UDK 544.23:537.622	ISSN 1580-2949
Original scientific article/Izvirni znanstveni članek	MTAEC9, 49(3)409(2015)
STRUCTURAL, THERMAL AND MAGNETIC PROPERTIES OF Fe-Co-Ni-B-Si-Nb BULK AMORPHOUS ALLOY
STRUKTURNE, TERMIČNE IN MAGNETNE LASTNOSTI MASIVNE AMORFNE ZLITINE Fe-Co-Ni-B-Si-Nb
Sabina Lesz1, Marcin Nabialek2, Ryszard Nowosielski1
1Silesian University of Technology, Institute of Engineering Materials and Biomaterials, Konarskiego Street 18a, 44-100 Gliwice, Poland 2Institute of Physics, Czestochowa University of Technology, Av. Armii Krajowej 19, 42-200 Czestochowa, Poland
sabina.lesz@polsl.pl
Prejem rokopisa - received: 2014-07-15; sprejem za objavo - accepted for publication: 2014-09-05
doi:10.17222/mit.2014.108
In the present paper the structure, thermal stability and magnetic properties of the Fe43Co22Ni7B19Si5Nb4 bulk amorphous alloy were investigated. The investigated alloy was cast as rods with three different diameters. The thermal stability associated with the glass transition temperature (Jg), crystallization temperature (Tx) and supercooled-liquid region (ATx = Tx - Tg) was examined with differential scanning calorimetry (DSC). The Curie temperature of the investigated glassy rods was determined from the results obtained with the DSC method. The magnetic properties and microstructure of the rods were examined with the vibrating-sample magnetometer (VSM) and X-ray diffraction (XRD) methods, respectively. The crystallization temperature (Tx) and the glass transition temperature (Tg) as well as the parameter of ATx = Tx - Tg as the criterion of the glass-forming ability (GFA) of the investigated alloy were determined. The investigated alloys have good soft-magnetic properties. Keywords: bulk amorphous alloy, structure, thermal and magnetic properties
Predstavljena je preiskava strukture, toplotne stabilnosti in magnetnih lastnosti masivne amorfne zlitine Fe43Co22Ni7B19Si5Nb4. Preiskovana zlitina je bila ulita kot palice s tremi različnimi premeri. Toplotna stabilnost, povezana s prehodom v steklasto stanje (Tg), temperaturo kristalizacije (Tx) in s podhlajenim področjem taline (ATx = Tx - Tg), je bila preiskovana z diferenčno vrstično kalorimetrijo (DSC). Curiejeva temperatura preiskovanih steklastih palic je bila določena iz rezultatov, dobljenih pri DSC-metodi. Magnetne lastnosti in mikrostruktura palic so bile preiskane z magnetometrom z vibrirajočimi vzorci (VSM) in z metodo rentgenske difrakcije (XRD). Določeni so bili temperatura kristalizacije (Tx) in temperatura prehoda v steklasto stanje (Tg) ter tudi parameter ATx = Tx - Tg kot merilo sposobnosti tvorbe steklastega stanja (GFA) preiskovanih zlitin. Preiskovane zlitine imajo dobre mehkomagnetne lastnosti.
Ključne besede: masivna amorfna zlitina, struktura, termične in magnetne lastnosti
1 INTRODUCTION	casting thickness (> 1 cm) by conventional mould-
ing.
1,2,4-7
A large number of studies on the development of	Among BMGs, the Fe-based BMGs are more
soft-magnetic metallic glasses have been carried out over	attractive for application since they do not exhibit only
the last 20 year"s-.It is.wellreco!ni,zed tha^the l.ow	good properties, such as excellent soft-magnetic proper-
glass-forming ability (GFA) of Fe-based alloys has	ties, a high strength and a good corrosion resistance, but
limited the potential of using them as engineering ma-	1-10
are also cheaper in comparison to the other BMGs.1-10
terials. For this reason extensive efforts have been carried	^ , .
out to improve the GFA of metallic materials and the	For the preparation of a Fe-based BMG, Fe80B20 is
understanding of the mechanism of the effects of various	often used as the starting alloy. Later the Nb metal with a
factors on the formation, crystallization, thermal stability	high melting temperature is added. The additions of
and property of bulk metallic glass (BMG). Bulk	small amounts of Nb to (Fe,Co,Ni)-(B,Si) alloys are
metallic glasses (BMGs) represent a new class of amor-	effective for the increase in the GFA through the increase
phous metallic alloys. BMGs are valuable materials for	in the stability of the supercooled liquid against crystalli-
environmental applications (e.g., solar cells, hydrogen	zation.3 A temperature interval of the supercooled-liquid
production, the systems for retention and purification of	region ATx has been suggested to evaluate the
dangerous pollutants, the nuclear industry, etc.) and for	glass-forming ability (GFA) of bulk amorphous alloys.
