Comparison of the corrosion behaviour of laser-annealed Ni-P and Ni-Mo-P deposits in H2SO4 and NaCl solutions

The corrosion behaviour of electroless amorphous Ni-P and Ni-Mo-P deposits before and after laser treatment was systemically compared using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques, and X-ray and SEM/EDS analysis and interferometry. EIS studies in 3.5 wt-% NaCl solution indicate that a suitable laser treatment can strongly improve the pitting corrosion resistance of the Ni-Mo-P deposit to Cl-attack compared with the Ni-P deposit and the best corrosion resistance of the Ni-Mo-P deposit appears at a laser scanning velocity of 12 mm s(-1). In 0.5 M H2SO4 solution, the corrosion mechanism of the Ni-Mo-P deposit is mainly associated with the dissolution of Mo from Ni-Mo solid solution. The as-plated Ni-Mo-P deposit exhibits better corrosion resistance than the Ni-P deposit, and this is true for the laser-treated Ni-Mo-P deposit at a laser scanning velocity <10 mm s(-1)