Microstructure and Properties of Nickel Layers Electrodeposited under Reduced Pressure and Temperature Gradient Conditions

Our previous studies showed that at a considerably high plating speed up to 1 mm/h, the nickel electrodeposits with smooth surface, few deposition defects and some improved properties could be prepared under the conditions of an additive-free bath at a reduced pressure of 5 kPa and a temperature gradient of 35°C/65°C. This paper aims at further analyzing the effect of bath pressure and temperature gradient on the surface morphology, the microstructure and the properties of electrodeposited nickel coatings in a subatmospheric environment. Our findings indicate that the surface quality, the microstructure and the properties of the deposited nickel coatings are, to some extent, affected by the applied bath pressure and the temperature gradient; favorable nickel electrodeposits can be only achieved when the electrolyte in the vicinity of cathode surface is in a boiling state. The temperature gradient influences the texture characteristic of nickel deposits, but the bath pressure has few effects on the preferred orientation. Grain-fining, microhardness, and corrosion resistance of nickel deposits are improved with increasing of the temperature-gradient and/or the reducing of bath pressure. These variations are closely relevant with the boiling-driven mass transfer effect and the vacuum-degassing effect during the electrodeposition in a reduced pressure bath