第 4 卷第 2 期 材 　料 　与 　冶 　金 　学 　报 Vol14 No12

　收稿日期 : 2005204213.　作者简介 : 王翠萍 (1963 - ) . 女 , 内蒙古通辽人 , 厦门大学教授 , E2mail : wangcp @xmu1 edu1cn.

2005 年 6 月 Journal of Materials and Metallurgy J une 2005

Design and development of theself2assemble Cu2Fe base composites

WAN G Cui2ping1 , L IU Xing2jun1 , O HNUMA Ikuo2 , KA INUMA Ryosuke2 ,

ISHIDA Kiyohito2

(11Department of Materials Science and Engineering , Xiamen University , Xiamen 361005 ;

21Department of Materials Science , Graduate School of Engineering , Tohoku University , Sendai 980 - 8579 , Japan)

Abstract : The Cu2Fe base alloys with liquid immiscible were prepared by gas atomization technique

and conventional solidification process , the self2assemble composite microst ructures in powders and

bulk materials can be obtained under gravity conditions , respectively , and the minor liquid phase al2ways forms the center of composite microst ructure. It is shown that the formation of the core2type

macroscopic morphology is st rongly connected with the existence of a stable miscibility gap of the liq2uid phase in the Cu2Fe base alloys. This result can be explained by a mechanism that the minor drop2let s as the second phase are forced to move into the thermal center due to Marangoni motion , which is

caused by the temperature dependence of interfacial energy between two liquid phases.

Key words : phase diagram ; liquid miscibility gap ; composite materials ; interfacial energy ; Ma2rangoni motion

中图分类号 : TB 331 　　　文献标识码 : A 　　文章编号 : 167126620 (2005) 0220127205

　　Alloys immiscible in t he liquid p hase region

are characterized by a layer st ruct ure similar tot hat of t he observed separation between oil and

water , and have t hus been considered to be not

of use for technical applications[ 1 ] . Much effort

has t hus been made to obtain a finely disperseddist ribution of bot h liquid p hases for t his kind of

alloys wit h liquid immiscible[2～5 ] . One of t he

mo st interesting t rials was an experiment in

space under microgravity conditions[3 ,4 ] , howev2er , an unexpected core microst ruct ure was ob2served consisting of two layers wit h t he Al2rich

p hase at t he core of t he sample of Al2In alloys ,instead of a uniformly dispersed st ruct ure[3 ] .

This fact suggest s t hat it is difficult to obtain a

finely dispersed microst ructure even wit hout in2fluence of gravity. The p urpose of t he p resentpaper is to design and develop t he self2assemble

composite materials by means of t he feat ure of

alloys with immiscible liquid p hase.

1 　Alloy design and experimentalprocedure

　　In the p resent st udy , some hypermonotectic

Cu2Fe base alloys were investigated. For exam2ple , t he alloys with the composition of Cu23114Fe23Si2016C ( mass f ractoin/ %) and Cu25114Fe23Si2016C ( mass f ractoin/ %) were pre2pared , where the alloy compositions were de2signed to fall into t he stable miscibility gap int he liquid state. Figure 1 shows t he vertical sec2tion ( Fe23Si)2(Cu23Si) of t he p hase diagram cal2culated using t he t hermodynamic parameters as2sessed by Wang et al [6 ] , where t he effect of car2bon is neglected. The volume f ractions of t he

two liquid p hases for Cu23114Fe23Si (mass f rac2toin/ %) and Cu25114Fe23Si ( mass f ractoin/ %)

alloys are also shown in Figs. 1B and 1C , re2spectively. It can be seen t hat t he volume f rac2tions of minor and major liquid p hases are about

40 % and 60 % respectively for bot h alloys. Pow2ders of 30 to 250μm in diameter were obtained

using conventional nit rogen gas atomization un2der an argon atmosp here , where the temperature

of t he melt before atomization was about 1 800to 2 130 K and t he gas p ressure for atomizing

was about 115 to 5 MPa. The cooling rate

was 1 03 to 1 04 ℃/ s , depending on t he size of t he

Fig1 1 　Calculated( A) Vertical section diagram( Fe23Si)2( Cu23Si) quasi2binary system,

and( B) and ( C) the volume fraction of two liquid phases with the Cu25114Fe23Si( mass fraction/ %)

and Cu23114Fe23Si( mass fraction/ %) alloys ,respectively

powder .　　Besides powder materials , t he bulk materi2

als were also investigated. Some Cu2Fe base al2loys of 350 g/ ingot were p repared in aluminacrucibles in a high f requency induction f urnace

under an argon atmosp here by t he following

processes. Af ter t he molten alloys are held for

about 10 min for homogenization , t he molten al2loys were t hen cast into a cylindrical cast2iron

mold.

