Inoue  Akihisa

Kato  Hidemi

Li  Xue

Makino  Akihiro

Yubuta  Kunio

MATERIALS TRANSACTIONS

Li, Xue

Makino, Akihiro

Yubuta, Kunio

Kato, Hidemi

Inoue, Akihisa

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Mechanical Properties of Soft Magnetic (Fe0.76Si0.096B0.084P0.06)100-xCux (x = 0 and 0.1) Bulk Glassy Alloys

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Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Mechanical Properties of Soft Magnetic(Fe0.76Si0.096B0.084P0.06)100-xCux (x = 0 and0.1) Bulk Glassy Alloys著者 Li  Xue, Makino  Akihiro, Yubuta  Kunio, Kato Hidemi, Inoue  Akihisajournal orpublication titleMaterials Transactionsvolume 50number 6page range 1286-1289year 2009URL http://hdl.handle.net/10097/52255Mechanical Properties of Soft Magnetic (Fe0:76Si0:096B0:084P0:06)100xCux(x ¼ 0 and 0.1) Bulk Glassy AlloysXue Li1;*, Akihiro Makino2, Kunio Yubuta2, Hidemi Kato2 and Akihisa Inoue31Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan2Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan3Tohoku University, Sendai 980-8577, JapanFe-based bulk glassy alloys (BGAs) are known to have great potential for structural applications because of their high strength andrelatively low material cost. However, their brittle nature hinders further applications. We have recently developed a new ductile(Fe0:76Si0:096B0:084P0:06)99:9Cu0:1 BGA with a strength of 3.3GPa and a large plastic strain of about 4% in compression. A well developed veinpattern on the fracture surface and highly-dense multiple shear bands on the surface of the specimen were observed. A large number of -Fe likeclusters (<10 nm) are found to disperse in the matrix glass. These clusters possibly act as nucleation sites for the -Fe nanocrystallization inslipping shear bands dynamically. This results in development of the multiple shear bands causing highly improved plasticity in the(Fe0:76Si0:096B0:084P0:06)99:9Cu0:1 BGA. [doi:10.2320/matertrans.ME200833](Received December 22, 2008; Accepted March 26, 2009; Published May 20, 2009)Keywords: iron-based bulk glassy alloy, plasticity, multiple shear bands, -iron1. IntroductionFe-based bulk glassy alloys (BGAs) with high strength,magnetic softness and relatively low material cost offer agreat potential for a wide variety of applications.1–6) How-ever, the Fe-based BGAs which have been developed to dateare lack in fracture toughness so that almost no plastic strainis obtained under uniaxial tensile or compressive deforma-tions at room temperature. The ductility of the Fe-basedBGAs is much inferior to that of non-ferrous BGAs.4,7–9) Thislack of plasticity followed by the catastrophic fracture limitsthe use of the BGAs in new structural applications. There-fore, great efforts have been made to improve the plasticdeformation ability of many types of BGAs and thecompressive ductility has been improved to a large extentby promoting multiple shear bands in Zr-,10,11) Cu-,12–14)Ni-,15,16) Ti-,17,18) Mg-,19) and Pd-based20) BGA compositescontaining second dendrite or particle phases, or fine porephase in the BGA matrices. However, improvements inductility of the Fe-based BGAs, which have higher strengththan the non-ferrous alloys, have not been achieved yet.We recently have reported that the addition of Psignificantly increases the glass-forming ability (GFA) ofthe ordinary melt-spun Fe-Si-B amorphous alloys, whosecritical glass forming size is less than 100 mm in thickness.A Fe76Si9B10P5 alloy, consisting only of iron metal andmetalloid elements, is found to exhibit high GFA of 2.5mmin the critical glass-forming diameter by the conventionalcopper-mold casting technique and high yielding stressof 3.3 GPa, followed by a plastic deformation of 0.7% incompression, which is rather larger than the Fe-based BGAs(3GPa7,8)). The iron-rich Fe-metalloid BGAs also show ahigh magnetization of 1.51 T, low coercivity of 0.8 A/m, andrelatively low material cost compared to those previouslyreported for Fe-based