Microstructures and Mechanical and Electrical Propertiesof Hypoeutectic Cu-1, C-3 and Cu-5 at%Zr Alloy WiresPreprocessed by Spark Plasma Sintering

Naokuni Muramatsu1 and Takashi Goto2

1New Metals Division, NGK Insulators, Ltd., Handa 475-0825, Japan2Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

Wires prepared by the solid-phase-compaction followed by heavy wire-drawing of atomized Cu­Zr alloy powders were studied.Microstructures and mechanical and electrical properties of wires drawn from hypoeutectic Cu-1, Cu-3 and Cu­5 at%Zr alloys, preprocessed byspark plasma sintering (SPS), were investigated. The microstructures of specimens formed by SPS of the powders changed into fine dual-phasedstructures comprising phases of Cu and the intermetallic compound Cu5Zr, which was dispersed in the Cu matrix. The volume fraction of theintermetallic compound Cu5Zr in SPS specimens increased with an increase in the Zr content. The ultimate tensile strength (UTS) values of thespecimens increased, while their electrical conductivity (EC) values decreased simultaneously. The alloy wires, preprocessed by SPS, containeddual-phased microstructures in which the intermetallic compound Cu5Zr was dispersed in the shape of small islands in the Cu matrix. Drawn Cu-1, Cu-3 and Cu­5 at%Zr alloy wires exhibited UTS values of 603, 698 and 789MPa, respectively, and EC values of 87, 70 and 52% IACS(International Annealed Copper Standard), respectively. The UTS values were about 40­56% lower and EC values about 28­60% higher thanthose previously reported for wires preprocessed by casting. The lamellar structures of the ¡-Cu and eutectic (Cu+ intermetallic compoundCu9Zr2) phases in the drawn wires preprocessed by casting improved the mechanical properties of the wires. The microstructures of theintermetallic compounds Cu5Zr, which was uniformly dispersed in the Cu matrix in the drawn wires preprocessed by SPS, helped increase theelectrical conductivity of the wires. [doi:10.2320/matertrans.M2013011]

(Received January 8, 2013; Accepted April 19, 2013; Published May 31, 2013)

Keywords: copper-zirconium alloys, hypoeutectic alloys, wire drawing, spark plasma sintering, mechanical properties, electrical conductivity,intermetallic compound phase

1. Introduction

Copper alloys used in electronic devices are expected toexhibit higher strengths and higher electric conductivities.During the development of such materials, the techniquesused for processing the raw materials and the followingintermediate thermal and mechanical processes greatly affectthe final material characteristics as well as the compositionsof the alloys.

Several studies investigating the production and character-istics of new copper alloy materials have been reportedrecently. These materials include Cu­Cr,1) Cu­Fe2) and Cu­Nb3) alloys that contain small amounts of hard metal particlesdispersed within their matrices. Some examples of suchmaterials are yellow brass or Cu with solid-phase-sinteredtungsten4,5) and Cu with Al2O3 dispersed by an internaloxidation method.6) Furthermore, drawn Cu­Ag alloywires7,8) with a eutectic lamellar structure prepared by castinghave been also studied. Sakai et al. studied Cu­Ag alloysreinforced by fiber-like structures in which the primary andeutectic phases underwent elongation during the cold wire-drawing process.9­12) Bevk et al.3) reported a high-strengthCu­12.5 at%Nb alloy that was heavily worked, leading to thedevelopment of Nb filaments within its matrix; the alloy wireexhibited an ultimate tensile strength (UTS) of 2230MPa.

We previously investigated the nanosized lamellar struc-tures of hypoeutectic Cu­0.5­5 at%Zr alloy wires that wereprepared by casting using a copper mold with a rod-shapedcavity and cold wire drawing. We also studied the effect ofthe lamellar structures on the mechanical and electrical prop-erties of wires drawn from the Cu-0.5­5 at%Zr alloys13­17)

and found that the UTS and electrical conductivity (EC)

values of these wires were 690­2234MPa and 16­83% IACS(International Annealed Copper Standard), respectively.