Macroscopic morp hologies and micro st ruc2t ures of t he ingot s were observed by camera andoptical microscopy , respectively. Samples for

examination of macroscopic morp hologies and

microst ruct ures were etched using a solution

( FeCl3 ∶HCl ∶H2 O = 10 g ∶25 mL ∶100 mL) .

2 　Results and discussion

Figure 2 ( A) shows a typical cross section

microst ructure of t he Cu2rich ( Cu23114Fe23Si2016C ( mass f raction/ %) atomized powder.

More t han 70 % of t he powder shows a two2layer

core microst ruct ure composed of an Fe2core and

Cu2perip hery , and t he Fe2core is seen to be loca2ted almost at t he center of t he sample. In t he

present st udy , we observed a very interesting

p henomenon , namely , a reversal of t he core and

perip hery p hases. Figure 2 (B) shows a typical

microst ructure of t he Fe2rich ( Cu25114Fe23Si2016C (mass f raction/ %) powder wit h a diameter

821 材 料 与 冶 金 学 报 　　　　　　　　　　　　　　　第 4 卷

less than about 50 mm. On t he ot her hand , four

types of typical macroscopic morp hology were

observed in the ingot s of Cu2Fe2X alloys solidi2fied in t he cylindrical cast2iron mold. Figure 3(a) shows a homogeneous morp hology in a cross

section of 4915Cu24915Fe21V (mass f raction/ %)

alloy. An irregular core2type macroscopic mor2p hology , in which it is difficult to distinguish

whet her the core is t he Cu2rich p hase or the Fe2rich p hase , was sometimes observed , as shown

in Fig13 ( b ) . Regular core2type macroscopic

morp hologies with the Fe2rich p hase as t he core

or wit h the Cu2rich p hase as t he core were ob2tained. Typical Cu2core and Fe2core macroscopicmorp hologies in a cross section of t he 48Cu248Fe24V ( mass f raction/ %) and 70Cu226Fe24V(mass f raction/ %) alloys are shown in Figs13(c) and (d) , where t he Fe2rich and Cu2rich p ha2ses are radially separated as two layers in t he in2ner and outer part s of ingot , like pencil2like

composite microst ruct ure , respectively.

Fig12 　( A) Microstructure of the Cu23114Fe23Si2016C( mass fraction/ %) alloys powders and

( B) Microstructure of the Cu25114Fe23Si2016C( mass fraction/ %) alloys powder

　　From t he examination of many alloys , it canbe concluded t hat the minor volume p hase al2ways occupies t he core part , i1e1 , t he Fe2coreand Cu2core st ruct ures are observed in t he Cu2rich and Fe2rich alloys , respectively. This meanst hat t he minor p hase droplet s that appear in t hemajor liquid p hase during cooling , most haverapidly assembled at the center of t he powder a2gainst t he temperat ure gradient [ 7～9 ] .

Young et al . [ 10 ] and Rat ke et al . [5 ,11 ] repor2ted that when there is an interfacial tension gra2dient between a sp herical droplet and a liquidmat rix , t he droplet s move towards t he regionwith lower interfacial energy due to Marangonimotion[ 12 ] . As the viscous resistance f rom t hemat rix is in p roportion to it s velocity , t he drop2let at tains uniform motion. The velocity of t hedroplet in such a steady state is given by

vm≈- 2 r

3 (3μd + 2μm )9σ9 T

9Τ9 x

, (1)

where r is t he radius of t he droplet , μd and μm

are the viscosities of t he droplet and mat rix liq2

uid p hases respectively ,σis t he interfacial ener2gy and x is t he distance[ 10 ,11 ] .

On the other hand , in order to estimate t he

cont ribution of t he interfacial energy gradientdriving the droplet , it may be usef ul to examinet he gravity effect described by Stokes equa2tion[12 ] :

vs≈2 gΔρr2

3μm·

μd +μm

3μd + 2μm, (2)

where g is t he gravity coefficient and Δρis t he

difference of density between the droplet andmat rix p hases.

For example , an Fe droplet wit h r = 5 μmexisting in liquid Cu wit h temperat ure gradient9 T9 x

= 1 000 K/ mm at T = 1 550 K , vm is about 55

mm/ s. This is about 118 ×104 times larger t hanvs ( = 310 ×10 - 6 m/ s) due to t he gravity ( buoy2ancy) effect .