BGAs including other metal ele-ments.21)We have investigated the effect of adding small amountsof copper, which has a large negative mixing enthalpy withFe and no-solubility into Fe in solid,22) on the structureand mechanical properties in the Fe-metalloid BGAs. Inthis paper, we intend to demonstrate excellent mechani-cal properties of a newly developed ductile (Fe0:76Si0:096-B0:084P0:06)99:9Cu0:1 BGA having high magnetization (1.5 T)as well as low coercivity (1.9 A/m).2. Experimental Procedure(Fe0:76Si0:096B0:084P0:06)100xCux (x ¼ 0 and 0.1 at%) alloyingots were produced by induction melting mixtures of pureFe (99.998mass%), Si (99.99mass%), B (99.9mass%), Cu(99.99mass%) and pre-alloyed Fe-26.5mass% P ingotsin a high purity argon atmosphere. Their compositions arenominally expressed in atomic percentage. From the masteralloys, ribbons and cylindrical rods were produced by themelt-spinning and copper mold casting techniques, respec-tively.The structure of the specimens was examined by theX-ray diffractometry (XRD) with Cu-K radiation, andtransmission electron microscopy (TEM). Thermal stabilityassociated with the onset temperatures for the glass transi-tion (Tg) and crystallization (Tx) of the glassy samples wasevaluated by differential scanning calorimetry (DSC) at aheating rate of 0.67K/s. Magnetic properties, such assaturation magnetization (M) and coercive force (Hc), weremeasured by a vibrating sample magnetometer (VSM)under an applied field of 400 kA/m and a B–H loop tracerunder a field of 800A/m, respectively. The mechanicalproperties of yield stress, fracture stress and compressiveplastic strain were measured by an Instron testing machine.The gauge dimensions of the testing sample were 1mm(circumferentially) and 3mm (longitudinally), and the strainrate was set to 5 104 s1. The deformation and fracturebehaviors were examined by scanning electron microscopy(SEM).*Corresponding author, E-mail: lixue@imr.tohoku.ac.jpMaterials Transactions, Vol. 50, No. 6 (2009) pp. 1286 to 1289Special Issue on Joining Technology for New Metallic Glasses and Inorganic Materials#2009 The Japan Institute of Metals3. Results and DiscussionThe as-cast (Fe0:76Si0:096B0:084P0:06)100xCux (x ¼ 0 and0.1) BGAs were confirmed to be of single glassy phase by theXRD analysis as shown in Fig. 1. These alloys have a widesuper-cooled liquid region, one of the parameters forexpressing GFA defined by the temperature interval betweenthe onset temperatures of the glass transition and crystal-lization (Tx), of 48 and 46K at a heating rate of 0.67K/s,respectively as shown in Fig. 2. These BGAs exhibits goodsoft-magnetic properties as shown in Fig. 3. The saturationmagnetization does not change so much from 1.51 T for thealloy without Cu to 1.50 T for the 0.1 at% Cu-added alloy.The alloy ribbons are found to have low Hc of 1.7–1.9A/m.We further measured the mechanical properties of theseFe-based BGA specimens, whose dimensions are 1.5mm indiameter and 3mm long, by compression testing. Figure 4shows the compressive true stress-strain curves for(Fe0:76Si0:096B0:084P0:06)100xCux (x ¼ 0 and 0.1) BGAs.The yield stress, defined in this work by a deviation of0.2% from the linear relation, and the elastic limit are3.25GPa and 1:9%, respectively, for both alloys. Afteryielding, the alloys exhibit a maximum stress of 3.3GPa thenstress gradually decreases with further increase in strain.Plastic strain is 0:7% for the alloy without Cu, which is anaverage of three samples (0.5–0.9%). On the contrary, itincreases significantly up to 4% for the 0.1% Cu-addedalloy, which is the best one among five samples (2.5–4%).The small amount Cu-addition results in highly improvementon plasticity in the Fe-based BMGs, which has been wellknown to be brittle in nature.8) As shown in the inset ofFig. 