Concurrence of de-alloying and re-alloying in a ternary Al67Cu18Sn15 alloy and the fabrication of 3D nanoporous Cu-Sn composite structures

Article abstract of DOI:10.1039/c4ra15622f

We report the concurrence of de-alloying and re-alloying in a ternary Al₆₇Cu₁₈Sn₁₅ alloy (at.%) de-alloyed in a 5 wt% hydrochloric acid (HCl) solution at 70 ± 2°C, and the fabrication of three-dimensional (3D) nanoporous Cu₃Sn-Cu-Cu₆Sn₅ composites in the form of self-supporting foils. Re-alloying occurred in Al₆₇Cu₁₈Sn₁₅ compared to de-alloying alone in binary Al-Cu alloys. Both Cu₃Sn and Cu₆Sn₅ phases formed through an accompanied re-alloying process. This finding further proves the temperature sensitivity of phase formation in the Cu-Sn system established from Cu-Sn diffusion couple studies, and demonstrates the capability of designing and creating nanoporous composite materials via de-alloying a multicomponent alloy.

Full text of DOI:10.1039/c4ra15622f

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Concurrence of de-alloying and re-alloying in a
ternary Al67Cu18Sn15 alloy and the fabrication of 3D
nanoporous Cu–Sn composite structures
Cite this: RSC Adv., 2015, 5, 9574
a
a
b
c
a
*
T. Song, M. Yan, Y. Gao, A. Atrens and M. Qian
We report the concurrence of de-alloying and re-alloying in a ternary Al67Cu18Sn15 alloy (at.%) de-alloyed in
a 5 wt% hydrochloric acid (HCl) solution at 70 ꢀ 2 ꢁC, and the fabrication of three-dimensional (3D)
nanoporous Cu3Sn–Cu–Cu6Sn5 composites in the form of self-supporting foils. Re-alloying occurred in
Al67Cu18Sn15 compared to de-alloying alone in binary Al–Cu alloys. Both Cu3Sn and Cu6Sn5 phases
formed through an accompanied re-alloying process. This finding further proves the temperature
sensitivity of phase formation in the Cu–Sn system established from Cu–Sn diffusion couple studies, and
demonstrates the capability of designing and creating nanoporous composite materials via de-alloying a
multicomponent alloy.
Received 2nd December 2014
Accepted 5th January 2015
DOI: 10.1039/c4ra15622f
www.rsc.org/advances
binary AB alloy involves the dissolution of A, and the diffusion
of B.17 Both the rate of dissolution of A, and the surface diffu-
1. Introduction
sivity of B, have a signicant inuence on the formation of the
nanoporous structure, including the size of the ligaments/
channels in the nanoporous B.20
De-alloying is the selective dissolution of one or more compo-
nents from an alloy, leaving behind a material enriched in the
nobler or less active alloy component. This approach was used
as early as during the Incan civilization to dissolve the more
active element Cu from dilute AuCu alloys to create the illusion
of a pure gold artefact.1 The last decade has seen a renewed
interest in this approach due to its capability of producing
nanoporous structures, which holds promise for applications as
sensors2,3 and catalysts based on their high specic surface
areas.4
There are two prerequisites for an alloy to undergo de-
alloying:5–7 (i) the constituting elements in the alloy should have
different electrochemical activities (e.g. A is less noble whilst B
is nobler in a binary AB alloy);5 and (ii) the concentration of the
nobler element B is below a critical composition, referred to as
parting limit, beyond which de-alloying does not take place due
to surface passivation by the nobler element B.6,7 Many binary
alloys meet these two requirements, including single solid-
solution alloys of Au–Ag,8 Pt–Co,9,10 and Au–Cu,11 and two-
phase alloys of Al–Cu,12,13 Al–Ag,14 Zn–Cu15 and Mg–Cu.12,16
They have been de-alloyed to produce nanoporous pure metals,
and the mechanisms that control the nanoporosity and pattern
formation have been investigated.6,7,9,10,12–19 De-alloying of a
Research on de-alloying over the last decade has been largely
focused on de-alloying of binary alloys (AB) with a view to
producing nanoporous structures of essentially pure metal B, and
understanding the de-alloying process. Only a few studies have
dealt with de-alloying of alloys containing a third element such as
22
24
Mg90ꢂxCuxY10,21 Mg77Ag18.4Pd4.6
,
Ag64Au30Pt6,23 Al75Pt15Au10
and Al66Au27.2X6.8 (X ¼ Pt, Pd, PtPd, Ni, Co and NiCo)
(in at.%).25,26 However, it should be pointed out that in these
ternary ABC alloys, the third element C introduced was similar
to the nobler element B, a slow diffuser. The purpose was to
slow down the surface diffusivity of B, in order to decrease the
ligament/channel size of the resulting nanoporous B.21–23,26 The
small amount of this third element C substituted for the noble
element B in the lattice of the precursor alloys.21–23,26 Accord-
ingly, de-alloying of these deceptively ternary alloys was no
different from the de-alloying of binary alloys.
