ANODIC BEHAVIOR OF NI-P ALLOYS STUDIED BY IMPEDANCE SPECTROSCOPY

Anodic behavior of electrodeposited Ni-P alloys with P content ranging from 6 to 28 at% was investigated in chloride and sulphate neutral solutions. Measurements were performed by potentiodynamic polarization and impedance spectroscopy methods. It was found that the tested alloys exhibit comparable corrosion resistance under open circuit conditions. However, anodic polarization rises significantly the differentiation in dissolution mechanism of Ni-P. Crystalline (low P) samples show active dissolution accompanied by the formation of a greyish-black nonprotective film on the alloy surface. On the contrary, amorphous (P rich) alloys exhibit passivation. Passive properties of these alloys are quite insensitive to the presence of chloride ions.