On the other hand, Kimura et al.18) reported that extrudedand spark-plasma-sintered (SPS) Cu­4.5 at%Zr alloys pre-pared by powder metallurgy exhibit fine hypoeutectic phasestructures as well.

This study aimed to develop a new material for wires bythe solid-phase compaction of atomized binary Cu­Zr alloypowders followed by heavy wire drawing. We focused on thefine microstructures formed during the rapid solidificationprocess. The microstructures and mechanical and electricalproperties of the drawn hypoeutectic Cu-1, Cu-3 and Cu­5 at%Zr alloy wires, preprocessed by spark plasma sintering,were also investigated.

2. Experimental Procedures

Cu-1, Cu-3 and Cu­5 at%Zr alloy powders were purchasedfrom Fukuda Metal Foil & Powders Co. Ltd.; these wereproduced by the high-pressure gas-atomizing method. Thepowders were sifted and only particles smaller than 106 µmin size were chosen. The sizes of the particles were measuredby the LASER diffraction method using a particle sizedistribution analyzer (Shimadzu SALD-3000J). These siftedpowders then underwent solid-phase compaction by sparkplasma sintering (SPS). An SPS apparatus (Model 3.2MK-IV,SPS Syntex, Kanagawa, Japan) was used to prepare testspecimens. The pressure of the process chamber was keptat about 1.5 Pa. Samples of the sifted powders (225 g inweight) were placed in a graphite cavity with dimensions of50 © 50 © 10mm and sintered by applying pulsed directcurrents of 3­4 kA. The following parameters were used

Materials Transactions, Vol. 54, No. 7 (2013) pp. 1213 to 1219©2013 The Japan Institute of Metals and Materials EXPRESS REGULAR ARTICLE

during the sintering process: heating rate = 0.4K/s; finalsintering temperature = 1173K, which corresponded toabout 0.9 times the melting temperature, Tm, of the testmaterial; holding time = 15min; and uniaxial pressure =30MPa.

For drawing the wires, the sintered plates of the alloyswere machined into round bars with dimensions of 10mm(diameter) © 50mm (length). The bars were drawn down toa diameter of 1mm (corresponding to a drawing ratio, ©,of 4.6) by swaging, groove rolling, and roller-die drawing,with intermediate annealing at 923K. Thereafter, wires withdiameters of 0.037­0.60mm (© = 11.2­5.6) were drawncontinuously using diamond dies. The drawing ratio, ©, isdefined by the eq. (1), with Ao and A being the original andfinal cross-sectional areas of the drawn wire specimens,respectively.

© ¼ lnðAo=AÞ ð1ÞSpecimens for scanning electron microscopy (SEM)

observations were prepared using a cross-section polishingapparatus (JEOL SM-9010). Thin film specimens forscanning transmission electron microscopy (STEM) obser-vations were prepared using a twin-jet-type electrolyticpolishing apparatus (Struers Tenupol-3) and an electrolytesolution that was a mixture of 30% nitric acid and 70%methanol. High-magnification microstructural imaging wasperformed using field-emission scanning electron microscopy(FE-SEM) (JEOL JSM-7000F), STEM (JEOL JEM-2100F)and the nanoelectron beam diffraction (NBD) method.Energy-dispersive X-ray spectroscopy (EDX) analyses werecarried out using a JEOL JED-2300T system and an electronbeam with a diameter of approximately 1 nm. Analyses of theintermetallic compound phases were performed by the X-raydiffraction (XRD) method using Co­K¡ radiation.

The electrical conductivities of the sintered and wirespecimens were calculated using eq. (2), where the electricalconductivity (EC) of a standard sample, confirming to theInternational Annealed Copper Standard (IACS), was0.017241 µ³m at 293K. µ is the electrical resistivity of thesamples measured using a monoprobe in the case of thesintered specimens and a four-probe technique in the case ofthe wire specimens. These wire specimens were 500mm inlength at room temperature.

