 HV).
Acknowledgments
The work was partially supported by the National Science Centre under research Project No.: 2012/07/N/ ST8/03437.
Table 4: Average microhardness after different mechanical-alloying times
Tabela 4: Spreminjanje povpre~ne mikrotrdote pri razli~nem trajanju mehanskega legiranja
Samples
Cu47Ti34Zr11Ni8 (7 h)
Cu47Ti34Zr11Ni8 (8 h)
Cu47Ti34Zr11Ni8 (9 h)
Cu47Ti34Zr11Ni8 (10 h)
The average microhardness (HV)
428
496
545
553
0
7
8
9
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