4, the distinguishable serrated characteristics attributedto the formation of shear bands are not clearly observed. Therelative smooth flow behavior should be closely related to thehighly-dense multiple shear bands, which is shown in Fig. 6.Figure 5 shows SEM images revealing that the Cu-addedglassy rod has the vein pattern on a fracture surface andmultiple shear bands on specimen surface while the Cu-freeone does not. The fracture surface exhibits a well developedvein pattern, which is usually observed in the non-ferrousductile BGAs. Moreover, density of multiple shear bands ishigh. The spacing between the shear bands is as small as 10–50 mm, which should be closely related to the absence of theserrated characteristics in the stress-strain curve and a largeplastic deformation for the Cu-added alloy shown in Fig. 4. Aresult showing relatively large plastic deformation has beenreported recently for Fe-based BGAs, and the large plasticdeformation was attributed to the formation of the well30° 40° 50° 60° 70° 80°X=0.1(Fe0.76Si0.096B0.084P0.06)100-xCuxrod 2.5 mmX=0Intensity / a.u.Diffraction angle, 2 θFig. 1 XRD patterns of (Fe0:76Si0:096B0:084P0:06)100xCux (x ¼ 0 and 0.1)bulk glassy alloy rods.600 700 800 900 1000 1100TgTxTcTemperature, T / K Exothermic / arb.unit  X=0.1X=0(Fe0.76Si0.096B0.084P0.06)100−XCuXrod 2.5 mm↑Fig. 2 DSC traces of (Fe0:76Si0:096B0:084P0:06)100xCux (x ¼ 0 and 0.1)bulk glassy alloy rods at a heating rate of 0.67K/s.−10 −8 −6 −4 −2 0 2 4 6 8 10−1.5−1.0−0.50.00.51.01.5 X=0 X=0.1Ribbon(Fe0.76P0.06B0.084Si0.096)100−xCux1.501.51M / T1.9X=0.11.7X=0Hc / A• m-1Magnetic /KOeMagnetization /TFig. 3 B–H loop traces of glassy alloy ribbons (Fe0:76Si0:096B0:084-P0:06)100xCux (x ¼ 0 and 0.1).050010001500200025003000350040004500True strain, εStress,σ / MPa2%X=0 X=0.1(Fe0.76Si0.096B0.084P0.06)100-XCuXR=5x10-4s-1Fig. 4 True compressive stress-strain curves of as-cast (Fe0:76Si0:096-B0:084P0:06)100xCux (x ¼ 0 and 0.1) glassy rod specimens at a strain rate of5 104 s1.Mechanical Properties of Soft Magnetic (Fe0:76Si0:096B0:084P0:06)100xCux (x ¼ 0 and 0.1) Bulk Glassy Alloys 1287developed vein pattern and the distinguishable highly-densemultiple shear bands.23) In general, plastic deformation ofglassy alloys is highly localized into shear bands, followed byrapid slipping of these shear bands and a sudden fracture.Therefore, the highly-dense multiple shear bands result inlarge plastic deformation.24) This fracture behavior with goodductility has not been observed for Fe-based BGAs to date.The origin of the unusual ductile fracture behavior ofthe Cu-added Fe-based BGA is important to be solved.Figures 6(a) and 6(b) show high-resolution TEM images andthe corresponding selected area electron diffraction (SAED)patterns taken from the cross-section of the as-cast rodspecimens with and without Cu element, respectively. Thedispersion of a large number of -Fe like clusters withdiameter less than 10 nm in the glassy matrix phase wasobserved in the TEM image, and a (200) peak from -Fe wasfound in the SAED pattern for the Cu-added alloy (Fig. 6(b)).An enlarged image of Fig. 6(b) is shown in Fig. 6(c). Thebars and arrows indicate the {110} lattice fringes of an -Fephase. The alloy without Cu exhibiting the low plasticdeformation of 0.7% shows a completely monolithic glassystructure. Therefore, the clusters observed in the alloy withCu exhibiting the high plasticity of about 4%, should berelated to the large plasticity.We have already reported that the simultaneous addition ofP and Cu to the ordinal Fe-Nb-B amorphous alloy introducesstructural inhomogeneity, such as nano-scaled -Fe clustersin the amorphous matrix, which might act as a nucleation sitefor -Fe phase crystallization. A nanocrystalline structurewith narrower grain size distribution can be obtained afterappropriate annealing.25) As the mixing enthalpy between Feand Cu is positive, a repulsive interaction should existbetween Fe and Cu atoms in the alloys. On the other hand,attractive interactions should exist between Cu and P, and Pand Fe. Therefore, the as-cast structure possibly consists oftwo phases; the major part with an Fe-metalloid based glassyphase, and