For de-alloying of ternary alloys (ABC), which consist of three
distinctly different elements, the only research reported to date
appears to be that by Feng et al.27 As with de-alloying of binary
AB alloys, which produces nanoporous structures of essentially
pure metal B, de-alloying of ternary ABC alloys has the potential
to produce nanoporous composite structures with constituting
elements B and C and with characteristics different from those
de-alloyed from binary alloys for various applications. In addi-
tion, de-alloying of ternary alloys is expected to show different
dissolution and diffusion behaviors due to the involvement of
the third distinctly element. Understanding their de-alloying
characteristics is necessary for the fabrication of more
aRMIT University, School of Aerospace, Mechanical and Manufacturing Engineering,
Centre for Additive Manufacturing, Melbourne, VIC 3001, Australia. E-mail: ma.
qian@rmit.edu.au
bShanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai
University, 200072 Shanghai, P.R. China
cThe University of Queensland, Division of Materials, School of Mechanical and Mining
Engineering, Brisbane, QLD 4072, Australia
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complex nanoporous metal structures aside from enhancing samples, it was found that complete de-alloying of each sample
the knowledge base of de-alloying. required about 480 min. On this basis, samples were de-alloyed
This paper studied the de-alloying of a ternary Al67Cu18Sn15 for various durations from 60 min to 480 min. This permitted a
alloy at 70 ꢀ 2 ꢁC in a selected acid solution. The rationale for the systematic study of the de-alloying process. De-alloyed samples
selection of an AlCuSn ternary alloy is given as follows. First, were removed from the acid solution, rinsed in distilled water
dense nanostructured intermetallic Cu6Sn5 anodes outperform and dehydrated with alcohol.
pure Sn anodes in lithium ion batteries, where the inactive Cu
The phase constitution and microstructure were character-
matrix can act as a stress buffer to accommodate the large ized using X-ray diffraction (XRD, Bruker D8 instrument, with
volume change caused by lithiation/delithiation during battery Cu Ka radiation, with a scanning rate of 1ꢁ minꢂ1), scanning
operation.28–30 The use of a nanoporous structure has proved to electron microscopy (SEM) in both the second electron (SE)
be effective to absorb the volume change of the anode material in imaging and backscattered electron (BSE) imaging modes (JEOL
lithium ion batteries, such as nanoporous SnO2 anodes31 and 7001, operated at 15 keV equipped with energy dispersive X-ray
nanoporous Ge–C anodes.32 Nanoporous Cu–Sn based compos- spectroscopy (EDX) made by INCA). Transmission electron
ites, if they can be created by de-alloying of a ternary AlCuSn alloy, microscopy (TEM) and selected area electron diffraction (SAED)
may have the potential to show desired strain-accommodation (from JEOL 2100, operated at 200 kV) were also employed to
capabilities due to their nanoporous structure. In addition, study the microstructure and phase constitution. Samples for
they may offer some good composite strain buffer ability too, like TEM analysis were prepared by grinding the as-dealloyed foils
the Sn–Cu composites.28–30 Second, Al is electrochemically more into powder, followed by dispersing the powder in ethanol by
active than both Cu and Sn.5 This allows the creation of various ultrasonic, and nally releasing just a few drops of the particles-
Cu–Sn based nanostructures via the de-alloying of AlCuSn alloys. containing ethanol solution on a 3 mm diameter carbon lm
Third, both Cu and Sn have fast self-diffusion rates,33 which are supported on a copper grid. Aer drying in air for 20 min, the
in favour of complete de-alloying of the entire sample. Addi- powder samples were ready for TEM analysis.
