The work aims to systematically investigate the co-deposition preparation method and performance optimization of Ni-Co-Cr ternary alloy coatings, addressing the critical challenge of integrating trivalent chromium (Cr3+) with nickel (Ni2+) and cobalt (Co2+) ions in an electrodeposition process. Therefore, the focus is placed on developing an efficient complexing agent system and optimizing key process parameters to achieve high-performance coatings with enhanced mechanical and tribological properties.
A synergistic sodium formate-urea complexing system was identified as the most effective for promoting Cr3+ reduction and co-deposition with Ni2+ and Co2+. This system destabilized the stable hexaaquachromium (Ⅲ) ion ([Cr(H2O)3]3+) by forming intermediate complexes like [Cr(H2O)5(HCOO)]2+ and [Cr(urea)n(H2O)6-n]3+, which lowered the reduction overpotential of Cr3+. Systematic screening revealed that sodium citrate and EDTA disodium were ineffective, while sodium acetate alone failed to facilitate Cr deposition. The addition of urea to sodium formate significantly increased Cr content in the coating (up to 7.4%) and hardness (877HV).
Cr3+ concentration: the optimal Cr2(SO4)3·xH2O concentration was 40 g/L, yielding a coating with 5.5% Cr and peak hardness (815HV). Deviations from this concentration reduced Cr content due to either insufficient active complexes or excessive stable [Cr(H2O)6]3+ formation. Temperature: lower temperatures (<40 ℃) favored Cr deposition, with Cr content dropping from 2.2% at 25 ℃ to 0.6% at 65 ℃. However, hardness peaked at 716HV (45 ℃) due to improved coating density and stress relief. Current Density: higher current densities (6 A/dm2) maximized Cr content (15.3%) and hardness (845HV). Excessive current (>6 A/dm2) induced cracking from high internal stress.
Cr doping reduced the average grain size of Ni75Co25alloy from 14.29 μm to 5.32 μm (a 63% reduction), attributed to Cr-induced inhibition of grain growth. Single-Phase FCC Structure: XRD confirmed a face-centered cubic (fcc) solid solution without secondary phases, indicating complete Cr dissolution in the Ni-Co matrix. Enhanced Mechanical Performance: hardness: nanoindentation hardness increased by 61.3% (from 773HV to 1247HV). Elastic Modulus: improved by 13.3% (from 181 GPa to 205 GPa). Adhesion Strength: critical load in scratch tests rose by 14.6% (from 13.7 N to 15.7 N). Wear Resistance: the wear rate decreased by 37.5% (from 0.08 mm3/(N·m) to 0.05 mm3/(N·m)), with wear mechanisms shifting from adhesive (Ni-Co) to abrasive (Ni-Co-Cr) dominance.
The role of formate-urea synergy in destabilizing Cr3+ aqua complexes was elucidated, enabling efficient co-deposition. Process-Structure-Property Relationships: low temperature (<40 ℃) and high current density (>4 A/dm2) were critical for maximizing Cr incorporation, while grain refinement and solid solution strengthening were the primary mechanisms for hardness enhancement. Performance Superiority: the optimized Ni73.5Co24Cr2.5 coating exhibited 1.6× higher wear resistance and 61.3% greater hardness than binary Ni-Co, making it suitable for demanding applications like protective coatings and tribological components.
A high-efficiency electrodeposition process is successfully developed for Ni-Co-Cr ternary alloys, overcoming the inherent challenges of Cr3+ co-deposition. The sodium formate-urea complexing system, combined with optimized parameters (40 g/L Cr2(SO4)3, 6 A/dm2, 45 ℃), can be used to prepare coatings with exceptional hardness, adhesion, and wear resistance. The findings provide a theoretical and technical foundation for industrial adoption of environmentally friendly trivalent chromium-based alloy coatings.
Key words
co-deposition /
Ni-Co-Cr alloy /
complexing agents /
hardness /
wear resistance
{{custom_sec.title}}
{{custom_sec.title}}
{{custom_sec.content}}
References
[1] LIU T T, SUN X P, ASIRI A M, et al.One-Step Electrodeposition of Ni-Co-S Nanosheets Film as a Bifunctional Electrocatalyst for Efficient Water Splitting[J]. International Journal of Hydrogen Energy, 2016, 41(18): 7264-7269.
[2] HONG S H, AHN S H, CHOI I, et al.Fabrication and Evaluation of Nickel Cobalt Alloy Electrocatalysts for Alkaline Water Splitting[J]. Applied Surface Science, 2014, 307: 146-152.
[3] TIAN L L, XU J C, XIAO S T.The Influence of pH and Bath Composition on the Properties of Ni-Co Coatings Synthesized by Electrodeposition[J]. Vacuum, 2011, 86(1): 27-33.
[4] TIAN L L, XU J C, QIANG C W.The Electrodeposition Behaviors and Magnetic Properties of Ni-Co Films[J]. Applied Surface Science, 2011, 257(10): 4689-4694.
[5] BASTOS A, ZAEFFERER S, RAABE D, et al.Characterization of the Microstructure and Texture of Nanostructured Electrodeposited NiCo Using Electron Backscatter Diffraction (EBSD)[J]. Acta Materialia, 2006, 54(9): 2451-2462.
