Carbon-triggered grain boundary engineering in CoCrFeMnNi HEAs: Decoupling the role of M₇C₃ precipitates on passive film stability and localized corrosion resistance

Abstract

This study uncovers a non-monotonic effect of carbon on the corrosion behavior of CoCrFeMnNiC_x high-entropy alloys (HEAs) in 0.5 mol/L NaCl solution. The microstructure of the HEAs investigated using X-ray diffraction, scanning electron microscopy, and transmission electron microscope, the corrosion behaviors were investigated using potentiodynamic polarization and electrochemical noise measurements. HEAs exhibited a face-centered cubic (FCC) structure, carbon addition promoting the formation of Cr-rich M₇C₃ carbides. While all alloys undergo active dissolution, a critical carbon content of 0.5at% yields the highest fraction of Cr in the passive film and a significant improvement in corrosion resistance. This is evidenced by 65% reduction in corrosion current density and 35% increase in polarization resistance. The enhancement is mechanistically linked to carbon-induced grain refinement, formation of Cr-rich M₇C₃ carbides, and the development of a more stable passive film with reduced charge carrier density. Electrochemical noise analysis confirms a suppression of metastable pitting events at the optimal carbon level.

Keywords

high entropy alloy / carbon content / corrosion / electrochemical behavior / passive film

References

[1] Yang X, Chen DZ, Feng L, Qin G, Wu SP, Chen RR. Enhancing the mechanical properties of casting eutectic high-entropy alloys via W addition. Int. J. Miner. Metall. Mater., 2024, 3161364.

[2] Zhou YQ, Yuan PH, Kong DC, et al. Pitting corrosion behavior of additively manufactured spherical WC/W2C-rein-forced stainless steels in chloride-containing solution. Int. J. Miner. Metall. Mater., 2025, 32122988.

[3] Kao YF, Lee TD, Chen SK, Chang YS. Electrochemical passive properties of Al_xCoCrFeNi (x = 0, 0.25, 0.50, 1.00) alloys in sulfuric acids. Corros. Sci., 2010, 5231026.

[4] Liu M, Zhang SD, Li FJ, et al. Effect of annealing treatment on the microstructure and hardness of Al_xCoCrFeNi (x = 0.75, 1.25) high entropy alloys. J. Mater. Eng. Perform., 2022, 3121444.

[5] Zhang MD, Zhang LJ, Liaw PK, Li G, Liu RP. Effect of Nb content on thermal stability, mechanical and corrosion behaviors of hypoeutectic CoCrFeNiNb_x high-entropy alloys. J. Mater. Res., 2018, 33193276.

[6] Ananiadis E, Lentzaris K, Georgatis E, Mathiou C, Poulia A, Karantzalis AE. AlNiCrFeMn equiatomic high entropy alloy: A further insight in its microstructural evolution, mechanical and surface degradation response. Met. Mater. Int., 2020, 266793.

[7] Zhu HJ, Han JY, Fang KW, et al. Corrosion behavior of CoCrCu_0.1FeMoNi high entropy alloy in 0.5 mol/L NaOH solution. J. Iron Steel Res. Int., 2025, 3251163.

[8] Nie SJ, Yi XN, Zhou HL, et al. Corrosion behavior of as-cast Al_0.75CoFeCr_1.25Ni high entropy alloy in 0.5 mol/L NaOH solution. J. Iron Steel Res. Int., 2024, 31112852.

[9] Lei Y, Li YN, Song XG, et al. Contact-reactive brazing mechanism of Al_0.3CoCrFeNi high-entropy alloys using a niobium interlayer. J. Iron Steel Res. Int., 2024, 31102546.

[10] Chen YY, Hong UT, Shih HC, Yeh JW, Duval T. Electrochemical kinetics of the high entropy alloys in aqueous environments–A comparison with type 304 stainless steel. Corros. Sci., 2005, 47112679.

[11] Senkov ON, Woodward CF. Microstructure and properties of a refractory NbCrMo_0.5Ta_0.5TiZr alloy. Mater. Sci. Eng. A, 2011, 529: 311.

[12] J.K. Xiao, H. Tan, J. Chen, A. Martini, and C. Zhang, Effect of carbon content on microstructure, hardness and wear resistance of CoCrFeMnNiC_x high-entropy alloys, J. Alloy. Compd., 847(2020), art. No. 156533.

[13] Li JB, Gao B, Wang YT, et al. Microstructures and mechanical properties of nano carbides reinforced CoCrFeMnNi high entropy alloys. J. Alloy. Compd., 2019, 792: 170.

[14] Li XL, Hao XX, Jin C, et al. The determining role of carbon addition on mechanical performance of a non-equiatomic high-entropy alloy. J. Mater. Sci. Technol., 2022, 110: 167.

[15] Stepanov ND, Yurchenko NY, Tikhonovsky MA, Salishchev GA. Effect of carbon content and annealing on structure and hardness of the CoCrFeNiMn-based high entropy alloys. J. Alloy. Compd., 2016, 687: 59.

