Download Report

JOURNAL OF RARE EARTHS, Vol. 33, No. 1, Jan. 2015, P. 93
Improving in-vitro biocorrosion resistance of Mg-Zn-Mn-Ca alloy in
Hank’s solution through addition of cerium
ZHANG Fan (张凡)1, MA Aibin (马爱斌)1, 2,*, SONG Dan (宋丹)1, 2,*, JIANG Jinghua (江静华)1, 3, LU Fumin (卢富敏)1,
ZHANG Liuyan (张留艳)1, YANG Donghui (杨东辉)1, 2, CHEN Jianqing (陈建清)1
(1. College of Mechanics and Materials, Hohai University, Nanjing 210098, China; 2. Changzhou Research Institute of Hohai Technology Co., Ltd., Changzhou
213164, China; 3. Marine and Offshore Engineering Research Institute, Hohai University, Nantong 226000, China)
Received 28 April 2014; revised 27 August 2014
Abstract: Two kinds of Mg-Zn-Mn-Ca alloys with and without cerium were designed and fabricated. In-vitro degradation tests
and electrochemical evaluations were carried out to compare their biocorrosion behavior in Hank’s solution at 37 ºC. After adding
cerium, the continuous network distributed Ca2Mg6Zn3 phases in Mg-2Zn-0.5Mn-1Ca alloy (Alloy I) were separated due to the
emerging non-continuously distributed Mg2Ca phase and Mg12CeZn phase. This change led to corrosion acceleration of Mg matrix at the initial stage but also sped up the formation of compact corrosion products for Mg-2Zn-0.5Mn-1Ca-1.5Ce alloy (Alloy
II), and therefore enhanced its biocorrosion resistance. Cerium containing Alloy II has the potential to be used as future biomaterials.
Keywords: biomedical Mg alloy; rare earth alloying; in-vitro degradation; corrosion resistance; rare earths
Due to its low density and high specific strength, magnesium and its alloys are widely used in many industrial
sections including aerospace component, computer parts,
mobile phones, etc. Compared to other commonly used
biomaterials, magnesium and its alloys have excellent
biocompatibility and biodegradability as well as an elastic modulus which is closer to that of human bones and
also a possibility of being gradually dissolved and absorbed after implanting in a physiological environment.
As a result, more and more attention has been paid to
their potential applications as biomedical materials. Recent applications include vascular stents and bone implants[1–3]. However, the Mg alloys commonly used in
recent researches were originally developed for structural
materials and therefore did not consider its bio-safety
necessary for use as biomaterial. Moreover, the degradation rate of these alloys in corrosive medium, especially
in Cl–-containing physiological environment, is so fast
that the implants can not hold their mechanical integrity
before restoration of the human tissue[4–6]. Furthermore,
the volume of hydrogen generated during the corrosion
process of the common magnesium alloys generally exceeds human tolerance[7]. These disadvantages limit the
further applications of commonly used Mg alloys as
biomaterials.
Research has shown that the alloying elements can be
an important factor to influence the corrosion resistance
of magnesium alloys. The common alloying elements include Al, Zn, Mn, Ca and rare-earth (RE) elements.
Among these alloying elements, Al has been regarded as
a neurotoxin which can induce dementia. While toxicity
researches about Zn, Mn, Ca have shown no harm to the
human health[8–10]. Although the toxicity of RE on the
human body is not entirely clear, one thing is reasonable
that toxic effects could be avoided by controlling the released concentration of the RE ions below the critical
toxic concentration[11].
Mn is mainly used to enhance ductility. More important is the formation of intermetallic phases which can
pick up iron (Fe) and can therefore be used to control the
corrosion of magnesium alloys due to the detrimental effect of Fe on the corrosion behavior[10]. In smaller
amounts, Zn contributes to strength due to solid solution
strengthening. It can also improve the castability. But
larger amounts (>2 wt.%) of Zn leads to a decrease of
the corrosion resistance[12]. Ca contributes to solid solution strengthening and precipitation strengthening. It
also acts, to some extent, as a grain refining agent and
additionally contributes to grain boundary strengthening.