ECð%IACSÞ ¼ 0:017241=µ � 100ð%Þ ð2ÞTensile tests were performed on the drawn wires at room

temperature using a multifunctional tensile-testing machinethat confirmed to the JIS B7721 Class 0.5 Standard(Shimadzu AG-I). The ultimate tensile strength (UTS) ofthe drawn wires were measured once (in the case of © = 4.6­7.0) and twice (in the case of © = 0), or three times (in thecase of © > 7.0) to obtain average values.

The hardness and Young’s modulus values of theintermetallic compounds were measured using a nano-indentation system (Agilent Technologies NanoindenterXP/DCM) under the continuous stiffness measurement(CSM) mode. During the measurement process, the triangularpyramid Berkovich indenter was excited with a frequency of45Hz and amplitude of 2 nm. Five indentations within adefined displacement range 20­40 nm were made on the

surfaces of the test specimens until the measured hardnessand Young’s modulus became almost constant. The resultswere the average of the five measurements.

3. Results and Discussion

3.1 Atomized powdersThe average sizes of the particles for the Cu-1, Cu-3 and

Cu­5 at%Zr alloy powders, sifted to less than 106 µm, were26, 23 and 19 µm, respectively. The particle sizes distribu-tions of these powders were almost log-normal in nature. Theparticle sizes decreased with an increase of the Zr content ofthe powders. This fact suggested that the viscosity of themolten alloys decreased when their compositions approachedto their eutectic point (Cu­8.6 at%Zr19)). The oxygen contentof the powders, measured using the He gas fusion infraredabsorption method, were approximate 0.100mass%. All thepowders exhibited the same content levels.

Figure 1(a) shows the scanning electron microscopicbackscattered electron image (SEM-BEI) of a cross-sectionof the particles for the Cu­5 at%Zr alloy powder; the particleswere approximately 36 µm in size. The atomized particleswere almost spherical in shape. Figure 1(b) shows a high-magnification image of the part A enclosed in the squarein Fig. 1(a). Dendrite-like microstructures of the ¡-Cu

(a)

(b)

1μm

10μm

A

(Eutectic)

(α-Cu)

Fig. 1 (a) SEM-BEI micrograph of cross-sectioned particles of theatomized Cu­5 at%Zr alloy powder and (b) high magnification image ofthe part A in the image (a).

N. Muramatsu and T. Goto1214

and eutectic phases were formed in the particle. The armsof the secondary dendrite were short. This suggested thatthese particles solidified rapidly during the atomizationprocess. The average value of secondary dendrite armspacing (DAS), measured at four other points, was0.81 µm. This was less than one-third of the value for theCu­4 at%Zr alloy rod that was rapidly cast into a coppermold, which exhibited a secondary DAS value of 2.7 µm.13)

On the other hand, the dendrite arms were not formed in thecase of the cast Cu­5 at%Zr alloy rod, owing to the presenceof small ¡-Cu phases,13) and hence its DAS value could notbe measured. This result indicated that the solidificationrates of the atomized powders were higher than those of thecast rods.

Figure 2(a) shows the X-ray diffraction (XRD) profiles ofthe atomized powder for the Cu­5 at%Zr alloy. In this profile,Cu and Cu5Zr phases (ICDD No. 40-1322) were identified,indicating that atomized powder is consisted of eutecticphase. Furthermore, other peaks, related to an unknownphase and indicated by the arrows, were also detected. Theseunknown peaks did not correspond to the diffraction anglesof any intermetallic compounds (such as Cu9Zr2) seen in theCu­Zr equilibrium phase diagram.19) We intend to investigatethe unknown phase further.

