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.