the minor part with a Cu-rich phase, which isconsidered to become the crystalline phase. A rapid increasein temperature has been reported in the vicinity of the highlystressed shear-slipping region.26) Considering this, the clustermight act as a nucleation site of -Fe nanocrystallizationpossibly taking place dynamically during the compressivetest. For a composite structure with a glassy and ductilecrystalline phases, the shear bands must interact with the(a)(b)(c)Fig. 6 High-resolution TEM images and the corresponding SAED patterns with the intensity profiles for (a) as-cast Fe76Si9:6B8:4P6 and(b) as-cast (Fe0:76Si0:096B0:084P0:06)99:9Cu0:1 BGAs. An enlarged image of (b) is also shown in (c).Fig. 5 The SEM images of (a) Fe76Si9:6B8:4P6 fractured specimen; (b) (Fe0:76Si0:096B0:084P0:06)99:9Cu0:1 fractured specimen; (c) the veinpattern on the fracture surface taken in (c) region indicated in (b); and (d) the multiple shear bands on the specimen surface taken in (d)region indicated in (b).1288 X. Li, A. Makino, K. Yubuta, H. Kato and A. Inouemicroscale ductile crystalline phase during the propagationof shear bands under loading and their propagation directionhave to be deflected, thus resulting in a shear band branching.At the same time, the shear bands are also blocked orbranched by other intersected shear bands. Thus, theformation of a large number of the branching shear bandsleads to a large increase in the macroscopic plasticity.Therefore, stress-induced dynamic nanocrystallization dur-ing compression is considered as a reason for the largeplasticity of the Cu-added Fe-based BGA. This result willopen the way for structural applications of high-strength Fe-based BGAs. Moreover, this Fe-based BGA composed offamiliar and low-priced elements is of great advantage forengineering industry, and thus significantly improves theconservation of natural resources and environment.4. Conclusions(1) (Fe0:76Si0:096B0:084P0:06)100xCux (x ¼ 0 and 0.1) alloysshow the high glass-forming ability with the critical glassforming diameter up to 2.5mm by the copper mold castingmethod.(2) Cu-added Fe-metalloid bulk glassy alloy, (Fe0:76Si0:096-B0:084P0:06)99:9Cu0:1, exhibits excellent mechanical proper-ties: maximum stress of 3.3GPa; Young’s modulus of163GPa and a large plastic deformation of about 4% incompression.(3) The well-developed vein pattern on the fracture surfaceand highly dense multiple shear bands on the surface of therod specimen near the fracture surface are observed in(Fe0:76Si0:096B0:084P0:06)99:9Cu0:1 alloy.(4) A large number of -Fe like clusters (less than 10 nm)are found to disperse in a glassy matrix. These clustersare considered to act as nucleation sites for the dynamicnanocrystallization of the -Fe phase in the shear bands. Thismight result in developing the high-dense multiple shearbands which are responsible for the macroscopic compres-sive plasticity of the alloy.AcknowledgementOne of the authors (XL) wishes to acknowledge thefinancial support of the Global COE Program ‘‘MaterialsIntegration (International Center of Education and Research),Tohoku University’’, MEXT, Japan.REFERENCES1) A. Inoue: Acta Mater. 48 (2000) 279–306.2) A. Inoue and B. L. Shen: Mater. Trans. 43 (2002) 766–769.3) B. L. Shen, M. Akiba and A. Inoue: J. Appl. Phys. 100 (2006) 043523.4) M. Stoica, J. Eckert, S. Roth, Z. F. Zhang, L. Schultz and W. H. Wang:Intermetallics 13 (2005) 764–769.5) B. L. Shen, A. Inoue and C. T. Chang: Appl. Phys. Lett. 85 (2004)4911–4913.6) S. J. Pang, T. Zhang, K. Asami and A. Inoue: Acta Mater. 50 (2002)489–497.7) A. Inoue, B. L. Shen, A. R. Yavari and A. L. Greer: J. Mater. Res. 18(2003) 1487–1492.8) X. J. Gu, S. J. Poon and G. J. Shiflet: J. Mater. Res. 22 (2007) 344–351.9) K. Amiya, A. Urata, N. 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Mechanical Properties of Soft Magnetic (Fe0.76Si0.096B0.084P0.06)100-xCux (x = 0 and 0.1) Bulk Glassy Alloys

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