Yang 2014 International Journal of Refractory Metals and Hard Materials
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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:[email protected](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:[email protected]://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:[email protected]://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.
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