Microstructure and Properties of Electrodeposited nc-TiO2/Ni–Fe and Ni–Fe Coatings

Abstract

In this study, nc-TiO 2 /Ni-Fe composite coatings, and Ni-Fe alloys as equivalents to their matrices, were obtained from citratesulphate baths in the electrodeposition process using direct current and pulse current conditions. The aim of the study was to examine the effects of TiO 2 nanoparticles and current conditions on the chemical composition, surface morphology, microstructure, microhardness and magnetic properties of the electrodeposited coatings. The results show that the concentration of Fe in Ni-Fe alloys is related to the current conditions and is higher in the case of pulse current electrodeposition, while such a relationship was not observed for composites. The reinforcement of composites with TiO 2 nanoparticles results in a more developed surface topography with many nodule-like structures. Composites and equivalent alloys deposited in pulse current are characterized by a finer grain size than those obtained in direct current. TiO 2 nanoparticles and their agglomerates, several tens of nanometres in size, are distributed randomly in the Ni-Fe matrix of composites deposited in both current conditions used. Incorporation of a high volume fraction of nc-TiO 2 , exceeding over a dozen percent, and decreasing the nanograin size in nc-TiO 2 /Ni-Fe composites electrodeposited under pulse current conditions, allow a higher hardness to be achieved than in their counterparts obtained using direct current. Magnetic measurements showed ferromagnetic ordering of pristine TiO 2 nanoparticles, however, the introduction of TiO 2 nanoparticles into the Ni-Fe matrix resulted in a decrease in coercivity and saturation magnetization.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Microstructure and Properties of Electrodeposited Nanocrystalline Ni-Co-Fe Coatings

“…However, Co 2+ and Fe 2+ ions were preferentially reduced before Ni 2+ ; thus, the anomalous electrodeposition took place. The anomalous character of electrodeposition of Fe and Co ions before Ni is a well-known phenomenon [ 15 ] and was also described in our previous works on electrodeposition of binary Ni-Co [ 27 ] and Ni-Fe alloys [ 28 ] from citrate-sulfate baths. Differences between Fe and Co concentrations in coatings were small, but a slightly higher concentration of Fe was achieved.…”

“…Electrodeposited coatings were characterized by a high hardness above 4.2 ± 0.4 GPa. The obtained values are in the range typical for electrodeposited Ni-based alloys [ 28 , 40 , 41 ]. The highest hardness of NCF2 coating may be related to both the smallest grains and the solid solution strengthening.…”

“…Low values of roughness parameters are in good agreement with surface morphology observations in SEM and correspond to a low number of irregularly shaped surface islands, discontinuities, or pores. It was found that the roughness parameters of Ni-Co-Fe coatings were in a similar range as for binary Ni-Fe [ 28 ] and Ni-Co coatings [ 27 ].…”

“…Moreover, our ternary Ni-Co-Fe coatings were characterized by smaller grains than binary Ni-Co and Ni-Fe alloys electrodeposited from citrate-sulfate baths [ 27 , 28 ]. It is probably due to the presence of two alloying elements in a nickel matrix and the addition of saccharin.…”

“…In all Ni-Co-Fe coatings, the microstructure consisted of equiaxed grains. Only a low number of elongated grains was noticed, which indicates that columnar grain growth, a characteristic of electrodeposited Ni-based coatings, was disturbed by organic additives [ 28 , 33 , 39 ]. Similar results were reported by Kolonist et al in Ni coatings electrodeposited from Watts bath in the presence of saccharin [ 39 ].…”