Synergistic Effect Mechanism of Different Ions on the Electrochemical Corrosion Behavior of TC4 Titanium Alloy
ZHAO Pingping1, SONG Yingwei1,2(), DONG Kaihui1,2, HAN En-Hou1,2
1CAS Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China
Cite this article:
ZHAO Pingping, SONG Yingwei, DONG Kaihui, HAN En-Hou. Synergistic Effect Mechanism of Different Ions on the Electrochemical Corrosion Behavior of TC4 Titanium Alloy. Acta Metall Sin, 2023, 59(7): 939-946.
Due to the compact passive film, titanium alloys exhibit excellent corrosion resistance. However, during practical applications, the passive film is inevitably damaged by aggressive ions. Among the common ions, F- is the most harmful to the passive film because of its high complexation with Ti. However, the destructiveness of F- varies with pH. Moreover, there are inhibitory ions that reduce the aggressiveness of F-. The acceleration effects of H+ and F- as well as the inhibition effect of Fe3+ on the corrosion behavior of TC4 alloy were examined in this work using electrochemical polarization curves measurements and electrochemical impedance spectroscopy (EIS). The results reveal that whereas H+ has slight destructive effect on the passive film, F- has a considerable aggressive effect. In particular, F- and H+ work synergistically to accelerate the corrosion of the TC4 alloy. The addition of Fe3+ can somewhat reduce corrosion of the TC4 alloy. This can be attributable to the fact that the faster cathodic reduction caused by Fe3+ moves the anodic curves from active-passive region to passive region. Meanwhile, F- is consumed by forming a compound with Fe3+, which mitigates the corrosive effect of F- on passive film.
Fig.1 OM images of TC4 alloy with low (a) and high (b) magnifications
Fig.2 Potentiodynamic polarazation curves (a) and EIS (b) of TC4 alloy in 3.5%NaCl solutions with different H+ concentrations (cH)
cH
Ecorr
icorr
bc
ipp
mmol·L-1
mV
μA·cm-2
mV·decade-1
μA·cm-2
0
-502
0.06
-223
4.48
25
-469
1.62
-143
4.50
50
-469
3.14
-159
4.51
100
-494
4.39
-204
4.51
Table 1 Fitting results of polarization curves of TC4 alloy in 3.5%NaCl solutions with different cH
Fig.3 Potentiodynamic polarazation curves (a) and EIS (b) of TC4 alloy in 3.5%NaCl solutions with different F- concentrations (cF)
cF
Ecorr
icorr
bc
ipp
mmol·L-1
mV
μA·cm-2
mV·decade-1
μA·cm-2
0
-502
0.06
-223
4.48
3
-500
0.09
-207
7.65
4
-558
0.12
-166
9.72
6
-648
0.19
-175
14.52
8
-734
0.10
-169
20.97
12
-627
0.20
-268
20.97
25
-744
0.13
-168
63.46
Table 2 Fitting results of polarization curves of TC4 alloy in 3.5%NaCl solutions with different cF
Fig.4 Potentiodynamic polarazation curves (a) and EIS (b) of TC4 alloy in 3.5%NaCl + 50 mmol/L H+ sol-utions with different cF (Inset in Fig.4b shows the EIS of TC4 alloy in 3.5%NaCl + 50 mmol/L H+ solutions with cF of 3, 4, 6, and 8 mmol·L-1)
cF
Ecorr
icorr
bc
ipp
mmol·L-1
mV
μA·cm-2
mV·decade-1
μA·cm-2
0
-469
3.14
-159
4.48
3
-892
64.00
-113
89.20
4
-908
78.27
-94
113.50
6
-916
130.43
-104
113.50
8
-955
189.57
-90
239.90
Table 3 Fitting results of polarization curves of TC4 alloy in 3.5%NaCl + 50 mmol/L H+ solutions with different cF
Fig.5 Potentiodynamic polarazation curves of TC4 alloy in 3.5%NaCl + 3 mmol/L F- solutions with different cH
Fig.6 Potentiodynamic polarazation curves (a) and EIS (b) of TC4 alloy in 3.5%NaCl + 50 mmol/L H+ + 3 mmol/L F- solutions with different Fe3+ concen-trations (cFe)
cFe
Ecorr
icorr
bc
ipp
mmol·L-1
mV
μA·cm-2
mV·decade-1
μA·cm-2
0
-892
64.00
-113
89.2
1
-892
64.00
-113
72.4
2
-450
9.57
-121
43.1
3
-84
8.68
-179
30.0
4
-43
7.83
-179
23.6
5
11
2.64
-206
18.2
Table 4 Fitting results of polarization curves of TC4 alloy in 3.5%NaCl + 50 mmol/L H+ + 3 mmol/L F- solutions with different cFe
Fig.7 Effects of Fe3+ on the cathodic (a) and anodic (b) polarazation curves of TC4 alloy in 3.5%NaCl solution
Fig.8 Sketch maps of the effect of different ions on the polarazation curves of Ti alloy (a) F- (b) H+ + F- (c) H+ + F-+ Fe3+
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