[6] SHI L, SUN C F, GAO P, et al.Mechanical Properties and Wear and Corrosion Resistance of Electrodeposited Ni-Co/SiC Nanocomposite Coating[J]. Applied Surface Science, 2006, 252(10): 3591-3599.
[7] YANG T, PENG C Z, XIANG L, et al.Fabrication and Corrosion Properties of Electroplated Ni-Co-Cr Alloy Coatings[J]. Applied Mechanics and Materials, 2013, 456: 438-441.
[8] 刘芳, 刘常升, 陶兴启, 等. 结晶器铜板表面处理的研究进展[J]. 表面技术, 2006, 35(3): 1-3.
LIU F, LIU C S, TAO X Q, et al.Progress in Surface Treatment of Copper Crystallizer[J]. Surface Technology, 2006, 35(3): 1-3.
[9] 白林, 陈登福, 刘鹏, 等. 结晶器铜板表面耐磨纳米复合镀层的制备及性能[J]. 表面技术, 2017, 46(7): 7-12.
BAI L, CHEN D F, LIU P, et al.Preparation of Wear Resistant Nano Composite Coating on Surface of Copper Crystallizer[J]. Surface Technology, 2017, 46(7): 7-12.
[10] LIU P, LI L, YU S, et al.Effect of Transition Metal Element Additions on the Mechanical and Electronic Properties of L10 CoNi Alloys[J]. Extreme Mechanics Letters, 2021, 42: 101128.
[11] MEENA S P, ASHOKKUMAR R, RANJITH KUMAR E.Effects of Cr Doping Concentration on Structural, Morphology, Mechanical and Magnetic Properties of Electrodeposited NiCoCr Thin Films[J]. Journal of Inorganic and Organometallic Polymers and Materials, 2019, 29(4): 1094-1099.
[12] MCNAUGHT A D, WILKINSON A.Compendium of Chemical Terminology[M]. Oxford: Blackwell Science Oxford, 1997, 231-272.
[13] SURVILIENĖ S, NIVINSKIENĖ O, ČEŠUNIENĖ A, et al. Effect of Cr(Ⅲ) Solution Chemistry on Electrodeposition of Chromium[J]. Journal of Applied Electrochemistry, 2006, 36(6): 649-654.
[14] MEENA S P, ASHOKKUMAR R.Effect of Different Current Density on Properties of Electrodeposited Ni-Co-Cr Thin Films[J]. Oriental Journal of Chemistry, 2018, 34(4): 1884-1889.
[15] TIAN Y, CHENG Z P, LANG X, et al.Fabrication and Corrosion Properties of Electroplated Ni-Co-Cr Alloy Coatings[J]. Applied Mechanics and Materials, 2014, 456: 438-441.
[16] 李燕. 电化学沉积镍钴铬防护涂层的研究[D]. 包头: 内蒙古科技大学, 2012: 15-17.
LI Y.Study on Electrochemical Deposition of Ni-Co-Cr Protective Coating[D]. Baotou: Inner Mongolia University of Science & Technology, 2012: 15-17.
[17] 游福仁. 电化学沉积厚镍钴铬防护涂层的研究[D]. 包头: 内蒙古科技大学, 2014: 13-15.
YOU F R.Study on Electrochemical Deposition of Thick Ni-Co-Cr Protective Coating[D]. Baotou: Inner Mongolia University of Science & Technology, 2014: 13-15.
[18] 杨添. 三价铬电沉积Ni-Co-(Cr)镀层及其耐蚀性研究[D]. 湘潭: 湖南科技大学, 2014: 15-18.
YANG T.Study on Ni-co-(Cr) Coating Electrodeposited by Trivalent Chromium and Its Corrosion Resistance[D]. Xiangtan: Hunan University of Science and Technology, 2014: 15-18.
[19] Brenner A.Electrodeposition of Alloys: PRINCIPLES and PRACTICE-ScienceDirect[J]. Academic Press, 1963, 361-362.
[20] SONG Y B, CHIN D T.Current Efficiency and Polarization Behavior of Trivalent Chromium Electrodeposition Process[J]. Electrochimica Acta, 2002, 48(4): 349-356.
[21] IBRAHIM S K, WATSON A, GAWNE D T.The Role of Formic Acid and Methanol on Speciation Rate and Quality in the Electrodeposition of Chromium from Trivalent Electrolytes[J]. Transactions of the IMF, 1997, 75(5): 181-188.
[22] KAMEL M M.Anomalous Codeposition of Co-Ni: Alloys from Gluconate Baths[J]. Journal of Applied Electrochemistry, 2007, 37(4): 483-489.
[23] PRZYŁUSKI J, BIENLINSKI J, KUCHARSKI M. Electrodeposited Cylindrical Thin Films of Co-Ni Alloys[J]. Surface Technology, 1979, 9(3): 179-185.
[24] PHARR G M, OLIVER W C, BROTZEN F R.On the Generality of the Relationship among Contact Stiffness, Contact Area, and Elastic Modulus during Indentation[J]. Journal of Materials Research, 1992, 7(3): 613-617.
Funding
Natural Science Foundation of China (52074053, 52274320); Natural Science Basic Research Program of Shaanxi Province (2025JC- YBQN-754); Shaanxi Province Common Technology Research and Development Platform for Rare Metal Equipment Manufacturing (2024ZG- GXPT-02)
PDF(17598 KB)