3.2 Spark-plasma-sintered specimensThe specific gravities of the spark-plasma-sintered (SPS)

Cu-1, Cu-3 and Cu­5 at%Zr alloy specimens, measured bymeans of Archimedes method, were 8.92, 8.85 and 8.79,respectively. These values were comparable to the gravity(8.79) of a compeletely consolidated Cu­4.5 at%Zr alloy.18)

The XRD profiles of the sintered Cu­5 at%Zr alloy specimenare shown in Fig. 2(b). The diffraction peaks of the Cu,Cu5Zr, and the unknown phases were the same as those of theCu­5 at%Zr alloy powder seen in Fig. 2(a). This suggestedthat the fundamental structure of this powder did not changeafter sintering. A few of the diffraction peaks in (b), however,sifted slightly toward smaller angles. This means that thelattice parameters of the sintered specimens were larger thanthose of the corresponding atomized powder. This might bebecause the lattice strains induced in the powder by rapidsolidification were reduced to a small degree. Similar trendswere noticed in the case of the SPS Cu-1 and Cu-3 at%Zralloy specimens as well.

Figures 3(a)­(c) show cross-sectional SEM images of theSPS Cu-1, Cu-3 and Cu­5 at%Zr alloys perpendicular to thecompression axis. A few voids can be seen in each specimen.This suggests the sintered specimens were sufficientlyconsolidated. The microstructures of the cross-sectionsparallel to the compression axis were similar to those of theperpendicular cross-sections. It is observed that the micro-structures were not heterogeneous. The volume fraction ofthe bright area of the microstructures increased with anincrease in the Zr content. In addition, the SEM-EDX resultsof the microstructures, shown in Fig. 3(c), did not show thepresence of Zr in the dark area. It might be reasonable totake the Zr content in this part shown in Fig. 3(c) lower thanthe detection limit of SEM-EDX system. As reported byMuramatsu et al.13) however, 0.3 at%Zr is soluble in thematrix of ¡-Cu phases. On the other hand, 16.9 at%Zr wasdetected in the bright phase. The detected Zr content in thebright phase was in accordance with the stoichiometriccomposition of 16.9 at%Zr for the intermetallic compoundCu5Zr. This fact shows that Zr existed mainly in theintermetallic compound phase. The intermetallic compoundCu5Zr was dispersed in the shape of small islands in the Cumatrix. Figure 4(a) shows the high-magnification micrographof FE-SEM-BEI for the SPS Cu­5 at%Zr alloy specimen.

20° 30° 40° 50° 60° 70° 80° 90° 100° 110° 120°

Cu

Cu5Zr

Unknown

(a)

(b)

2θ

Inte

nsity

, I(a

rb. u

nits

)

Fig. 2 X-ray diffraction profiles of (a) the atomized powder and (b) thespark-plasma-sintered specimen of the Cu­5 at%Zr alloy.

(c)

10μm

(b)

10μm

(a)

10μm

(Cu5Zr)

(Cu)

Fig. 3 SEM-BEI micrographs of cross-sections of spark-plasma-sintered Cu-x at%Zr alloys perpendicular to the compression axis.(a) x = 1, (b) x = 3 and (c) x = 5.

Microstructures and Mechanical and Electrical Properties of Hypoeutectic Cu-1, C-3 and Cu-5 at%Zr Alloy Wires 1215

