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Short communication

Fabrication of MoCu composites by a diffusion-rolling procedure

Yihang Yang, Gaoyong Lin, Xiaoying Wang, Diandian Chen, Aokui Sun, Dezhi Wang

Key Laboratory of Ministry of Education for Non-ferrous Materials Science and Engineering, School of Material Science and Engineering, Central South University, Changsha 410083, PR China

a b s t r a c ta r t i c l e i n f o

Article history:

Received 25 September 2013

Accepted 9 November 2013

Keywords:

MoCu

Refractory composite

Laminates

Microstructure

Diffusion-rolling

A plastic deformation approach to Mo matrix composites remains a longstanding challenge in the processing of

refractory metal. Toward this objective, we explored a selective fabrication of the diffusion-rolling procedure.

With diffusion bonding initially, a primary sandwich sheet was achieved. The interfacial strength of Mo/Cu

was enhanced by the plastic deformation after rolling. Ultrathin Cu

Mo

Cu sheet and Mo

Cu alloy sheet withCu matrix containing distributed uniformly brous Mo were fabricated. HR-TEM analysis revealed that atomic-

level interdiffusion of Mo and Cu was present at the interface. Therefore, it is concluded that the diffusion-

rolling procedure can be potentially employed as a joining method for the fabrication of Mo Cu composites.

2013 Elsevier Ltd. All rights reserved.

1. Introduction

MoCu composites combinethe refractory properties of Mo withthe

high conductivity of Cu and can be tailored to specic applications by

adjusting therelative amounts of these constituents [1]. These materials

that have high thermal conductivity and a low coefcient of thermal ex-

pansion have become desirable. MoCu composites areused in industri-al applications as electrical contacts, electroerosion segments for hard

metals and heat sinks for packaging microelectronic devices[16].

In general, good solid solubility is essential for sound bond proper-

ties[7,8]. In the case of low inter-solubility metals of Mo and Cu[911],

well-designed bonding procedure remains a challenge. MoCu compos-

ites are traditionally processed by Cu inltration of Mo preforms

[4,5,12]. Laminated composites of MoCu are processed by explosion

bonding [13]. In1998, Saito et al. invented a process, named accumulative

roll bonding (ARB), to impose severe plastic strain ontometallic materials

through the rolling process[14,15]. Different from ARB, the authors now

propose an alternative plastic deformation procedure of diffusion-rolling

[16]for refractory metal composite manufacturing at high productivity

and quality. In this paper, the principle of the diffusion-rolling procedure

and some convincing experimental results are presented.

2. Experimental

Fig. 1schematically represents the multi-stages of diffusion-rolling.

In order to obtain one-body solid material and avoid cracks during

rolling of refractory metal Mo, the diffusion bonding employed initially

was not only a bonding process but also a constraint on its surface. First,

a Mo sheet and two Cu sheets were stacked in the order of CuMoCu.

Before stacking, the sheet surfaces were degreased with acetone and

cloth polished. Then, the three sheets were bonded together by diffu-

sion at 900 C and 10 MPa process pressure for a time of 30 min.

Multi-pass rolling with a thickness reduction of 35% was conducted

for thinner sheet fabrication and bonding strength improvement. At

this stage, ultrathin CuMoCu sheets can be achieved. After that, the

length of rolled composites was sectioned into three partitions. The sec-tioned sheets were again surface-treated, stacked, diffusion bonded and

rolled. The whole process was repeated again and again. At last, MoCu

alloy sheets can be achieved.

As-received commercially pure Mo sheets with a thickness of

3.6 mm and a purity of 99.95 wt.% were used as the core materials.

Oxygen-free copper sheets with a thickness of 2.0 mm and a purity of

99.99 wt.% were used as the cladding materials. The dimension of Mo

sheet was 50 100 mm2, and two Cu sheets were 15 mm longer

than Mo plate for the convenience of roll bite.