tionally, Cu atoms can diffuse interstitially into Sn even at room
temperature to enable intermetallic formation.34,35 These char-
acteristics imply that AlCuSn alloys are promising candidate
3. Results
3.1 Phase constitution of precursor
ternary precursors for the creation of a Cu–Sn based nanoporous
structure via de-alloying of the Al. The composition of the ternary
Al67Cu18Sn15 alloy was determined as follows. The concentration
of 67 at.% Al was chosen to be close to the parting limit of Al6,7
whilst the relative concentrations of Cu and Sn were chosen to
match the ratio of 1.2 : 1 for Cu to Sn in Cu6Sn5.30 The selection of
Fig. 1 presents the XRD patterns and a typical SEM micrograph
of the precursor Al67Cu18Sn15 alloy, which consisted of three
phases: a-Al(Cu, Sn) solid solution, b-Sn(Al, Cu) solid solution,
and the Al2Cu intermetallic. At room temperature, the solubility
limits of Cu and Sn in Al are 5.5 wt% 36 and 0.12 wt%,37
respectively, whilst b-Sn(Al, Cu) contains only up to 0.06 wt% Al
and 0.005 wt% Cu.38 Hence, the solid solutions are essentially a-
Al(Cu) and metallic b-Sn. Fig. 1 shows the a-Al(Cu) phase (dark
contrast), the Al2Cu phase (grey contrast), and the Sn phase
(bright contrast, enveloping the Al2Cu phase), using the BSE
imaging mode. These observations are consistent with the Al–
Cu–Sn ternary phase diagram.39
ꢁ
the de-alloying temperature (70 ꢀ 2 C) is based on the phase
formation sequence in the Cu–Sn system established from Cu–Sn
diffusion couple studies,35 which identied that below 60 ꢁC only
Cu6Sn5 forms while at or above 60 ꢁC both Cu6Sn5 and Cu3Sn can
develop.35 Feng et al.27 have recently reported the formation of
Cu6Sn5 by de-alloying of an Al10Cu3Sn alloy at 60 ꢁC but no
ꢁ
formation of Cu3Sn was observed. The selection of 70 ꢀ 2 C is
expected to lead to the formation of Cu3Sn and this will allow us
to compare the phase formation in de-allying with the observa-
tions made from diffusion couple studies.
3.2 Phase constitution and morphology evolution during
dealloying
The following observations are notable aer various durations
of de-alloying from 60 to 480 min according to the XRD patterns
shown in Fig. 2a and b.
2. Experimental
The Al67Cu18Sn15 alloy was prepared from 99.99% purity Al,
99.99% purity Cu and 99.999% purity Sn using arc melting
under argon. The alloy was remelted four times to ensure
chemical homogeneity. The molten alloy from the fourth
remelting was sucked into a water-cooled copper mould with a
cavity of 8 mm in diameter and 30 mm in length, by the pres-
sure differential between the mould and melting chamber. Disc
samples were cut from the rod, ground and polished into 0.6
mm thick foils (8 mm in diameter).
De-alloying of the foil samples was carried out at 70 ꢀ 2 ꢁC in
200 ml of 5 wt% HCl aqueous solution. A hot plate and a
mercurial thermometer were used to control the temperature.
Fig. 1 XRD pattern and SEM BSE microstructure of the Al67Cu18Sn15
According to the preliminary tests performed on three disc precursor.
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(i) The a-Al(Cu) had disappeared aer the rst 60 min de-
alloying, and there were new phases, identied to be Cu3Sn,
Cu and Cu6Sn5 with a preponderance of the Cu3Sn phase. In
addition, there was a noticeable decrease in the intensity of the
XRD peaks for both Al2Cu and Sn. Fig. 3 shows the micro-
structures aer 60 min, 120 min and 180 min de-alloying. The
preferential de-alloying of a-Al(Cu) can be seen from Fig. 3a.
