Journal of Non-Crystalline Solids · Letter to the editor Microstructure and fracture surface of the two-component melt-spun amorphous/amorphous composite Mirosława Różyckaa, Krzysztof

Journal of Non-Crystalline Solids 412 (2015) 49–52

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LETTER TO THE EDITOR

Letter to the editor

Microstructure and fracture surface of the two-component melt-spunamorphous/amorphous composite

Mirosława Różycka a, Krzysztof Ziewiec a,⁎, Artur Błachowski b, Krzysztof Ruebenbauer b, Krystian Prusik c

a Institute of Technology, Faculty of Mathematics, Physics and Technical Science, Pedagogical University of Cracow, ul. Podchorążych 2, PL-30-084 Kraków, Polandb Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University, ul. Podchorążych 2, PL-30-084 Kraków, Polandc Faculty of Computer Science and Materials Science, University of Silesia, ul. 75 Pułku Piechoty 1A, PL-41-500 Chorzów, Poland

⁎ Corresponding author.E-mail address: [email protected] (K. Ziewiec).

http://dx.doi.org/10.1016/j.jnoncrysol.2015.01.0070022-3093/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t

Article history:Received 27 October 2014Received in revised form 10 January 2015Accepted 13 January 2015Available online xxxx

Keywords:Metallic glasses;Mössbauer spectroscopy;Scanning electron microscopy (SEM);Transmission electron microscopy (TEM)

The purpose of the research is to identify the differences in the final microstructure, fracture and short rangeorder of the Ni55Fe20Cu5P10B10 alloy melt-spun after the ejection of the homogeneous liquid from the standardsingle chamber crucible and from the crucible with double chamber as the flux of two liquids i.e.: Ni–Fe–B andNi–Cu–P. The preparation of the alloys involved remelting Ni55Fe20Cu5P10B10, Ni40Fe40B20 and Ni70Cu10P20compositions in the arc furnace under titanium gettered argon atmosphere starting from pure metals99.95 wt.% Ni, 99.95 wt.% Fe, 99.95 wt.% Cu and Ni–B, Fe–B, Ni–P, and Cu–P master alloys. The Ni55Fe20Cu5P10B10melt-spun ribbonswere obtained bymeans of twomethods: thefirst onewasmelt-spun from a traditional singlechamber crucible while the second onewas produced using two componentmelt spinning (TCMS) performed inthe protective helium atmosphere. The research was conducted by using transmission electron microscopy(TEM), scanning electron microscopy (SEM), and Mössbauer spectroscopy. The results of the microstructureexamination show that the TCMS alloy is amorphous/amorphous composite and boundaries between the stripesof the differentiated chemical composition coincide with the features of the ductile fracture. The Mössbauerspectroscopy of the alloys confirms that the special feature of the TCMS alloy is that it is composed of the regionswith differentiated chemical composition.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

Metallic alloys with amorphous matrix are very promising forpractical applications due to their excellent properties useful inmagnetic,electrical and structural applications [1–3]. However, the use of thesema-terials is still restricted due to their brittleness, high costs of productionand limited possibility of formation amorphous/amorphous and amor-phous/crystalline composites. These limitations can be removed byusing a low-cost technology in the formation of amorphous/amorphousand amorphous/crystalline compositeswith the controllablemorphologythat enhances the ductility and is based on the use of low-cost precursors[4]. Amorphous/crystalline composites are obtained for systems withliquid miscibility [1,5–7]. An interesting group of metallic glasses isprepared based on liquid immiscible alloys in such systems as La–Zr–Al–Cu–Ni [8], Nd–Zr–Al–Co [9], and Ni–Nb–Y [10]. However, for thesecases [8–10] the manufacturing of the two-phase metallic glasses is re-stricted to the alloys with a special composition. Furthermore, themicrostructure of these alloys presents a large scatter of particle sizesdue to liquid phase separation. The variation of themelt spinningmethodwith the two chamber crucible (TCMS) proposed recently [11,12]

overcomes these limitations. This method enables low-cost productionof an amorphous/amorphous compositewith heterogeneousmicrostruc-ture of the “wood-like” appearance from two glass forming melts. Thepurpose of this research is to show the interesting features of theNi55Fe20Cu5P10B10 TCMS composite.

2. Experimental

The Ni40Fe40B20, Ni70Cu10P20 and Ni55Fe20Cu5P10B10 alloys wereprepared starting from pure elements: 99.95 wt.% Ni, 99.95 wt.% Fe,99.95 wt.% Cu, Ni–P, Cu–P, Ni–B, and Fe–Bmaster alloys. The precursorswere arc-melted under argon Ti gettered atmosphere. Then the alloyswere melt-spun in helium atmosphere at 40 m/s and ejection pressureof 150 kPa. The crucible orifice diameter was 1.2mm. The ribbons of theNi55Fe20Cu5P10B10 nominal composition were obtained by ejection intwo ways. The first one was obtained by two component melt-spinning (TCMS) of the Ni40Fe40B20 and Ni70Cu10P20 liquid alloys(Fig. 1). The other alloy Ni55Fe20Cu5P10B10 was melt-spun from asingle-chamber. The microstructure and phase analysis of the TCMSsample was investigated using JEOL 300 kV transmission electronmicroscope (TEM). Cross-section of the Ni55Fe20Cu5P10B10 TCMS andfractures of the TCMS ribbon aswell as Ni55Fe20Cu5P10B10 ribbon ejectedfrom single chamber crucible after tensile test performed at strain rate 1

Fig. 1. The diagram showing TCMS technique [14].