industrial applications in different areas (e.g., aerospace,	An addition of amount fraction of Nb 4 % was found to
automotive, electronics, computer, telecommunication	be very effective in improving the GFA of Fe- and
areas, etc.).1-12	Co-based glassy alloys.7
These multi-component metallic alloys can be ob-	As BMGs can be produced by adding four and five
tained at low cooling rates of 1 K/s to 100 K/s, which	elements to the basic ternary alloys, small amounts of the
allow an increase in the time (from milliseconds to minu-	elements such Ni, Co and Si were added. A partial sub-
tes) before the crystallization, enabling a greater critical	stitution of Fe with the other magnetic elements, Ni or
Co, may significantly enhance the GEA and soft-magnetic properties of the Ee-based glass-forming alloys. The metalloid elements of Si and B play a crucial role in the formation of BMGs. They also affect the GEA, the thermal stability, the crystallization and the properties of BMGs. These materials have a strong affinity with the conventional BMG base elements such Ee and rare-earth elements, i.e., they have a large, negative heat of mixing with these base elements. The metalloid elements result in crystallization, degrading the GEA of the BMGs, but, on the other hand, due to a small atomic size of the Si and B atoms, a proper addition can tighten the alloy structure, stabilizing the alloy against crystallization.3
The Ee-Co based glassy alloys exhibit good soft-magnetic properties, i.e., a high saturation magnetization (0.8-1.3 T) and a low coercivity (1-2.5 A/m).3 Magnetic properties of these alloys are dependent on the Ni and Ee contents. A decrease in the coercivity (Hc) with the increasing Co content was found to originate in the reduction of saturation magnetostriction.3 Coercivity Hc is proportional to the ratio of saturation magnetostriction (As) to saturation magnetization (/s), i.e.:8
Hc »AV ^ pd
J.
(1)
and the slope is related to the volume (AV) and density (pd) of internal defects in the glassy structure.8
Due to their unique properties, the Ee-Co based glassy alloys have been commercialized in the following application fields: precision-mould material, precision-imprint material, precision-sensor material, precision-machinery material, surface-coating material, cuttingtool material, shot penning material, fuel-cell separator material and so forth.12,910
In the present paper the structural, thermal and magnetic properties of a Ee-Co-Ni-B-Si-Nb bulk amorphous alloy with a selected chemical composition was investigated.
2 EXPERIMENTAL PROCEDURE
Investigations were carried out on amorphous rods with a composition of [(Eeo.6Coo.3Nio.1)o.75Bo.2Sio.o5]96Nb4. Ee-based master-alloy ingots with a composition of [(Ee0.6Co0.3Ni0.1)0.75B0.2Si0.05]96Nb4 were prepared by induction melting of pure Ee, Co, Ni, Nb and pure B and Si crystals in an argon atmosphere. The Ee43Co22Ni7B19Si5Nb4 alloy composition represents the nominal atomic percentages. The master alloy was melted in a quartz crucible using an induction coil. Rods with (1.5, 2.5 and 3) mm diameters were prepared with the pressure copper-mould casting method.11
The microstructure of the rods was examined with the X-ray diffraction (XRD) method. The X-ray method was performed using a Seifert-EPM XRD 7 diffracto-meter with filtered Co-Ka radiation.
The thermal stability associated with the glass transition temperature (Tg), crystallization temperature (Tx) and supercooled-liquid region (ATx = Tx - Tg) was examined with differential scanning calorimetry (DSC) at a heating rate of 0.1 K/s. The Curie temperature of the investigated glassy rods was determined from the results obtained with the DSC method.
High-field magnetization curves were measured with a vibrating-sample magnetometer (VSM) in a magnetic field up to 2 T. The magnetizing field was parallel to the sample length to minimize the demagnetization effect. The magnetization curves were analyzed using the least-squares method.
3 RESULTS AND DISCUSSION
It was found from the obtained results of the structural studies performed with X-ray diffraction that the diffraction patterns of the surface rods with (1.5, 2.5 and 3.0) mm diameters of the Ee43Co22Ni7B19Si5Nb4 alloy consist of a broad-angle peak, indicating the existence of an amorphous phase (Figure 1).
