Microstructure and Electrochemical Properties of CoCrCuFeNiNb High-Entropy Alloys Coatings

doi:10.1007/s40195-014-0117-4

Abstract

Abstract:

The CoCrCuFeNiNb high-entropy alloys coatings were prepared by using plasma-transferred arc cladding process. The microstructure and electrochemical behaviors of the coating were investigated in detail. The experimental results indicated that the coating consists of a simple fcc solid solution phase and an order (CoCr)Nb-type Laves phase. The polarization curves, obtained in 1 and 6mol/L hydrochloric acid solutions, clearly indicated that the general corrosion resistance of the coating at ambient temperature was better than that of 304 stainless steel. The coating displayed a lower corrosion current and lower corrosion rate. Electrochemical impedance spectroscopy demonstrated that the impedance of the coating was significantly higher than that of the 304 stainless steel.

Key words: CoCrCuFeNiNb, High-entropy, alloy Coating, Corrosion behavior

Cheng Jiangbo, Liu Dan, Liang Xiubing, Xu Binshi. Microstructure and Electrochemical Properties of CoCrCuFeNiNb High-Entropy Alloys Coatings[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(6): 1031-1037.

Figures/Tables 12

Fig. 1 XRD pattern of the coating

Fig. 2 SEM images of the sample: a cross section; b surface of the CoNiCuFeCrNb coating

Table 1 Chemical compositions of the different region in the coating (in at%)

Region	Fe	Co	Ni	Cr	Cu	Nb
Dendrite	28.69	17.26	16.62	17.10	15.25	3.09
Interdendrite	17.51	14.89	17.25	13.84	6.90	29.61

Table 2 Enthalpies of mixing (ΔH mix), entropies of mixing (∆S mix), Ω and atomic size difference (δ) for the CoCrCuFeNiNb coating

ΔH _mix (kJ/mol)	ΔS _mix (10^-3J/mol)	Ω	δ (%)
-5.89	14.90	4.86	5.16

Fig. 3 Potentiodynamic polarization curves of the HEAs coating in comparison with 304 SS in 1 mol/L hydrochloric acid solution

Table 3 Electrochemical parameters of the CoCrCuFeNiNb HEAs coating and 304 SS in 1 and 6 mol/L hydrochloric acid solutions

Material	1 mol/L hydrochloric acid solution			6 mol/L hydrochloric acid solution
Material	E _corr (V)	i _corr (A/cm²)	r _corr (mm/year)	E _corr (V)	i _corr (A/cm²)	r _corr (mm/year)
CoCrCuFeNiNb	-0.305	1 × 10^-5	0.08	-0.397	8.93 × 10^-5	0.74
304 SS	-0.450	7.29 × 10^-4	7.58	-0.426	2.07 × 10^-3	21.5

Fig. 4 Potentiodynamic polarization curves of the HEAs coating in comparison with 304 SS in 6 mol/L hydrochloric acid solution

Fig. 5 Nyquist plots of impedance spectra of the HEAs coating and 304 SS in 1 mol/L hydrochloric acid solution

Fig. 6 EIS equivalent circuits for 304 SS and the coating in 1 mol/L hydrochloric acid solution

Table 4 Fitted results for EIS of the coating and 304 SS in 1 and 6 mol/L hydrochloric acid solution

Sample and solution	R _s (Ω cm²)	C _f (μF/cm²)	n _f	R _f (Ω cm²)	L _dl (H)	R _ct (Ω cm²)	n _dl	C _dl (μF/cm²)
304 SS in 1 mol/L solution	2.051	292.9	0.9089	46.51	50.78	18.72	-	-
Coating in 1 mol/L solution	2.323	691.8	0.7308	487.9	245	241	-	-
304 SS in 6 mol/L solution	0.6952	654.3	0.899	12.05	1.433	2.288	-	-
Coating in 6 mol/L solution	1.453	250.6	0.7391	171.3	-	105.1	0.7558	130.6

Fig. 7 Nyquist plots of the HEAs coating and 304 SS in 6 mol/L hydrochloric acid solution

Fig. 8 The equivalent circuit for the coating in 6 mol/L hydrochloric acid solution

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