In binary Mg-Ca alloys, the Mg2Ca phase is formed
which can improve creep resistance due to solid solution
strengthening, precipitation strengthening and grain
boundary pinning. Larger amounts of Ca (>1 wt.%)
can lead to problems like hot tearing or sticking during
Foundation item: Project supported by National Natural Science Foundation of China (51141002), Natural Science Foundation of Jiangsu Province
(BK2011249) and the Fundamental Research Funds for the Central Universities of China (2011B08214)
* Corresponding authors: MA Aibin, SONG Dan (E-mail: aibin-ma@hhu.edu.cn, songdancharls@hhu.edu.cn; Tel.: +86-25-83787239)
DOI: 10.1016/S1002-0721(14)60388-4
94
JOURNAL OF RARE EARTHS, Vol. 33, No. 1, Jan. 2015
casting[8].
RE elements are introduced into magnesium alloys
normally by master alloys. In general, the RE can be divided into two groups: elements with large solid solubilities in Mg (such as Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and
Lu) and elements with limited solubility in Mg (Nd, La,
Ce, Pr, Sm, Eu). All RE elements can form complex intermetallic phases with Mg, which can act as obstacles
for impeding dislocation movement at elevated temperatures and cause precipitation strengthening. The RE elements with limited solubility form intermetallic phases
early during solidification. Thus, RE elements can arrest
grain boundaries at elevated temperatures and contribute
to higher strength mainly by precipitation strengthening.
This mechanism increases the service temperature of Mg
alloys in transportation industry and improves creep resistance as well as corrosion resistance[13].
In this work, one novel kind of Mg-Zn-Mn-Ca alloy
(nominal composition: Mg-2Zn-0.5Mn-1Ca, designated
as Alloy I) and another RE-containing Mg alloy (nominal composition: Mg-2Zn-0.5Mn-1Ca-1.5RE, designated
as Alloy II) were designed and fabricated after considering the influence of alloying elements on both human
health and corrosion properties of magnesium alloys.
Here, Ce was chosen as an additional RE element by
considering its availability and its reported benefits for
health[14–16]. In-vitro degradation tests and electrochemical evaluation (including open circuit potential, potentiodynamic polarization curves and electrochemical impedance spectra) together with corrosion morphologies
observation were carried out to investigate the biocorrosion behaviour of two new alloys in Hank’s solution
at 37 °C. The influence of the Ce alloying on magnesium alloy was researched by analysis of the microstructure change and degradation products of the novel
alloy.
Table 1 Chemical composition of experimental alloys (wt.%)
1 Experimental
1.1 Materials
Two kinds of alloys were prepared from high purity
Mg (99.99%), pure Zn (99.9%), Mg-5 wt.%Mn master
alloy, Mg-30 wt.%Ca master alloy and Mg-25 wt.%Ce
master alloy. Melting and alloying operations were carried out in a stainless steel crucible, under the protection
of a mixed gas atmosphere of SF6 (0.3 vol.%) and CO2
(Bal.). Pure Zn and master alloys were added to the pure
Mg melts at 730 ºC. The melts were then kept for 30 min
at 730 ºC to ensure that all the required alloying elements
had dissolved in the molten alloy. It was then cooled to
700 ºC and poured into a steel mold, which had been
pre-heated at 200 ºC, to form an ingot. The chemical
compositions of the alloys were analyzed by inductively
coupled plasma optical emission spectrometry (ICP-OES)
(Iris Advantage 1000, USA), as listed in Table 1.
Alloys
Zn
Mn
Ca
Ce
Mg
Alloy I
2.13
0.43
Alloy II
2.00
0.50
0.90
–
Bal.
1.02
1.35
Bal.
1.2 Microstructure characterization
The microstructures of the alloys were examined by
BX51M (Olympus, Japan) optical microscopy (OM) and
S340-N (Hitachi, Japan) scanning electron microscopy
(SEM) with energy dispersive spectrum (EDS). The
preparation of OM/SEM samples consisted of grinding
on SiC paper up to 2000 grit and subsequent mechanical
polishing. Before observation, the samples were etched
using 4 vol.% nitric acid in ethanol for 5–8 s, thoroughly washed with water and alcohol, and then dried
by hot air.