From the figure, it can be observed that the dual-phasedmicrostructure consisted of the dark (Cu) and bright(intermetallic compound Cu5Zr) phases. The monotone ofthe bright area (Cu5Zr) means it was a single-phasedstructure. On the other hand, the multiple tone of the darkarea (Cu) suggests the Cu grains had different orientations.It was observed that fine oxide particles existed along theoriginal powder’s boundaries. Figures 4(b) and 4(c) showthe Kikuchi patterns obtained from the point 1 (Cu5Zr)and point 2 (Cu), which were in contact with each other.The channeling patterns corresponding to the points weredifferent. This suggests that the Cu5Zr and Cu phases haddifferent orientations, and there was incoherence betweenthem. This result is in contrast to the coherence between theeutectic (Cu + Cu5Zr) and Cu phases in the cast Cu-0.5, Cu-1 and Cu-2 at%Zr alloys previously reported by Muramatsuet al.17) In addition, the microstructures of the SPS Cu-1,Cu-3 and Cu­5 at%Zr alloy specimens, shown in Fig. 3, aremore homogeneous than those of the cast Cu-0.5­5 at%Zralloy rods13,16,17) and exhibited a finer dual-phased structure.This fact indicates that the SPS specimens can potentially bedrawn into wires. This feature is one of important character-istics of alloys prepared by the SPS process which canincrease or decrease the temperature of the specimen in ashort period.

Figure 5 show the STEM images and NBD patterns of theSPS Cu­5 at%Zr alloy specimen. Figure 5(a) is a STEM-BFimage and Fig. 5(b) is a high-magnification high-angle

annular dark-field (HAADF) image of the portion A inFig. 5(a). Figures 5(c), 5(d) and 5(e) are the NBD patternsof the points 1 (Cu5Zr), 2 (Cu) and 3 (an oxide particle) inFig. 5(b), respectively. The image in Fig. 5(a) shows clearlythe dual-phased microstructures of the dark phases (Cu) andthe bright phases (Cu5Zr). The curved lines located betweenthe arrows indicate boundaries of the original atomizedpowder particles. No dislocation substructure with a highpile-up density was observed in the Cu phases. The Cuphases exhibited coarsened grain structure after theirrecovery and recrystallization. The HAADF image inFig. 5(b) shows the bright phase (Cu5Zr) dispersed in thedark phase (Cu). It can be observed that oxide particles ofapproximate 30­80 nm in size were dispersed along theoriginal boundaries of the powder particles.

The EDX results corresponding to the points 1 (Cu5Zr), 2(Cu) and 3 (an oxide particle) are shown in Table 1. On thebasis of the data listed in Table 1, it can be said that thephases at points 1, 2 and 3 are of the intermetallic compound(Cu5Zr), Cu, and an oxide phase (comprising Cu, Zr and O),respectively. The EDX results suggest that the SPS Cu­5 at%Zr alloy specimens consisted of Cu, Cu5Zr, and someCu­Zr­O-system phases. The EDX results suggest that singlephases of Cu and Cu5Zr were formed during the sinteringprocess. These single phases were presumably the results ofthe change from the dendrites, which comprised of the ¡-Cuand the eutectic (Cu + intermetallic compound Cu5Zr)phases shown in Fig. 1.

The lattice plane spacings obtained from the diffractionpatterns are shown in Table 2. Also listed in the table are theinterplanar spacings calculated at the specific lattice planes ofthe intermetallic compounds Cu5Zr, Cu9Zr2 and Cu8Zr3(those for hypoeutectic Cu-0.5­5 at%Zr alloy wires werereported previously elsewhere13­17)), and those of the Cu,and the Cu8O7, Cu4O3 and Cu2O2 phases. The lattice planespacings corresponding to the d1, d2 and d3 spots, obtainedfrom the point 1 in Fig. 5(c), were in good agreement withthose of the intermetallic compound Cu5Zr. In addition, thosecorresponding to the point 2 in Fig. 5(d) agreed with those ofthe Cu. Those related to the point 3 in Fig. 5(e), however,were not in accordance with those of any copper oxides,because it was a Cu­Zr­O-system phase. Through theseresults, it can be reasonable to consider that the Cu of theeutectic phase diffused during sintering and the surroundingCu grains coarsened and linked with the original ¡-Cu matrixin a network-like manner with those undergoing recovery andrecrystallization. On the other hand, it seems that the Cu5Zrof the eutectic phase was left behind and its structure changedinto a single-phased one. This can be understood on the basisof the fact that there was incoherence between the Cu andCu5Zr phases shown in Figs. 4(b) and 4(c). Moreover, thiswas also speculated from the Cu5Zr dispersions, which leftsome traces of distribution of the eutectic phase in thedendrites shown in Fig. 1(b).