Single lap shear specimens were prepared for the evaluation of inter-

facial strength. Thesespecimenswere tested in tension using an Instron-

3369 machine, such that the 1 mm long bond line was subjected to a

shear stress. The tests were carried out at room temperature and at a

loading rate of 1 103

m/min. A scanning electron microscope (SEM,Quanta-200) was used to examine the interface. Image of highresolution

transmission electron microscopy (HR-TEM) was collected on a FEI

Tecnai G2 F20 operated at 200 kV. The cross-sectional TEM sample was

prepared by tripod polishing and Ar ion beam thinned to perforation.

3. Results and discussion

3.1. Layer structures evolution

The layer structures of all-stages of diffusion-rolling procedure were

shown inFig. 2.Fig. 2a shows the diffusion bonded CuMoCu sheet.

Int. Journal of Refractory Metals and Hard Materials 43 (2014) 121124

Corresponding author. Tel.: +86 731 88877221; fax: +86 731 88830202.

E-mail address:dzwang@csu.edu.cn(D. Wang).

0263-4368/$ see front matter 2013 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.ijrmhm.2013.11.003

Contents lists available atScienceDirect

Int. Journal of Refractory Metals and Hard Materials

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / I J R M H M

http://dx.doi.org/10.1016/j.ijrmhm.2013.11.003http://dx.doi.org/10.1016/j.ijrmhm.2013.11.003http://dx.doi.org/10.1016/j.ijrmhm.2013.11.003mailto:dzwang@csu.edu.cnhttp://dx.doi.org/10.1016/j.ijrmhm.2013.11.003http://www.sciencedirect.com/science/journal/02634368http://www.sciencedirect.com/science/journal/02634368http://dx.doi.org/10.1016/j.ijrmhm.2013.11.003mailto:dzwang@csu.edu.cnhttp://dx.doi.org/10.1016/j.ijrmhm.2013.11.003http://crossmark.crossref.org/dialog/?doi=10.1016/j.ijrmhm.2013.11.003&domain=pdf

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After diffusion bonding, ultrathin sheets were achieved by multi-pass

rolling.Fig. 2b shows the roll processed CuMoCu sheet with a thick-

ness of 600 m. The interface of Mo/Cu was at.Fig. 2c shows the roll

processed CuMoCu sheet with a thickness of 350 m. But the inter-

face of Mo/Cu has a slightly wave-like structure.

When the thickness of CuMoCu sheet approaches to the limit of

rolling mill, the procedure of diffusion-rolling was repeated again and

again.Fig. 2d shows the two-cycle processed MoCu laminate with a

thickness of 230 m. The interface of Mo/Cu has a severe wave-like

structure, but the layers were uniform and coherent. When the process

repeated once again, Mo layers became fragmented, displaying multiple

necking due to inhomogeneous deformation of layers and shear bands

crossing the layers. Finally, a compositesheet with Cu matrix containing

uniformly distributed brous Mo was fabricated, as shown inFig. 2e.

3.2. Bond strength

In order to evaluate the diffusion-rolling effect on the bond strength

of CuMoCu clad sheet, the shear tensile test was conducted.Fig. 3

shows the shear tensile specimen and bond strengths of two types of

Mo/Cu interface. It reveals that the diffusion-rolling processed Mo/Cu

interface was twice as strong as the diffusion bonded one, and that

it reached a maximum tensile strength equivalent to 70% of that of

Cu (about 250 MPa), which suggests that interfacial strength was

Fig. 1.Schematic illustration of diffusion-rolling procedure.

Fig. 2.Cu

Mo

Cu sheets and multi-stages processed Mo

Cu alloy.

122 Y. Yang et al. / Int. Journal of Refractory Metals and Hard Materials 43 (2014) 121124

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[16] Yang YH, Lin GY, Chen DD, Zhang R, Wang DZ, Qi F. Fabrication of AlCu laminatedcomposites by diffusion rolling procedure. Mater Sci Technol Lond 2013.http://dx.doi.org/10.1179/1743284713Y.0000000397(in press).

[17] Zhang RG, Acoff VL. Processing sheet materials by accumulative roll bondingand reaction annealing from Ti/Al/Nb elemental foils. Mater Sci Eng A2007;463:6773.

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