For the phase analysis, X-ray diffraction (XRD) measurements were performed using a Bruker D8 Advance
(Bruker AXS, Germany). The samples were investigated
in parallel beam geometry, using Cu Kα1 radiation. The
diffraction patterns were measured from 2θ (10º–90º) for
each sample with the scanning rate of 2 (º)/min.
1.3 Immersion test
Table 2 presents the chemical composition of the
Hank’s solution used in this work. Hank’s solution was
made using BS004 Hank’s Balance Salts (without sodium bicarbonate, Merck Millipore Beijing Skywing),
sodium bicarbonate (reagent grade) and distilled water.
The initial pH value of Hank’s solution was 7.4, which is
similar to that of human’s blood plasma.
The immersion tests were conducted for 10 d at
37±0.5 ºC using water bath to evaluate the rate of in-vitro
degradation, under the condition of refreshing the Hank’s
solution each day. Samples for immersion testing with a
dimension of 10 mm×10 mm×5 mm were cut from the
cast ingot. Pure magnesium sample was used here as
contrast. The specimens were polished with emery papers up to 2000 grit, cleaned ultrasonically in alcohol,
and then dried in open air. All specimens were immersed
in 500 mL beaker containing 300 mL Hank’s solution.
Hydrogen bubbles from each specimen were collected
into a burette.
1.4 Corrosion morphology observation
After the immersion test, the specimens were cleaned
with chromate acid (200 g/L CrO3+10 g/L AgNO3) for 5
min to remove the corrosion products, and then cleaned
with distilled water and dried in air. The surface morTable 2 Chemical composition of Hank’s solution used in
this work (mmol/L)
Solution NaCl CaCl2 MgSO4 KCl KH2PO4 Na2HPO4 D-Glucose NaHCO3
Hank’s
137
1.261
0.814 5.33
0.44
0.338
5.56
4.17
ZHANG Fan et al., Improving in-vitro biocorrosion resistance of Mg-Zn-Mn-Ca alloy in Hank’s solution through …
95
phologies before and after removal of corrosion products
were observed by a HIROX KH-7700 digital microscope
regularly. The chemical compositions of the corrosion
products were examined using a PHI 5000 VersaProbe
(UlVAC-PHI, Japan) X-ray photoelectron spectroscope
(XPS) and EDS. For the XPS analysis, the specimen was
removed from the solution, washed with distilled water,
dried and then some corrosion products were collected
for XPS analysis by scraping the surface.
tential through a frequency domain from 100 kHz down
to 10 mHz. The EIS was recorded after achieving a steady
state OCP. The potentiodynamic polarization tests were
carried out with a scanning rate of 1 mV/s over the potential range from –1.8 V vs. SCE to different anodic limits.
1.5 Electrochemical measurement
Fig. 1 shows the microstructures of Alloy I and Alloy
II. The grain size of Alloy I is about 125 μm, but that of,
the Ce-containing, Alloy II was reduced to 65 μm. For
both alloys, second phases, mainly strip-like, distributed
along the grain boundaries while some granular phases
were also found within the inner grains. It is obvious that
the non-continuously distributed part of second phases
increased after rare earth alloying. Fig. 2 shows the
chemical composition of the second phases identified by
EDS. For Alloy I, the second phases at the grain boundary and inner grain were composed of Mg, Zn and Ca
elements as shown in Fig. 2(a), and the atomic ratio of
Zn to Ca was about 1.25. According to the ternary phase
diagram of Mg-Ca-Zn[17] and the XRD patterns shown in
Fig. 3, the second phase was identified as ternary
Ca2Mg6Zn3 phase. However, after the addition of Ce, additional Mg2Ca and Mg12CeZn phase appeared in Alloy
II. The addition of Ce changed the composition and the
distribution of the second phase, thus further affecting
the corrosion properties of the alloy.