Table 3 shows the hardness (HIT) and Young’s modulus(E) values of the intermetallic compound Cu5Zr phase for theSPS Cu­5 at%Zr alloy specimen, measured by means ofnanoindentation. The average values and standard deviationswere obtained by the five time measurements. The HIT valuesof the intermetallic compound Cu5Zr phase was 6.3GPa.

2μm

(a)

(b) (c)

Point 1 (Cu5Zr)

Point 2 (Cu)

Fig. 4 (a) High-magnification FE-SEM-BEI micrograph of the spark-plasma-sintered specimen of the Cu­5 at%Zr alloy, and (b) and (c)Kikuchi patterns of the points 1 and 2 in the image (a), respectively.

N. Muramatsu and T. Goto1216

The HIT values can be converted into the Vickers hardnessHv using eq. (3).20)

Hv ¼ 0:0924�HIT ð3ÞThus, the Hv value of Cu5Zr phase is 585. This value was24% higher than that of the intermetallic compound Cu9Zr2,which is 470 « 30Hv, as determined by Glimois21) and 6.5times of the hardness of oxygen free copper (OFC) (C10200),which is 89Hv.22) The Young’s modulus, E, of theintermetallic compound Cu9Zr2 was 159.5GPa, which is35% higher than that of OFC, 118GPa.23)

3.3 Drawn wire specimensWires were drawn from rod-shaped specimens with

dimensions of 10mm (diameter) © 50mm (length). Therod-shaped specimens were prepared from 50 © 50 ©10mm plates of the SPS Cu-1, Cu-3 and Cu­5 at%Zr alloys

by turning. It was possible to draw down all the sinteredspecimens to wires of 1mm in diameter (© = 4.6) withoutany breakage. The Cu-1, Cu-3 and Cu­5 at%Zr alloyspecimens were further drawn into wires of 0.037mm indiameter (© = 11.2), 0.16mm in diameter (© = 8.3), and0.60mm in diameter (© = 5.6), respectively. Wire-drawabil-ity of the alloy specimens trended to become higher with adecrease in their Zr content, that is, a decrease in the amountof Cu5Zr. The UTS and EC values of the wires thus obtainedwere 603MPa and 87% IACS, 698MPa and 70% IACS, and789MPa and 52% IACS, respectively. Figure 6 shows therelationship between drawing ratios and the UTS and thatbetween the ratios and the EC for the drawn wires. The UTSincreased with an increase in the drawing ratio. On the otherhand, the EC remained almost constant for all the drawingratios. The corresponding values of the Cu-1, Cu-3 and Cu­5 at%Zr alloy wires drawn from cast rods with almostthe same drawing ratios were 998MPa and 68% IACS(© = 10.4), 1572MPa and 28% IACS (© = 8.6), and1773MPa and 24% IACS (© = 5.9), respectively.13­17) Theserelations between UTS or EC and © are also shown in Fig. 6for comparison. The UTS values of the wires drawn from theSPS specimens were about 40­56% lower, while the ECvalues were 28­60% higher than those of the wires from thecast rods.

Figure 7 shows the cross-sectional SEM images of the Cu-1, Cu-3 and Cu­5 at%Zr alloy wires parallel to the drawingaxis. The images of (a)­(c) are those of the drawn Cu-1 at%Zr

Table 1 Results of EDX analysis of the spark-plasma-sintered Cu­5 at%Zralloy specimen. The points 1­3 correspond to the points 1­3 in Fig. 5(b).