Fig. 3b shows remnants of Sn and a surface nanoporous
structure (with an average ligament width of 40 ꢀ 8 nm) on the
Al2Cu substrate, which is interpreted to be Cu3Sn and/or Cu
according to the XRD results in Fig. 2a and c. With the progress
of de-alloying, the nanoporous structure on the Al2Cu substrate
became increasingly coarser (see Fig. 3c and d) while the
amount of Cu3Sn and/or Cu continued to increase (see Fig. 2a).
(ii) No Sn was detected by XRD aer 240 min de-alloying, and
there was a noticeable decrease in the intensity of the XRD
peaks for Al2Cu. The SEM BSE image in Fig. 4a conrmed the
absence of Sn. The surface nanoporous structure aer the rst
180 min de-alloying (Fig. 3b–d) had further developed aer 240
min de-alloying as shown in Fig. 4b. TEM selected area electron
diffraction (SAED) identied the presence of both Cu3Sn and
Cu6Sn5 (Fig. 4d), consistent with the XRD results.
(iii) The Al2Cu phase remained aer 300 min de-alloying but
had disappeared aer 480 min de-alloying (Fig. 2b), indicative
of complete de-alloying of the Al2Cu phase. This was conrmed
by the microstructures shown in Fig. 5a and b, in which no
Al2Cu was observed. The three strongest XRD lines in the 2q
range of 23–47ꢁ for each of the Cu3Sn (JSPDS reference no. 03-
065-4653), Cu (00-004-0836) and Cu6Sn5 (01-076-2703) phases in
the International Centre for Diffraction Data (ICDD) database
are shown in Fig. 2c to assist in phase identication.
Fig. 3 (a) SEM image showing preferential de-alloying of a-Al(Cu)
(circled); (b) remnants of Sn (arrowed) and nanoporous Cu3Sn and Cu
on Al2Cu substrate; (c) and (d) surface nanoporous structures after 120
min and 180 min de-alloying.
ligament width of 170 ꢀ 50 nm was obtained on the surface
(Fig. 5a and b) and throughout the longitudinal section (Fig. 5c
and d). The inhomogeneous microstructure observed aer 240
min (Fig. 4c) and 300 min de-alloying (Fig. 4e and f) had evolved
into a homogenous nanoporous structure (Fig. 5c). TEM
examination conrmed the nanoporous nature of the product
(Fig. 5e). Also, the existence of Cu3Sn and Cu6Sn5 was identied
by SAED and high resolution TEM images (Fig. 5f), consistent
The microstructure of the nal dealloyed product is shown
in Fig. 5. A nanoporous microstructure with an average
Fig. 2 (a and b) XRD patterns of Al67Cu18Sn15 alloy after de-alloying in
a 5 wt% HCl solution for up to 480 min; and (c) three strongest Fig. 4 (a) and (b) surface nanoporous structures of Cu3Sn–Cu–
diffraction lines (in 2q range of 23–47ꢁ) for each of the Cu3Sn, Cu and Cu6Sn5; (c) inhomogeneous microstructure on cross section; (d) TEM
Cu6Sn5 phases in the ICDD database together with XRD patterns SAED results of Cu3Sn and Cu6Sn5 after 240 min de-alloying; and (e)
obtained from samples after 60 and 480 min de-alloying.
and (f) inhomogeneous microstructure after 300 min of de-alloying.
