Mechanical and corrosion properties of electrochemically deposited Ni-Nb₂O₅ composite coatings on mild steel for marine applications

Figures & data

Table 1. Bath composition and deposition conditions.

Bath composition
NiSO4	300 gl^-1
NiCl2	60 gl^-1
H3BO3	45 gl^-1
NaC12H25SO4	4 gl^-1
Deposition conditions
Current density	5 Adm^-2
Temperature	50°c
PH	3–4

Figure 1. (a) Represents the SEM image of bare mild steel. (b–f) Demonstrates the surface topography of electrodeposited samples by SEM at concentrations of 0, 0.25, 0.50, 0.75, and 1 gl⁻¹ of niobium oxide, respectively.

Figure 2. XRD plots of Ni and Ni-Nb₂O₅ coating.

Figure 3. EDAX analysis of Ni- Nb₂O₅ Coating.

Table 2. Elemental composition of Nickel- Nb₂O₅ coated specimen.

Elements (weight %)	O	Fe	Ni	Nb	C
Nickel- Nb2O5 coated sample	—	0.81	31.95	0.01	0.00

Figure 4. Texture coefficient plots of nickel and Ni- Nb₂O₅ coatings.

Figure 5. Polarisation curves of Ni and Ni-Nb₂O₅ composite coated samples.

Table 3. Tafel extrapolation data.

Corrosion media	g/l	-Ecorr (V vs SCE)	Icorr (A cm^-2)	C.R. (mil/yr)	% IE (ɳp)
3.5% NaCl	Blank	0.638	8.958	3.875	—
	Nickel	0.573	4.986	3.584	44.3
	0.25	0.530	2.045	2.392	77.7
	0.50	0.525	1.756	2.113	80.4
	0.75	0.520	1.425	1.978	84.1
	1.0	0.461	1.078	1.683	87.9

Figure 6. Nyquist graphs for Ni and Ni-Nb₂O₅ composite coating.

Figure 7. Equivalent circuit for the Nyquist plots. R: Resistance; CR: Current Rectifier; QR: Quick Response.

Table 4. Impedance spectroscopy data.

Corrosion media	gl^-1	Rp (Ωcm^2)	Cdl (µF/cm^2)	%IE(ɳz)
3.5% NaCl	Blank	10.92	386	—
	Nickel	20.44	313	46.6
	0.25	49.97	275	78.1
	0.50	58.99	205	81.5
	0.75	72.42	176	84.9
	1.0	98.29	159	88.8

Figure 8. Microhardness of Ni and Ni- Nb₂O₅ coating.

Figure 9. AFM image of Nickel coating.

Figure 10. AFM image of Ni- Nb₂O₅ Coating.

Table 5. Roughness data.

Coating	Ra (nm)	Rq(nm)
Nickel	78.8	102
Ni-Nb2O5	102	135

Figure 11. 3D profile of Ni- Nb₂O₅.

Figure 12. 2D profile of Ni- Nb₂O₅.

Figure 13. Normal load vs stroke.

Figure 14. SEM Image of the scratch path.

Figure 15. Contact angle of nickel coating.

Figure 16. The contact angle of Nickel- Nb₂O₅ (1 g/l) coating.