The effect on the microstructures of electroless nickel coatings initiated by pulsating electric current

In this study, pulsating electric current was applied during the electroless Ni plating process. The applied current is controlled to avoid the formation of an immersion (displacement) deposit. The effects of the current density (0.5 and 1.0 A/dm²), duty cycle (0 to 100%, in a step of 10%), and bath pH value (4.4 and 4.8) were investigated systematically. The as-plated coatings were examined by atomic force microscopy, transmission electron microscopy, X-ray diffraction, synchrotron X-ray absorption spectroscopy, etc. Amorphous or amorphous-like microstructure was obtained for all as-plated coatings and the phosphorus content was higher than 8.9 wt.%. Experimental results showed that pulsating electric current can initiate Ni nanocrystallization (∼ 5 nm), improve crystal growth, and accelerate electroless Ni deposition. An obvious increase in deposition rate was also observed with pulsating electric current.