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De-alloying of the Al2Cu phase also occurred in this process,
as informed by the notable decrease in the intensity of the Al2Cu
XRD peaks. Considering both the release of H2 and the presence
of free Cu in the nal de-alloyed product, the de-alloying
process of Al2Cu may be described by eqn (2) below
Al2Cu(s) + 6HCl(l) / 2AlCl3(l) + Cu(s) + 3H2(g)
(2)
As mentioned previously, the only other study of de-alloying
of ternary AlCuSn alloys was that by Feng et al.27 Table 1 lists the
distinct differences between this study and Feng et al.'s work.27
(i) Different precursors. The precursor used in ref. 27 was
based on Cu3Sn while this study is based on Cu6Sn5 (18 : 15 ¼
6 : 5) aiming to obtain a nanoporous Cu6Sn5, as the Cu6Sn5
compound has proved to outperform pure Sn as anode
material.28,29
(ii) Different electrolyte solutions. Both NaOH and HCl
solutions are able to dissolve Al from Al-based alloys for de-
alloying.12–14,24,40,41 The selection of HCl solutions is comple-
mentary to the selection of NaOH solutions for the de-alloying
of AlCuSn alloys27 and it can also show the inuence of elec-
trolyte on the de-alloying of AlCuSn alloys.
(iii) Different de-alloying temperatures. Detailed ꢁ Cu–Sn
Fig. 5 Nanoporous structures of Cu3Sn–Cu–Cu6Sn5 produced after
480 min de-alloying: (a) and (b) surface; (c) and (d) cross section; (e)
bright field (BF) TEM image confirming the nanoporous structure; and
(f) HRTEM image and TEM SAED results of Cu3Sn and Cu6Sn5 phases.
The nanoporous Cu3Sn–Cu–Cu6Sn5 composite is produced in the
form of self-supporting foils (0.6 mm thick and 8 mm in diameter).
diffusion couple studies have indicated that below 60 C only
ꢁ
Cu6Sn5 forms while at or above 60 C both Cu6Sn5 and Cu3Sn
can form.35 Indeed, Feng et al.27 selected 60 C and conrmed
ꢁ
only the formation of Cu6Sn5 although the ratio of Cu : Sn of
their precursor was designed to be 3 : 1. In contrast, by selecting
ꢁ
70 ꢀ 2 C, both Cu6Sn5 and Cu3Sn formed during de-alloying,
consistent with Cu–Sn diffusion couple studies.35
with the XRD results. EDX analyses detected no Al but did detect
Cu and Sn (as presented in the inset in Fig. 5c). In addition, the
atomic ratio of Cu : Sn detected by EDX analyses is around
78 : 22, which is clearly greater than the ratio of Cu to Sn in
either Cu3Sn (3 : 1) or Cu6Sn5 (1.2 : 1.0). This supports the
detection of free Cu in the de-alloyed sample by XRD. The
nanoporous Cu3Sn–Cu–Cu6Sn5 composite is produced in the
form of self-supporting foils (0.6 mm thick and 8 mm in
diameter).
As a result of the differences discussed above, Feng et al.
obtained nanoporous Cu–Cu6Sn5 (ref. 27) while this study
attained nanoporous Cu3Sn–Cu–Cu6Sn5. These two different
studies are complementary to each other and together they
show the signicances of precursor composition, electrolyte
type, and de-alloying temperature in the de-alloying process of
ternary AlCuSn alloys. Also noticed from the XRD results shown
in Fig. 2a and b is a small presence of the SnO phase in the
samples de-alloyed for 60–300 min. This can be attributed to
oxidation in the de-alloying solution. However, no SnO phase
was detected aer de-alloying for 300 min (Fig. 2b). The
consumption of Sn by oxidation could be one of the reasons
responsible for the lower Sn content in the nal product of
Cu3Sn–Cu–Cu6Sn5 than in the precursor alloy.
4. Discussion
4.1 De-alloying of ternary AlCuSn alloys
a-Al(Cu) has a large volume fraction in the precursor ternary
Al67Cu18Sn15 alloy (Fig. 1). De-alloying of the Al67Cu18Sn15 alloy
started with the preferential dissolution of a-Al(Cu), as evi-
denced by its quick disappearance aer 60 min de-alloying
4.2 Re-alloying of Cu and Sn among de-alloying
The XRD results together with the ICDD information (Fig. 2)
revealed that, there was formation of both Cu3Sn and Cu6Sn5
(Fig. 2a). This is similar to the observations made from the
14
de-alloying of other Al-based alloys (binary Al65Ag35
,
AlCu,12,13,40,41 or ternary Al66Au27.2X6.8 (X ¼ Pt, Pd, PtPd, Ni, Co
and NiCo)26). It was noticed that there was release of hydrogen
(H2) as gas bubbles during de-alloying. Hence the de-alloying
process of the a-Al(Cu) phase may be described as follows
Table 1 De-alloying of ternary AlCuSn alloys
De-alloying system
Feng et al.'s paper27 This study
2a-Al(Cu)(s) + 6HCl(l) / 2Cu(s) + 2AlCl3(l) + 3H2(g) (1)
Precursor composition (at.%) Al10Cu3Sn
Al67Cu18Sn15
5 wt% HCl
Electrolyte solution
20 wt% NaOH
De-alloying temperature (ꢁC) 60
70 ꢀ 2
where the Cu atoms released from this process are limited to
the solubility of Cu in a-Al.
