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 zi nc, or eta phase, undergoes a decomposition process to an iron-deficie nt GAMMA-like, or G, phase at temperatures near 150-degrees-C. The pha se transformation is preceded by a polygonization process, driven by s train energy and/or supersaturation in the material. The G phase nucle ates on boundaries within the eta phase and grows into 30- to 80-nm eq uiaxed grains. The activation energy for the transformation varies wit h iron content, which may indicate that solute effects influence bound ary diffusion of zinc.