The DSC curves determined on the Ee43Co22Ni7B19Si5Nb4 rods with the diameters of (1.5, 2.5 and 3) mm in the as-cast state for the studied alloy are shown in Figures 2 to 4, and summarized in Table 1. Table 1 also gives information about the thermal properties of the studied amorphous-alloy rods. The onset crystallization temperatures Tx for the glassy rod samples with the diameters of (1.5, 2.5 and 3) mm are slightly different and equal to (828, 827 and 826) K (Figures 2 to 4), respectively. It is seen that Tx decreases from 828 K to 826 K with an increase in the diameter of the rods. On the basis of an analysis of DSC curves the glass transition temperature Tg and supercooled-liquid region
Figure 1: X-ray diffraction patterns of the bulk amorphous Ee43Co22Ni7B19Si5Nb4 rods
Slika 1: Rentgenogrami masivnih amorfnih palic Ee43Co22Ni7B19Si5Nb4
Figure 2: DSC curve of the Ee43Co22Ni7Bi9Si5Nb4 glassy-alloy rod with a diameter of 1.5 mm
Slika 2: DSC-krivulja palice premera 1,5 mm iz steklaste zlitine Ee43Co22Ni7Bi9Si5Nb4
ATx = Tx - Tg for the glassy rod samples with the diameters of 1.5 mm to 3 mm are determined, too. The value of the supercooled-liquid region is an experimental parameter that determines the glass-forming ability of the tested alloy. The glass transition temperature Tg and supercooled-liquid region ATx for the glassy rod samples with the diameters of (1.5, 2.5 and 3) mm are: Tg = 794 K, ATx = 34 K (Figure 2), Tg = 790 K, ATx = 37 K (Figure 3), Tg = 797 K, ATx = 29 K (Figure 4), respectively. The value of the Curie temperature TC for the Ee43Co22Ni7B19Si5Nb4rods with the diameters of (1.5, 2.5 and 3.0) mm is (652, 650 and 655) K, respectively. Similar values of Tg and TC were obtained in19, where the results are Tg = 813 K and Tc = 643 K for the [(Eeo.6Coo.3Nio.1)o.75Bo.2Sio.o5]96Nb4 alloy in the form of a rod with a diameter of 4 mm.
Figure 4: DSC curve of the Ee43Co22Ni7B19Si5Nb4 glassy-alloy rod with a diameter of 3.o mm
Slika 4: DSC-krivulja palice premera 3,o mm iz steklaste zlitine Ee43Co22Ni7B19Si5Nb4
Table 1: Thermal (Tg - the glass transition temperature, Tx - the crystallization temperature, ATx - the temperature interval of the supercooled-liquid region) and magnetic (TC - the Curie temperature, Ms - the saturation induction) properties of the bulk glassy Ee43Co22Ni7B19Si5Nb4 rods with the diameters of (1.5, 2.5 and 3.o) mm
Tabela 1: Termične (Tg - temperatura prehoda v steklasto stanje, Tx -temperatura kristalizacije, ATx - temperaturni interval področja superpodhlajene taline) in magnetne (TC - Curiejeva temperatura, Mg - nasičenje indukcije) lastnosti masivnih steklastih palic Ee43Co22Ni7B19Si5Nb4 s premeri (1,5, 2,5 in 3,o) mm
Diameter
O/mm
1.5
2.5
3.o
Thermal properties
Tg/K
794
79o
797
Tx/K
828
827
826
ATx/K Tx-Tg
34
37
29
Magnetic properties
TC/K
652
65o
655
Ms/T
1.o7
1.22
1.18
Figure 3: DSC curve of the Ee43Co22Ni7Bi9Si5Nb4 glassy-alloy rod Figure 5: Magnetic hysteresis loops of the bulk amorphous
with a diameter of 2.5 mm
Ee43Co22Ni7B19Si5Nb4 rods
Slika 3: DSC-krivulja palice premera 2,5 mm iz steklaste zlitine Slika 5: Magnetne histerezne zanke masivnih steklastih palic
Ee43Co22Ni7B19Si5Nb4
Ee43Co22Ni7B19Si5Nb4
The saturation induction (Ms) of the studied glassy rods is (1.07, 1.22 and 1.18) T for the samples with the diameters of (1.5, 2.5 and 3) mm, respectively (Figure 5).
The obtained magnetic properties allow us to classify the studied bulk amorphous alloy in the as-cast state as a soft-magnetic material. These excellent magnetic properties lead us to believe that the Fe-based amorphous alloy could be used as a new engineering and functional material intended for the parts of inductive components.
4	CONCLUSIONS
Bulk metallic glass rods with the diameters of (1.5, 2.5 and 3) mm and a composition of Fe43Co22Ni7B19Si5Nb4 were made by pressure copper-mould casting. The glassy rods show good soft-magnetic properties and thermal stability.
A high magnetization of 1.07 T to 1.22 T of the Fe43Co22Ni7B19Si5Nb4 rods leads us to believe that the Fe-based bulk glassy alloy with a Ni addition will be used as a new engineering material for the parts of micro-motors, force sensors and other applications. Moreover, force sensors based on the newly developed amorphous alloys may operate in a high-temperature range. The temperature of the operation of such a sensor is limited mainly by the Curie temperature and the value of TC for the Fe43Co22Ni7Bi9Si5Nb4 alloy is in the range from 650 K to 655 K.
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