ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Tailoring microstructure and corrosion resistance of Ni–Co alloys: the critical role of boric acid

Narmin Mahmood and Hassan H. Abdallah

Chemistry department, College of Education, Salahaddin University-Erbil, Erbil, Iraq

E-mail: hassan.abdullah@su.edu.krd

Received: 10 September 2025  Accepted: 27 November 2025

Abstract:

Nickel–cobalt (Ni–Co) alloys are valued for their magnetic, catalytic, and corrosion-resistant properties. In this study, Ni–Co alloys were electrodeposited onto copper substrates from a choline chloride–ethylene glycol (1:2) deep eutectic solvent (DES) containing iodine, with boric acid (BA). UV–visible spectroscopy revealed a gradual color change from deep blue-green (Co-rich) to pale yellow (Ni-rich), indicating variation in metal–ligand speciation and complex formation. Electrodeposition was carried out potentiostatically at 83 ± 2 °C under a constant current. Cyclic voltammetry confirmed the reduction potentials of Ni²⁺ and Co²⁺ ions in the DES, verifying their co-deposition behavior. Surface morphology and microstructure analyses (FE-SEM and XRD) showed a transition from hexagonal close-packed (HCP) to face-centered cubic (FCC) structures with increasing nickel content. Electrochemical impedance spectroscopy (EIS) demonstrated that the 80Ni–20Co coating exhibited the highest charge-transfer resistance (R_ct = 1462.5 Ω cm²), indicating superior corrosion protection due to stable passive film formation, while the 50Co–50Ni alloy displayed the lowest double-layer capacitance (C_dl = 1.394 × 10^-3 F cm^-2) and highest hardness (78.8 HV), signifying a dense and coherent microstructure. These results reveal how BA and alloy composition synergistically influence the microstructure, corrosion resistance, and mechanical properties of Ni–Co coatings from DES-based electrolytes.

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Keywords: Ni–Co alloys; Electrodeposition; Deep eutectic solvents; Boric acid; Corrosion behavior

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04564-w

Chemical Papers 80 (3) 2953–2966 (2026)