Rectangular specimens were molded into epoxy resin
with only one side, with area of 1 cm2, exposed for the
test. Pure magnesium samples were used here as contrast.
The working surface was ground with SiC emery papers
up to 2000 grit. Before the electrochemical measurement,
all the specimens were immersed in Hank’s solution from
1 h up to 10 d. Electrochemical tests were carried out at
37 °C in a beaker containing 250 mL Hank’s solution on
a PARSTAT 2273 advanced electrochemical system using a standard three-electrode configuration. The configuration was made up of a saturated calomel electrode
(SCE) as a reference, a platinum electrode as a counter
and the sample as a working electrode. All the samples
were first used to measure electrochemical impedance
spectroscopy (EIS), and then their potentiodynamic polarization curves were obtained. Before the EIS step, the
open circuit potential (OCP) curve of each sample was
recorded up to 1800 s. The impedance diagrams were
recorded at the OCP by applying a 5 mV sinusoidal po-
2 Results
2.1 Microstructure characterization
Fig. 1 Microstructures of Alloy I and Alloy II
(a) OM image of Alloy I; (b) OM image of Alloy II; (c) SEM image of Alloy I; (d) SEM image of Alloy II with the arrows indicating
the non-continuous second phase
96
JOURNAL OF RARE EARTHS, Vol. 33, No. 1, Jan. 2015
Fig. 2 EDS analysis of the secondary phases in the cast samples
(a) Alloy I; (b) Alloy II
Fig. 3 XRD patterns of Alloy I and Alloy II
2.2 Immersion test
Fig. 4 presents the hydrogen evolution data of the
samples immersed in Hank’s solution. The curves can be
summed up into three stages. In the initial stage (less
than 50 h), the corrosion products formed gradually on
the surface and all the samples showed low degradation
rate. During the immersion period from 50 to 150 h, the
degradation rate of all the samples increased. This may
be related to the local pitting corrosion which occurred
on the surface of corrosion products. After 150 h of immersion, the degradation rate of HP Mg sample increased
further, whereas the other two alloys showed almost constant degradation rates. This phenomenon is probably
due to the corrosion barrier effect caused by the second
phases in the alloys. Table 3 lists the average degradation
rate of each sample. The mean degradation rate of HP
Mg is the highest, while the Ce-containing Alloy II
Fig. 4 Hydrogen evolution of as cast samples immersed in
Hank’s solution
Table 3 Degradation rate (mL/cm2/d) of the samples
Samples
Steady period
Average
Alloy I
3.25
2.79
Alloy II
2.36
2.02
HP Mg
5.09
3.76
shows the best corrosion resistance.
Fig. 5 shows the surface morphologies of each sample
immersed in Hank’s solution. It is obvious that there are
white corrosion products heterogeneously distributed on
each sample surface. Fig. 6 shows the surface morphologies of each immersed sample after the removal of corrosion products. The HP Mg sample showed an almost entirely corroded morphology with several obvious corrosion pits (dark pits in Fig. 6(c)). Alloy II maintained the
most “no-corroded” area (bright area in Fig. 6(b)), thus
showed the best corrosion resistance after a long period
ZHANG Fan et al., Improving in-vitro biocorrosion resistance of Mg-Zn-Mn-Ca alloy in Hank’s solution through …
97
Fig. 5 Macro morphologies of the samples after immersion in Hank’s solution for 10 d
(a) Alloy I; (b) Alloy II; (c) HP Mg
Fig. 6 Macro morphologies of the samples after removal of corrosion products
(a) Alloy I; (b) Alloy II; (c) HP Mg
of immersion which is in accordance with the hydrogen
evolution data.