[16] H. Park, H. Kwon, K.T. Kim, et al., Cryogenic tensile behavior of carbon-doped CoCrFeMnNi high-entropy alloys additively manufactured by laser powder bed fusion, Addit. Manuf., 86(2024), art. No. 104223.

[17] Zhou HL, Liu HQ, Li J, Li CT, Yang HK, Qiao YX. Effect of carbon addition on mechanical and corrosion properties of CoCrFeNiMn high-entropy alloy. Metals, 2026, 16150.

[18] F.C. Zhu, C.J. Wu, Y. Liu, H.P. Peng, X.Y. Zhu, and X.P. Su, Effect of C content and annealing on dendrite structure evolution and corrosion resistance of CoCrFeMnNi alloys, J. Alloy. Compd., 988(2024), art. No. 174335.

[19] H. Luo, S.W. Zou, Y.H. Chen, Z.M. Li, C.W. Du, and X.G. Li, Influence of carbon on the corrosion behaviour of interstitial equiatomic CoCrFeMnNi high-entropy alloys in a chlorinated concrete solution, Corros. Sci., 163(2020), art. No. 108287.

[20] X.M. Wei, L.J. Zhang, F.Y. Zhang, et al., Effect of carbon addition on the microstructure and corrosion resistance of the CoCrFeNi high-entropy alloy, Corros. Sci., 231(2024), art. No. 111965.

[21] E.M. Paschalidou, R. Lindblad, L.Z. Medina, D. Karlsson, U. Jansson, and L. Nyholm, Corrosion studies on multicomponent CoCrFeMnNi(C) thin films in acidic environments, Electrochim. Acta, 404(2022), art. No. 139756.

[22] S.L. He, F.Y. Zhang, H.S. Jin, F. Wang, L.Q. Wang, and F.X. Yin, Microstructure, mechanical and corrosion properties of carbon-supersaturated Al_0.5CoCrFeNi high-entropy alloy films, J. Alloy. Compd., 1036(2025), art. No. 182118.

[23] Xu XB, Xu DK, Chen SH, Wang S, Han EH. Thermal aging behavior of an as-rolled Fe–17Cr–12Ni–2.6Mo–1.6Mn–0.044C (in wt%) austenitic stainless steel. J. Mater. Sci. Technol., 2026, 249: 120.

[24] Qiao YX, Zhang WT, AlMasoud N, et al. Improved passivation and anticorrosion behaviors of selective laser melted Inconel 718 alloy in acidic solutions. Adv. Compos. Hybrid Mater., 2023, 66204.

[25] Zhang PJ, Ma L, Zhou PJ, et al. Cavitation erosion-corrosion behavior of Co–6Ti–11V–9Cr superalloy in 3.5% NaCl solution. J. Iron Steel Res. Int., 2025, 32124440.

[26] C.P. Jiang, J. Zhang, Y.N. Chen, et al., On enhancing wear resistance of titanium alloys by laser cladded WC-Co composite coatings, Int. J. Refract. Met. Hard Mater., 107(2022), art. No. 105902.

[27] Guo LY, Lu YC, Hsueh CH. Effects of erbium addition on microstructure and mechanical properties of CoCrNi medium entropy alloy. J. Mater. Eng. Perform., 2024, 33104856.

[28] Bai T, Chen P, Guan KS. Evaluation of stress corrosion cracking susceptibility of stainless steel 304L with surface nanocrystallization by small punch test. Mater. Sci. Eng. A, 2013, 561: 498.

[29] Maleki-Ghaleh H, Hajizadeh K, Hadjizadeh A, et al. Electrochemical and cellular behavior of ultrafine-grained titanium in vitro. Mater. Sci. Eng. C, 2014, 39: 299.

[30] Liu L, Li Y, Wang FH. Electrochemical corrosion behavior of nanocrystalline materials—A review. J. Mater. Sci. Technol., 2010, 2611.

[31] Li ZM. Interstitial equiatomic CoCrFeMnNi high-entropy alloys: Carbon content, microstructure, and compositional homogeneity effects on deformation behavior. Acta Mater., 2019, 164: 400.

[32] Xu LL, Zheng ZB, Yang HK, et al. Adapting medium manganese steels for different wear conditions: Insights from aluminum modification. J. Iron Steel Res. Int., 2025, 32103504.

[33] H. Feng, H.B. Li, J. Dai, et al., Why CoCrFeMnNi HEA could not passivate in chloride solution?–A novel strategy to significantly improve corrosion resistance of CoCrFeMnNi HEA by N-alloying, Corros. Sci., 204(2022), art. No. 110396.

[34] Boroujerdnia M, Obeydavi A. Effect of nitrogen addition on the structural, mechanical and corrosion properties of Fe-CoCrMnNiN_x high-entropy nitride ceramic thin films. Int. J. Miner. Metall. Mater., 2025, 3251208.

[35] Wang TY, Li CT, Song LJ, et al. Effect of temperature on corrosion behaviors of copper in high-level nuclear waste disposal environment. J. Mater. Res. Technol., 2025, 36: 5717.