PointO

(at%)Cu

(at%)Zr

(at%)

1 ® 83.5 16.5

2 ® 100.0 ®

3 34.3 55.3 10.4

dd1

d2 d3

d12

d3

d1

d2 d3

2μm

(a)

(c) (d) (e)

A

1μm

(b) Point 1 (Cu5Zr)

Point 2 (Cu)

Point 3 (Oxide)

(Cu5Zr)

(Cu)

Fig. 5 STEM images and NBD patterns of the spark-plasma-sintered Cu­5 at%Zr alloy specimen. (a) STEM-BF image. (b) Highmagnification HAADF image of the portion A in the image (a). (c), (d) and (e) NBD patterns of the points 1, 2 and 3 in the image (b),respectively.

Microstructures and Mechanical and Electrical Properties of Hypoeutectic Cu-1, C-3 and Cu-5 at%Zr Alloy Wires 1217

alloy wire (© = 11.2), Cu-3 at%Zr alloy wire (© = 8.3) andCu­5 at%Zr alloy wire (© = 5.6), respectively. After heavywire-drawing, the dispersion of Cu and the intermetalliccompound Cu5Zr phases observed in (a)­(c) became morehomogeneous. It seems that the intermetallic compoundCu5Zr is hardly deformed due to its high hardness (listed inTable 3) and incoherence to the Cu matrix. On the otherhand, the Cu matrix is easily deformed during drawing. As aresult, the dispersion of Cu5Zr becomes more homogeneous.These dispersed microstructures differed significantly fromthe small and fine lamellar structures, which consisted of the¡-Cu and eutectic (Cu + Cu8Zr3 or Cu + Cu9Zr2) phases

seen in the Cu-0.5­5 at%Zr alloy wires.13­17) This suggestedthat microstructures of the ¡-Cu and the eutectic (Cu +Cu9Zr2) phases were effective in improving the mechanicalstrength of the corresponding wires. On the other hand,the microstructures of the intermetallic compound Cu5Zr,dispersed homogeneously in the Cu matrix, were effectivein improving the electrical conductivity of the correspondingwires. The mechanical property of the drawn hypoeutecticCu­Zr alloy wires preprocessed by SPS is attributable to theCu5Zr dispersive reinforcement and the high electricalconductivity is supported by the Cu grains linking with eachother in a network-like manner. In the future, we aim to studythe relationships between the microstructures present in thewires and the mechanical and electrical properties of thewires in greater detail and establish principles for developingnew hypoeutectic Cu­Zr alloy wire materials with highstrength and high electrical conductivities.

4. Summary

The microstructures and mechanical and electrical proper-ties of drawn hypoeutectic Cu-1, Cu-3 and Cu­5 at%Zr alloywires preprocessed by spark plasma sintering (SPS) wereinvestigated. The following results were obtained.(1) The microstructures of the sintered specimens formed

from the alloy powders changed into fine dual-phasedstructures comprising single phases of Cu and theintermetallic compound Cu5Zr. The intermetallic com-pound was dispersed in the shape of small islands inthe Cu matrix. Finally, the volume fraction of the

Table 2 Spacings of the lattice parameters, obtained from the NBD patternsof the points 1­3 seen in Fig. 5(b). The spacings of the lattice planes ofthe phases of the intermetallic compounds Cu5Zr, Cu9Zr2, and Cu8Zr3, andthose of copper, various copper oxides (Cu8O7, Cu4O3 and Cu2O)obtained by calculations, are also shown for comparison.

