Comparison of Corrosion Resistance of Phenylalanine, Methionine, and Asparagine-Induced Ca-P Coatings on AZ31 Magnesium Alloys
WANG Xuemei1, YIN Zhengzheng1, YU Xiaotong1, ZOU Yuhong2, ZENG Rongchang1,3,4()
1.School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China 2.School of Chemical and Biological Engineering, Shandong University of Science and Technology, Qingdao 266590, China 3.School of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450002, China 4.Hubei Key Laboratory of Advanced Technology for Automotive Components, Wuhan University of Technology, Wuhan 430070, China
Cite this article:
WANG Xuemei, YIN Zhengzheng, YU Xiaotong, ZOU Yuhong, ZENG Rongchang. Comparison of Corrosion Resistance of Phenylalanine, Methionine, and Asparagine-Induced Ca-P Coatings on AZ31 Magnesium Alloys. Acta Metall Sin, 2021, 57(10): 1258-1271.
Ca-P coating not only enhances the corrosion resistance of biodegradable magnesium alloys but also contributes to the formation of new bones and promotes bone integration around implants. However, the Ca-P coatings may have defects like porosity, low adhesion, and coarse grains, which lead to prefailure in the early stage and then the coatings cannot meet the requirements of long-term clinical service. Amino acids can induce the formation of calcium-bearing phosphates on biodegradable magnesium alloy. To clarify the influence of amino acid groups on film formation, Phenylalanine (Phe), Methionine (Met), and Asparagine (Asn) were used to regulate the degradation rate of magnesium alloy. Three amino acid-induced Ca-P (Ca-PPhe, Ca-PMet, and Ca-PAsn) coatings were prepared on AZ31 magnesium alloy via a constant temperature water bath method at a temperature of 60oC. Additionally, the morphology of the coatings, composition distributions, and phase structures were observed and analyzed via SEM, EDS, XRD, FTIR, and XPS. The corrosion resistance of the coating in simulated body fluid (Hank's solution) was investigated through electrochemical polarization, AC impedance, and hydrogen evolution tests. The formation mechanisms of amino acid additive-induced Ca-P (Ca-PPhe, Ca-PMet, and Ca-PAsn) coatings on AZ31 magnesium alloy were probed. Results showed that the thicknesses of Ca-P, Ca-PPhe, Ca-PMet, and Ca-PAsn coatings were about (3.47 ± 0.47), (6.06 ± 0.77), (7.63 ± 1.70), and (8.23 ± 1.37) μm, respectively. The main constituents of the amino acid-induced Ca-P coatings were CaHPO4 and Ca10(PO4)6(OH)2 (HA). The results of electrochemical polarization curves, EIS, and hydrogen evolution tests demonstrated that the addition of amino acids enhanced the corrosion resistance of the Ca-P coatings, which was ascribed to the inhibition and adsorption of amino acid molecules on AZ31 magnesium alloy. The adsorption of the amino group was mainly achieved through the coupling of the lone pair electrons of nitrogen atoms with the surface, whereas the carboxyl group combined with Mg2+ via their oxygen atoms. Additionally, heteroatoms in amino acids could share their lone pair electrons with the vacant molecular orbitals of the magnesium alloy. A formation mechanism of amino acid-induced Ca-P coating was proposed.
Fund: National Natural Science Foundation of China(52071191);Natural Science Foundation of Shandong Province(ZR2020ME011);Open Foundation of Hubei Key Laboratory of Advanced Technology for Automotive Components(XDQCKF2021006)
About author: ZENG Rongchang, professor, Tel: (0532)80681226, E-mail: rczeng@foxmail.com
Fig.1 Preparation diagram of Ca-P coating and its amino acids (Phenylalanine (Phe), Methionine (Met), and Asparagine (Asn)) modified coatings (Ca-PPhe, Ca-PMet,and Ca-PAsn, respectively) on AZ31 Mg alloy
Fig.2 SEM images of Ca-P coating (a-c), Ca-PPhe coating (d-f), Ca-PMet coating (g-i), and Ca-PAsn coating (j-l) on AZ31 magnesium alloy surface
Point
C
N
O
Mg
Ca
P
1
4.02
1.48
38.71
32.71