2.3 Electrochemical measurements
Fig. 7 illustrates the OCP curves of the alloy samples
compared with HP Mg. All the OCP curves of the samples experienced two stages, which are, the rapid growth
at initial stage and the subsequent stage of slow decline
until balance. Both alloy specimen possessed higher initial OCP values than that of HP Mg, and the initial OCP
value of Alloy II sample was the highest due to the addition of Ce. Furthermore, the required time for the cast
alloy samples to arrive at their peak OCP value are less
than that of HP Mg, and this time tends to decrease with
Fig. 7 OCP curves of the samples immersed in Hank’s solution
for the initial 1800 s
the addition of Ce. This initial potential increase to a
maximum is consistent with an incubation period for the
initiation of corrosion. Considering that the steady OCP
value represents the corrosive tendency of a sample at the
initial stage, the lowest steady OCP value for Alloy II
sample indicates that it will easily undergo corrosion
during the first hours of immersion. This phenomenon is
consistent with the hydrogen evolution data.
Fig. 8 presents the potentiodynamic polarization curves
of the samples. Both polarization curves of the two alloys
are similar in shape, but are different from that of pure
magnesium. The corrosion potential (Ecorr) and corrosion
current density (icorr) were calculated from the intersection of the anodic and cathodic Tafel line extrapolations
as listed in Table 4. Although the Ecorr of the two alloys
Fig. 8 Potentiodynamic polarization curves for the samples after
immersion in Hank’s solution for 1 h
98
JOURNAL OF RARE EARTHS, Vol. 33, No. 1, Jan. 2015
Table 4 Ecorr and icorr of as-cast samples and HP Mg
related with the pitting corrosion of magnesium alloy[20–22]. It is obvious that the capacitive arc diameters of
the as-cast alloy samples are much larger than that of HP
Mg not only at the early stage but also after a long period
of immersion. Moreover, the Alloy II sample always had
a maximum diameter of the capacitive arc.
In order to provide better explanation of the corrosion
behavior of each sample in Hank's solution, Randles
equivalent circuit was used to fit the electrochemical impedance spectroscopy data as shown in Fig. 9(d).
Wherein Rs, Rct and C represent the solution resistance,
the charge transfer resistance and the double layer capacitor or an oxide film capacitance, respectively. Taking
into account the inductive reactance behavior exhibited
by the specimen in the low frequency area, the inductive
components L was added in the Randles equivalent circuit. Zsimpwin impedance fitting software was used to
obtain the parameters of each component in equivalent
circuit. The charge transfer resistance is the most important parameter, which can be used to characterize the
corrosion resistance of each sample. Table 5 is a list of
the Rct values for each sample, Alloy II sample had the
highest Rct value which indicates the best corrosion resistance in Hank’s solution.
Samples
Ecorr/V
icorr/(A/cm2)
HP Mg
–1.481
5.74×10–5
Alloy I
–1.465
2.65×10–5
Alloy II
–1.458
1.14×10–5
show only a slight difference (–1.458 V for Alloy II and
–1.465 V for Alloy I), the icorr of Alloy II (1.15×10–5
A/cm2) is much lower than that of Alloy I (2.65×10–5
A/cm2). In the Tafel extrapolation method for measuring
the corrosion rate, the corrosion current density, icorr
(mA/cm2) is estimated by Tafel extrapolation of the cathodic branch of the polarization curve, and icorr is related
to the average corrosion rate using[18] Pi=22.85icorr.
Therefore, the icorr of the alloys can characterize the corrosion resistance and the relative relationship of icorr is in
accordance with the result of immersion test.
