مهشید تفرشی

In this research, Zn-Ni and Zn-Ni/PTFE coatings were electrodeposited from sulfate-based electrolytes. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to investigate the corrosion properties of the coatings. Hardness and tribological behavior of the coatings were examined by the Vickers microhardness testing machine and the pin-on-disc method, respectively. Chemical composition and morphology of the as-deposited and worn surfaces of the coatings were studied by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). According to the results, the corrosion current density of the Zn-Ni film was about 30% of that of the composite coating. Hardness of the alloy film was partially decreased by the incorporation of Polytetrafluoroethylene (PTFE) particles. However, the wear loss and coefficient of friction of the Zn-Ni/PTFE coating were, respectively, about 43% and 57% of those of the Zn-Ni film. Moreover, wear mechanism was changed from plastic deformation and adhesive wear to slight abrasion by the co-deposition of PTFE particles.

Zn–Ni alloy coatings were electrodeposited from acidic sulphate baths. In this study, the effect of plating parameters and bath composition on the cathodic current efficiency, as well as hardness, morphology and chemical composition of the coatings were investigated. The morphology and chemical composition of the coatings were investigated using scanning electron microscopy equipped with EDAX analyzer. Results showed that surface morphology and chemical composition of the films were strongly dependent on the electrodeposition parameters. Ni content and hardness of the coatings were increased and the cathodic current efficiency was decreased by enhancing the bath temperature and Zn (II)/Ni (II) ratios, or reducing the current density and bath pH. Electron microscopy images showed that cracks appeared on the coatings surface with increasing temperature due to the high residual stress. In addition, the structure of the coatings became finer with increasing the current density, resulting in the formation of voids and porosities. Studies on the bath pH revealed that only the coatings which were deposited in baths with pH=2 had a dense and uniform surface. Moreover, increasing the Zn (II)/Ni (II) ratios in the bath caused brittleness of the coatings.

Zn–Ni alloy coatings were electrodeposited from an acidic sulfate bath, while their microstructures, corrosion properties and wear behavior were investigated. To study their structures, X-ray diffraction (XRD) was used. To evaluate the wear behavior, wear tests via pin-on-disc were performed. Hardness measurements were carried out via Vickers microhardness testing machine. Secondary and backscattered electron micrographs were taken from the worn surfaces and chemical compositions of the coatings were also investigated using Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS) analyzer. X-ray diffraction (XRD) technique was also used to determine the phase structures of the coatings. The results indicated that the amount of nickel in the coating had a strong impact on their properties so that by increasing the amount of nickel an increase in the coating hardness was obtained. Finally, Zn-14% Ni coating which contained a single phase -Ni5Zn21 face centered cubic had the lowest coefficient of friction as well as wear rate among all other coatings with different chemical compositions.

Zn–Ni alloy coatings were electrodeposited from acidic sulphate bath. In this study effect of plating bath temperature on hardness, morphology, chemical composition of the coating and cathodic current efficiency was investigated. The morphology and chemical composition of the coatings were investigated using Scanning Electron Microscopy (SEM) equipped with EDX analyzer. X-ray diffraction (XRD) technique was used to analyze the structure of the coatings. To investigate the corrosion properties of the coatings, Tafel Polarization experiments and electrochemical impedance spectroscopy (EIS), were used. Results showed that the amount of nickel in the coating increased by increasing deposition temperature. The amount of nickel had a great effect on structure, morphology and hardness of the coatings. In addition, as deposition temperature increased cathodic current efficiency reduced which in turn led to reduction of hardness. SEM results showed that at low temperatures the structure had fine grains and with increasing temperature, the structure became coarser. Coatings with 14 wt% Ni, had maximum corrosion resistance among all the coatings with different chemical composition. This coating had a  phase hexagonal structure and this was the main reason for the increased corrosion resistance of the coatings.