1 Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, Nanjing Institute of Technology, Nanjing 211167, China 2 School of Materials Engineering, Nanjing Institute of Technology, Nanjing 211167, China;
Cite this article:
Xinxian FANG,Yajun XUE,Yuming DAI,Zhangzhong WANG. DEPOSITION MECHANISM OF Ni-W-Cu-P COATING AND ITS CORROSION BEHAVIOR IN ACID SOLUTION. Acta Metall Sin, 2016, 52(11): 1432-1440.
The application of steel in acidic media faces a big challenge due to the corrosion problem. Quaternary Ni-W-Cu-P alloy act as a potential coating material applied to acidic media because of its superior corrosion resistance. However, mechanism of deposition and corrosion of Ni-W-Cu-P coating plated on the surface of steel component is rare in the previous studies. In this work, the Ni-W-Cu-P coatings were deposited onto carbon steel 65Mn substrates via electroless plating. The anti-corrosion properties of the coatings in room and warm acidic solution (20%H2SO4) were evaluated by dipping and electrochemical test, respectively. Their deposition mechanism, composition and structure were investigated using SEM, EDS and XRD, respectively. The results show that the Ni-W-Cu-P coating is composed of spherical and block particles in the early stage of electroless plating, which are gradually transformed into spherical and strip cellular structure with the increasing electroless plating time. With prolonging electroless plating time, the Ni and W contents in the Ni-W-Cu-P coatings increase logarithmically and lineally, respectively. However, the Cu content decreases logarithmically, the P content reaches the maximum value after electroless plating for 60 min and then gradually decreases. The Ni-W-Cu-P coating is amorphous when it is annealed at low temperature, upon increasing the annealing temperature to over 400 ℃, it gradually transforms from amorphous to crystalline. The thermal stability of Ni-W-Cu-P coating can be significantly improved by co-depositing tungsten and copper element. Corrosion resistance of the amorphous coating annealed at 400 ℃ is better than that of amorphous coating as-plated and nanometer crystalline coating annealed at 500 ℃ in both room and warm acid solution. As-plated coatings and those annealed at 400 ℃ are found to corrode selectively, while pitting is observed to be the main corrosion mechanism of coatings annealed at 500 ℃. With increasing the corrosion time, the corrosion rates and corrosion current densities of the Ni-W-Cu-P coatings increase, however, their impedance values decrease.
Fund: Supported by National Natural Science Foundation of China (No.51301088), Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology (No.ASMA201414) and Innovation Fund Key Project of Nanjing Institute of Technology (No.CKJA201202)
Fig.1 SEM images of Ni-W-Cu-P coatings after plating for different times
(a) 1 min (b) 5 min (c) 10 min (d) 20 min (e) 30 min (f) 120 min
Zone
Ni
W
Cu
P
Fe
A
9.18
1.83
4.56
1.17
83.26
B
18.99
1.11
11.14
2.31
66.45
C
10.67
2.98
5.93
1.50
78.92
D
26.54
7.32
14.85
3.59
47.70
F
57.43
6.04
20.74
3.49
12.30
G
55.18
4.75
19.63
6.37
14.07
H
61.18
6.74
19.78
7.67
4.63
I
63.64
4.94
19.49
6.41
5.52
Table 1 EDS results of different characteristic zones of Ni-W-Cu-P coating in Fig.1 (mass fraction / %)
Fig.2 Variation of chemical composition of Ni-W-Cu-P coatings with plating time
Fig.3 XRD spectra of Ni-W-Cu-P coatings annealed at different temperatures
Fig.4 Variation of corrosion rate (v) of Ni-W-Cu-P coatings annealed at different temperatures with dipping time
Structure
Ni
W
Cu
P
O
NP
74.58
10.04
8.48
6.90
-
M
71.40
11.60
10.06
6.94
-
WCS
80.14
6.32
3.91
7.21
2.42
GCS
74.55
12.03
6.32
7.10
0.00
CS
75.30
10.62
4.17
4.40
5.51
WS
77.17
8.66
3.82
4.35
6.00
GS
72.56
13.26
6.60
7.58
0.00
Table 2 EDS results of different structures in corroded samples surface in Fig.5 (mass fraction / %)
Fig.5 Surface morphologies of Ni-W-Cu-P coatings after corroded for different times (Insets show high magnified images) (a) as-plated, 19.5 h (b) annealed at 400 ℃, 25.5 h (c) annealed at 500 ℃, 19.5 h (d) annealed at 500 ℃, 44.5 h
Fig.6 Polarization curves of Ni-W-Cu-P coatings as-plated (a), annealed at 400 ℃ (b) and at 500 ℃ (c) (E—potential, icorr—current density)
Fig.7 Bode plots for as-plated Ni-W-Cu-P coatings (a), and then annealed at 400 ℃ (b) and 500 ℃ (c), and variation of their impedance values (|Z|) with corrosion time (d)
Coating
0 h
34 h
56 h
80 h
152 h
224 h
As-plated
0.88
4.07
30.28
62.10
77.10
463.10
Annealed at 400 ℃
1.17
1.39
1.57
1.63
2.31
2.17
Annealed at 500 ℃
0.71
0.72
2.57
3.54
292.90
1040.00
Table 3 Corrosion current density of Ni-W-Cu-P coatings corroded in 20%H2SO4 solution for different times (10-5 Acm-2)
Fig.8 SEM images of Ni-W-Cu-P coatings after corroding for 224 h (a) as-plated (b, c) annealed at 400 ℃ (d) annealed at 500 ℃
Zone
Ni
W
Cu
P
O
Fe
S
A
37.03
18.87
8.38
15.59
12.53
7.60
-
B
30.51
24.63
13.27
13.99
10.30
2.04
5.26
C
58.04
14.45
4.88
11.37
7.90
3.36
-
D
71.78
4.78
7.73
11.26
3.41
1.04
-
E
68.75
7.42
7.03
11.55
4.43
0.82
-
Table 4 EDS results of different characteristic zones of corroded samples surface in Fig.8 (A—corrosion film in Fig.8a) (mass fraction / %)
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