Fig. 9 represents the Nyquist plots of as cast samples
and HP Mg after immersion in Hank’s solution. All the
samples have similar shape of the Nyquist spectra, which
consist of a capacitive arc in the high frequency stage
and an inductive loop in the low frequency stage. Nadine
et al.[19] pointed out that the capacitive arc was caused by
dissolution of metal in corrosive media and the diameter
of the capacitive arc was associated with charge transfer
resistance which could indirectly characterize the corrosion resistance. The larger the capacitive arc diameter,
the better the corrosion resistance of the material. The
inductive loop is more complex and it is proposed to be
Table 5 Fitting values of Rct (Ω·cm2) for the samples
Time
HP Mg
Alloy I
Alloy II
1h
804
3336
3761
2d
720
1092
1728
10 d
194
302
411
Fig. 9 Nyquist plots of the samples after immersion in Hank’s solution for 1 h (a), 2 d (b), 10 d (c) and equivalent circuit of the samples (d)
ZHANG Fan et al., Improving in-vitro biocorrosion resistance of Mg-Zn-Mn-Ca alloy in Hank’s solution through …
99
Fig. 10 EDS analysis of corrosion products of the samples immersed in Hank’s solution for 1 d
(a) Alloy I; (b) Alloy II
2.4 Corrode surface characterization
Fig. 10 illustrates the EDS analysis of corrosion products of the as-cast alloy samples immersed in Hank’s solution for 1 d. For the Alloy I, the corrosion products
showed a morphology with coarse grains and some
cracks on the surface. The EDS spectra indicates that in
the rough area of corrosion morphology, C, O, Mg were
the main elements constituting the corrosion products, in
addition to a small amount of Cl and Ca. As for the Alloy
II, the product had formed relatively dense agglomerates
as illustrated in Fig. 10(b). From the result of the spectra,
its corrosion product mainly contains C, O, P, Mg, and
Ca. The appearance of P in Alloy II indicates that there
are some phosphates in the corrosion products, which
made them more dense.
Fig. 11 shows the XPS spectra for corrosion products
of AlloyⅠafter immersion in Hank’s solution for 10 d.
The main elements of the corrosion products in this stage
for Alloy I samples are O, Mg, Ca, and C. Fig. 12 represents the XPS peak fittings for Ca 2p, C 1s, O 1s and P
2p orbital. Wherein, Ca element is mainly present in the
form of a divalent corrosion product, C element is in the
form of carbonate ion, whereas Mg mainly includes two
forms, as carbonate and magnesium hydroxide. P element is mainly present as phosphate and the content is
relatively small. The analysis of Alloy II sample showed
a similar result. It can therefore be deduced that the corrosion products of the two alloys had no obvious difference after long period of immersion.
Fig. 11 XPS survey spectra for corrosion products of Alloy I
after immersion in Hank’s solution for 10 d
3 Discussion
As mentioned above, the addition of Ce resulted in the
change of the composition and distribution of the second
phase. After adding cerium, the second phase in the
as-cast alloy changed from a single Ca2Mg6Zn3 distributed along the grain boundary to the discontinuous intergranular mixture of a new RE-containing phase and
Ca2Mg6Zn3. The Ce alloying broke the distribution form
of the second phase, thus formed a new intermittent-like
distributed Ce-containing phase. These two factors resulted in the different performance in subsequent immersion tests and electrochemical tests for the as-cast alloys.
Since the electrode potential of magnesium is very
negative, there usually exists a potential gap between
100
JOURNAL OF RARE EARTHS, Vol. 33, No. 1, Jan. 2015
Fig. 12 XPS peak fittings of Alloy I
(a) Ca 2p; (b) C 1s; (c) O 1s; (d) P 2p
magnesium matrix and the second phase, which constitutes a micro electrical coupling and results in a preferential corrosion of magnesium matrix around the second
phase when the magnesium alloy was immersed in corrosive medium. For the above reasons, the volume fraction and distribution of second phases in magnesium alloys had a significant impact on its corrosion resistance.
When the second phase in the alloy exists in the form of
isolated coarse particles, it plays the role of accelerating
the corrosion of substrate; when the second phase is distributed along the grain boundary as a continuous network structure, it acts as a barrier to prevent the further
development of corrosion[23–25].
In Alloy I, cathodic Ca2Mg6Zn3 phase was a continuous network distribution around the grain boundary.
