ELECTROFORMING A N D MECHANICAL PROPERTIES OF IRON-NICKEL ALLOY FOIL

A method of electroforming smooth, bright, iron-nickel alloy foil, of thickness about 0.1 111111, is developed. The electrolyte, mainly a solution of ferrous chloride and nickel chloride, is operated at a temperature of 95T, and at current densities of between 5 and 20 A/dm2. Below that temperature, and at current densities greater than 20 A/dm2, the foil becomes cracked. The amount of nickel co-deposited in the alloy can be increased up to a limit of 6.24 per cent, by reducing the current density and/or increasing the concentration of nickel chloride in the electrolyte. As the nickel content of the foil rises, the material suffers increasingly from hydrogen embrittle-ment. The main mechanical properties of the alloy foil are more affected by hydrogen embrittlement, the amount of which is influenced by current density and the concentration of nickel chloride, than by changes in grain size. This behaviour is in contrast with that of electroformed iron foil, for which the mechanical properties are largely controlled by the influence of. the current density and electrolyte temperature upon its grain size. However, when the other process conditions are held constant, the mechanical properties of the alloy foil behave like the iron foil in decreasing with increasing foil thickness, owing to increases in average grain size.