De-alloyed product
Cu–Cu6Sn5
Cu3Sn–Cu–Cu6Sn5
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during de-alloying at 70 ꢀ 2 ꢁC from the early stages (60 min) of together with the experimental observations of this study.
de-alloying to the end (480 min). This means that there has been Previous Cu–Sn diffusion couple studies have established that
re-alloying that occurred between the Cu atoms released from Cu6Sn5 can form over a wide range of temperatures3,27,35,42–44,46,47
ꢁ
reactions (1) and (2) and the Sn atoms in the precursor. These down to ꢂ2 C (Table 2) while Cu3Sn forms mainly at temper-
re-alloying processes may be described by eqn (3) and (4) below. atures above 100 ꢁC.35,42–44,46,47 Dreyer et al.3 reported that Cu3Sn
ꢁ
nucleated at the temperature of 87 C in their Cu/Cu6Sn5 thin
3Cu(s) + Sn(s) / Cu3Sn(s)
6Cu(s) + 5Sn(s) / Cu6Sn5(s)
(3)
(4)
lm diffusion couple study. Itꢁ is clear from Table 2 that the
formation of Cu3Sn at 70 ꢀ 2 C observed in this study is the
lowest temperature reported to date for the intermetallic
formation of Cu3Sn with solid experimental data. This improves
the knowledge base of phase formation in the Cu–Sn system.
Experimental studies have further established that once
nucleated, the apparent activation energy (Ea) for the growth of
Cu3Sn (70.28 kJ molꢂ1), determined over the temperature
range of 120–200 ꢁC, is smaller than that for the growth of
Cu6Sn5 (84.3 kJ molꢂ1 determined over the temperature range
of 70–200 ꢁC).48 This implies that Cu3Sn tends to grow easier
than Cu6Sn5. The preponderance of Cu3Sn over Cu6Sn5 in the
de-alloyed product can be attributed to this reason.
Aer the disappearance of Sn, de-alloying of Al2Cu continued
to release free Cu atoms by reaction (2). However, because of the
absence of Sn, reactions (3) and (4) no longer occurred. The
Cu–Sn diffusion couple studies at temperatures above 100 ꢁC
have identied another reaction, described by reaction (5)
below,35,45,49 for the formation and continued growth of Cu3Sn
in Cu–Sn diffusion couples.