Recently , Cu core solders plated wit h a Pb2Sn eutectic alloy for a B GA joint s have been de2veloped and used , where the Cu core solder ball

921第 2 期　　王翠萍等 : Design and develop ment of the self2assemble Cu2Fe base composites

shows bot h higher st rength and high elect ronic

conductivity in t he core and a low melting point

in t he perip hery. We show a promising B GA ballconsisting of a Cu2base core wit h a Pb2f ree low

melting solder perip hery. A powder of 24Cu216Sn260Bi ( mass f raction/ %) was prepared , in

which a stable liquid miscibility gap appeared asp redicted by t he t hermodynamic database for mi2cro2solder alloys[13 ] . The egg2type st ruct ure of

Cu2Sn rich core wit h Sn2Bi rich perip hery was

obtained. The commercial size of Cu2core ball

plated wit h Pb2Sn eutectic solder is about 700μm , but a size less t han 100μm is required for

t he chip scale package which is very difficult to

p roduce by t he conventional plating method. By

means of t he p resent method , t he size of egg2type powder is about 80μm.

Fig13 　Appearance of a cross section of the ingots for (a) 4915Cu24915Fe21 V ( mass fraction/ %) ,

( b) 52Cu244Fe24 V ( mass fraction/ %) , ( c) 48Cu248Fe24 V ( mass fraction/ %) ,

and ( d) 70Cu226Fe24 V ( mass fraction/ %) alloys solidif ied in a cast2iron mold

031 材 料 与 冶 金 学 报 　　　　　　　　　　　　　　　第 4 卷

3 　Conclusion

On t he basis of atomizing process and con2ventional solidification process , t he self2assem2ble Cu2Fe base compo sites wit h a liquid miscibil2ity gap including t he egg2type powder and pencil2like composite st ruct ures can be designed and

developed based on t hermodynamic calculations.

This simplified fabrication met hod may open up

new applications for t hese alloy materials.

Acknowledgment

This work was supported by a Grant2in2Aidfor the Development of Innovative Technology.

References :

[ 1 ] Predel B. Constitution and t hermodynamics of monotectic

alloys2a survey [ M ] . In Thermodynamics of Alloy Forma2tion , Chang Y A , Sommer F , Eds. Minerals , Metals and

Materials Society , 1997.

[ 2 ] Rat ke L , Diefenbach. Liquid immiscible alloys[J ] . S Mater

Sci Eng , 1995 , R15 : 263.

[ 3 ] Ahlborn H , Lo hberg K. Aluminium2indium experiment

SOL UO G 2 a sounding rocket experiment on immiscible al2loys [ A ] . In 17 t h Aerospace Sciences Meeting [ C ] . Paper

7920172 (New Orleans , 1979) , 3.

[ 4 ] Predel B , Rat ke L , Fredriksson H. Systems wit h a misci2

bility gap in t he liquid state fluid sciences and materials sci2ence in space[ M ] . In Fluid Sciences and Materials Science in

Space : A European Perspective , Walter H U , Ed , Spring2er2Verlag Berlin Heidelberg New York London Paris Tokyo ,

1987 , 517.

[ 5 ] Prinz B , Romero A , Rat ke L . Casting process for hyperm2onotectic alloys under terrest rial conditions[J ] . J Mater Sci ,

1995 ,30 :4715.

[ 6 ] Wang C P , Liu X J , Ohnuma I , et al . Phase equilibria in

Fe2Cu2X ( X : Co , Cr , Si , V) ternary systems[J ] . J Phase

Equilibria , 2002 ,23 :236.

[ 7 ] Wang C P ,Liu X J , Ohnuma I ,et al . Formation of Immis2cible alloy powders wit h egg2type microst ruct ure [ J ] . Sci2ence , 2002 , 297 :990.

[ 8 ] Wang C P , Liu X J , Takaku Y , et al . Formation of core2type macroscopic morphology in Cu2Fe base alloy wit h liquid

miscibility gap [J ] . Metall Mater Trans , 2004 ,35A : 1243.

[ 9 ] Liu X J , Wang C P , Ohnuma I , et al . Calculation of t he

driving force of self2formation for composite microst ructure

in immiscible alloys[J ] . Progress in Natural Science , 2005 ,

15 :169.

[ 10 ] Young N O , Goldstein J S , Block M J . The motion of

bubbles in a vertical temperature gradient [ J ] . J Fluid

Mech , 1959 ,6 :350.

[ 11 ] Rat ke L , Voorhees P W. in Growt h and Coarsening[ M ] .

Springer2Verlag Berlin Heidelberg New York , 2002. 239.

[ 12 ] Marangoni C , Physik D , Dante K L . Ueber die ausbrei2t ung der t ropfen einer flussigkeit auf der oberflache einer

anderen[J ] . Ann Phys Chemie , 1871 , 143 :337.

[ 13 ] Ohnuma I , Liu X J , Ohtani H , et al . Thermodynamic da2tabase for phase diagrams in micro2soldering alloys [J ] . J

Elect ronic Mater , 1999 , 28 :1164.

131第 2 期　　王翠萍等 : Design and develop ment of the self2assemble Cu2Fe base composites