Utilization of Ni-Cu/Al2O3 co-deposition composite coatings on mild steel surface via electroplating method and evaluation of its tribological, electrochemical properties

The present study successfully applied NiCu and Ni-Cu/Al2O3 composite layers on St37 steel substrates using sodium citrate and potassium oxalate as complexing agents. The alloyed NiCu and composite Ni-Cu/Al2O3 coatings were scrutinized for their physical, mechanical, chemical, electrochemical, and tribological properties using various techniques including XRD, SEM/EDS, microhardness test, PDP, EIS, FESEM/MAP images, and dry tribological pin-on-disk wear analysis. The XRD patterns of the Ni-Cu/Al2O3 composite coatings disclosed the presence of FCC crystal structure in both Ni and Cu phases, as well as the successful formation of Ni-Cu/Al2O3 nanocomposite coatings on mild steel substrates. Incorporating Al2O3 particles resulted in a 48 % increase in microhardness compared to NiCu coatings. Furthermore, Ni-Cu-Oxalate coatings exhibited a higher microhardness with respect to Ni-Cu-Citrate coatings. Varying the type of complex species in the Ni-Cu/Al2O3-Citrate coatings led to a 9.7 % increase in microhardness in regard to Ni-Cu/Al2O3-Oxalate coatings. The pin-on-disk wear analysis revealed that the Ni-Cu/Al2O3-Citrate coatings had a 35 % lower friction coefficient compared to Ni-Cu/Al2O3-Oxalate coatings. The composite NiCu coatings with reinforcing Al2O3 particles exhibited superb wear resistance compared to the alloyed NiCu coatings. The morphology of the coating's surface was found to be more uniform and adhesive for the Citrate coating compared to the irregular-shaped Oxalate grains. The Ni-Cu/Al2O3-Oxalate and Ni-Cu/Al2O3-Citrate coatings demonstrated an outstanding improvement in specific wear rate approximately 94.1 % and 62.7 %, respectively, with respect to the Ni-Cu-Oxalate and Ni-Cu-Citrate coatings. The worn path analysis substantiated that the composite Ni-Cu/Al2O3 and alloyed NiCu coatings were subjected to mixed adhesive, abrasive, plastic deformation, and delaminated wear mechanisms. Finally, the composite Ni-Cu/Al2O3-Citrate coatings showcased superior hardness, a more uniform and adhesive microstructure, and brilliant anti-wear properties.