Fig. 3. a) Wood-like appearance of the TCMS Ni55Fe20Cu5P10B10 microstructure;b) swirling of the fluxes; c) EDS line scan of the area form the dotted rectangle of b.

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mm/min were observed by means of scanning electron microscopewith EDS JEOL 6610. Mössbauer transmission spectra were collectedusing the RENON MsAa-3 spectrometer equipped with the LNDKr-filled proportional detector. The interferometer based on He–Nelaser was used for the calibration of the velocity scale. A commercial57Co(Rh) source kept at room temperature was applied for 14.41-keVresonant transition in 57Fe. Processing of the Mössbauer data wasperformed using the Mosgraf-2009 software.

3. Results and discussion

TEMmicrostructure of the TCMSNi55Fe20Cu5P10B10 alloy is presentedin Fig. 2a. The microstructure of this sample forms the darker bandsmarked as “A” and lighter bandsmarked as “B” (Fig. 2a). Electron diffrac-tion pattern presented in Fig. 2b fromboth areas “A” and areas “B” showsbroad diffusive rings. This proves that the electron beam is scattered onthe amorphous structure. These diffusive rings are located in the similar

Fig. 2. TEM micrograph for the TCMS Ni55Fe20Cu5P10B10 ribbon; a) TEM image with the darker areas marked as “A” and the brighter areas marked as “B”; b) electron diffraction patternfrom area “A”; c) electron diffraction pattern from area “B”.

Fig. 4. SEM images of the fractures after tensile breaking in amorphous Ni55Fe20Cu5P10B10 alloys obtained by melt-spinning using; a) single chamber crucible; b) two chamber crucible(TCMS); c–f) EDS maps showing the distribution of Ni, Fe, Cu and P for the SEM image from b); dotted lines represent coincidence between fracture lines and the boundaries betweenareas with different chemical compositions.

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position which corresponds to the range of values between 1.9 Å and2.3 Å. These distances are close to the values obtained for glassy Ni–P[13] and Fe–P [14], i.e. d = 2.02 Å and d = 1.97 Å, respectively.

Fig. 5. 57Fe Mössbauer spectra for the Ni55Fe20Cu5P10B10 and TCMS Ni55Fe20Cu5P10B10

amorphous alloys.

Differentiation of contrast between areas “A” and “B” observed in themicrostructure of the TCMS alloy, may be due to the content of thespecies having different atomic numbers. Thus, the “A” areas are darkerbecause they contain more Ni (Z = 28) and Cu (Z = 29) and “B” areasare enriched in Ni (Z = 28) and Fe (Z = 26).

SEM micrographs of the TCMS Ni55Fe20Cu5P10B10 alloy show thelamellar morphology that has a “wood-like” appearance consisting ofthe brighter and darker bands (Fig. 3). EDS line scan done across thevortex shown in Fig. 3c shows that bands have differentiated chemicalcomposition. These areas are essentially extended along the meltspinning direction MSD. There are also frozen areas of vortices. Thevortex presented in Fig. 3c is Fe-rich and its environment is enrichedin Ni, Cu and P. The EDS line scan indicates that the bright areas arerich in Ni, Cu and P, and the dark areas are rich in Fe. The analysis of

Table 1The Mössbauer parameters for the Ni55Fe20Cu5P10B10 and TCMS Ni55Fe20Cu5P10B10

amorphous alloys. The symbol A stands for the relative contribution of the given iron siteto thewhole spectrum, IS denotes the isomer shift of the given sub-spectrum versus roomtemperature α-Fe, QS means the absolute value of the quadrupole splitting, while thesymbol bBN stands for the average magnetic hyperfine field.

Sample A (%) IS (mm/s) QS (mm/s) bBN (T)

Ni55Fe20Cu5P10B10 98 0.18 0.01 12.12 0.45 0.58 –

TCMS Ni55Fe20Cu5P10B10 89 0.14 0.03 21.011 0.17 0.59 –

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boron was not registered, but it is expected that the dark areas are alsoenriched in B. Probable explanation for the formation of a suchmicrostructure is that the fluxes of Ni–Fe–B and Ni–Cu–P liquids werepartially mixed during the passing through the hole in the crucible,however the rapid cooling during the contact of the alloy with therotating copper roller prevented the extensive diffusion of the speciesand homogenization of the alloy was not possible. Comparison ofthese observations (Fig. 3) with the TEM results shows that thesebands have glassy microstructure and the TCMS alloy is an amor-phous/amorphous composite.