It has long been established that at room temperature, Cu
atoms can diffuse fast (interstitially) into the lattice of Sn,
particularly along the c-axis direction in the lattice of Sn,34 and
then react with Sn to form Cu6Sn5.35,42,43 This occurs at room
temperature and from the formation of many other interme-
tallic compounds which typically occurs at a much higher
temperature. The free Cu atoms released by de-alloying
according to eqn (1) and (2) were expected to be chemically
reactive, as would also be the newly exposed Sn atoms in the
precursor alloy. In addition, the de-alloying or removal of the Al
atoms from the ternary precursor alloy Al67Cu18Sn15 naturally
le Cu and Sn atoms in contact. This enables the formation of
ꢁ
Cu6Sn5 and Cu3Sn during de-alloying at 70 ꢀ 2 C. The forma-
tion of Cu3Sn and Cu6Sn5 is based on the interactions between
Cu and Sn atoms, similar to the recent study of dealloying of
ternary Al–Au–M (M ¼ Ni, Co or NiCo) alloys by Zhang et al.,25
who discussed the importance of the interactions between Au
and other atoms. Our study supports Tu's observation35 that
“the ordered 3-phase (Cu3Sn) was found only in those speci-
mens that had been annealed above 60 ꢁC”, although no
experimental data were given by Tu. It has been found that there
was formation of just Cu6Sn5 during de-alloying of a ternary
1
5
9
Cu6Sn5ðsÞ þ CuðsÞ/Cu3SnðsÞ
(5)
5
It is plausible that the same reaction may have also occurred
in the de-alloying process studied contributing to the prepon-
derance of Cu3Sn over Cu6Sn5 in the nal de-alloyed nano-
porous Cu3Sn–Cu–Cu6Sn5 structures. However, the noticeable
presence of both Cu and Cu6Sn5 detected by XRD aer 480 min
Al10Cu3Sn alloy in a 20 wt% NaOH solution at 60 C.27
Table 2 lists the detailed literature data on intermetallic
formation in the Cu–Sn system under various conditions
ꢁ
Table 2 Intermetallic formation in the Cu–Sn system
Diffusion couple
Temperature (ꢁC)
Duration
Intermetallic compounds
Ref.
Cu/Sn
Cu/Sn
Cu/Sn
Cu/Sn
ꢂ2a
NA
Cu6Sn5
Cu6Sn5
Cu6Sn5
Cu6Sn5
42
42
Room temperature
15 days
One year
10 days
NA
Room temperature
42 and 43
35
42
27
This study
44
3
42 and 43
42
45
46
35
47
44
Room temperature
Cu/Sn
60a
Cu6Sn5 and Cu3Sn
Cu6Sn5
Cu6Sn5 and Cu3Sn
Cu6Sn5
Cu3Sn nucleation
Cu6Sn5 and Cu3Sn
Cu6Sn5 and Cu3Sn
Cu6Sn5 and Cu3Sn
Cu6Sn5 and Cu3Sn
Cu6Sn5 and Cu3Sn
Cu6Sn5 and Cu3Sn
Cu6Sn5 and Cu3Sn
Cu3Sn
Cu/Sn (de-alloying of Al10Cu3Sn)
Cu/Sn (de-alloying of Al67Cu18Sn15
Sn–5Bi–3.5Ag solder/Cu
Cu/Sn
Cu/Sn
Cu/Sn
SnPb solder/Cu6Sn5/Cu3Sn/Cu
Lead-free solder/Cu
Cu/Cu6Sn5
Lead-free solder/Cu
Sn–5Bi–3.5Ag solder/Cu
Cu/Sn
60
8 h
)
70 ꢀ 2
60 min
30 days
NA
36 h
60 h
80 days
>50 h
10 min
NA
30 days
10 min
3–4 min
70, 100 and 120
87
100
100
100, 125 and 150
100, 125, 150 and 170
115–150
150
150, 170 and 200
200
220
35 and 43
45
SnPb solder/Cu
Cu6Sn5 and Cu3Sn
a
Without experimental data. NA: not available.
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de-alloying suggests that reaction (5) may have only occurred to
a small extent by the end of the 480 min de-alloying process.
The two predominant reasons are: (i) reaction (5) is slow; it has
been found that a large amount of residual Cu6Sn5 and Cu still
8 K. Zhang, X. Tan, J. Zhang, W. Wu and Y. Tang, RSC Adv.,
2014, 4, 7196.
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,
determined over the temperature range of 115–150 ꢁC 35
)
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Acknowledgements
T. Song is nancially supported by a China Scholarship Council
(CSC) Scholarship and a RMIT fee waiver scholarship. Y. Gao 26 Y. Wang, J. Xu and B. Wu, Phys. Chem. Chem. Phys., 2013, 15,
acknowledges the Program for Professor of Special Appoint- 5499.
ment (Eastern Scholar) at Shanghai Institutions of Higher 27 Y. Feng, S. Zhang, Y. Xing and W. Liu, J. Mater. Sci., 2012, 47,
Learning (no. TP2014042).
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28 H. C. Shin and M. Liu, Adv. Funct. Mater., 2005, 15, 582.
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