Nitrogen Modulation of Micro-arc Oxidation: Densification and Corrosion Resistance of Zirconium Alloy Coatings

doi:10.15541/jim20250406

Abstract

Abstract:

Zirconium alloys used in nuclear reactors undergo severe zirconium-water reaction during loss-of-coolant accidents. Conventional micro-arc oxidation (MAO) coatings, limited by their high porosity, offer insufficient protection. In this study, nitrogen was innovatively introduced into the MAO process to suppress arc concentration, thereby achieving simultaneous structural optimization and nitrogen doping of the coating. Experimental results demonstrate the successful fabrication of a dense zirconium oxide coating through this approach. The porosity is significantly reduced to 4.96% (representing a 62% reduction), surface roughness is decreased, and a tight, crack-free bond with the substrate is achieved. Simultaneously, nitrogen is incorporated into the crystal lattice, forming a characteristic Zr-O-N bonding structure. Benefiting from this synergistic optimization of the microstructure and chemical composition, the dense coating exhibits a corrosion current density as low as 1.61×10^-8 A·cm^-2 in a 0.1 mol/L LiOH solution, which is one order of magnitude lower than that of a conventional MAO coating. This work confirms that a nitrogen atmosphere can simultaneously facilitate structural regulation and chemical modification, providing a new pathway for developing high-performance accident-tolerant zirconium alloy cladding coatings.

Key words: zirconium alloy, micro-arc oxidation, nitrogen doping, corrosion resistance

CLC Number:

TG174

JI Ruonan, WEI Daqing, WANG Qingyu, LI Yongchang, ZHANG Tian, DU Qing. Nitrogen Modulation of Micro-arc Oxidation: Densification and Corrosion Resistance of Zirconium Alloy Coatings[J]. Journal of Inorganic Materials, 2026, 41(8): 1095-1102.

Figures/Tables 9

Fig. 1 Micro-morphologies and ImageJ binarization processed images of (a) MAO and (b) MAO-N2 coatings

Fig. 2 Cross-sectional morphologies and corresponding element distributions of (a) MAO and (b) MAO-N2 coatings Colorful figures are available on website

Fig. 3 (a) OES full spectra and (b) XRD patterns of coatings

Fig. 4 XPS spectra of MAO and MAO-N2 coatings (a) XPS full spectra; (b, c) N1s XPS spectra of (b) MAO and (c) MAO-N2 coatings before and after etching; (d) O1s, (e) N1s and (f) Zr3d XPS spectra of MAO and MAO-N2 coatings

Fig. 5 TEM results of MAO-N2 coating (a) TEM image and EDS mappings; (b) HRTEM images; (c) FFT pattern

Table 1 Chemical composition of the area presented in Fig. 5(a)

Element	C	N	O	Si	Zr
Chemical composition/ % (in atom)	14.05	3.70	45.35	1.58	35.32

Fig. 6 Results of polarization curves and EIS tests (a) Potentiodynamic polarization curves; (b) Bode plots of |Z| vs. frequency and the equivalent circuit model; (c) Nyquist plots; (d) Bode plots of phase angle vs. frequency

Table 2 Polarization analysis

Coating	E_corr/V	I_corr/(A·cm⁻²)	b_a/V	b_c/V	R_p/(Ω·cm²)
MAO	-0.175	5.51×10^-7	0.1944	-0.2004	5.116×10⁶
MAO-N₂	-0.605	1.61×10^-8	0.2287	-0.1576	1.371×10⁷

Table 3 Fitting results of EIS data

Coating	R_s/(Ω·cm²)	R_p/(Ω·cm²)	Q_p/(F·cm⁻²)	n_p	R_ct/(Ω·cm²)	Q_dl/(F·cm⁻²)	n_dl
MAO	82	4.26×10⁴	1.83×10^-6	0.55	3.92×10⁴	2.91×10³	0.50
MAO-N₂	82	1.54×10⁵	9.20×10^-7	0.58	5.05×10⁴	3.75×10^-5	0.75

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