ETA TO G-PHASE TRANSFORMATION IN ELECTRODEPOSITED IRON-ZINC ALLOY COATINGS

The eta to G phase transformation in electrodeposited iron-zinc alloy coatings is a rapid diffusional phase transformation occurring in the nanometer-scale microstructure of the coatings. Iron-supersaturated zinc, or eta phase, undergoes a decomposition process to an iron-deficient GAMMA-like, or G, phase at temperatures near 150-degrees-C. The phase transformation is preceded by a polygonization process, driven by strain energy and/or supersaturation in the material. The G phase nucleates on boundaries within the eta phase and grows into 30- to 80-nm equiaxed grains. The activation energy for the transformation varies with iron content, which may indicate that solute effects influence boundary diffusion of zinc.