Preparation And Properties Of Electrodeposited Nickel-cobalt Allo

The preparation of nickel-cobalt alloys by electrodeposition inevitably involves the use of various additives,but this introduces various impurities that can compromise the quality of the coating.In this paper,Ni-Co alloy was prepared in a sulfate-chloride salt bath by means of pulsed electrodeposition,and the use of additives in the plating solution was reduced.The electrocrystallization behavior during the deposition of Ni-Co alloy is studied and the deposition mechanism is analyzed.In previous studies,there are more studies on plating solution,process parameters,wear resistance and corrosion of plating layer for Ni-Co alloy at room temperature,but less studies on higher temperature.The prepared Ni-Co alloys were annealed at different temperatures and two annealing times of 10 min and 30 min were chosen.The effect of heat treatment on the corrosion resistance and hardness of the nickel-cobalt alloy was studied.The deposition experiments show that the electrocrystallization mode is a three-dimensional transient nucleation controlled by diffusion,and the deposition rate accelerates with increasing cobalt content in solution.In solutions with low cobalt content,cobalt ions promote the deposition of nickel ions;however,with too much cobalt,the complexed particles of Co²⁺hinder the further deposition of nickel.In addition to the effect of cobalt content,the scanning rate at the cathode end and the increase of electrode potential during deposition will also accelerate the deposition rate of nickel-cobalt alloy.In addition,the Ni-Co alloy prepared by electrodeposition has a strong（2 0 0）crystallographic orientation,and the cobalt enters the crystal structure of nickel in a replacement manner to form a single solid solution.The performance test results of Ni-Co alloy show that the hardness of the deposited Ni-Co alloy shows a trend of increasing and then decreasing with the increase of cobalt content,and the hardness of Ni-41.2wt%Co is the largest;the corrosion resistance also has a similar trend of change,and the corrosion resistance of Ni-10wt%Co is the best.Compared with the deposited state,the corrosion resistance of Ni-Co alloy after annealing has improved to a certain extent,and the best corrosion resistance is obtained after annealing at 300°C for 10 min;the hardness with different degrees of decrease,and only some Ni-Co alloy has a weak annealing strengthening phenomenon after annealing at 200°C for 10 min.The（1 1 1）diffraction peak intensity of the plated layer increased and（2 0 0）diffraction peak intensity decreased after annealing.The corrosion type before and after annealing did not change,still pitting corrosion,corrosion morphology in the shape of a flower petal.The passivation film of Ni-Co alloy consists of metal oxide and metal hydroxide,and the ratio of metal oxide to metal hydroxide on the surface of the plating increases after annealing.