The fracture of the Ni55Fe20Cu5P10B10 ribbon melt-spun afterejection from the single-chamber crucible is shown in Fig. 4a, andfracture of the TCMS Ni55Fe20Cu5P10B10 alloy with its EDS mapping ispresented in Fig. 4b–f, respectively.

The fracture presented in Fig. 4a has a smooth appearance typical fora brittle glassy alloys, which is a result of intense localization of plasticflow within a single dominating shear band which is consistent withthe observations of Spaepen [15]. According to these findings, thedeformation of metallic glasses at low temperatures and high stressesis extremely inhomogeneous and plastic deformation is highly localizedin thin shear bands. On the other hand, the fracture of the TCMSNi55Fe20Cu5P10B10 (Fig. 4b) presents more developed surface than inthe Ni55Fe20Cu5P10B10 alloy produced by using traditional singlechamber crucible (Fig. 4a). The fracture surface of the TCMSNi55Fe20Cu5P10B10 forms a ductile vein-like pattern (Fig. 4b). EDSmapping (Fig. 4c–f) reveals that there are strips of the differentiatedchemical composition corresponding to the regions enriched withNi–Fe–B and Ni–Cu–P formed during rapid freezing of the two differentalloys. Furthermore, the segments of the ductile fracture coincide withthe boundaries between these Ni–Fe–B and Ni–Cu–P strips (markedwith dotted lines) Fig. 4c–f. The observation that the diverse composi-tion of the Ni–Fe–B and Ni–Cu–P strips influenced fracture formationin the TCMS Ni55Fe20Cu5P10B10 alloy is in agreement with findings ofConcustell et al. [16] where the Ni–Nb–Y amorphous/amorphous com-posite microstructure enabled the formation of multiple shear bands.The amelioration of ductility is associated with the precipitation of asecond phase in the amorphous matrix. This influences the formationand paths of the shear-bands due to their disruption [16,17].

Mössbauer spectra are presented in Fig. 5, while the essential resultsare given in Table 1. The upper spectrum corresponds to amorphousNi55Fe20Cu5P10B10 alloy ejected from the single chamber crucible. Thedata indicate that there is a definitemagnetic order of the ironmagneticmoments at room temperature and the observable average hyperfinefield in comparison to the analogous Ni55Fe20Cu5P20 alloy [14]. On theother hand, the isomer shift is smaller. This indicates a higher electrondensity on iron nuclei in Ni55Fe20Cu5P10B10 than in Ni55Fe20Cu5P20.The replacement of phosphorus by boron maintains amorphous stateand enhances magnetic ordering temperature. Some traces (2%) ofiron phosphide are observed. The lower spectrum of Fig. 5 belongs tothe amorphous TCMSNi55Fe20Cu5P10B10 alloy obtained by simultaneousejection of the Ni40Fe40B20 and Ni70Cu10P20 alloys. The spectrum iscomposed of two components. Dominant component (89%) can beattributed to the Ni–Fe–B amorphous phase with isomer shift IS =0.12 mm/s, quadrupole splitting QS = 0.02 mm/s and hyperfine fieldbBN = 23 T. Slight reduction of the hyperfine field and increase of theisomer shift in comparison to these values are an indication of the trans-fer of some elements from Ni70Cu10P20 alloy — mainly phosphorus andcopper. The minor non-magnetic component (11%) is similar to the

spectrum of iron phosphides. Therefore, probable explanation of thefact is that some amount of iron migrated from Ni40Fe40B20 toNi70Cu10P20. Hence, a composite alloy contains only about 11% of homo-geneous glassy solution of Ni, Fe, Cu, P and B.

4. Conclusions

1. The results of TEM observations and electron diffraction patternsconfirm that the TCMS Ni55Fe20Cu5P10B10 is amorphous and itconsists of stripes of differentiated chemical composition, whereasSEM observations and EDS analysis show that these stripescorrespond to Ni–Cu–P and Ni–Fe–B areas forming microstructurewith the wood-like appearance.

2. The unique microstructure of the TCMS alloy influences the forma-tion of the ductile fracture that is related to the arrangement of theamorphous stripes with the differentiated chemical composition.While the traditionally melt-spun Ni55Fe20Cu5P10B10 alloy presentsbrittle fracture, the special feature of the fracture found in theTCMS Ni55Fe20Cu5P10B10 alloy is ductile appearance of the fracture,where ductile segments of the fracture coincide with the boundariesbetween the Ni–Cu–P and Ni–Fe–B stripes.

3. The Mössbauer study confirms that 89% of the iron sites whichcorrespond to the Ni–Fe–B stripes and 11% of iron sites in the TCMSNi55Fe20Cu5P10B10 composite alloy can be attributed to the regionsthat are formed by mixing and homogenization of the two Ni–Fe–Band Ni–Cu–P liquids which results in the formation of the non-magnetic constituent of the microstructure containing all alloyingspecies i.e. Ni, Fe, Cu, P and B.

Acknowledgments

The work described in this paper was supported by a grant from theNational Science Centre (NCN) (project number 2012/05/B/ST8/02644).

Infrastructure of the laboratorywas co-financed by the European Re-gional Development Fund under the Infrastructure and EnvironmentProgramme.

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