When Ce was added to the alloy, as illustrated by the
XRD results, the Mg2Ca and Mg12CeZn appeared in the
alloy wherein Mg12CeZn was a relatively cathodic phase
and the Mg2Ca an anodic phase[26]. On the one hand,
these intermittent-like distributed phases broke the netlike structure and weakened the corrosion barrier. Furthermore, the Mg12CeZn phase accelerated the corrosion
of the magnesium matrix as a cathode while the Mg2Ca
phase corroded preferentially as anode. The role of the
new phases produced two consequences: Firstly, an increase of hydroxyl ions in the solution which promoted
the generation of phosphate ions; secondly, an increase in
calcium and magnesium ions in the solution. These two
consequences together lead to the generation of a more
compact calcium and magnesium phosphate. The protective effects of phosphate together with the accelerated
corrosive effect of the cathodic phase formed a competitive relationship. In the case of Alloy II, the phosphate
formed was compact and the protective effect dominated,
thus resulted in its better corrosion resistance.
EDS analysis of the corrosion products formed at the
initial stage of immersion in Fig.10 showed that the addition of Ce had a certain impact on the formation of corrosion product in the early stage. Due to the corrosion of
the magnesium matrix, the first reaction which occurred
in solution was the generation of magnesium hydroxide
and hydrogen. At this stage, the number of the hydroxide
ions in the solution determined the time when the phosphate ions appear. Due to the role of the discrete second
phases, Alloy II generated, in the initial stage, more hydroxide ions with calcium and magnesium ions, thereby
promoting the formation of phosphate. Thus, the addition
of Ce accelerated the formation of phosphate, thereby
accelerating the formation of a dense film of corrosion
product. Due to the protective effect of phosphate, Cecontaining Alloy II exhibited a better corrosion resistance.
4 Conclusions
(1) The addition of cerium in Mg-2Zn-0.5Mn-1Ca al-
ZHANG Fan et al., Improving in-vitro biocorrosion resistance of Mg-Zn-Mn-Ca alloy in Hank’s solution through …
loy (Alloy I) enhanced its in-vitro biocorrosion resistance
and reduced its degradation rate. The alloy containing
1.35 wt.% Ce (Alloy II) had the potential to be used as
future biomaterials.
(2) Adding cerium in Mg-Zn-Mn-Ca alloy resulted in
a change of the composition and distribution of the second phases. The second phase in Alloy I was mainly
Ca2Mg6Zn3 phase with a continuous network distribution,
while a discrete distribution of Mg2Ca phase and
Mg12CeZn phase appeared in the Ce-containing Alloy II.
(3) The change of second phase in Alloy II led to the
formation of more dense corrosion products which finally enhanced its corrosion resistance.
Acknowledgement: Authors would like to thank Changzhou
Applied Basic Research Programs (CJ20110005) and Nantong
Applied Basic Research Programs (BK2012042) for financial
support.
References:
[1] Mani G, Feldman M D, Patel D, Agrawal C M. Coronary
stents: A materials perspective. Biomaterials, 2007, 28(9):
1689.
[2] Witte F, Hort N, Vogt C, Cohen S, Kainer K U, Willumeit
R, Feyerabendc F. Degradable biomaterials based on
magnesium corrosion. Curr. Opin. Solid State Mater. Sci.,
2008, 12(5-6): 63.
[3] Witte F. The history of biodegradable magnesium implants:
A review. Acta Biomater., 2010, 6(5): 1680.
[4] Witte F, Kaese V, Haferkamp H, Switzer E, Meyer-Lindenberg A, Wirth C J, Windhagen H. In vivo corrosion of
four magnesium alloys and the associated bone response.
Biomaterials, 2005, 26(17): 3557.
[5] Staiger M P, Pietak A M, Huadmai J, Dias G. Magnesium
and its alloys as orthopedic biomaterials: A review. Biomaterials, 2006, 27(9): 1728.
[6] Mueller W D, Nascimento M L, de Mele M F L. Critical
discussion of the results from different corrosion studies of
Mg and Mg alloys for biomaterial applications. Acta Biomater., 2010, 6(5): 1749.
[7] Song G L. Control of biodegradation of biocompatable
magnesium alloys. Corros. Sci., 2007, 49(4): 1696.
[8] Li Z J, Gu X N, Lou S Q, Zheng Y F. The development of
binary Mg-Ca alloys for use as biodegradable materials
within bone. Biomaterials, 2008, 29: 1329.
[9] Crossgrove J, Zheng W. Manganese toxicity upon overexposure. NMR Biomed., 2004, 17: 544.