Point-1 Point-2 Point-3

Symbol Spacing/nm Symbol Spacing/nm Symbol Spacing/nm

d1 0.3431 d1 0.1809 d1 0.5686

d2 0.2427 d2 0.1087 d2 0.2653

d3 0.1716 d3 0.0829 d3 0.1895

Phase System of symmetry Lattice plane Interplanar spacing/nm

Cu5Zr cubic

(200) 0.3435

(220) 0.2429

(400) 0.1717

Cu9Zr2 tetragonal

(200) 0.3428

(220) 0.2424

(400) 0.1714

Cu8Zr3 orthorhombic

(121) 0.3403

(311) 0.2422

(215) 0.1740

Cu cubic

(200) 0.1808

(311) 0.1090

(331) 0.0829

Cu8O7 tetragonal

(100) 0.5817

(210) 0.2601

(222) 0.1899

Cu4O3 tetragonal

(101) 0.5010

(211) 0.2517

(301) 0.1904

Cu2O cubic

(100) 0.4217

(111) 0.2435

(210) 0.1886

Drawing ratio, η

2000

1500

1000

500

0

UT

S /M

Pa

0

0

2 4 6 8 10 12

2 4 6 8 10 12

Drawing ratio, ηE

C (

%IA

CS)

100

80

60

40

0

20

Cu-xat%Zr

Cu-xat%Zr

, 13-17) : x = 1

, 13-17) : x = 3

, 13-17) : x = 5

, 13-17) : x = 1

, 13-17) : x = 3

, 13-17) : x = 5

Fig. 6 Relationship between the drawing ratio and ultimate tensile strength(UTS) and that between the drawing ratio and electrical conductivity (EC)for the drawn Cu-x at%Zr (x = 1, 3 and 5) alloy wires. Open symbols areobtained by this work, and closed ones are cited from the previousstudy.13­17)

Table 3 Hardness (HIT) and Young’s modulus (E) of the intermetalliccompound Cu5Zr measured over a defined range 20­40 nm using thenanoindentation technique.

Cu5ZrHardnessHIT/GPa

Young’s modulusE/GPa

Average 6.3 159.5

Std. dev 1.1 18.4

N. Muramatsu and T. Goto1218

intermetallic compound Cu5Zr phase in the sinteredspecimens increased with an increase in the Zr content.

(2) The ultimate tensile strength (UTS) values of thesintered specimens increased, while their electricalconductivity (EC) values decreased simultaneously.

(3) The Cu-1, Cu-3 and Cu­5 at%Zr alloy wires prepro-cessed by SPS exhibited dual-phased microstructures inwhich the intermetallic compound Cu5Zr was dispersedfinely within the Cu matrix.

(4) Finally, the drawn Cu-1, Cu-3 and Cu­5 at%Zr alloywires preprocessed by SPS, whose diameters anddrawing ratios (©) were 0.037mm and 11.2, 0.16mmand 8.3, and 0.60mm and 5.6, respectively, exhibitedUTS and EC values of 603MPa and 87% IACS,698MPa and 70% IACS, and 789MPa and 52% IACS,respectively. These values were about 40­56% lower(in the case of the UTS values) and about 28­60%higher (in the case of the EC values) than thosepreviously reported for wires preprocessed by casting.

(5) The results showed that the lamellar structures of the ¡-Cu and eutectic (Cu + intermetallic compound Cu9Zr2)phases in the drawn wires preprocessed by casting wereeffective in improving the mechanical properties of thewires. The microstructures of intermetallic compoundCu5Zr, which was uniformly dispersed within the Cumatrix in the drawn wires preprocessed by SPS, wereadvantageous for improving the electrical conductivityof the wires.

Acknowledgements

The authors wish to thank Professor Hisamichi Kimuraand Mr. Akira Okubo of the Institute for Materials Research(IMR), Tohoku University for their support during this study.

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10μm 10μm 10μmD. A.

(a) (b) (c)

(Cu5Zr)

(Cu)

Fig. 7 SEM-BEI micrographs of the cross-sections of the Cu-x at%Zr alloy wires parallel to the drawing axis (D. A.). (a) x = 1; © = 11.2,(b) x = 3; © = 8.3, and (c) x = 5; © = 5.6.

Microstructures and Mechanical and Electrical Properties of Hypoeutectic Cu-1, C-3 and Cu-5 at%Zr Alloy Wires 1219