THE EFFECTS OF STRUCTURAL RELAXATION AND CRYSTALLIZATION ON THE CORROSION BEHAVIOR OF ELECTRODEPOSITED AMORPHOUS NI-P ALLOYS

The annealing-induced change in the corrosion behavior of electrodeposited amorphous Ni-P alloys in 1 M HCl was examined together with the crystallization and structural relaxation behavior. When the amorphous alloys contain 22.5 at% or less phosphorus, the anodic current density becomes higher as a result of crystallization. The formation of a phosphorus-deficient FCC Ni phase by crystallization is responsible for the high anodic current density. By contrast, when the amorphous alloys containing about 25 at% phosphorus are crystallized by annealing up to 340-degrees-C, the anodic current density does not significantly change, possibly because crystallization results in the formation of a metastable single phase without introducing serious alloy heterogeneity. The electrodeposited amorphous Ni-P alloy specimens relaxed by annealing show the same anodic polarization curve as the as-deposited specimens, whereas the melt-spun amorphous Ni-P alloys show a significant change in the anodic polarization curve as a result of annealing-induced relaxation. The electrodeposited and melt-spun alloys seem to be in different amorphous states, and do not come to the same state by relaxation, possibly because of the great difference in their formation processes.