14.40
8.68
2
3.94
0.81
48.05
28.83
11.02
7.35
3
4.32
0.74
63.35
12.32
10.77
8.50
4
3.57
0.83
60.56
9.79
14.26
11.00
5
3.30
0.48
60.42
11.17
14.28
10.35
6
3.18
1.23
63.74
5.43
13.96
12.45
7
2.84
1.50
58.95
1.52
18.04
17.15
8
3.35
1.52
44.31
2.99
23.73
24.00
9
3.11
1.06
61.40
1.68
16.68
16.07
10
3.26
1.86
38.99
3.39
24.87
27.63
11
3.06
1.38
52.89
0.06
20.62
21.98
12
4.09
2.21
39.93
6.01
23.74
24.02
Table 1 EDS analysis results of points 1-12 in Fig.2
Fig.3 Cross-sectional SEM images and corresponding Ca and P mapping images of Ca-P coating (a), Ca-PPhe coating (b), Ca-PMet coating (c), and Ca-PAsn coating (d) on AZ31 magnesium alloy surface
Fig.4 XPS survey plots (a, d, g) and high-resolution spectra (b, c, e, f, h, i) of Ca-PPhe coating (a-c), Ca-PMet coating (d-f), and Ca-PAsn coating (g-i)
Fig.5 FTIR of Ca-P coating (a), Ca-PPhe coating (b), Ca-PMet coating (c), and Ca-PAsn coating (d) on AZ31 magnesium alloy surface
Fig.7 Polarization curves of AZ31Mg alloy, Ca-P coating, Ca-PPhe coating, Ca-PMet coating, and Ca-PAsn coating (Eb—broken shield potential)
Sample
Ecorr / mVSCE
icorr / (10-6 A·cm-2)
βa / (mV·dec-1)
βc / (mV·dec-1)
Rp / (106 Ω·cm2)
AZ31
-1481.47
17.30
258.19
-127.67
2.14
Ca-P
-1402.11
6.54
257.40
-230.00
8.06
Ca-PPhe
-1435.36
3.80
387.58
-271.98
18.29
Ca-PMet
-1423.59
2.99
315.89
-241.74
19.89
Ca-PAsn
-1416.23
1.36
145.42
-111.57
20.16
Table 2 Tafel analysis results of AZ31Mg alloy, Ca-P coating, Ca-PPhe coating, Ca-PMet coating, and Ca-PAsn coating
Fig.8 Nyquist (a) and Bode (b) curves of AZ31 Mg alloy, Ca-P coating, Ca-PPhe coating, Ca-PMet coating, and Ca-PAsn coating (Zim—imaginary part of impedance, Zre—real part of impedance, |Z|—impedance modulus)
Fig.9 Equivalent circuits of AZ31 Mg alloy (a), Ca-P coating (b), and Ca-PPhe/Met/Asn coating (c) (Rs—solution resistance, CPE—constant phase element, Rct—charge transfer resistance, L—equivalent inductance, RL—inductive resistance, R1—coating resistance)
Sample
Rs
CPE1
n1
R1
CPE2
n2
Rct
L
RL
Ω·cm2
10-5 Ω-1·s·cm-2
kΩ·cm2
10-5 Ω-1·s·cm-2
Ω·cm2
H·cm2
Ω·cm2
AZ31
85.88
1.278
0.9056
-
-
-
578.5
439.7
231.5
Ca-P
57.25
0.136
0.6946
-
2.616
0.6438
593.8
3.7
6856.0
Ca-PPhe
70.00
0.875
0.6515
289.6
1.582
0.7757
7266.0
-
-
Ca-PMet
84.64
1.859
0.6809
226.3
1.693
0.8297
7465.0
-
-
Ca-PAsn
80.93
0.742
0.6782
157.8
1.873
0.8144
8552.0
-
-
Table 3 EIS analysis results of AZ31 Mg alloy, Ca-P coating, Ca-PPhe coating, Ca-PMet coating, and Ca-PAsn coating
Fig.10 Hydrogen evolution rate (HER) curves of AZ31Mg alloy, Ca-P coating, Ca-PPhe coating, Ca-PMet coating, and Ca-PAsn coating
Fig.11 Digital camera photographs (a, d, g, j, m) and SEM images (b, c, e, f, h, i, k, l, n, o) after 160 h immersion for AZ31 Mg alloy (a-c), Ca-P coating (d-f), Ca-PPhe coating (g-i), Ca-PMet coating (j-l), and Ca-PAsn coating (m-o)
Point
C
N
O
Mg
Ca
P
1
3.98
1.45
63.07
14.16
8.72
8.61
2
6.02
1.09
62.60
15.06
7.62
7.60
3
5.79
0.93
70.34
10.79
5.20
6.95
4
8.20
1.91
68.69
5.62
7.70
7.88
5
5.75
1.45
70.74
1.33
9.04
11.68
6
5.29
1.32
65.10
3.51
15.99
8.79
7
3.42
1.31
61.38
5.99
13.20
14.69
8
11.40
4.92
61.09
3.52
10.20
8.87
9
12.38
5.05
58.08
2.51
11.36
10.62
10
6.45
1.86
63.70
3.46
13.96
10.57
11
6.96
1.97
70.64
2.69
10.55
7.19
12
5.61
1.87
62.78
3.33
14.22
12.18
13
5.36
1.65
60.92
3.70
15.83
12.97
14
4.92
1.73
60.67
3.93
16.60
12.15
15
4.84
1.46
61.37
2.42
14.84
15.07
Table 4 EDS analysis results of points 1-15 in Fig.11
Fig.12 FTIR of AZ31 Mg alloy (a), Ca-P coating (b), Ca-PPhe coating (c), Ca-PMet coating (d), and Ca-PAsn coating (e) immersed in Hank's solution after 160 h
Fig.13 XRD spectra of AZ31 Mg alloy (a), Ca-P coating (b), Ca-PPhe coating (c), Ca-PMet coating (d), and Ca-PAsn coating (e) immersed in Hank's solution after 160 h
Fig.14 Schematics of the formation mechanisms of Ca-PPhe (a, b), Ca-PMet (c, d), and Ca-PAsn (e, f) coatings
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