[36] Liao XY, Zheng ZB, Liu TL, et al. Achieving high impact–abrasion–corrosion resistance of high-chromium wearresistant steel via vanadium additions. J. Mater. Res. Technol., 2024, 29: 2425.

[37] Cao SX, Zhu M, Yuan YF, Guo SY, Zhu GT. Corrosion behavior of CoCrFeMnNi high entropy alloy in 3.5% NaCl solution with and without 0.05 M NaHSO₃. J. Mater. Eng. Perform., 2023, 32167545.

[38] Zhu YS, Yu SJ, Chen S, et al. Electrochemical behavior of FeCoNiAl_0.75Cr_1.25 high-entropy alloy in Na₂SO₄ solution with acidic pH. J. Iron Steel Res. Int., 2025, 3251151.

[39] Li XX, Chen LY, Hu WB, et al. Corrosion and passive behavior of SLM and wrought TA15 titanium alloys in hydrochloric acid solutions. J. Iron Steel Res. Int., 2025, 3251356.

[40] Zhang XQ, Qiang SH, Fan JX, et al. Annealing treatment on corrosion resistance deterioration of LPBF 316L SS in 0.1 mol/L HCl solution. J. Iron Steel Res. Int., 2025, 3251286.

[41] Park JS, Jin SW, Yun SJ, et al. Optimizing microstructure of medium Ni-bearing steel to ensure high resistance to corrosion and corrosion-assisted mechanical degradation. Int. J. Miner. Metall. Mater., 2025, 3271607.

[42] Huang JY, Qiu YB, Guo XP. Cluster and discriminant analysis of electrochemical noise statistical parameters. Electrochim. Acta, 2009, 5482218.

[43] Liu W, Wang DZ, Chen XH, Wang CG, Liu HD. Recurrence plot-based dynamic analysis on electrochemical noise of the evolutive corrosion process. Corros. Sci., 2017, 124: 93.

[44] Pistorius PC, Burstein GT. Aspects of the effects of electrolyte composition on the occurrence of metastable pitting on stainless steel. Corros. Sci., 1994, 363525.

[45] Homborg AM, van Westing EPM, Tinga T, et al. Novel time-frequency characterization of electrochemical noise data in corrosion studies using Hilbert spectra. Corros. Sci., 2013, 66: 97.

[46] Pujar MG, Mudali UK, Singh SS. Electrochemical noise studies of the effect of nitrogen on pitting corrosion resistance of high nitrogen austenitic stainless steels. Corros. Sci., 2011, 53124178.

[47] Na KH, Pyun SI. Effects of sulphate, nitrate and phosphate on pit initiation of pure aluminium in HCl-based solution. Corros. Sci., 2007, 4962663.

[48] Z.X. Ye, M. Zhu, W. Lan, and Y.F. Yuan, Enhanced anti-corrosion performance and hardness of FeCoNi medium entropy alloys via deep cryogenic treatment and cyclic deep cryogenic treatment, Mater. Chem. Phys., 348(2026), art. No. 131742.

[49] Qi W, Wang WR, Yang X, et al. Effect of Zr on phase separation, mechanical and corrosion behavior of heterogeneous CoCrFeNiZr high-entropy alloy. J. Mater. Sci. Technol., 2022, 109: 76.

[50] Qiao YX, Wang XY, Yang LL, et al. Effect of aging treatment on microstructure and corrosion behavior of a Fe–18Cr–15Mn–0.66N stainless steel. J. Mater. Sci. Technol., 2022, 107: 197.

[51] Tian Y, Liu JN, Xue MM, et al. Structure and corrosion behavior of FeCoCrNiMo high-entropy alloy coatings prepared by mechanical alloying and plasma spraying. Int. J. Miner. Metall. Mater., 2024, 31122692.

[52] N. Alexiadis, A. Fuchs, T. Troßmann, I. Bösing, J. Thöming, and F. La Mantia, Modeling and simulation of passive film formation and breakdown in chloride ion containing electrolytes–A Point Defect Model extension, Corros. Sci., 256(2025), art. No. 113166.

[53] Zhang CL, Zhu M, Yuan YF, Guo SY, Wei GY. Effect of pH on corrosion behaviour of CoCrNi MEA imposed by alternating current in Na₂CO₃/NaHCO₃ solution. Corros. Eng. Sci. Technol., 2023, 588696.

[54] Gao WB, Gu Y, Han QL, et al. Corrosion and passivation behavior of sensitized SAF 2507 super-duplex stainless steel in hot concentrated seawater. J. Iron Steel Res. Int., 2025, 3293026.

[55] Shi BX, Qin LZ, Xu D, et al. Exploring corrosion protection evolution of rust layer on high-Cr-content weathering bridge steel in simulated tropical marine atmosphere. Int. J. Miner. Metall. Mater., 2025, 3281913.

[56] Qiao YX, Wang TY, Chen ZL, Wang J, Li CT, Chen J. Corrosion techniques and strategies for used fuel containers with copper corrosion barriers under deep geological disposal conditions: A review. Int. J. Miner. Metall. Mater., 2024, 31122582.

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