[10] Xu L P, Yu G N, Zhang E L, Pan F, Yang K. In vivo corrosion
behavior of Mg-Mn-Zn alloy for bone implant application.
J. Biomed. Mater. Res. A, 2007, 83A(3): 703.
[11] Feyerabend F, Fischer J, Holtz J, Witte F, Willumeit R,
Drücker H, Vogt C, Hort N. Evaluation of short-term effects of rare earth and other elements used in magnesium
alloys on primary cells and cell lines. Acta Biomater., 2010,
101
6(5): 1834.
[12] Zhang S X, Zhang X N, Zhao C L, Li J N, Song Y, Xie C
Y, Tao H R, Zhang Y, He Y H, Jiang Y, Bian Y J. Research on an Mg-Zn alloy as a degradable biomaterial.
Acta Biomater., 2010, 6: 626.
[13] Xin Y, Hu T, Chu P K. In vitro studies of biomedical
magnesium alloys in a simulated physiological environment: A review. Acta Biomater., 2011, 7: 1452.
[14] Colon J, Hsieh N, Ferguson A, Kupelian P, Seal S, Jenkins
D W, Baker C H. Cerium oxide nanoparticles protect
gastrointestinal epithelium from radiation-induced damage
by reduction of reactive oxygen species and upregulation
of superoxide dismutase. Nanomed-Nanotechnol., 2010,
6(5): 698.
[15] Kostova I, Manolov I, Momekov G, Tzanova T, Konstantinov
S, Karaivanova M. Cytotoxic activity of new cerium(III)
complexes of bis-coumarins. Eur. J. Med. Chem., 2005,
40(12): 1246.
[16] Chen A M, Shi Q S, Feng J, Ouyang Y S, Chen Y B.
Effect of Ce3+ on membrane permeability of Escherichia
coli cell. J. Rare Earths, 2012, 30(9): 947.
[17] Liu C M, Zhu X R, Zhou H T. Phase Diagrams of
Magnesium Alloys. Changsha: Central South University
Press, 2006. 186.
[18] Zhao M C, Schmutz P, Brunner S, Liu M, Song G L,
Atrens A. An exploratory study of the corrosion of Mg
alloys during interrupted salt spray testing. Corros. Sci.,
2009, 51: 1277.
[19] Nadine P, Riera C, Dabosi F. Investigation of magnesium
corrosion in aerated sodium sulfate solution by
electrochemical impedance spectroscopy. Electrochim.
Acta, 1990, 35(2): 555.
[20] Cao C N. On the impedance plan displays for irreversible
electrode reactions based on the stability conditions of
steady-state-II. Two state variables besides electrode
potential. Electrochim. Acta, 1990, 35(5): 837.
[21] Pardo A, Merino M C, Coy A E, Viejo F, Arrabal R, Feliú
S. Influence of microstructure and composition on the
corrosion behaviour of Mg/Al alloys in chloride media.
Electrochim. Acta, 2008, 53(27): 7890.
[22] Ghoneim A A, Fekry A M, Ameer M A. Electrochemical
behavior of magnesium alloys as biodegradable materials
in Hank's solution. Electrochim. Acta, 2010, 55: 6028.
[23] Zhao M C, Liu M, Song G, Atrens A. Influence of the bphase morphology on the corrosion of the Mg alloy AZ91.
Corros. Sci., 2008, 50: 1939.
[24] Song Y, Shan D, Chen R, Han E H. Effect of second phases
on the corrosion behaviour of wrought Mg-Zn-Y-Zr alloy.
Corros. Sci., 2010, 52: 1830.
[25] Song Y, Han E, Shan D, Yim C D, You B S. The role of
second phases in the corrosion behavior of Mg-5Zn alloy.
Corros. Sci., 2012, 60: 238.
[26] Zhang E L, Yang L. Microstructure, mechanical properties
and bio-corrosion properties of Mg-Zn-Mn-Ca alloy for
biomedical application. Mater. Sci. Eng., A, 2008, 497: 111.