The microstructure, internal stress and mechanical properties of electrodeposited iron foils

Iron foils about 25 μm thick were electrodeposited from a sulphate-chloride electrolyte at current densities ranging from 3.0 to 27.5 A dm −2. The internal stresses in the foils were measured by an X-ray diffraction method and were found to have a maximum value of 610 N mm −2 at a current density of 20 A dm −2. The mechanical properties of the foils were determined by a tensile test which showed that the ductility was a minimum for foils deposited in the range 12.5–20 A dm −2, above which it remained more or less constant. The 0.2% offset yield stress measured on small specimens during internal stress determination had a pronounced maximum value of about 605 N mm −2 at 20 A dm −2, whereas the same property measured on large specimens showed no definite decrease beyond 20 A dm −2. The grain size of the foils decreased with increasing current density. At about 20 A dm −2 the grain morphology showed a pronounced change from relatively large grains with normal, often smoothly curved boundaries to very small grains, many of which had straight boundaries forming fairly regular hexagonal polygons, probably formed by dendritic growth at the highest current densities.