Structure of zinc-nickel alloyelectrodeposits

Zinc-nickel alloys with 0 to 13 wt % of nickel were electrodeposited from a chloride bath. The structure and microstructure change of as-deposited all oys versus the nickel content in the deposits is shown here. From X-ray dif fraction an electrodeposited phase diagram in which the substitution of Zn by Ni atoms in eta or gamma structure induces a lattice distortion has been defined. in contrast to the thermodynamic phase diagram, the delta phase d oes not appear in as-deposited coatings. Two composition ranges have been d efined, the first of which corresponds to the formation of a solid solution sursaturated in nickel (eta(d)) for the alloys containing up to 7.4 wt % o f nickel. The second, corresponds to the formation of a gamma phase out of equilibrium unsaturated in nickel. For an increase in nickel, the added ato ms are preferentially incorporated into this unsaturated gamma phase, and t he eta(d) phase gradually disappears up to 13 wt % of nickel. The delta pha se is obtained in electrodeposited alloys only after heat treatment at 200 degrees C. The delta phase recrystallized from metastable phases eta(d) and gamma(d). (C) 1999 Kluwer Academic Publishers.